Let's Make Robots!

Rover 5 + Bluetooth + Android

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I'm working on a new robot with the Rover 5 chassis. Here's my setup: Arduino Uno, Adafruit Motor Shiled w/  2x SN754410 + BlueSmirf Silver.

Here are some temp pics, it's still work in progress.

I managed to cook one of the  SN754410 while using a 64KHz pwm.. :)

 

 

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Firstly, you will fry most "H" bridges at 64KHz because the "no smoke" logic cannot switch quick enough. The L293D is only rated up to 5KHz and while I could not find a specification on the SN754410 it's switching times are similar.

Secondly if you did have a motor controller that could handle 64KHz you would find your motor torque severly diminished because the inductive reactance of the windings just went through the roof. Only motors with very low inductance can be driven at high frequencies.

Third, the stall current of the Rover 5 motors are 2.5A for each motor. The SN754410 is only rated at 1A continuous and 1.5A max. Even if you parallel the outputs your pushing the chip beyond it's rated limits if you stall for mor than a few seconds. The simplest solution is to stack your chips with at least 2 chips in a stack.

 

The chips were stacked, you can see in the first photo. I did my research, I simply forgot to edit the pwm value.. Thanks for the response!

How did you end up using so high frequency? Take a look at this page: http://arduino.cc/playground/Main/TimerPWMCheatsheet.

The default Arduino frequencies are:

Timer0 ~1kHz
Timer1 ~500Hz
Timer2 ~500Hz

I use Timer0 for motor control and never had any problems at the default frequency. And remember, Timer0 is also used for millis and delays, never change the frequency of this timer.

I saw the Arduino at the end of the platform and wondered if the Rover's wires were long enough.  It looks like you've extended them?  Looking at the wires, have you got the 2 motor version?

Nice pic of the (remains of the) chip!  -> can the chips handle the stall current of the motors?

See:

https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B__O096vyVYqNzE3OWYyMTctZmFkMC00YjY1LTg0Y2ItNWUwMjQwZWZmMGI1&hl=en_US

They're rated at 2.5A stall current.

I've got the 2 motor version and I'm currently not using the encoders. I extended the wires with male/male jumper wires. The rover 5's wires are long enough, it's just that they have a different socket at the end.