Round chassis + wheel encoder


I’m wondering if anyone has ever combined Pololu’s Round Robot Chassis with any sort of quadrature encoder. I’d like to be able to track the distance moved by the twin gearbox motors and came across this product, but the pcb and the encoder wheels are way too big for the small tamiya wheels to fit into.

Anyone have any thoughts? Should I roll my own?


I’m a fan of harvesting very small, medium resolution quadrature encoders from old ball-based computer mice. Generally the older the mouse, the better, since A) you’re less likely to miss it when it’s gone and B) the components are larger, more discrete, and generally easier to figure out.

You can find all sorts of example pages on this by Google searching something like “computer mouse quadrature encoder.” You might find a reflective type, like the one you linked to, but generally what you’ll find is one IR emitting led, a rotating slit disk, and a receiving component with two IR photo-transistors in it. You can desolder them, or just cut up the circuit board, but either way you’ll want to grab a multimeter and figure out the connections while you can still plug it into a PS2 port! Everything you need to make it work (i.e. current limiting/pull up/down resistors, etc…) should be there on the board. PS2 devices run on 5V, so it should be easy to connect to a 5V microcontroller.

Here’s a neat trick, most webcams and cell-phone cameras don’t have a near-IR blocking filter, so you can use one to see when the IR led is lit up!

So, what are your plans for your encoder-equipped robot?

Good luck,


That sounds like a great idea; I thought about ball mice too but don’t have any with me now to fiddle with the results. Looks like I’ll be out scavenging this week.

The main obstacle is in fitting all of the electronics and disks under that tiny space between the round chassis’ gearbox and 36mm dia wheels. There’s about 10mm or 3/8in of clearance in-between.

I’m thinking of a robot that will ‘explore’ its surrounds and map its ‘history’ of steps it took to get to a spot, amongst other sensor readings. That data gets dumped to a pc, probably wirelessly, and then i’m gonna ‘massage’ the data. You might have guessed by now that it’s a project in its infancy. Not even past the conceptualization phase yet so that’s all I have. :slight_smile:

Thanks for your tips, they are much appreciated.


Sounds very cool!

And you don’t necessarily have to stick the encoder disks out by the wheels. Most encoder-motors have the disk connected to the back of the motor’s output shaft, which keeps it out of the way, and gives you higher resolution with the same equipment. If it turns out that you can’t measure the slits going by that fast you can replace the original disks you harvested from the mouse with something with fewer slits, even something you cut out of a piece of paper.