Here so I can find them! I recently joined the Melbourne Combat Robotics group, and it’s a great excuse to finally use the lulzbot for a 150g antweight. I print with HIPs, and I tried a few things, and got the base layer lifting until I tried:


Extruder: 220

Bed: 100


That seems to be sticking. Pics to come…


So, those cheap plastic chopping boards *look* like excellent robot chassis material, but the quality control is abysmal! Fortunately Daiso sell bamboo chopping boards (well, “rubber wood”, apparently), which are planed and thicknessed, and thus much more suitable. The upshot being, have some video:

You’ll have to take my word for it, but the signals from a stock futaba R/C remote are being captured by an Arduino (unless that one is a Teensy, I can never remember), converted into relevant values for each wheel per the relevant cos(theta) function for a three wheel holonomic, and then fed to a stock R/C brushless ESC to drive the wheel. Quite fast. At some point I will also have build photos for the legs, but after I get the axles working, probably.

I had a post brewing about sinusoidal commutation and brushless motor control, but many other people have written about it already. In the meantime, here – have a photo of 4 motors’ worth of power MOSFETS:
2013-11-04 13.53.49_mid

Oh! So the whole point of that little lecture on DC motor control was to point out this:


This sexy AutoDesk Inventor 3D simulation has motors bolted via the static face to the chassis, with a minimum of distance between the support and the wheel. Because that’s optimal, and because that’s normal for brushed motors. The motors have only just arrived, the simulation only has 4 parts *and it is already wrong* because it makes assumptions.

Which is not a big deal. But it’s a warning. “It worked in CAD” is an insidious trap for young players – the question is, when it fails to work in real life, do you change the part to match the drawing, or the drawing to match the part?

I think I now have all the parts for the tiny project I’ve had in mind.

It starts with the omniwheels:



These are smaller than I expected, but that’s fine, everything else is going to be small too. Omniwheels are slightly less useful than Mecanum wheels , because you can’t create the kind of sideways movement you can with Mecanum wheels, but that leads to some drive theory a little outside the standard “4 wheels and a gripper” paradigm.

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