Lynxmotion Tech Support

Hi,

I'm currrently on a project with the 4WD rover. I'm planning to use the SABERTOOTH 2x5 controllers and my microcontroller is a TMS320F28069.
Why not use one of the many "supported" ones, well, I used this one a lot and I like it. Plus, I already wrote most of the libraries already in another project.

Thing is, I'm kinda new to motor control and I read the user guide and saw that I could use a PWM output with a Low-Pass filter to control the analog input of the sabertooth.
Will the motor speed be controlled with the duty cycle of my signal ? (0-49 = reverse, 50 = stop, 51-100 = forward)
And will the frequency matter much, as long as I'm over 1kHz (recommended in the guide)?

Thanks a lot

Alex

I attached an image showing a block diagram of the output circuit to show what I want to use.

In the above scenario the filter is changing the pwm to a DC voltage. So the frequency of your PWM is essentially removed. I can't say it will be exactly at 50% though.

_________________
Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

Okay, but the voltage will vary with the Duty Cycle right?

That's the idea, yep.

_________________
Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

And maybe one last precision, I heard that PWMs used as DACs are imprecise. I don't need so much accuracy, I'd be glad to have maybe 6 speeds + stop in the beginning. But if I want to have more resolution, should I use a better filter? Maybe two first order filter in series?

Before you go guessing how many steps in the entire range why not just try it and see what precision you can achieve with PWM. There are different methods of communicating with the sabertooth. You don't need to use PWM / filter / analog in.

_________________
Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

Yeah that's true... Sorry for bothering :\

I just want to make sure they will work with my controller. I won't be using R/C for sure, maybe some wireless command via serial (XBEE probably), but it will mostly be automated.
And I think it will be much easier to control via PWM than via serial, even if it's less secure, it's not critical.