How many CIMs in your drivetrain?

[Jared Russell]

Originally Posted by CryptoStorm

Isn't that basically what your calculation is based on though?

Yes, by putting two CIMs together in a gearbox you are basically creating a "super motor" with the same free speed but double the stall torque, stall current, and free current.

Obviously with larger loads the two CIM gearbox will be more efficient (at one CIM's stall load, the single CIM gearbox is stalled and therefore has 0% efficiency, whereas the two CIM gearbox is near its max power point).

At lower loads, the one CIM gearbox will be more efficient (at some tiny load just >0, both gearboxes are running at roughly free speed, but the two CIM gearbox is drawing twice as much current).

[ratdude747]

Originally Posted by Jared Russell

Maximum power and maximum efficiency occur at two separate points on the motor curve for brushed DC motors.

Maximum power occurs when P(out)=radial velocity * torque is maximized, which is at half free speed and half stall torque.

Maximum efficiency occurs when P(out) / P(in), or (radial velocity * torque) / (current * voltage) is maximized. This always occurs somewhere between the maximum power point and free speed (it varies from motor to motor depending on free current).

Originally Posted by Ether

The max power (rated power) of the DC brushed motors used in FRC occurs at roughly half the free speed.

The max efficiency occurs at a higher speed.

EDIT: Jared beat me to it.

Well, obviously I wasn't taught correctly. Then again, the class was using AC motors (both single and 3 phase), and with those, we found such to be true. Maybe inductive (AC) motors behave differently?

(Sorry for the misinformation, I feel kinda dumb here).

[cbale2000]

A lot of interesting discussion (and Math) in this thread.

What are peoples thoughts on using a combination of CIMs and MiniCIMs in drive systems?

My team is planning on using 4 CIMs + 2 MiniCIMs in our drive system for the second time this year (on a pair of 3 CIM ball shifters). Do you loose efficiency doing this due to the differences in the MiniCIM performance? Worth the extra weight?