I recently purchased a mini maestro 24 and some servos, as I am working on a motion control project… I have to say I’m very, very new to all this, and only recently discovered pololu. The board works great, and so far I managed to control the servos, and use a switch to send them to different positions (thanks to the script tutorial). All works great and seems pretty responsive.
Now, I want connect a potentiometer to the board, in order to get feedback on positioning. The pot I have comes from the GWS S777CG servo, I took it out after modding the servo for continuous rotation (which works great). The diagram in the manual shows the potentiometer connected to the +5V regulator output of the board, and not to the VSRV servo voltage… I planned to crimp the cables with 3-pin housing, to be able to easily connect/disconnect and swap it around - but obviously if I can’t connect the pot to the VSRV it’s not the way to go.
Also, it says that the potentiometer should have a resistance of at least 1 Kohm not to draw too much current - how do I know? It’s pretty small, as it’s an internal servo pot…
The output voltage of a potentiometer will range from the voltage applied to one side of the pot to the voltage applied to the other as you move the wiper. Since you should not apply more than 5 V to the Maestro channel inputs, you should not connect your potentiometer to any voltage that is over 5 V (unless you really know what you’re doing and are taking additional precautions). Also, using a regulated voltage is usually desirable because it keeps the potentiometer output from being a function of how well charged your battery is.
I expect your pot to be over 1K (otherwise, the servo would be wasting a lot of power through it), but the best way to tell is with a multimeter. Just set the meter to measure resistance and connect it across the two ends of the potentiometer (the resistance between the two non-wiper leads will always be constant and independent of the pot position). If you don’t have a multimeter, I strongly recommend you get one as it is highly useful to have one when working with electronics like this. You can get an inexpensive one at a local electronics store for around $20 if you’re on a limited budget.
So inversely, would there also be a max resistance not to exceed? I have a few 300k laying around, would it be fine to use them with the mini maestro 24?
Also, I have a few questions about the maestro…
- What is the max amp it can withstand? I have 2 gws S777cg, the doc that came with them says they can draw up to 16A.
- If I was to add quite a few more, should I power them independently from the maestro?
- And if I do so, do I simply connect the signal wire only on the maestro, and keep the 6V/grnd lines separate?
- Also, what is the max rate of digital inputs on the board - I mean, how many counts can it register (like from a wheel encoder), and how likely is it to get saturated if I connect a few “fast” digital inputs?
Sorry for asking so many questions, I’m learning about all this, and didn’t find these specific answers in the manual or searching around.
300k is a pretty high. You can try it and see how it works for you, but something closer to 10k would probably give better results.
To answer your other questions:
The Maestro will probably be able to deliver as much current as the wires you are able to connect to it can handle, and if it gets damaged, the servo power traces can pretty easily be repaired by soldering a wire across the damaged trace. I think connecting two of those servos would be fine.
You would need to connect the signal and ground wires to the Maestro. The same ground wire would also connect directly to your separate servo power supply along with the power wire.
The Maestro does not have any built-in feature for processing quickly-changing digital inputs. You might be able to do something using the internal scripting feature, but we have not characterized what would be possible, and I expect that you would not be able to handle any signals that are faster than 100 Hz. If you need to read encoders, you might be better off getting a programmable controller such as a Baby Orangutan or Orangutan SVP.
Excellent, thanks for your time!