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 An issue with pwm controllers/servo controllers
 
 9/14/2007 7:56:35 AM
AeGis
3 posts


An issue with pwm controllers/servo controllers

Hey guys, I'm experiencing a weird issue with my new serializer. I'm not sure if anyone has encountered this before or if there is a fix for this.

Basically, I'm using the serializer as an interface to an all-terrain rover - final year project for uni. The rover has 2 motors connected to the on-board H bridges, and a mounted robotic arm which uses 5 Hitec Hs-422 servos and one mini servo. The problem is that when i try to drive the motors, the serializer also randomly moves the robotic arm, even though no instructions were given for that. This seems to occur when motors are accelerating or sufficient load is applied to wheels. For now I'm using hyperterminal, however I don't think that is the issue. If anyone has encountered something similar before or maybe can suggest a solution, I would be very grateful.

 

Thanks in advance

 

 9/14/2007 3:38:57 PM
ringo
36 posts


Re: An issue with pwm controllers/servo controllers

We did recently hear of a behavior like this. The user was able to solve the problem by adding a large Capacitor to the power input connection. I believe his problem was the voltage was sagging from the motor current draw. This could be the same problem you are seeing. Either that or the motor you are using a drawing too many amps for the H-bridges. When they get stressed they can cause some erratic behaviour on the board. Do you know how much current your motors pull when you load them?

 

Ringo

 


Ringo Davis, Hardware Technical Lead RoboticsConnection.com
 9/15/2007 7:16:23 AM
AeGis
3 posts


Re: An issue with pwm controllers/servo controllers

Hey Ringo.

Thanks for your reply. I've just tested the motors, and they don't seem to be drawing excessive current. The peak current for each motor running at 9.6V 100pwm  while holding the wheels stationary is around 2.8amps, so they shouldn't go over the h-bridges rated peak currents. The motors also have bypass capacitors installed, but am not certain what capacitance values they are - got em off an old R/C car and they got nothing written on them. I will probably try bigger capacitor values to see if that would make a difference. Which capacitance value would you suggest to try?   

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