Lazy Sabertooth?

Lynxmotion
1

Okay so I’ve got a bit of an odd issue here. Today I was toying around with my robot (okay, so right now it’s just plywood and some wheels :slight_smile: ) and the motor controller started acting up. I’m using a Sabertooth 2X10 in PWM mode.

My controller is an Atmega48 running at 8MHz. Two PWM channels are hooked up to S1 and S2 on the Sabertooth. The 0V is tied in with the ground on the microcontroller per the SB’s instructions. The motors are hooked up to M1 and M2 respectively and are BaneBots 42mm 48:1. The SB doesn’t seem to have any problem powering these motors in forward or reverse so I’ve ruled out pretty much any kind of load issue (but I could be wrong). The Atmega is powered via the SB’s 5V output. The power source is a 12V lead acid battery and I’ve verified it is fully charged.

Dip switches on the SB are 111011.

Basically what happens is the motors are supposed to go forward and then it ‘turns’ by reversing the voltage on one motor to make a zero-turning style turn and then go forward some more. Fairly simple task. I had it working most of the day but then at one point after power on it seemed to ‘give up’. The motors would only go forward when they were on the ground and when a turn was issued (or a reverse direction) it would go forward about a foot and stop. However when you lifted the bot off the ground the wheels would run just fine, go forwards and backwards, etc. It was as if the controller couldn’t handle the extra load anymore and it would just give out. No error lights were showing on the SB and the Status 1 light is lit solid green.

I have changed the Atmega with a brand new chip, checked all my wires, changed batteries… I’m at a loss. The only thing remaining to check/change is the Sabertooth.

Unfortunately the SB is already out of warranty so repairing/replacing is probably out of the question but I sent a request to support anyway. I figured I’d ask for advice or something to check in the meantime.

Thanks!
Kelly

2

xcesmess,

I do not believe that the 5vdc output from the SB is capable of powering your Atmega48 without causing a problem with the 5vdc on the SB. That may be your problem.

Just a thought.

Regards,
TCIII

3

I could see that being a possible problem… I need to check the voltage coming out of the SB to make sure it is a solid 5V. The data sheet for the M48 says that the stable operating voltage is 2.7V to 5.5V with a maximum of 6V. I’ll take a look at it and see. If all else fails I do have 5V regulator I can run off the battery (or another power source if needed) to power the Atmega. I was hoping to keep things clean and less wires :slight_smile:

Thanks
Kelly

4

Well I’ve located the problem finally. I have a couple of relays onboard that control power to the motors (so they don’t consume power while ‘stopped’). It seems they have come down with a problem. Bypassing them causes the bot to act as normal.

Thanks
Kelly