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How to avoid damaging servos


I have just purchased 2 6-channel Maestro cards to drive a series of cockpit gauges on my Boeing 737 home simulator project. I have 7 gauges , 2 of which are double gauges, ie having two servos driving a pair of concentric pointers on a single dial. I have began my testing with the Pololu utility program and successfully got all 6 gauges working with the sliders ( I did find that using a USB power lead did not allow more than 4 servos to work; a fifth one always cause the utility to crash out. A proper large amp power supply caused that problem to go away)

My problems is: I seemed to have burnt out two of the servos, each connected to one of the double gauges. I have no idea what I did wrong and I certainly dont want to burn out more gauges. How do I avoid this??

Thanks for any advice, cheers NobbyH


I am sorry to hear that a couple of your servos are no longer working. From your description, it sounds like the servos in your double gauges had their outputs mechanically coupled. If that was the case, then the servos were probably fighting against each other in order to maintain the specific position they were commanded to go to, which could be why they failed. In general, it is not trivial to couple the outputs of servos together in a way that they do not fight each other. Accordingly, we do not recommend doing it.

If the servo outputs on your double gauges were not mechanically coupled, can you tell me more about that part of your system and include pictures that clearly show your setup? Could you also tell me how you are supplying power?


Hi Jonathon, Thanks for the reply and message.

A third servo has now stopped working, this time on a single-pointer gauge that previously was configured sensibly. I don’t think the issue is necessarily just related to some gauges being double pointers, although I admit that double gauges have an extra potential of the pointers clashing with one another. The gauges are very simple. They all have a pair of plastic gears to allow the dials to rotate at greater than 180 degrees permitted by the Top Power SG90 servos. The double gauges have a concentric shaft which is very loose and easy to keep the pointers clear of one another. Maybe there was a problem there at first that I hadn’t noticed.

The single gauge that has stopped working, seemed to suddenly make distress noises and became very hot. After quickly shutting the system down I realised it had become permanently damaged. What I would like to understand better is: what are the fragility issues of the cheaper “hobby” servos, and how to avoid them. How can the Pololu utility software help avoid these issues in the set-up process? Since the gauges are geared, they do not need to use the whole 180 degree movement of the servo to cover the atmost 45 degree dial.
I presumed that leaving some slack at each end of the rotation using the Maestro utility minimum and maximum parameters would stop the servos being driven beyond the end points and hence overheating?? The Maestro documentation doesn’t seem to discuss these sort of issues. Am I misunderstanding how these things operate?

My power supply a large PC-type that supplies 3 voltsges (3.3,5,and 12 volts) at very large ampage. I think the 5v actually measures about 5.2 volts off-load.

Thanks again for help

Cheers NobbyH

Hi Again,

I meant to say 280 degree dial not 45 degrees !

Cheers NobbyH

It sounds like that third servo was drawing large amounts of current before it died. In general, this can occur from something like the servo trying to move past its internal mechanical end stop, or it could be from the load being too large at the servo output. However, without knowing more about your setup, it is difficult to narrow down what exactly happened. How much load do the gauges place on the servo outputs? You said your supply can output 3 different voltages; what voltage are you supplying to the servos? What servos are you using? (It would help if you link to a datasheet or product page for them.) Can you post your Maestro settings file? (To generate this, you can click File > Save settings file from inside the Maestro Control Center) Can you also post pictures that clearly show what is connected to the output of your servos (e.g. the plastic gears and gauges)?

Your idea of “leaving some slack at each end of the rotation” is good for the reason you mentioned: preventing the servo from hitting its internal end stops. The Maestro can be set up to help user’s prevent their servos from hitting their internal end stops by following the second to last FAQ on the FAQ tab of the Maestros’ product page.


Hi Jonathon,

Thanks for your further advice. I think I now have a much better understanding of the sensitivity issue of cheap “hobby” servos, and also how to best avoid damage issues when calibrating them.
Clearly one should ensure that the rotation is centralised and constrained from rotating beyond limits in each rotation direction at the start, and then expand the range so that the pointer just reaches its endpoints on the dial. This may imply moving the pointer relative to its spindle if necessary.

Before replacing my third faulty servo, I decided to give it one more test before throwing in the bin. I attached it to my second Mini Maestro card, and yes of course, it came back to life! This was after many prior tests including system reboots as is my usual practice. No such luck with the other two dead servos, and they will have to be binned and put down to the cost of experience.

It would be helpful if the Maestro documentation has some discussion on the perils of calibrating servos. Also on the manual, it be would better if the paragraph explaining the meaning of the various parameters of the control utility was positioned directly after the first section showing the panel, instead of after the “Errors” and " another less relevant paragraph. I totally missed it at first glance since I wasnt interested in any of the more sophisticated aspects of Maestro use.

Cheers NobbyH

I am glad that servo is working! Can you quote the paragraph you are referring to?


Hi Jonathan,

It’s a small point, but I am a bit of a stickler on technical documentation. I meant that section 4e Channel Settings should be directly after the first introduction of the Utility i.e. before the Errors paragraph. I realise the tabs in the utility suggest different but they are also in an odd order. The script discussion should be last of the sequence.

As soon as one first invokes the utility, one wants to know what do these parameters that I am using mean?

Regards NobbyH

Thank you for your feedback; we agree that would be a better order, and we have moved the Channel Settings section to be 4.b.