Hi, i’m using some hitec digital servos in an application which uses a mini maestro to get the servo to complete two cycles every 20 minutes and then stop. Up until this point i’ve been using analog servos, with no issue, except the servos were not strong enough and kept stripping gears. I didn’t figure on the digital ones holding station though.
A couple of thought on how to get around this… can i disconnect servo +ve from the board and use the second channel (unused) and run a line from the
control pin => relay => servo +ve
and set this to turn on before / off after the swipe sequence?
or can I / would I be better to use one (not sure which) of the switches i see here…
ie. pololu.com/catalog/product/1211 ?
Or is there a really easy way around this which I have missed? (probably most likely! lol)
Any thoughts would be appreciated.
I’m not sure I am understanding you correctly. When you say,
do you mean they are holding the position they were commanded to go to even though you have stopped sending RC servo pulses?
It sounds like you want your servos to sometimes be back driven. Generally servos are not meant to be back-driven and we do not recommend doing it. That said, both of your ideas for disconnecting servo power sound like they would work. I am not sure if there is a problem with connecting power to the signal/ground lines of a servo while disconnecting power. For example, with microcontrollers, this kind of thing can get you into trouble where you are powering the micro off of its IO lines.
Thanks for your response. You’re correct in what I meant by ‘hold station’. I don’t want them to be back driven, but they will be underwater, sometimes in a fair bit of current. If some weed gets caught on them for example, I don’t want them constantly fighting to hold their position as it will chew through the batteries.
Am I correct in assuming that the signal post will power independently of the servo power (ie power off the board).
Also, would the pololu switch be lower power as it is not physically connecting a relay - and do you think the signal pole would have enough power to do this (I guess it is <@20mA?)
As far as the power to the servo signal input - I was going to use another channel to do this, however are you suggesting that the controller may still send signals to the servo trying to tell it to go ‘home’ ?
Yes, the Maestro’s microcontroller powers the signal lines independently of the servo power.
If you are using the Maestro’s onboard regulator, you only have 20mA in total available to peripherals. There are more details about this in Section 1.A of the User’s Guide. The IO pins are protected by 220Ohm resistors so they are limited to sourcing/sinking 22mA. I suspect the difference in power between the two options is probably small compared to the power your servo is using.
Also, I occurred to me that perhaps your Maestro is still sending pulses to the servo. Have you verified that you have actually stopped sending signals to your servo?
Pretty sure there are no pulses being sent (you can back drive an analog servo plugged in). I knew about the 20mA regulated for peripherals, I was just unsure as to whether the singal pins were restricted the same.
Thanks for your help, I think i may go with the pololu switch and see how i go.