CIM motor driver for "shooter" application

[whophil]

Hi all, new to electronics and robotics.

I'm looking to use a CIM motor in a direct drive (non-geared) "shooter" application with each motor driving a flywheel weight of 2 lbs. The load of the projectile is negligible. I am looking to achieve a flywheel rotation speed around 5000 rpm and will be controlling the speed with PWM.

I know the stall current on the CIM motor to exceed 130 A, but a motor driver for this current is prohibitively expensive.

Is there anybody who has run the CIM in direct drive for a shooter that can comment on the transient start-up current draw as the motor works to spin up the flywheels? If so, what motor driver were you using? Is it feasible to reduce the start-up current draw using a PWM ramp-up?

I will be handling the PWM through my microcontroller so I just need something simple with a high current capacity and fast ( > 10 kHz) switching.

Thanks,
Phil

[EricH]

I've used a "Big CIM" with minimal gearing for a shooter before, but it's been a while. The Big CIM is essentially the same as a CIM in terms of power output, IIRC.

The mechanical setup, as I recall, was about a 1:1 (via belt) to about a 1.5:1 (via chain). I don't think it was any higher than a 2:1 gearing slowdown overall max.

If I remember the electronics setup, we ran that particular line off a 40A snap-action breaker through a Victor 884 speed controller, with zero problems. I don't know if there was any rampup in the programming, but I do know that we didn't load the projectile in until the wheel setup was going at close to full speed. (The Jaguar speed controller will also work.)

If your projectile is going to be just moving through the shooter, without stopping, I don't think you need to worry about any 130A current. Just have some form of loader that won't load unless the wheel is already spinning near the target speed. Depending on your application, that could be as simple as a hand or as complex as a linear feed made with powered belts, where the power turns on to load the shooter.

Remember, keep the CIM moving. If it stops completely, then you'll probably hit the stall current. If it's moving, and moving fast, it won't get anywhere near the stall--free current is 3A, max power is at 68A.

[whophil]

Hey EricH. Thanks for your insight. Sounds like I should be OK on the current draw as long as I have a decent motor driver. I'd definitely spring for the Victor or Jaguar controllers if I had the money, but unfortunately their costs are driven a little high by the inclusion of the motor control components.

I have found a few (theoretically) suitable made-in-China motor drivers on eBay -
e.g. http://www.ebay.com/itm/High-Current-DC-Motor-Driver-Module-MOSFET-control-for-Robot-Arduino-Projects-/220984305430?pt=LH_DefaultDomain_0&hash=item3373b0 e716#ht_7302wt_1398

http://www.ebay.com/itm/High-Current-Dual-Motor-Driver-Module-Board-Heat-Sink-PWM-Signal-NEW-/221043792022?pt=LH_DefaultDomain_0&hash=item33773c 9896#ht_12684wt_1398


but I'll have to consider whether I want to take the risk on those.

[Dale]

Some observations.

We used a normal CIM on this year's shooter. It was geared down via chain about 2:1. It was driving two 9" 2lb pneumatic wheels as our solution for storing energy via a flywheel and shooting the ball. It worked great..very consistent.

Our Jaguar powering this shooter was just barely able to bring it up to speed from a dead stop without shutting down for over current.

[Ether]

Originally Posted by Dale

Our Jaguar powering this shooter was just barely able to bring it up to speed from a dead stop without shutting down for over current.

If you have speed feedback, you can limit the applied voltage at low speeds to prevent Jag shutdown.

[roystur44]

Here is a short video of our prototype shooter using a direct driven CIM. We controlled the speed using a Jag and a custom PWM circuit generator.

http://www.youtube.com/watch?v=SjDmMAaj8ZA

Startup to final speed was a few seconds. Ball compression was 2", 2 6 " KOP wheels

Here is a pwm circuit from Jameco that might do what you need

https://www.jameco.com/webapp/wcs/st...0001_120539_-1

[Ether]

You can generate an RC Servo Signal using an old laptop computer.

http://www.chiefdelphi.com/media/papers/2702