Inverted Pendulum

All posts tagged Inverted Pendulum

My current project is a reaction wheel inverted pendulum – a single DOF version of this:

To that end, I’ve been milling and drilling and tapping, oh my.


For a man who buys machine screws by the hundred, it’s surprising how often I don’t have the right machine screws. Nonetheless. One of those is a motor mount, and one will form the back side of a clamp. The idea is that it’s adjustable along the length of the stick, otherwise I have to do math first. This way I can ballpark the wheel mass, and then tweak it physically.

Motor mounted:

Turns out, of course, the mounting screws for these aren’t in a square. That’s actually pretty common for these – so common I had an adapter plate lying around. Since it mattered to me that the holes be pretty precise, I used one to make up a jig. I don’t care so much about the location of the motor in terms of centred and plumb – it’s constrained pretty well by the slots. But in relation to each other I want the holes spot on. So, time to make a jig.

Drilling the top hole allowed me to put in one screw, which then holds the whole thing in place while I drill the rest.

The first screw, of course, went in fine. The second had that moment of joy swivelling the motor into place as the screw hole swung under the screw and it clicked into place.  With those two in, the last two went in perfectly first time. I love it when a plan comes together. The motor itself is within half a mm of centre – not bad for a freehand jig. It’ll do fine.


And that’s the idea. Screws I’m currently missing are countersunk M3, so I can actually mount the motor and still put the clamp on the mast, and M5x14mm. I have M5x12, which are just long enough, except for one corner. I got carried away in the initial assembly and cranked a little too hard with only one screw, stripping the top thread out of the hole. So I grabbed an M5x16, which is too long. By about 2mm. And apparently I have no 14mm.


Still, at some point I need to think about mounting electronics, so the 16 may give me space to add a 2mm plate for the ESC and battery. And so it goes ….