Motor Direction


Can the 12V DC Pololu motors be revered in direction by reversing polarity, or will it damage the gearbox

cheers T

1 Like

Hi Anthony
If they are “normal” brushed motors (2 wire connection) the answer is YES. This should not harm any gear box.
Cheers Bob


Thanks for your help appreciated, cheers T

1 Like

To be more sure, you can ask this to the pololu forum too.


Thanks will do

Best regards


Hi Anthony,

Welcome to the forum :slight_smile:

As Bob has said, any brushed motor will be totally happy wired with either polarity. Some will have a little + next to one terminal but this is mostly so you can make sure your wiring is consistent with what way you would expect the motor to spin. This is especially handy if you have multiple motors being driven by a single channel of a motor driver, you don’t want to have to trial and error your way through wiring them until they are all turning as expected.

1 Like

Thank you cheers T

1 Like

The only exception to this might be if there’s any timing built in to the brush orientation, but I’m not sure if that’s much of a thing if at all. But back in the day when all electric RC cars used brushed motors, you could buy flash balanced ones with ball bearings and adjustable timing, which makes me think it’s perhaps a possibility with some specific-use motors…?

In which case reversing the polarity might mean having a small amount of retard instead of advance, probably not a deal-breaker in any case.

1 Like

Hi Him
Mostly applies to brushed generators. On some the brush position could be fine tuned for minimal arcing. An example is an automotive generator (not the modern alternator) which is as noisy as and arcs like mad if rotated in the reverse direction, If charging a battery for radio use completely unusable. I personally found out this the hard way.
Cheers Bob
PS: This is why some motors are noisy when used as generators.

1 Like

This is interesting…

This is a quite basic motor from a cordless stick vac, obviously set up with some advance. Rotation is clockwise from this point of view

Hi Kim

How do you know. Can’t tell just by looking at it. I believe brushed motors are set up with the brushes in sync with rotor position so they can be operated the same in either direction. Special built for purpose motors may be tuned a bit but I wouldn’t bet on it.

A test might be to measure the speed in both directions under no load. That might provide a clue.
Cheers Bob

Can’t you see those three notches?

Surely this motor isn’t made specifically for this application, and may be run in either direction depending on how it’s employed.

The centre notch is empty - the end cap is rotated against the motor direction; obviously advanced.

ETA: I expect when a manufacturer orders a bunch of these wholesale, the position of the end cap is one of the things they have to specify.

Your 10 cents
Cheers Bob

How would you explain those notches otherwise? If the tab on the end cap was in the centre notch, the leads would like up perfectly with the vent holes and the motor would be symmetrical.

Why would it look like this if it wasn’t because of advanced timing? You think if the tab was in a different notch it wouldn’t change the timing? Come on.

Seems pretty straight up to me. And interesting, that I just happened to have this lying around at the time and noticed it after my first reply to this thread - never seen anything like it on such a basic motor before.

As I have not had anything to do with the manufacture or anything else with that motor. Nor do I have it in front of me so I would be guessing and I won’t do that.

I don’t know how we got to here as I just pointed out one of the differences between a motor and generator and why a generator does not perform as well when running in the “reverse” direction. Sorry I said anything and will leave it at that.
Cheers Bob
By the way I can see actually 5 notches with maybe 2 more where what looks like the brush springs emerge.

There are four points where the can is crimped in to hold the end plate. I wouldn’t think of them as notches, since there’s no missing metal. Sorry if my pic wasn’t clear enough, but there won’t be another one because the jigger is back together.

Hi Kim
Yes, when enlarged I can just about make out the little tag in the bottom notch. It is not immediately apparent as at first it looks like 4 notches with a tag in the top one.
You are probably right. At a guess (and it would only be a guess) I would say the bottom notch would optimise the brush position for present rotation, the top notch optimised for the reverse and the centre for bi-directional use. I must admit this is the first time I have come across this as mostly the motors I have dealt with have been required to run in both directions and any purchased “off the shelf” the ultimate direction of rotation at manufacture would be unknown.

So I think in a way we are both right. While probably not specifically manufactured for that application It is probably ordered for that application and rotation direction which is set during manufacture. I think it would be difficult to change after manufacture without damage as the material used it that sort of application is very hard and difficult to work with the facilities normally available in the home workshop.
Cheers Bob

1 Like

Hm, I was thinking I’d need to get that end cap off at some point, so I guess that might be a destructive process.

You might’ve noticed this thread I posted, where I note the trickiest aspect of disassembly will be removing the apparently pressed on impeller…

The least bad idea I had to do it was to remove the motor’s end cap, support the back of that plastic shroud as well as possible, and push the impeller/rotor assembly down until the back of the impeller bears down on the front of the shroud (both of them nice and flat with a decent amount of area), and just have a go at punching the spindle out of the impeller.

Levering it off from behind (a <2mm gap) seems like a terrible idea, and I can’t imagine any others short of fiddly mucking around with heat and cold, which also doesn’t seem too smart given the shroud is plastic…

Hi Kim

Not Easy. Those points will be swaged over with a machine and I think are a do and forget operation. Never to be repeated.

Also if the brushes behave like most other brushes I have had dealings with they will pop out of their holders and can be a real devil to get them re positioned and back over the commutator when reassembling. Mostly a 2 person operation. Higher quality (read much more expensive) motors which are repairable have the brushes removed and replaced by unscrewing a cap on the outside so the end plate can be replaced without brushes and these fitted later. Much easier believe me.

As for removing the impeller without damage, without actually seeing it I can’t think of any way of doing this. It might also be a case of assemble and forget. Not meant to be replaceable.

Unfortunately most things seem to be throw away these days. Took all the fun out of it.
Cheers Bob

I’d prefer not to destroy it in case my little project can’t be made to work for some reason, but otherwise I don’t need it.

I guess if it doesn’t want to punch out of the impeller, I can attack the motor with an angle grinder, slowly enough so I don’t melt the important plastic bit, then I can try twisting it off.

Having your way with modern junk sure can take some ingenuity. Took me like two hours to figure out how to get the bastard apart to that point. If it’s a phone or laptop or something you can usually Google up a disassembly guide to avoid guessing where all the hidden clips and screws are, but no dice with something like this.