Maestro 12 Channel moving servos during PC Boot

During boot-up on my PC controlling the Maestro 12 channel, if I have my channels set on Startup or Error to ‘Ignore’, it sets them to 2000uS which causes my servos to move and will hold 2000uS until I start up the software which then sets them to 1500uS (neutral).

If I change the setting, and put it to ‘Go To 1500uS’, then for about the first 2 seconds of boot up, it will set them to 2000uS, and then will change back to 1500uS.

Is there anything I can do to keep it from moving anything until I am running the controlling software?


I am sorry you are having trouble with your Maestro. Could you describe how everything is wired up, where the power comes from, and what type of servos you are using? Also, could you explain how you measured the 2000us? What are the LEDs doing during that first two seconds?

The Maestro really should do what it claims to do in the channel settings, which makes me think you are getting some kind of a glitch when your computer turns on but before the Maestro actually receives power.


Power is coming from a PC power supply (5v rail) to the servo power rail. Logic side is USB.

I have two speed controls tied into channels 0 and 1, on boot up, the Maestro LEDs flash a couple of times, when this happens, the two Victor 883 speed controls (LED Indicators), go full forward, which would be a pulse of 2000mS.

I’ll do more digging this afternoon with it to see exactly which LEDs on the Maestro are blinking.

Could it be that BIOS is connecting to the Maestro on boot just to verify something is connected, and then turns it over to the OS to finalize initiating communication with the board?


Could you say exactly what connections you have made? For example, did you connect ground to the PC power supply? Is the servo cable the only connection to the speed controller? If you could take a clear picture showing all the connections, that might help a lot.

I do not know anything about the Victor 883, but it might interpret a lot of different pulses as a “full forward” signal. So while it might be a 2000us pulse, it might just be that the way you power everything up results in the signal line being high for a very long time, even a few seconds, and the 883 interprets that as “full forward”. If you have access to an oscilloscope, you should take a look at what is actually happening on the signal line.

You can run the Maestro Control Center software to see exactly what the Maestro thinks it is doing; simply running the program should not affect the servo pulses. I would be interested to hear what you see there and on the LEDs. In particular, the Maestro should double-blink its yellow LED if it is actually outputting any pulses.


Sorry, someone just reminded me that the Mini Maestros unfortunately do not do the double-blink. However, I would still like to know what all the LEDs are doing when your speed control is not doing what you intend.



I am going to recheck my wiring. I do not believe that I tied PC PSU ground to the Maestro, as I was assuming that the same ground would be through USB.

When I turn power on, the Maestro flashes the yellow status LED one time, and then it has no activity, that’s when the Victors get signal. Once the PC brings up the USB connection, the USB light turns green, and the Victors get a neutral signal.

I will go over all of my wiring when I have better light tomorrow afternoon.

I know that I have a Victor on Channel 0 and Channel 1. I have a couple of servos attached to channels 3 and 4, and I have another speed controller tied to channel 2. The only channels that activate are 0 and 1, I don’t see any motion on any other channel.

As I said, I’ll go through more wiring tomorrow and make a list exactly how everything is wired.


Okay, I’m sitting here looking over everything.

I have Victors on Channel 0 and Channel 1. The board is plugged in via USB and it also is connected to the 5v rail of the PSU, both +5v and ground.

What I’m seeing is, since the PSU gives the controller power before USB connected, I get a signal jump on channel 0 and channel 1, which causes the victors to go ‘full foward’, even though the pololu software has configured both of those channels to default to 1500uS. On power up I see one blink of the yellow LED, and then the victors go full forward, and then the green light turns on, and the motors stop. Takes about 3 seconds or so for this to happen.

Now, if I disconnect the PSU power from the pololu, this does not happen, as I’m assuming it has to power up through the USB bus to get 5v power. The reason I’m feeding it the external +5v is to power other servos and a gyro on-board as well, so I really do need the 5v rail.

Should I just disconnect the +5v from the pololu itself, and tie each servo/gyro power directly instead of trying to use the nice servo outputs?



The servo power rail is just connected directly to the outputs and not to any of the digital circuitry on the Maestro, so I bet you will get exactly the same result if you connect the power supply to a single speed controller, with the Maestro out of the picture. If so, your problem is not with the Maestro. But if that works fine, can you work up from there, adding one part at a time, and find the step at which it stops behaving the way you expect? For example, it sounds like the problem is unrelated to the PC, so that should just not be in the picture. If you can make the simplest setup that does not behave the way you expect, it should be pretty easy to find the problem.


By disconnecting the +5v I was feeding it, solves the problem.

I have built a work around for this for now as I’m out of time for the project. I am using a relay off another channel from the Maestro that will connect the +5v rail back into the line once the PC has booted and is running.

This works fine for now, but I will work on troubleshooting later when I have time after this competition.

You are correct that I can take the PC out of the loop, it does it even with USB disconnected. No idea why feeding the power rail +5v would be causing this, but, the work around works, so I’ll go with that for now. :slight_smile: