Chief Delphi - Camera \ EMF problems...

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Re: Camera \ EMF problems...

Quote:

Originally Posted by Schmitty!

We had a similar issue, not with the FP motors, but with the Mabuchi motor.

Schmitty,
Your video demonstrates the high impedance theory pretty well. The PWM cables act as nice little antennas and pick up the arcing of the brushes as you described. Many motors like the FP and Mabuchi have internal capacitors and/or series inductors to limit the EMI radiation. I have lobbied for teams to be able to add suppression and I will continue in the future. In most cases, when the RC is enabled, the output impedance of the RC is sufficient to reduce or eliminate the crosstalk. Although we didn't spend much time analyzing, wrapping the PWM cable in a ferrite core may have eliminated much of the disturbance and wouldn't have violated any of the robot electrical rules.

I am aware of one team adding capacitors across the PWM cables. I would never recommend this as the capacitance would almost certainly affect the rise time and pulse width making control less reliable and causing some unusual loading on the outputs of the RC.

Re: Camera \ EMF problems...

Quote:

Originally Posted by Tristan Lall

In fact, a team in the Galileo division (was it 177?) mentioned a similar issue,...
...That team felt that it was an item worthy of FIRST's consideration for next year, because the effect ought to be minimal. Note, however, that I believe that their proposed solution involved a non-polarized capacitor across the leads, instead of to the frame or case of the motor.

Tristan,

The team was not 177. It was 173 (Rage) but I am familiar with their problem. You are correct that a non-polarized cap, installed across the motor terminals, eliminated the problem but was not legal this year.

BTW, Rage's technical mentors are (IMHO) top notch and there was no wiring error that I could find.

Regards,

Mike

Re: Camera \ EMF problems...

Quote:

Originally Posted by Mike Betts

It was 173 (Rage) but I am familiar with their problem. You are correct that a non-polarized cap, installed across the motor terminals, eliminated the problem but was not legal this year.

Yes, it was us. We consulted with the inspectors before adding the capacitors, and were told it was not legal.
We went through the competition without it, and the camera still worked.
I hope FIRST looks into this issue.