Monday, December 27, 2010

TOBL: HS-82MG-360

A key ingredient for this project is a solid drive system. I opted to take the servo route as opposed to straight motors. Servos come pre-geared-down, they're easy to mount, and easy to control. What's not to love? Well they're perhaps less interesting from a controls standpoint, and in certain applications they scream rookie. If you've been following this project though, you know they're not trivial to work with, especially micro servos.

I've encountered plenty of problems with these little guys. Finally though, after buying two HS-81s, two HS-82MGs, and three HS-81 gearsets, then breaking two spline gears and a potentiometer, I have created the perfect (for my purposes) servo. Behold, the HS-82MG-360:

They said it couldn't be done. Seriously:

That's right it is spinning 360 degrees proving that impossibility is no match for being both stubborn and patient. If you're really interested in building one of these miniature torque monsters then you should see this post for details. The quick summary of how to make an HS-82MG-360 is as follows:
1. Replace the spline gear with the plastic one from an HS-81 gearset.
2. Cut out the first mechanical restrictor, found in the top of the gearcase with a pocket knife.
3. Cut out the second mechanical restrictor, found in the potentiometer. This holds the gears in place so be careful not to cut too much.
4. Cut the three wires connecting the potentiometer to the control board.
5. Solder small low-watt resistors to the loose wires keeping in mind you should:
a. Pick resistors of the same value such that their sum is the value indicated on the potentiometer. In this case, the pot read 5k and used two 3kohm resistors, so it doesn't have to be exact. I'm pretty sure the control board is just looking for a value somewhere in the designated vicinity.
b. Connect them such that the two outside wires initially from the potentiometer are individually connected to the central wire. Red-Yellow and Green-Yellow in this case.
6. Cover the exposed leads of the resistors with your choice of hot glue, heat shrink, or electrical tape.
7. Reassemble and test.

Control is handled the same way as before only this time the delay corresponds to a speed instead of a an angle. With this particular servo that's 600usec to 2400usec, 1500usec is neutral. Until next time...

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