Now all I need is an arm! Wait, why can't this arm lift anything?!? That other arm costs WHAT?!?

LLM AI is absolutely amazing. The ability of machines to see, to converse, and to understand is unprecedented and miraculous. One might be forgiven for wondering why we don’t already have robots walking among us, doing household chores. At least until one surveys the robot arms available to hobbyists.

Generally speaking, the arms hobbyists can readily afford use servos that are only just sufficient for the arm to move itself. More powerful arms are available, but they come with a heftier price tag. But why?

The XD-3420 DC motor is commonly available. It’s large but not ridiculously so, a little heavier than one might wish but again not prohibitive in weight. It produces a reasonable torque/speed curve running at 24 VDC. The motor under load might produce 1kgf/cm of torque rotating 60 times per second. Using proper gear reduction (240:1) we might expect to see a theoretical maximum without considering losses of perhaps 36 ft lbs of torque rotating once every 4 seconds. Lets say we have 14.4 ft lbs after losses and we see that this motor could give us an arm a yard long that could lift objects nearly 5 lbs in weight. The motor runs around 25 USD, so 150 USD would give us motors for 6 degrees of freedom. More components are needed of course; magnetic encoders, microcontrollers, motor drivers, buck converters, gearing, and software, but none of these things need be particularly expensive.

This is what I’ll be focusing on developing. More to come soon!

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