[HH] Robotic arms controllable from Linux

[Greg London]

The only one I know of is this:

http://www.imagesco.com/robotics/owi-535.html

But I assume you consider that a "toy".

The problem is:

Motors aren't cheap.
Power FETs aren't cheap.
heat sinks aren't cheap.

I've been working on making a "generic" motor controller and it's *hard*
because motors that aren't "toy" motors end up taking a lot of current,
which translates into really hefty FETs, and a lot of voltage, and that
translates into a lot of power, which then requires really big heatsinks,
all of which is expensive.

Once you start getting into "not-a-toy" robot arms, you're probably
looking at several hundred dollars at a minimum, at which point, if you're
spending that much money, you probably want to pay for the specs you want,
and don't want to pay for specs you don't want.

Trying to get 1 horsepower out of a low voltage DC motor that you can
switch on and off rapidly via PWM ends up being a pain. Motor voltages for
higher powers quickly jump from 12v to 24v to 48v and even 96v. Several
voltage jumps push you into more expensive FETs because they all have
different max voltages they can handle.

I think I came up with a design that has basically two possible FETs, one
for 48 and below, the other for over 48v, handling currents somewhere up
to 80 to 100 amps or so. Even with low Vds fets, it still ended up needing
some serious heatsinking if you want the motors on all the time.
heatsinks, it turns out, can be more expensive then the cost of all the
electronic components combined.

It all got rather depressing, and I put the design on the shelf (or,
technically, on my harddrive) and left it there. When I've feeling more
motivation, I might dust it off and give it another go.

Here's an off the shelf controller that handles up to 24v at 40amps motors
for $90. You'll need three or four for a robot arm. So, you're already
looking at $300 and up.

The short of it is that they make "toy" robots because "not-a-toy" robots
are really, really, expensive.

Greg



> I'm looking for a robotic arm that can be controlled via Linux or
> Arduino. Cheap but not a tow. There is one out there that litters my
> google results but it is not really usable as anything but a toy. It
> costs about $50 and sold under a few different names.
>
> Anyone have know of any?
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