Running Mini Maestro and servos from a SMPS

I’ve got a project at the moment that uses a pololu mini maestro 12 to drive 9 servos and a Syren 10 Speed controller. The speed controller works fine. 6 of the servos opperate in pairs via servo reversing Y leads in a push/pull arangement.
5 of the Servos are hexatronic HX12Ks, though I will likley replace these with something more reliable.
2 of the servos are Hitec 5805MG Mega servos, which pull 800ma unloaded.

I could not find details on the Maestros current taking capabilities, so have been running the 2 pairs of hextronics, and the 2 hitecs using Y leads to provide the power to avoid burnign out the PCB tracks.

Because this is a static item, and pulls such heavy currents I wish to run it off a mains transformer. However I have been getting some strange “twitching” and “spasming”. I wondered if this is due to the switch mode power supply infering with the servo PWM.

Q1: Is it ok to use a SMPS to power a mini maestro and servos? or will this cause the behaviour I am seeing?
Q2: If this is causing the problem, is there anything that can be done to get them to work together? (this is a problem I am seeing alot with speed controllers, i have contacted several companies, all of which can tell me why there is a problem, non can tell me how to fix it)
Q3: is using Y lead to power my servos the best option? would doing more than one servo like this cause any problems? (would the voltages accumilate?)
Q4: Any other suggestions?

Here are pictures of what I am doing: *wont let me post pictures
The 5 servos in the body controll the Up/down Left/Right and Rotation of the head. The 2 Mega servos pull the cables to move the tail up and down, and side to side. The two small servos inside the head control the jaw opening and closing. the speed controller drives the motor at the top, which turns the central shaft and makes the fins move up and down. … 000981.jpg … 000981.jpg

Many thanks in advance!

Hello, Zakari,

How much current is your power supply rated for? There is no reason it should not work with your Maestro and servos if it can provide enough current, but you need to make sure that this is the case. What have the other companies told you about the “problem” with respect to speed controllers?

If you have access to an oscilloscope, you can use it to find out whether there is an unusual amount of noise or ripple on the power supply leads, or if your servos are drawing too much current and potentially causing the Maestro to reset. If noise is the problem, you could try adding a large capacitor (at least 100 uF or so, like this) between the power and ground leads where they connect to the Maestro.

I am not sure exactly what kind of Y leads you are using with your servos and how you are connecting them, but I do not think using them should be a problem, as long as you make sure that each servo wire is connected to the appropriate voltage or signal.

- Kevin

Hey kev thanks for the reply. This capacator solution is one i have heard before, is there any equation for working out values required? or did you get the value from experience/knowledge?

Previously companies have just said “do not use with SMPS” regarding speed controllers, they explained it as “speed controllers use bursts of current to control speed, if the pulses coming from the power supply do not match this, it may provide unwanted power, or may nnot provide nessessary power to match the pulses of the controller” or something like that.

I’ve just tried running this thing off of batteries, and im still getting jittering. Please have a look at my new post. :slight_smile: thanks!

Cancel that.
If i put the servos directly into the maestro, no jitter. if i connect them via a Y lead (2 servos into one port) no jitter. If i connect them via my fusion servo reverser, no jitter. The jitter only comes from my 2 ripmax servo reversers.
If i put these into my transmitter/receiver, no problem. The jitter only comes when running a rpimax servo reversing Y lead from the mini maestro 12…

apart from “buy 2 more fusion Y leads”, do you have any ideas?


I am glad you were able to narrow down the source of the problem to that particular combination of devices. Do you have access to an oscilloscope that you could use to look for differences between what your receiver and the Maestro send to the reverser, or differences between the outputs from the Ripmax and the Fusion reverser?

Also, it might still be a good idea to check the power supply in case voltage irregularities are causing the problems with the reverser. How much current is it rated for? If you want to try a capacitor, you can use as big of one as is practical for your installation; I did not use any particular equation to calculate a value.

- Kevin