PC ATX power for Arm drawing 10A with SBEC? or Buck regs?

Hi All,

I’m building a robot arm controlled from a PC via the pololu mini maestro that I expect to draw up to 10A if I don’t stall all the servos at once…I’m using these servos: 3XQ-power S5040D, 1Bluebird BMS-35A and a couple of much smaller ones.

A dedicated high current power supply is very expensive and bulky - but since the arm is only intended to operate in conjunction with a PC - which already has a power supply that could handle that current - it seems to me the best way forward is to regulate one of the ATX 12v power rails down to 7.4v

I’m new to the RC world though, and BECs, UBECs, SBECs and ESCs confuse me.

I think I just want a 10a UBEC or SBEC- something like the Castle Creations BEC Pro - but all the wiring diagrams I’ve seen only show it hooked up to an ESC.

So my question is - can I use a UBEC/SBEC without an ESC?

Alternatively - could I set up say 4 cheap Buck regulators based on the LM2596 in parallel? (eg compare.ebay.co.uk/like/39050556 … pla&crdt=0)


Hello, Kevin.

A BEC is essentially just a voltage regulator, so there shouldn’t be any reason you wouldn’t be able to use one by itself (without an ESC). If you’re talking about the diagrams here, I think they show an ESC to emphasize the importance of disconnecting the ESC’s red wire (so that the receiver isn’t powered by both the ESC and the standalone BEC).

We generally don’t recommend connecting regulators in parallel, since it’s difficult to ensure their voltages match and that the load is distributed evenly across them. If you can find one, it’s much better to use a single regulator that can provide enough current. Also, please note that many servos are designed to be powered with no more than 6 V, so you should make sure to check the specs on your servos and choose an appropriate voltage for all of them.

- Kevin (too)

aahh - many thanks Kevin too, I think I get it now.

That Castle creations diagram (castlecreations.com/support/ … _guide.pdf) was really confusing me because it doesn’t show the servos (which would be plugged into the receiver). I didn’t understand what a receiver did either - but reading your reply I finally clicked that a receiver supplies the PWM signals AND the power for the servos.

In my case the pololu mini maestro would be equivalent to the receiver in that diagram right? So good news, I can use a cheap switching BEC/regulator (£10~£25) to power my monstrous (raarrghh) Arm from the PC - 80kgcm shoulder lift torque and 35kgcm in the elbow is hopefully enough for a 2 foot reach and to lift nearly 1kg at full extension! (arm length will weigh about 1kg).

No need to reply - unless I’m being dense and still haven’t understood … and yes don’t worry - I’ll be powering the smaller normal voltage servos off the ATX 5V rail.


Yes, the Maestro would provide the pulse width signals instead of the receiver. You might have to think carefully about your power connections (you will probably have to power some of your servos separately instead of through the common power rail on the Maestro); if you’d like to post a proposed wiring diagram, we can help you check it.

- Kevin