Author Topic: Known Issue with Dimension Engineering Sabertooth Speed Controller in RC mode  (Read 5668 times)

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Offline vidamTopic starter

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Last weekend, I spent the entire time fiddling with  RC mode settings for the Sabertooth. I was trying to get RC mode to work reliably for the differential drive robot using remote controller Futaba transmitter and RC receiver. I manually recalibrated the trim for throttle because sometimes when the receiver is turned on the robot starts moving on its own even after I calibrated the transmitter trim settings. I even went back to the store where I purchased the transmitter and they witnessed the same phenomenon. I accused them of giving me a bad RC, but they said this is not the problem. Because we connected servos to the receiver and we were able to control the servos just fine. The store suggested it could be due to signal interference like from some guy down the same street with the same transmitter and channel. But that didn't seem highly likely given that "interference is more twitchy than the kind of movement we encountered on the robot".

I went home and read the sabertooth manual and found the problem documented in the manual. I could not believe my own eyes. I wasted like an entire weekend on this issue only to find out the problem was in this manual in a small paragraph on page 12 "A note on certain microprocessor receivers". And I quote from the 2x10 Sabertooth manual:

"A note on certain microprocessor receivers
Some receivers, such as the Spektrum AR6000, will output servo pulses before a valid
transmitter signal is present. This will cause the Sabertooth to autocalibrate to the receiver’s
startup position which may not correspond to the center stick position, depending on trim
settings. This may cause the motors to move slowly, even when the transmitter stick is centered.
If you encounter this, either consult your receiver manual to reprogram the startup position, or
adjust your transmitter trims until the motors stop moving. As a last resort, you can enter R/C
microcontroller mode which will disable Sabertooth’s autocalibration."


After reading this it all started to make sense why my robot seems to work some of the time with the receiver and other times not. It is because the Sabertooth enters some kind of autocalibration mode all on it's own. You can imagine how frustrating the past weekend has been.

My solution is read the receiver signals in my Axon MCU and then output the PWM commands to the Sabertooth in microcontroller mode. I just hope that this will work as I have no other solution.

Today at work, a colleague had a robot with the Sabertooth 2x5 RC speed controller with a JR RC transmitter receiver. He had the same problem as I had. Sometimes you could control the robot and other times the robot would move on its own when you turn on the receiver even after you calibrate the throttle the last time it worked.

I told him about my experience with the Sabertooth 2x10 and his response was so your telling me the Sabertooth is crap. And I was like yeah at least for RC mode.

There is 2 RC models where Sabertooth did not work-- JR RC and Futaba RC. I can get the exact model numbers if anyone else wants to avoid running into this problem.
« Last Edit: August 12, 2008, 01:46:21 PM by vidam »

Offline GHF

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I actually had this same problem with my GWS 75MHz + Naro receiver + Sabertooth 2x10. I fixed it by turning on the transmitter after turning on the receiver. The trouble is that the receiver outputs garbage when the transmitter isn't on, but the Sabertooth thinks that's the right signal, so it calibrates itself to the garbage signal.

I actually love my Sabertooth, especially for its autocalibration (once you get it working)... after having some very bad experiences with Robot Power's Scorpion XL, which is probably the only thing in the same price class with similar specs.

Offline vidamTopic starter

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I fixed it by turning on the transmitter after turning on the receiver. The trouble is that the receiver outputs garbage when the transmitter isn't on, but the Sabertooth thinks that's the right signal, so it calibrates itself to the garbage signal.


Don't you mean you turn on the receiver after you turn on the transmitter?

 


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