
Rob-bot

Hi All, I am working on a wheelchair based robot that utilizes 2 24 VDC motors and will be controlled by EZ B V4 controller and a Sabertooth 2X32 motor controller. The problem Im having is that when I hook up the positive 24VDC line to the Battery + terminal I get positive potential through all remaining terminals. So, basically if I put a volt meter probe on the detached negative and the other on and sabertooth controller terminal I get 24VDC, which I think would cause a short. I tried calling and emailing Sabertooth Tech support with no response for a couple of days, so any help at all is highly appreciated ?
Thank you.
Edit: Woops. Here's the correct answer:
Peak motor amp draw + 20% overhead = correct fuse size.
@ptp, I don't ever remember seeing a drawing of the sabertooth's inners. They probably want to protect that information.
Sabertooth has a built-in current limiting, i presume the model 2x32 will cut the power if try to pull more than 32 Amps (continuous).
The motor fuse should be aligned with your motor's max recommend amps.
If you don't have the fuse the Sabertooth will cut the power when the safe limit is reached for your model.
This can be an "operational problem" replacing fuses every time your bot gets stuck...
To avoid that check the sabertooth manual.
Set the motor limit below the motor fuse, that way the fuse will help you with
catastrophic or multiple failures e.g. (motor controller, motor stalled etc etc)
Thank God for this forum and its contributors. I hope one day soon I can also help others here too.
We know little about your bot and how you have it set up and wired. It sounds like you may be using all the original motors, brakes and wiring from the power wheelchair?
You say you added the Breaks in the Power Output tab in the DE software? Did you set the Turn-On, Turn-Off Delay and the E-Stop delay below the Mode window? You may have to adjust these to get the brakes to work as needed.
Also are you supplying power to your breaks? I've read that the default of a power wheelchair braking system is locked on when there is no power in case the power system shuts down (for obvious reasons). EDIT: (I now see RR mentioned this as I was writing my post. I'd pay attention to what he suggests).
Here is a cut from the the ST 32 manual:
In this mode, the power outputs are used to operate electromagnetic brakes. P1 corresponds to motor 1
and P2 corresponds to motor 2. When the motor stops, the brakes activate after the Turn-On Delay.
When the motor is commanded to move again, the brakes deactivate immediately, but the motor does
not turn until the Turn-Off Delay has elapsed. If an emergency stop is commanded, the brakes will
activate after the E-Stop delay has elapsed.
Lastly, if you have rewired to the braking system did you install blocking diodes? If not you need them. If so you may have them in the wrong direction.
Hope this is helpful.
The size of the diodes need to be sized to the amount of amps that this part of the circuit is passing. That usually depends on the amp draw of all devices added together. You also should use fast switching diodes.
Good luck.
I plan on becoming an active member of the forum as from previous threads I read were very Informative. You're a great bunch of fellow robot enthusiasts and I look forward to sharing my progress pics from the robot I am building.
Thanks,
Rob