Thread: LMD18201
View Single Post
  #4   Spotlight this post!  
Unread 15-07-2007, 10:25
ebarker's Avatar
ebarker ebarker is offline
Registered User
AKA: Ed Barker
FRC #1311 (Kell Robotics)
Team Role: Mentor
 
Join Date: Jan 2006
Rookie Year: 2006
Location: Kennesaw GA
Posts: 1,437
ebarker has a reputation beyond reputeebarker has a reputation beyond reputeebarker has a reputation beyond reputeebarker has a reputation beyond reputeebarker has a reputation beyond reputeebarker has a reputation beyond reputeebarker has a reputation beyond reputeebarker has a reputation beyond reputeebarker has a reputation beyond reputeebarker has a reputation beyond reputeebarker has a reputation beyond repute
Re: LMD18201

Pins 7 and 8 you should ground. If you had a long cable run from controller to the motor then you could use the current sense but you should be able to safely ignore that for now. Just ground 7 and 8.

Yes I think that the outputs will be pulsing. They will pulse alternating between the configuration needed and open circuit.


But here is where it gets wierd. 'Classical' PWM in the rest of the EE world generally means a signal with some duty cycle, between 0 and 100%.

RC PWM is a little different. It is a 2ms period wave that has an on time of 1 to 2 ms. 1.5ms is neutral or centered and correlates to digital PWM value of 127 in an Robot Controller.

I googled around and found this. You may find it interesting.

http://homepages.which.net/~paul.hil...eedAndDir.html

http://homepages.which.net/~paul.hills/

I need to put this on a scope sometime and play with it. Playing with signals really helps reinforce these concepts. Offhand it looks like that there may need to be a translation between RC PWM and what you need. I may get a chance to do that this week. We have had 2 robots out for weeks on display and teaching and are just getting them back.

BTW, A Victor has circuits added to greatly beef up the current handling capability.

This is a great exercise for students to go through. It really gives you an appreciation for why commercial items cost what they do.

Ed

Last edited by ebarker : 15-07-2007 at 10:30.