When I plug a servo into my ArduPilot board, it starts off rotating clockwise slowly, but continues accelerating and turning until it pegs against full-clockwise rotation, and the motor continues to strain against the stop. That to me sounds like the wrong type of signal is being sent out - like it's treating the servo like it's a motor at 50% throttle instead of neutral position. Has anyone experienced this before?

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What position are you plugging the servo into on the Ardupilot ?
I plugged it into port 1 and 2, just to make sure it was not just the ESC output port. It may also be of note that it's a Futaba S3003, which is a "standard sized" servo - not the mini-servos usually associated with control surfaces.

Also of note, I'm running on an external battery source, so the PSEL is jumped, not using a Batt+ESC on the input side.
Kyle, I just tested exactly that configuration (Futaba S3004 and BATT power) and it works fine. Are you using the latest code?

Please note that if you choose to use BATT power rather then Rx power, the Rx must have its own power source. The ArduPilot board will not power the Rx and servos by itself.
Chris,

Many good questions! I was hoping that maybe it was just an obvious problem like "you have the servo plugged in upside down." (well, maybe not THAT obvious!)

Truth is I am using Michal's Google Earth / ArduSim setup for a simulation, and his C++ version of the code. I am not as concerned about the airplane actually flying as much as the software doing what I want it to, such as taking pictures at way points, so I trying to do as much as I can in a simulator where crashing / flying off towards the horizon is a humorous error instead of a tragic one!

On the other note, let me make sure I understand how the BATT / PSEL works. I am powering BATT supplied by a 4x cluster of AA batteries for a total of 5v connected to the board. Does this only power the chip and not the servos? If so, 4x AA's should power the chip for a looong time! IF that is the case, do I need to have an additional power source supplied to input channel CTRL in order to activate the servos?
"IF that is the case, do I need to have an additional power source supplied to input channel CTRL in order to activate the servos?"

Yes, that's correct. In that configuration, the servos get their power from the Rx (or ESC on the output side, if you're flying electric), not ArduPilot.

Just out of curiosity, why are you using the BATT configuration? It's mostly designed for people who fly gas and want power redundancy on their RC and autopilot gear, so a short or something catastrophic in the autopilot won't kill the RC system too.
Ah, thanks for clarifying that!

The ultimate goal of my project is to build a glider that will be carried aloft by a weather balloon to hopefully 100k+ ft, be released, and fly home - taking photos all along the way. If that is successful, then "more ambitious" goals could follow. Therefore, at this point at least, a motor is really not part of the equation.
So you'll have no RC system at all? If so, you'l have to modify the code so it isn't looking for an autopilot-on toggle.

If you want to power both the servos and ArduPilot from the same battery, there is a work-around I describe here.
Ah, that must have been one of the changes present in Michal's code. One of the reasons for testing in a sim was that I want to test the viability of some fairly unusual functions, only begin navigational servo controls once decent begins. The whole trip could take over an hour, and I am concerned about battery life, on the other hand, adding extra batteries would be less to worry about than wondering if your UAV turned on or if it's been rendered an expensive paper airplane!

Oh, after looking at the described work-around, I found my obvious answer - I added _additional_ solder to the PSEL/BATT jump, instead of un-soldering then resoldering for BATT. This would appear to create voltage flow into the servo output side, causing the servos to move on their own.
wow.. that's a great idea about the balloon carrying the glider, etc!
the balloon would just take the glider very far away and pretty high, then
the glider would free itself and glide back home taking pics on the way back...
that would fix the battery limitations issue for controlling the motor therefore
being able to travel so far away because it would only use the battery for the
microcontroller, servos, etc... =)

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