I'm considering making a softball pitching machine for batting practice. Searching around on the web, I didnt fine any "true" build-it-yourself instructions--only "buy all the parts and assemble it" instructions.
Have any of you guys tried to make a pitching machine before? Any suggestions on where to start? I was thinking of using an old gas engine from an edger as the power source.
If I remember correctly, they're pretty similar to tennis ball throwing machines -- the balls fall onto a spinning rubber wheel that throws them. You might look up information and schematics for those to supplement what you get that's baseball-specific.
I remember at least one robot project that threw tennis balls. I can't remember the name, though. Its web page had some basic mechanical drawings of the thrower.
The basics of a ball throwing machine are two wheels counter-rotating at the same speed, a feed chute, and a mechanism to time ball releases. Note that the same basic mechanism can be scaled up to fire 2x4's hard enough to penetrate 1" plywood - when powered by a large V8 engine. (See www.srl.org for inspiration on that one!)
If you can get two closed-loop motor controllers and two motors strong enough, you can do it all with electronics and not have to worry about gearing to make the wheels spin at the same speed. This also gives you the flexibility to turn one wheel faster than the other, to impart backspin or forespin or side-spin (when mounted sideways) or similar. Note that just powering both wheels off of the same shaft with chain-drive won't work unless you have a reverser in there somewhere - you can't have both wheels turning the same direction if it is to work.
I think there is a "simpler" version that uses one powered wheel and one unpowered wheel, but I'm not certain how well that would work, since it would always have a certain amount of spin on the ball. You could also use low-pressure pneumatic tires where one rolls on the other to spin it, and they "squish" around the ball when it is time to throw, but that might be unpredictable.
You could probably build a single wheeled machine pretty easy with an adapter of some sorts off the motor shaft (or even some sorta pulley setup) and a boat trailer wheel or some other small, narrow wheel, like a temp spare from a car.
Position the drop tube so that it doesnt cause the ball to come back around and smack you in the face. (hey , if it had enough backspin, it's possible)
That woud only give you a pretty basic one. I wouldn't expect any curveballs or anything.
Thanks for the suggestions guys! I'm not looking for any crazy throws or for it to even be super exact, so your comments are all valid. Any suggestions on where to pick up a cheap motor that may have enough power for this?
For a cheap single-wheel side-pitcher, find a used lawnmower engine if you want gas, or a surplus electric treadmill motor (usually 120v universal/brushed motor - may want to build or buy a speed control for it) if you want electric. Loads of used lawnmower engines around - check the local repair shops and ask about lawnmowers that need only minor repairs to the engine but were not worth repairing because a new mower is $150 and shop time is $50/hr. Probably find one that needs a simple tuneup and some gaskets for $20 or maybe even free if you buy the repair parts from them. Most have a keyed shaft so from there go to a go-kart shop and find a keyed wheel hub that will fit that shaft size. Pick a wheel and tire that fits - may be able to use a cheap "minispare" from a junkyard, or the go-kart place might have something cheap. 1" plywood will "probably" be strong enough to mount it all to. Engine on top, shaft sticking through with wheel on bottom. Ball chute on top that curves down to below and guides the ball next to the wheel. Be sure to have at least a short straight section to get the ball started in the direction you want it pitched. Parallel to the wheel and guide track put a braced 2x4 that will squeeze the ball against the spinning tire. Hmm - maybe use appropriate-sized PVC pipe with a cutout that the wheel fits into? Then you have a straight "barrel" for the ball and an easy guide. Use large-radius 90 degree bends to feed the balls down into the guide. For a "ball releaser", take a look around the internet for "marble machines". Some of them have a nifty back-and-forth gating arrangement that moves one marble at a time. Scale that up, probably out of 4x4's or 2x4's or whatever, add a spring that brings it back and a long "pull" cable or pedal-operated cable and you can serve pitches to yourself. Or just use a variation on the marble machine's "timer" so it is automatic until it runs out of balls to serve.
Note that many lawnmower engines have standard pipe threads in the exhaust port so you can use standard off-the-shelf black iron pipe fittings to relocate/extend the exhaust. You can probably get a combination of adapters that, along with a trip to an auto-parts store , would allow you to fit a cheap car muffler to really quiet the lawnmower engine down. The advantage to a lawnmower engine - if you want a gas powerplant - is the integrated gas-tank and starter pull. Small engines are best - 1 hp is PLENTY for this work as the spinning tire will have LOTS of inertia.
One caution when going electric - make sure that if you get a series-wound brush motor that your setup can't over-speed. Series wound motors will speed up until they self-destruct if they don't have sufficient load on them. Induction motors (fan motors, air compressor motors, etc.) don't have this problem but have a fixed speed that is a lot harder to control. DC "shunt" motors don't have the problem either and you can build or buy simple speed controls for them, too, but you may have trouble finding one in a useful voltage range. 12V works if you want to run it off your car.
I'm actually in the process of trying to build a tennis ball machine, which as others have pointed out, can be pretty similar. The main difference I've noticed from looking at a few is that baseball machines seem to have inflated wheels to deal with the harder balls, while tennis ball machines tend to have solid wheels since the balls give more.
I also saw another very related thread about tennis ball machines, so I'm hoping we can combine the two related pursuits here.
I've decided to go with 12VDC from batteries because that seems pretty common for tennis ball machines.
My main challenges have been 1) finding motors, 2) finding wheels, and 3) electronics to allow for control of speed, spin, direction (via other motors).
1) While there seem to be tons of motors on the Net, few seemed to match the power and speed (RPM) range I need (or think I need, I'm somewhat new to this type of stuff). I looked at a lot of robotics sites, and some of the surplus sites too. The most useful ones have been http://www.robotmarketplace.com/store.html (where I got the motors I'm using), http://www.surpluscenter.com/, and http://herbach.com/ Some motors on ebay looked promising, but that's hit or miss.
If there are other good sources of fairly powerful motors PLEASE SHARE! There must be a huge number of motors available in the world, but the selection I could find at good prices (e.g., <$40) available in low numbers for hobby use, was frustratingly limited.
I don't know what power I need, but I used electric scooters as a guide where a 100-200 watts seems low to mid powered and probably sufficient. Somewhere I also got the notion that drawing 1-2 Amps unloaded was the right neighborhood.
I also calculated I wanted 3-5k RPM depending on the wheel diam and desired ball speed. The few tennis machines I've examined seem to have 6" wheels, although my sense is baseball machines have larger diameter wheels.
2) Finding wheels has been surprisingly challenging as well. Again, I'm focused on solid wheels for tennis balls, but they probably both share the same issue of balance, and perhaps folks in this community can help us both there. I looked a lot at caster wheels, and bugged a few sales people, but had trouble getting much help or attention when I only wanted two. I also wanted them to be fairly light (as they seem to be on tennis ball machines), and that was hard to find. Ultimately I ended up making my own with glued up MDF and a router table. They seem okay, but now the problem is balancing.
I probably would have had a balancing problem with caster wheels, as those sales people were not very encouraging about spinning their wheels at 4K. My wheels probably aren't too far off on an absolute weight basis - a rough test of taping on pennies suggested a penny or two is about the amount of weight I need in the right place. But when I spin the wheels at 3-4K the vibration is pretty bad.
I haven't really figure out how to balance them carefully SUGGESTIONS PLEASE!. I tried putting them on a rod across two parallel plates to allow it to roll and find it's heavy spot. But it wasn't precise enough and there was two much friction to make it work well. Now I'm trying to rig up some sort of strobe triggered by the vibration which is an approach I've seen to weighing tires.
3) Looking into options for controlling them has really sent me into what could be a whole new hobby: microcontrollers and electronics. This may be partly because I'm being cheap. You can buy lots of ready to go speed controllers for this scale of DC motors in the $50-100 range (I believe). But once I came across microcontrollers I got pretty enthusiastic about all the flexibility it could give me to program the thing. Perhaps this is more an issue for tennis ball machines, because baseball machines don't oscillate back and forth.
That's probably a longer post than it should be, but I've been spending a lot of time on this, and I'm hoping to share ideas and get some tips.
Probably best to keep most of this in the forum, but I'm happy to share more details by email too. I'm timwhunt at yahoo.
In case anyone can offer some helpful suggestions, I'll give an quick update. I've managed to get two 8" wheels spinning (opposite directions) at about 3,500 RPM. I poked a tennis ball between them and it was indeed thrown. Problem is, it was much slower than I had hoped. By my calcs, the edge of the wheels is moving at about 83 MPH, yet the balls only went about 37 MPH. I figure it is partly conservation of momentum (wheels slow when ball is accelerated), but the ball is pretty light compared to the wheels so I wouldn't expect such a dramatic difference. Other possibilities are the ball is sliding on the wheels and not getting up to their speed or perhaps the compression of the ball as it is squeezed between the wheels is absorbing a lot of energy. I have a homemade tach I'll use to see what happens to the wheel speed when a ball is introduced, so that should shed some light.
Before this post gets as long as the last, anyone have any ideas? Anyone have any actual measurements from a working ball machine for wheel size and RPM?
I have been thinking of building one too, for a long time now. It seems to be difficult to find the motors and wheels. I am surprised by your mph figures for the 8" wheels at 3500rpm. Could you give me the following info?
- weight of the wheels (I have been hoping to make each wheel about 10-12x wieght of the ball which is about 600gms from my mech engineering friends who have built similar machines), this should smooth out the spike when the ball goes through - texture of the wheels (smooth/patterned for grip), compressible/hard - amount of squeeze you put on the ball (distance between the wheels)
Also, how thin are the wheels? I have been thinking of using 2 sets of two wheels each in order to create a groove in between to guide the ball. Could you arrange to post pics of the setup somewhere?
I think vibrations maybe reduced by concentrating the weight of the wheels closer to the axis and make them skinnier towards the edge.
The diam/RPM => MPH calculation was simply the [circumference (in ft)] X RPM X [60 min per Hr] / [5280 ft per mile]. Thus it assumes no slow down of the motor when the ball is introduced, which is not realistic, but the wheels have significantly greater mass than the ball, so hopefully it is in the ball park.
Sorry I don't know the weight of the wheels. I don't have a suitable scale, but I've been meaning to rig something up to weigh them. My guess is about 2 pounds each, with weight concentrated somewhat at rim. Per your other comment, concentrating the weight at the hub would seem to help balance problems, but the wheels would of course not have as much momemtum to throw the ball.
You don't mean 600 *grams* per ball do you? I think that's over a pound, so perhaps gms is something else.
These wheels are 2 inches wide, flat hard surface. I've tried to give them more grip by spray painting them with a rubbery coating (Plastidip), but it's not as "grippy" as I had hoped. The one machine I examined in person had about 1/4" thick smooth rubbery tread. The Silent Partner web site referred to the wheel coating as urethane, which I perhaps incorrectly thought of as polyurethane. I first applied about 10 coats of polyurethane, but it ended up pretty slippery. Perhaps a different finish would be better.
In all the few examples I've seen, flat wheels of 2" width or so have been used. I haven't seen any of the split wheel design, but maybe it would work well. Still, I'd tend to start with what I've seen works in these machines.
I'll have to measure the distance between the wheels. I've tried two so far, and the second was tighter and threw the ball significantly faster because I think my main problem was slipping against the ball.
I'll try to post some pictures of my set up, but you may find the following pictures from Silent Partner more informative (because they actually have a machine that works!). Check out the picture near the end of the manual at http://www.sptennis.com/manuals/BallMachines.pdf Based on what I think was an approximate match with the battery in the foreground, I think the wheels are 6 inches in diameter, and you can approximate other measurements from that.
Nice investigation :-), I too found the link for the portalac PE12V7.2 battery and its dimensions. The battery is rated 8AH, so based on their battery life calculations for the machine, we could get a loose estimate for their propulsion motor power as well (assuming they eat up most of the power). Looks simple inside the box, which is encouraging. I would do the same calculations and maybe add 10-20% speed to make up for losses, but anyway, the exact speed does not really matter for now, we need to figure out what affects the speed of the ball first, I think. Yes, I meant grams, since I think a ball weighs about 57grams. You seem to have heavier wheels, so maybe the squeezing action affects it more. You are right about getting more momentum by concentrating the mass around the rims, but would a larger mass closer to the axis generate the same momentum and be easier to balance? I feel a wheel surface that would dig into the ball felt would reduce slippage, but if you have noticed that commercial ball machines have smooth wheels, there must be some reason for it.
- do you already have a motor propulsion system? What motors do you have if yes? - are you using some kind of bearing to support the wheels? where did you find these?
So following your suggestion, Silent Partner quotes up to 4 hours running time on one (8AH) battery, that's 2 amps per hour, or about 1 amp per motor. Probably a bit less than that as I suspect you can't really get a full 8AH out of those batteries bofore the voltage drops too far, but perhaps I'm cynical.
Oh, the 600grams was for the wheel, I thought you meant for the ball! Makes sense now.
They draw about 2amps unloaded, and like I think I mentioned, the no load speed is closer to 3,500 RPM, not the 4,200RPM stated on the Web page. I wish they were a little faster, but I'm not sure that's my problem with speed (could be slippage).
I have the wheels mounted directly on the motors, which is what I've seen for the two examples I know (Silent Partner, and the machine I examined in person - a Prince model). I was going to put each wheel on an axel between two bearings with sprockets and chains to the motors, but then I found those two examples and went with directly mounting them on the motors. That's a lot easier and cheaper, but it removes the ability to adjust RPM through sprocket sizes, and makes it harder to find motors that work (are fast enough).
I agree that "grippiness" of the wheels is probably very important, but the two examples I've seen had smooth wheels. However, I wouldn't hesistate to try something with a little tread..
Right now my wheels are 2 1/8" appart. If I remember right I thought the silent partner wheels looked like they were 2" appart, so maybe I'll try that. BTW, there are other pictures of the machine on their site, including one looking into the hole where the balls come out, so you can see the gap between the wheels.
I'm going to try a tighter gap and try to rig something up to measure the speed drop in the motors when the ball goes through. I'll let you know what I find.
Quick update: I moved the wheels about 1/8th" closer, and the ball is clearly being thrown faster. I'll have to get out the video camera to measure the speed, but it's encouraging. Looks like slippage probably was keeping my ball speed down. Now it takes some significant force to push the ball between the wheels, but when they are running at speed it whips right through. I'll update when I get a chance to make some measurements.
Another update: I measured the speed with smaller (2" gap) and it varied from 41 to 49 MPH over 3 balls. Better, but still a little slow.
I also measured the wheel speed while it throws a ball. It was spinning around 3,000 RPM before the ball was introduced, and the minimum speed measured when a ball was thrown was about 2900 RPM. Looks like the wheels keep their speed pretty well. But 2900 RPM would be 69 MPH, so perhaps I'm still getting some slippage (since ball speed was 41-49 RPM). I hesitate to make the gap smaller (but I might). I'd rather have better grip on the wheels.
Do you think it is underpowered? How do you feel about the AME motor you bought? I am thinking of going with 6" wheels, hence I will need slightly higher RPMS.
I have no real idea of how to mount the wheels on the motor shafts. Could you give me a few pointers of how to start or give me some helpful links? Again, there seems to be a dearth of information on this.
In fact, I've been tempted by that very same motor. I expect that motor would be fine for having enough power, but my concern is that it is probably series wound, and apparently they can be harder to control (than permanent magnet motors). You can try to find out from Surplus Center what type of motor it is. I think I tried once, and didn't get a definative answer, but you may have more luck. The issue with Series Wound motors is that they can "run away" (spin faster and faster out of control) if they don't have a load and their power is cut. that seems like a risk with our application, where they are just spining a flywheel. I'm no expert at this stuff, but I've tried to get some advice with another post in this forum (http://forums.makezine.com/comments.php?DiscussionID=1078&page=1).
I would also prefer 6" wheels and only went with 8" because what seemed like the best motor I could find (the one I got) wasn't as fast as I wanted.
Those wheels look nice, but I would check into them a bit more to see if the tread is strong enough to not fly apart when spinning fast. There is quite a lot of centrifical force at those speeds, and unless the treat is attached really well and pretty strong, it may fly appart. See if the folks behind the site can give you an opinion of whether they will stay together if spun at 5,000 RPM. I suspect they will initially be a little shocked that they might be used for such an application.
Yes, attaching the wheels to the motor was another area that surprised me because I haven't found a standard way to do it. I've had to invent something. I think it's working pretty well, though. I take a bolt that fits inside the wheel (1/2" in my case), and I drill it out straight down through the head to match the diameter of the motor shaft. Then I add set screws across the head (into a flat that a wrench would grip) to grip the motor shaft. The wheel goes on the bolt and is held on with a nut (and washers and lock washers). The set screw part is a little suspect as they can come loose, so I might switch to putting a pin through the bolt and the motor shaft. Any chance you have a drill press? This takes some pretty careful drilling to get the hole for the motor shaft centered in the bolt. I can describe how I do it more if it would help.
Anyway, I am close to making my first purchase, my choices being the AME motor, the series wound and this one. I am still tempted by the series wound one, I am not really concerned about runaway, but the motor characteristics means that speed will probably drop quite a bit when the ball goes through.
www.usfirst.org has some nice docs scattered around
That FR801-001 motor does look tempting. I like the speed. I agree it is a little high on the amps, though. In reality, I think you'll be operating much closer to the no load current, but you'll have to be able to handle LARGE current draws when the motors first start. Those AME motors draw about 22 amps when stalled or first starting. That's not small, but not causing problems for me. But those FR801-001 motors draw 114 AMPs stalled! Don't know, but it could make motor control circuits harder or more expensive. Do you have any plans yet for your motor control circuit? (I haven't had a chance yet to look at those links on motor controls) Are you going to buy or build something?
I've been building PWM speed control using an ATMEGA microcontroller. The microcontroller will be able to control lots of other things (ball release, motors to adjust angle of the ball throw, LCD for user interface). It's a bit involved, but I'm having fun with it and it has launched a new hobby (just what I needed!). If you're interested, I've gotten some help on the motor control circuit at AVRFreaks (a great website for help with using microcontrollers like ATMEGAs). My motor control discussion is at http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=41420&postdays=0&postorder=asc
I would also be tempted by those series wound motors, and I'm curious to see what you figure out about the runaway worry. I'm guessing by motor characteristics effecting speed drop with the ball going through, you're looking at some speed vs. torque chart. You might be right, but I suspect the bigger issue is the relative masses of the wheels and the ball, as the ball goes through so fast the power of the motor doesn't have enough time to impact (hold) the RPM. But that's just a hunch. I wonder what mine would do if I cut the power to the wheels as I put a ball through. Would be hard to control so that the RPM matched what it would be under power at the moment the ball went through.
BTW, that FR801-001 motor looks like it is reversable. The spec sheet does say CCW in some places, but it also said reversable. Reversable would be convenient for building it. You might want to make sure the speed is the same both directions. Some reversable motors are biased in one direction. The AME motor is supposed to be biased, but I spoke to someone at AME before I bought it and he said it was not very biased, and indeed they seem to spin about the same RPM both directions for me.
I heard back from Hansen just yesterday, after I had emailed them earlier about their motors. They have series 16 and 21 motors that looks promising. The series 21 looks a bit stronger and perhaps better for us. I'll compare the torque specs to the AME motors, which seem to have enough power. However, I still don't know what the prices are or if they sell in small numbers (or have a distributor who does).
This is how I feel about the runaway problem: - the series wound motor is well suited for applications where it always started with a load which makes our app somewhat ideal - the wheels are heavy enough and will come up against considerable air resistance at the several thousand rpm speeds to form a load for the size of the motor - I am not certain what the 5000/7000 rpm spec means. It could mean the motor speed at "no load" is limited by the internal frictional losses, or they might have a separate speed limiting winding, or it could just be the limit of the motors design. I will try and contact the company. - we can add multiple safety cutoff devices and the motor will always be under supervision when it is running - if the wheel comes apart, I would be more worried about the flying pieces hurting somebody than the motor going bust
I think the cost of the motor makes up for the issue, this is a cheap motor for prototyping. The last link in my earlier post talks about controlling speed of a car starter motor which is a powerful series wound device.
I was thinking of building a simple PWM drive using a 555 (I have used this quite often earlier) and a power MOSFET driver initially and switch to a microcontroller after I get the mechanical parts right. I am fairly comfortable with the electrical and the electronic stuff, I am a rank amateur with the mechanical part.
That all sound good, and selfishly, I'm very interested to see how the series wound motor works.
Glad to hear you're comfortable with the electrical/electronics stuff that is very new to me. Since I've got decent programming experience, and a no electronic experience, I find using a microcontroller easier that using more parts (e.g., 555). But that has lead to a whole other set of investments (that I hope to use for other projects).
I heard back from Hansen. As I feared, the motors a bit expensive. One of the more promising ones in the 21 series (121-14512) is $125 each or $75 each if buying 10.
Here is an amazing collection of links: http://amasci.com/amateur/elehob.html there are lots of component online stores under the surplus suppliers link, they have a huge array of components, I found one more motor at allied electronics: http://www.alliedelec.com/ (this is an amazing store, check for motors, dc, direct drive, there is a 5200rpm but little wimpy motor of 22 something watts) And another mechanical link selling single pieces of mechanical parts like couplings, etc from a huge collection (a little pricey, but worth it I think) http://www.sdp-si.com/
If you have not seen these already, I think you will discover a new world here. Check out the collection of power mosfets on allied for example, and every component is complete with data sheets
I just bought an oscilloscope on ebay, keeping my finger crossed and hope it works fine when it arrives like the seller said. Will buy components and build a motor drive in a few days and test it on small dc motors first. Have contacted FASCO multiple times, no contact at all, I need some more info on the series wound motor, otherwise I will have to settle for the first robotics part :-(
Hi guys, I've read with great interest about your ball machine projects. I've been wanting to make one for years but never got around to do it. I've thought about using 2 electric fan motors with its own 3 speed controller. This would be very cost effective as the fans are very cheap and the replacement motors are readily available. The problem is I don't know whether the motors can develop enough rpm (but this can be countered by larger throwing wheels), whether the motors have enough torque and lastly the portability as the motors are mains operated. As for the wheels, I've thought about making your own by using some existing rim and cast some sort of rubber (don't know what to use yet) layer and shape it using a lathe. What do you guys think? The sites you have mentioned are very interesting and helpful. I live in Australia and the parts are not as easily accessible. Cheers
I do not speak from experience, but in my opinion, having an ac outlet at the court will open up the possibility of using ac motors which are cheaper and powerful, and probably make the machine a little lighter (assuming you will not require a power supply for electronics), the torque should be enough (not sure about small fan motors, but maybe you could strip motor from blenders or food processors). If you have experience machining metal using a lathe, then you could probably build something the way you want it, so it is a good idea. If you could get hold of textured rubber from conveyor belts or something, maybe you could rivet it to the wheels. At one point of time, I considered using an ac motor, but run it using a cheap car inverter (not sure if you get cheap car inverters in australia) and a 12v battery. But the a.c. supply generated by an inverter may not be a true sine wave and hence may not run a motor efficiently. You could probably research this.
I've not looked into AC motors, and the courts I'm closest to do not have power outlets. Seems like you're asking good questions, but I don't have many answers. I'd say try experimenting with a fan motor if you can get one cheaply. do you have anything for measuring the speed?
I'd like to know if I could cast some rubber on my home made wheels. Any sites or products you would suggest? If you're going to try attaching rubber to the wheels, I suggest makeing the attachment very strong as stuff has tended to fly off my wheels when I spin them fast.
if you want to make something simple to practice batting indoors or outside if the wind isn't too bad, make a pitching machine like I did,I used an electric leaf blower and hooked some PVC pipe to it to shoot practice golf balls works great, if anyone wants any more info on it let me know. randallburchett@roadrunner.com
Do you think these plastic wheels would serve the purpose at high rpms and impact? mc-master-carr #2781T57 These would probably be pretty light, but I am thinking of adding weight on the axel separately. I am also thinking of carving a pattern on the rolling surface for grip. I felt these are easier to mount and balance compared to the metal ones.
I've looked through the wheels at McMaster Carr many times, and always had some concern about the wheels I could find there not being quite right. In fact, I found just that same wheel (8" diam) in my McMaster Carr shopping cart when just went to look it up!
I think those wheels would probably be fine for weight and durability, but I have two concerns:
1) they appear to be crowned. That is, it looks like the tread is curved and not flat, which will make it hard to get consistent throws I would think. Maybe I'm wrong, but it looks crowned in the picture. Perhaps you could file/sand/machine them flat. Maybe you can ask if the tread is flat or crowned.
2) The durometer rating of 70D means they are somewhere between a bowling ball and hard hat for hardness. which sounds very slippery. You did say you would carve a pattern, or perhaps you could add some coating (but I don't have a good solution there.)
Certainly they are cheap so probably worth a try. The plain 3/4" bore (no bearing) sounds good.
But one concern is how to mount them. Unlike those wheels at McMaster-Carr, most seem to come with bearings. My question is, can those bearings be removed and replaced with some kind of hub? The the question is can I get/make a hub that will fit well?
If I had a metal lathe, I assume I could work something up, but I don't. I've seen some (I think at ServiceCaster.com) that can be bought without bearings and they have a 1 & 3/16" diam hub. I could buy a shaft of that diamer and drill out the center to match the motor shaft, but then what's a good way to attach the hub to the wheel? I think bearings are often just pressed into place, so perhaps I could just do the same?
An alternative I've considered is to leave the bearings in since they make it a conenient diameter like 1/2 or 3/4 " (and I have a decent way of converting standard bolts of those diams into motor adaptors), but add a round plate at the end that would be bolted through the wheel and gripped tightly on the axel. The plate would keep the bearing from turning, while I still use the bearing to mount the wheel on an axel.
Yes, I was aware that it is probably slightly crowned, I was hoping to flatten it out. I have never used a lathe, but if I am to start, I would rather work with wood or plastic than metal (I think it would be easier to flatten and just make horizontal grooves every few millimeters for grip (since the plastic is almost certainly hard like you pointed out). I do not like the ones with bearings since it is extra work to do something with them, there are probably a few better wheels at mcmaster with bearings. I was thinking of not using the center hole at all, but drilling 4 or more holes around the center an using a shaft welded to a disc and bolts to hold on to the wheel. This way I think the impact will be spread out when the ball goes through and the plastic will work fine. For this idea, I would have better liked caster wheels with solid plastic all around, though, instead of just the protrusion in the center.
The metal ones with the bearing also seem to have a protrusion (for lubrication?) which may not be good for dynamic balancing. The plastic ones with metal bearings may come apart at high speeds.
I am hoping to find metal workshops around to use, If you are in the SF bay area, here is an interesting place which seems very reasonable: http://www.techshop.ws/
I bought the series wound motors, I will let you know how they turn out.
I'm very curious to see how the motors work out - please keep me posted! do you have a battery or other power source?
I'm jealous of options like techshop. I've heard of something like that (perhaps that exact same one) but they were in CA and I'm in PA.
I would think you could flatten the crown pretty easily with the right equipment. Come to think of it, it might be doable with a jig and a router table. (I'm thinking in terms of stuff I have or can make) I'll have to keep that in mind!
I agree the bearing are extra work. The thought was to increase the options we could consider.
With your idea of a shaft welded to a disk, I would worry about my abilty to get it all centered precisely, but perhaps you have ability or tools I lack. I don't have a welder for that matter! If you have access to a lathe you might be able to create something similar with good precision.
Hi Tim, Centering will certainly be an issue, I guess your method of drilling into a bolt would not have been too much easier either, but it seems you got it to work fine. I got one more idea today, how about using a threaded pipe through the center of the wheel and fit two flanges, one threaded for holding on to the pipe (which will hopefully be centered), another plain and bolt them with the wheel in between. Pipe and flange dimensions at mcmaster seem to be a little wierd to me though (3/4 inch pipe to fit my wheel bore does not seem to have a 3/4 inch outer dia). I also need to find a way to mate the motor shaft to this contraption. What do you think? -red_arm
For centering in the bolt I used a trick I learned in a robotics book. I use a drill press to drill the bolt diameter (1/2" in this case) into a piece of clamped down stock (1.5" of plywood glued together), then without moving anything, I change the bit to the motor shaft diameter and put the bolt in the 1/2" hole and drill out the bolt. I'm not sure it's perfect, but it is at least pretty close. When I balanced my wheels I made sure that I always kept the position (rotation) of the bolt in the wheel the same in case an imperfection in the bolt drilling was making a difference in the balance.
I like the pipe idea. I would still expect to have to do some balancing because I wouldn't count on the pipe flanges to be perfectly centered/weighted.
But since I've had good luck with my bolt drilling approach, personally I would try that first with a 3/4" bolt and fender washers on each side. BTW, I think that even loose fitting fender washers on my 1/2" bolts can throw off the balance, so I look for tighter fitting washers that stay centered.
I'd be less worried about adding strength with bolts through a flang, but I'm just guessing it would be okay (don't know) -Tim
Sounds like your projects are coming along nicely. I read you looking for wheels to use, and what comes to mind are either cheap freeway-rated trailer wheels (from Northern, formerly Northern Hydraulics, or Fleet Farm/Farm 'n Fleet or other similar stores) or "donut" spare tires from a junkyard. 60mph is around 900 rpm for a small auto tire. Makes the machine a bit bigger, but allows use of lower-speed motors.
What about the set screw hole? Did you buy a bolt with a hole in the head? How about thread for the set screw? Did you tap the hole or is the set screw self tapping?
I drilled the hole in the head and tapped it myself. I'd never tapped a hole before, but it went pretty smoothly. I first found the set screws and then found a taping tool to match, all at Lowes. I actually drill all the way through the head and tap all the way through so I can put set screws on both sides.
BTW, I found tapping/drilling fluid/oil (I got "CoolTool" at McMaster Carr) to be very helpful both for drilling (to keep temp down) and tapping, although I'd say it was less important for tapping.
Thought it might be helpful to say I was able to take a look at a baseball pitcher over the weekend. It was built for special plastic balls that were pretty hard but light. It was more consumer oriented, but it claimed to throw balls up to 80 MPH. Unfortunately, I couldn't get a look at the motors. The wheels were about 10" in diam and 1" wide. They were light, and made of hard plastic, with a thin (~1/32") thick rubber coating. The one thing that surprised me was that the fit between the wheels was very tight. It was surprisingly hard to push a ball through the wheels when it wasn't running. But they wipped right through when it was running.,
Hello, Hope you all will be fine...well i've a very similar plan to design a TENNIS BALL LAUNCHER...after reading the posts i've came to a conclusion for the devices which i'll need but still some problems are there...hope you people will be helping... According to the previous posts... AME 12v Blower motor (204-1021) (Quantity:2) <b> (Will it be able to sustain the load of the rollers???)</b> <a href="http://www.robotmarketplace.com/marketplace_motors_ame.html">at RobotMarketPlace</a>
Rollers (IFI-WHEEL-XYY-ZZ 6" OD, 2.0" Width) (Quantity 2) <b>(Will the motors be able to handel its wait??? and will it be fine or should i fine some without bearings???)</b> <a href="http://www.ifirobotics.com/robot-traction-wheels.shtml">at IFIRobotics</a>
These are few of my conclusion for components and the querries which i have regarding them... I've prepared a model of the device, can you people also verify that. <a href="http://jamshids.brinkster.net/model.htm">Model</a> Thanking you in advance... With Best Regards Jamshid
I'm waiting to hear what success red_arm has with the FASCO motors before commenting on the motor choice. The AME motors I have seem like nice sturdy little motors, but as I've commented, I would like to have them a little faster.
For other motor options, you might want to poke around all the links at the site red_arm pointed out: http://amasci.com/amateur/elehob.html Certainly I'd be interested to hear if you found anything that looked promising. I'd look for things like no-load current of 1-2 amps, RPMs at 5-10K, and decently sized shafts.
I have concerns about those rollers (wheels). I fear that they might come apart at high speeds. red_arm might have some new insights on wheels as well as it sounded like he might try some caster wheels from McMaster-Carr.
Thanks for posting your design. A few comments:
I've had trouble finding PVC pipe that seemed to be the right diameter. the closest looks like 3" diameter, but that might be too loose.
You probably want to mount the motors at the shaft end/face for better stability, and many motors come with bolts or tapped holes there for that purpose. Think of the motors on one side of the base with the shafts going through the base and the wheels on the other side.
Just to be clear, for a tennis machine, you'd want the wheels arranged one on top of the other (not side to side) to provide for top and under spin. (not sure if I should take the orientation of your design literally)
Lastly, the motors have to be reversable for your design. The AME motors are reversable, but I'm not sure about the FASCO. If they are not reversable, you'd have to turn one motor around, which doesn't too bad, but the design wouldn't be so nice and simple anymore.
No more comments to make over Tim's, but in your design, it seems like moving the pipe around for increasing elevation (moving the motors as well) will increase the complexity of the ball feed. The FASCO motors are reversible. I do not have a tachometer/video camera or a 12V supply yet to measure speed of the motors yet, though I have received the motors and checked them with a 6V supply :-)
Updates: - busy learning tools in the metal workshop, starting with a lathe, and going on to a milling machine and MIG welder - Ordered plastic wheels from mcmaster (2781T57) alongwith shaft and key stock. Planning to use a more complex keyed shaft approach for coupling to motor on advice from someone at the metal workshop, now that I have access to a milling machine. Still toying with the idea of having bearing support on the free end to prevent axial movement and reduce vibration, but I cannot find a suitable closed bearing. wheels are to be held axially using snap rings - for the tread, I will experiment with anti-slip floor tape from mcmaster, hoping the adhesive will be strong enough, I have ordered two extra wheels on which I hope to knurl a pattern on the lathe as an alternative - I am leaning towards Tim's approach of starting with a microcontroller for the motor speed, almost decided on the ATMEGA 8535 board from futurlec.com. Toying with the simulator to make sure it will meet my needs. It will help me take measurements as well - not decided on whether I want to invest in a 7AH battery or a larger one (~12AH) yet, suggestions? I want atleast an hour's play even with my crude machine, including simple oscillation.
Also, Tim, have you designed a mechanism to easily change to distance between the wheels for experimentation? What material are you using for the chassis/frame?
Great to have the update. Good luck with all of that. As I've probably already said, I'm jealous about the metal workshop you have access to. Sounds like you are doing the wheel mounting the right way.
Please tell me how the wheels themselves workout.
Bearing support on the free end makes sense, although the two examples I've seen haven't used it. You've probably seen these at McMaster-Carr, but just in case, would 3813T13 work? That's the kind of bearing I was looking at when I was thinking about putting a bearing at the end. Not sure what you mean by "closed".
Sounds like you already had some interest or at least knowledge in electronics, so you might find microcontrollers a fun addition to your arsenal. This project is what prompted me to get into them, and there's lots of stuff I'd like to do with them separate from this project (1st up is triggering slave flashes for photography). I'm planning to use an ATMEGA32, which might be more than I need, but isn't that much more expensive if I'm getting plain chips and only making one of these. If I need the extra capacity at all it will be because of the text on LCD user interface I have hopes of adding. I think the 8535 is close to identical excep it has less Flash memory. I've got a general AVR programmer (STK500) so I can choose chips flexibly. Not sure what kind of setup you're considering. The folks at avrfreaks.net are pretty excited about the Dragon, which I think can be used for programming and on chip debugging, and it's not that expensive. Starting with a board like the ones at futurlec might be a lot easier.
As for batteries, I've been very lucky and found two electric scooters put out in the trash, and both had 2 higher capacity batteries.
Thanks for the guidance...well as my power source is concerned i can only exceed till 24V to 30V DC and my runtime will be not more than 5-10 mins...yes my tilting method for elevation will be to use some other motor connected to the PVC to help it lift...my range is short enough that is i have to shoot for not more than 2-3 meters...still i didn't get how i would need the rollers to be at top...even saying on top what makes the difference as both rollers are gonna function simultaneously so i don't think so placement would matter but still can you justify it how...??? Well guys can you also upload your device and model pics/videos/designs etc to some where so that we all could see and share...
My comments of top-bottom vs. side-side were assuming you wanted to control the spin of the balls as one often wants to for tennis (top spin, or underspin). If you're going to run both motors at the same speed, then I agree the orientation doesn't matter.
I've finally posted some pictures at flickr. Have a look at <a href="http://www.flickr.com/photos/76392020@N00/">my tennis ball machine picture set</a>