CIM ? feeling foggy

We have looked at the curve, but what would the optimal RPM be for a CIM ? The application is the shooter and the concern is recovering wheel speed. We are using the spinbox which has a 1.2 overdrive, this allows us to lower motor speed. I am not sure if this is good.

If your concern is recovering wheel speed, you want your CIM to be spinning at roughly half the free speed at your setpoint. That way, when the speed drops due to a frisbee passing through, you are near the max power point on the operating curve. Also, the more command headroom you have at your setpoint, the faster the recovery.

For a more thorough answer, please answer these questions:

  • what motor controller(s) are you using for the shooter?
  • what motors(s)
  • what is the total gear ratio from motor(s) to wheel(s)
  • wheel(s) diameter
  • what is your setpoint operating speed(s)
  • what is the current draw or voltage at those operating speed(s)
  • what speed sensor are you using?
  • how are you decoding the speed sensor signal?
  • what’s your speed control method (PID, bang-bang, TBH, etc)

We are using:

1 CIM motor
1.2 overdrive AM spinbox
US Digital HB 5M encoder
Jag motor controller CAN
8 inch pneumatic wheel
1650 RPM

The exit velocity seems to be right on, accuracy is good at a conservative feed rate. When using a fast feed rate the accuracy falls off a bit.

  • what motor controller(s) are you using for the shooter?
  • what motors(s)
  • what is the total gear ratio from motor(s) to wheel(s)
  • wheel(s) diameter
  • what is your setpoint operating speed(s)
    - what is the current draw or voltage at those operating speed(s)
  • what speed sensor are you using?
    - how are you decoding the speed sensor signal?
    - what’s your speed control method (PID, bang-bang, TBH, etc)

Is 1650 rpm the setpoint speed of the wheel or the motor?

If you’re only spinning the wheel at 1650 rpm, why do you have a speed-increasing gearbox? That’s not giving you max acceleration at the setpoint. You want a 1.5:1 speed reduction gearbox. That will allow your motor to be spinning at 2500rpm when the wheel is spinning 1650.

The motor speed is 1650 at 1.2:1 overdrive, this gives us 1980 RPM wheel speed, PID control (the encoder is on the motor shaft). We went with the overdrive gearbox to give us plenty of headroom for full court shooting. We can achieve a solid 5000 RPM wheel speed without losing all of the torque at full motor speed and voltage.

I think that the 1650 motor RPM puts us into a good torque scenario but poor efficiency, if that matters.

Your original post was expressing a concern about “recovering wheel speed”. I assumed what you meant by that is coming back up to the operating speed after a frisbee goes through.

If that is the case, you’ve got your motor at the wrong operating point. It’s way to slow.

We went with the overdrive gearbox to give us plenty of headroom for full court shooting.

Well that’s new information which could change the answer.

Optimizing your gear ratio for best response from your motor at 1980 rpm wheel speed is one thing.

Finding the right compromise gear ratio for operating at two widely differing operating speeds is a different question

What is the fastest speed you want to operate at?

  • what is the current draw or voltage at the 1980 rpm wheel speed?

  • how are you decoding the speed sensor signal?

I think that the 1650 motor RPM puts us into a good torque scenario but poor efficiency, if that matters.

Gearing your motor for 1650 rpm motor speed at the 1980 rpm wheel operating speed does not give you optimum recovery response.