paper: Drivetrain Acceleration Model

[Richard100]

Ether - Very nice, thanks for developing this. Do you think it could be extended to include wheelbase parameters and predict motor current draw when turning (say differential steering)? We've had trouble in this area during drive system design.

[Ether]

Originally Posted by Richard100

Ether - Very nice, thanks for developing this. Do you think it could be extended to include wheelbase parameters and predict motor current draw when turning (say differential steering)? We've had trouble in this area during drive system design.

Possibly. You can find several links here for static analysis of turning force (which relates to motor current) for skid-steer vehicles.

[cadandcookies]

The executable works very well functionally-- I was able to run it with no problems and create some nice graphs based on it.

The only problem I've noticed is that I really have no idea what any of the variables are until I look back into the original program for comments.

I don't think I've quite expressed my appreciation for this program enough-- it is really nice to have such a good model for generating a good estimate of how fast a given drive train setup will move.

[Ether]

Originally Posted by Ether

You can find several links here for static analysis of turning force (which relates to motor current) for skid-steer vehicles.

Due to changes made by the web host, many of those links are now broken.

So I collected everything together in one place and posted it here.

[lemiant]

Thank you so much for making this. You're my go-to resource for FRC physics and the community wouldn't be the same without you.
On line 84 voltage drop is calculated, but you don't ever seem to account for it when calculating the torque of the motors, is that correct?

[Ether]

Originally Posted by lemiant

On line 84 voltage drop is calculated, but you don't ever seem to account for it when calculating the torque of the motors, is that correct?

No. It is accounted for in the motor torque calculation. See the last paragraph in the voltage drop model rev E.pdf document:

In the C code, there is an accel(V) function which computes the vehicle acceleration given its speed V. The vehicle speed V is directly related to the motor speed Wm through the wheels and the transmission, assuming no wheel slip. This motor speed Wm is then used in the formula Tm=Toffset-Tslope*Wm derived above to obtain the motor torque (see line 77 in the code). By using this formula for motor torque, the voltage drops due to current are automatically included in the calculation.

If you change the values of Rone and/or Rcom, you will definitely see the effect of changed voltage drop in the model's output.

Thanks for the words of encouragement.