Home Racing World

We have robotic vacuums, and one of the wheel drive motors has failed. (higher than normal resistance to turning) It looks like a simple 2 terminal DC motor just like in a slot car. The encoder is not part of the motor, so I can move that to a new motor. Unfortunately there is no model number or identifying mark on the motor to help me order a replacement. The motor housing is plain cylindrical, roughly 1"x1" with roughly 1/16" diameter shaft.

For people who are used to working with various little DC motors, where would you look on the internet to get a replacement? I'd like to just replace the little motor myself, and I expect some of the other drive motors will eventually need replacement. I've been browsing digikey, but there are oodles of options, many of which are silly expensive for no obvious reason.

I might be able to put it on an oscilliscope eventually, but for now I can't specify the drive signal.

electric goldmine might be where you might want to start. or ebay. type in "electric dc motor" in the all categories box. there are thousands on ebay. start with price with shipping lowest. i am sure you will find one. good luck.

I'm not sure how much I need to worry about torque and RPM for these? Since each wheel has a drive motor it might run unevenly if they're different enough. The encoder should take care of some of that, but it may confuse the unit's software and just cause an error message anyway.

You might find the motor you need on-line, and at a really great price. Trouble is you need the minimum order of 10,000. :lol: :lol: :lol:

I'll settle for a price that's better than the shipping charge for returning the whole vacuum. ;)

Latest data: Professor Motor says: bad motor draws 1 Amp at 10V, good motor draws 0.1 Amp at 10V

Super to have a couple new places to look! I hope I can find a few with the right dimensions and performance. I love my robot vacuums! :D

I've made some progress. My anonymous motor looks similar to Mabuchi type RS-385. The sticky issue is I need a "dual-shaft" version, which doesn't seem to be the most common type.

I will check my motor bin - I keep odd motors for when an appliance or toy breaks down. Give me the dimensions and any spec you have.

The physical dimensions match the diagram here http://www.mabuchi-motor.co.jp/cgi-bin/ ... D=rs_385ph except that they are dual shaft (5-6mm each side) and a 2.0mm diameter shaft. These have a range of voltage ratings, but I'm expecting the operating voltage is max 12V due to the battery. Unloaded current ca. 0.1A, loaded current < 1A. I've found some candidates on eBay, but currently I'm waiting to see if the manufacturer will just send me a replacement.

The pinion is same as a common 12t OD=7mm ID=2mm slot car pinion. :)

I've found an equivalent 12 CPR disc hall effect encoder at a robotics site.

HAHA - after all the time I spent investigating this motor+encoder, I finally thought I'd search to see if anyone else took apart one of these and put some info about repairing it on the internet. Unexpectedly, the first results that popped up were a couple places selling the exact replacement parts! :? I just didn't expect to find replacement parts for this anywhere except the original manufacturer, who doesn't offer them. They're a little pricey, but so is sourcing motor, pinion and encoder separately. I might still build my own replacement just for giggles. :music-rockout:

I found a page where someone opened up one of these motors and found their problem to be brush dust filling the gaps in the commutator. I had no luck with the service department so far, and ordered a couple replacement motors already, so I'll have to try opening and cleaning my failed motor as well. (If nothing else I'd need to remove the encoder to use it on a new motor anyway.)

http://froodystuff.blogspot.com/2014/03 ... -none.html

I cleaned the stuff from between the commutator plates and now the motor works normally again. This is the first time I've taken a motor apart in a non-destructive manner. ;) HOWEVER....

When I opened this motor up to clean it I discovered something that puzzled me - the brushes are pre-formed with a cupped surface that seems like it should be aligned with the commutator, but instead it is mounted orthogonal to the axis of the motor. The blog linked above has a photo which shows the same thing - a cropped zoom is below. Since we run-in the motors in part to get the brushes to wear down to a shape flush with the commutator surface, shouldn't the pre-formed cupped surface of the brand-new brush cradle the commutator rather than be perpendicular to it so only the edges contact? The original cupped shape is kind of difficult to see in the crop below, but you can see how in the photo the commutator has worn into the edges of the original brush surface shape.

Is this normal, or were these brushes mounted wrong?