Thread: Would This work? wiring pwm question
View Single Post
  #2   Spotlight this post!  
Unread 19-02-2011, 02:51
dtengineering's Avatar
dtengineering dtengineering is offline
Teaching Teachers to Teach Tech
AKA: Jason Brett
no team (British Columbia FRC teams)
Team Role: Mentor
  
Join Date: Jan 2005
Rookie Year: 2004
Location: Vancouver, BC
Posts: 1,831
dtengineering has a reputation beyond reputedtengineering has a reputation beyond reputedtengineering has a reputation beyond reputedtengineering has a reputation beyond reputedtengineering has a reputation beyond reputedtengineering has a reputation beyond reputedtengineering has a reputation beyond reputedtengineering has a reputation beyond reputedtengineering has a reputation beyond reputedtengineering has a reputation beyond reputedtengineering has a reputation beyond repute
Re: Would This work? wiring pwm question
Yes, but....

Yes, this would work. All the grounds are tied together inside the cRio at some point anyway, and there is no significant current travelling along the line, so I can see no technical or engineering issue that would prevent this from working.

However I do note

<R57> Every relay module, servo, and PWM speed controller shall be connected via PWM cable to the Digital Sidecar and be controlled by signals provided from the cRIO-FRC via the Digital Sidecar. They shall not be controlled by signals from any other source.

This is more intended to explain that the cRio has to control the relays and speed controllers, however it also says "shall be connected via PWM cable". The catch is that it doesn't define PWM cable. Is PWM cable the standard Red/White/Black three conductor cable, or is PWM cable any cable that carries a PWM signal?

I can see an inspector claiming that if it isn't standard, unmodified "PWM cable" similar to that supplied in the KoP that is is not PWM cable. While I would interpret things differently, I also couldn't say that the other inspector's interpretation would be "wrong".

So I think you are correct in assuming that this wiring plan would work, but you have good reason to be concerned about taking it to tech inspection. My suggestion is to a) Ask the Q&A system for official guidance b) Bring "PWM Cables" of the correct length, in the event a ruling on this does not go your way or c) just use the standard cable if you've got it kicking around.

Jason