Counter-Rotating Wheels for shooting PingPong Balls and motor speed controller

Discussion in 'The Projects Forum' started by CaptainPrice, Jun 15, 2010.

  1. CaptainPrice

    Thread Starter Active Member

    Aug 12, 2009
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    So Im looking for a pair of wheels (that I will position and mount the distance of a ping pong ball away). Each wheel will have a motor that I want to be able to control the speed of (or just general speed relative to the other wheel). The wheels will counter-rotate so when a pingPong ball is placed between them it will fire out.

    SO
    I am looking for where I can find the hardware. Like the Wheels, what motor to use and how to control them or their speed, so when i make the rest of the circuit it can adjust the spin and speed of the ball.
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    A minerature baseball pitching machine? As a first guess- 4 in dia. X 3/4 in plywood wheels with 1/2 in foam tires driven by two 15 to 20 W DC motors with independent PWM controls.
     
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  3. Bernard

    AAC Fanatic!

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    For simplicirty, I would use direct drive, with face mount motors having at least 5/16 in dia. shafts. 'Seems to have a decent shaft size , motor needs to be around 1/25 hp. Found some at Surplus Center: 10-2424, .14 hp, 5/16", $19.99, 10-1674, 1/25 hp, 28V, 5/16", $18.99; 10-2520, 1/7 hp, $19.99.
    For initial launch speed of 50 ft /sec, RPM will need only need to be about 2500. Each wheel could have a strobe disc attached, read with reflective IR sensor to allow speed control. Also might use a LED strobe light to monitor speed & differential speed.
     
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  4. CaptainPrice

    Thread Starter Active Member

    Aug 12, 2009
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    thanks for your input Bernard
    I didnt realize the motors might cost me 40 bucks. ill have to look around more
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    You could use a single motor if you used a V-belt or chain drive to link the two spindles together. You might miss out on some interesting effects though, like sideways spins, etc.

    If you wanted more predictability, you might consider using compressed air and a PVC or other kind of pipe. Loading the balls and valving the compressed air might be challenging.
     
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  6. Bernard

    AAC Fanatic!

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    Would $4.95 be better? Look at Electronic Goldmine # G 17287, with 7.5 mm dia shaft; maybe shrink wheels to 3 in & do not feed it golf balls. Also has undocumented encoder attached.
     
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  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    Funny things those ping pong balls. They have this unique characteristic of very low mass.

    I tried the pnuematic tube, but had disappointing result, as the balls virtually stalled as they exited the tube. I suspect due to the large low pressure area as the air expanded behind it.

    I tried the wheel thingy as well, but again, even at high speeds, little energy is transferred to the ball.

    In the end, the only thing that worked for my needs was a spring steel 'paddle' that tensioned in an involute housing, driven off a cycling clutch. A perforated 'barrel' is required to reduce head pressure. I used a steel screen. If you preload a vertical magazine, you can pump balls out at a very quick rate.
     
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  8. CaptainPrice

    Thread Starter Active Member

    Aug 12, 2009
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    I want to keep the two motors so I can play with spins and stuff. $5 amotor is good. Ill just be shooting pingpong balls no golf balls :). The end result should have dials or something to adjust the motor speeds to create the spins and overall speed of the launched ball.
     
  9. CaptainPrice

    Thread Starter Active Member

    Aug 12, 2009
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    interesting. I dont know what to take exactly from this. Ill probably make the wheels a tight fit, maybe a bit spongy on the outer layer so it can squeeze the ball some upon shooting.
     
  10. sceadwian

    New Member

    Jun 1, 2009
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    If properly controlled the spin can make the ball go further. I'm with Wookie though you shouldn't use two motors you should use a pair of commonly geared motors or the spin will be unknown unless you can precisely control the EXACT speed of each motor. Some spin will probably be desired.

    Just a suggestion, the ball straight out of a pair of wheels is going to have a nearly random trajectory. Trying slotting a PVC tube so that the wheels juuuust barely peak into the tube, the wheels give the ball the juice it needs and foot or two of barrel will give it some straightness.

    Some high end paintball guns use a very slightly curved barrel to give the balls some spin on the way out so their trajectory is more predictable. The curve is usually backspin, but be careful, a heavily spun ping pong ball can actually turn around within a few dozen feet and hit the shooter =P
     
  11. CaptainPrice

    Thread Starter Active Member

    Aug 12, 2009
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    so what would be the easiest way to control the motors? Is there like a simple little IC or something? cause I have never really played with motors much, (only a scooter motor and controller)
     
  12. sceadwian

    New Member

    Jun 1, 2009
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    For something like this don't worry about a controller, just make sure both wheels are driven from the same motor and geared to spin in mirrored directions, it's easy with a simple belt drive.

    Another random tip. Attach a fly wheel, or otherwise use heavy wheels. The extra mass of the wheel will cause the motor to take longer to spin them up but will maintain their speed when the balls suck the motion out of them. Use big enough fly wheels and you can fire streams of pingpong balls before they start to slow down even with weaker motors. Use strong motors good flywheels and a decent feeder and you could probably empty a 55 gallon drum of ping pong balls in 30 seconds =)
     
  13. CaptainPrice

    Thread Starter Active Member

    Aug 12, 2009
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    what is the encoder on it?? what does it do? I've never heard of such a thing.
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    The encoder outputs a signal which can be processed to give RPM. Look up shaft encoder.
     
  15. retched

    AAC Fanatic!

    Dec 5, 2009
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    I think rolling some screen or chicken wire into a barrel will give you the best result.

    You need to move air OUT of in front of the ball in the barrel VERY quickly, else the pressure will slow the ball quite quickly.

    GetDeviceInfo's ideas are golden in this regard. Listen to him, he speaks the truth. ;)

    As for the shaft encoders and the one or two motor design, I would start with the 1 motor turning both wheels.

    You can always increase pulley size on either wheel to change speed and get the spins you want, then when you get a handle on using the encoders, throw the second motor on to see how difficult it really is to keep two motors at synchronized speeds. Especially when incurring odd loads.

    Do both. Start with one motor and a belt drive.
     
  16. sceadwian

    New Member

    Jun 1, 2009
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    retched, just drill holes in PVC tubing, it's going to be much straighter than a roll of chickenwire or other mesh, or better yet use a table saw to cut long slits.
     
  17. retched

    AAC Fanatic!

    Dec 5, 2009
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    I agree. Make a tube like the ones used on submachine guns for barrel cooling.

    Here is a paintball barrel. You can see the twist that sceadwian was talking about, and the airholes we have been talking about.

    [​IMG]
     
  18. retched

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  19. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    My pingpong ball gun was made to fire at an individual standing within 20'. The 'gun' was pivot mounted, servo driven. The project was for a couple of fellows who wanted the device to help tune thier reflexes for thier martial arts involvement. The 'gun' would fire a ball into fixed area at the 20', but doing so randomly. It provided for a very intense workout, and some hilarious facial colorations after a session.

    Not sure what your needs are in ball trajectory, but I can make one suggestion that could save you tons of time. There just isn't enough mass in the ball for spinning wheels to impart enough energy into the ball for substantial flight.
     
  20. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Maybe 35 ft isnt substantial, but thats what my two wheeler throws a ping pong ball. Lower wheel [ 4 1n X 3/4 in plywood with 3/4 X 3/8 closed-cell foam band ] is driven by a Johnson HC970, 12V PM motor. Upper identical wheel pivets sothat it contacts lower wleel. Both wheels brought up to speed[ wild guess 5K RPM ], upper arm lifted, ball injected & away it goes. Drawing not to scale.
     
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