Monday, September 06, 2010

sources for gear motors

I've had an interesting ongoing email conversation with a person in Mexico who bought my plans and was very interested in building a solar parabolic heating system for himself. He had been having trouble getting the specific gear motor that I recommend in the plans.

In any DIY (Do It Yourself) project sometimes it is necessary to improvise.

It occurred to me to suggest to him that he look for a discarded cordless screwdriver or drill. Often people throw these away when the batteries no longer hold a charge. Both of these products contain a planetary drive gear reducer and a DC motor, just what we need to build the drive mechanism for a tracking solar parabolic collector. In both of the tools I look at here, the gear drive has metal gears on the output side so they should be able to handle lots of torque.

Here (click to enlarge) is a 1970s vintage Skil Supertwist cordless screwdriver. This is a great screwdriver, still working today after replacement of the NiCd batteries. You can see at the left side the 3 volt reversable DC motor and the metal gear box case. The driver end is a standard 1/4" hex socket which should be easy to adapt to the rest of the mechanism. In the case of my plans, this would drive the end of the drive screw in the linear to angular motor drive.

It would also be necessary to compensate for the lower operating voltage of this motor. That could be as simple as a resistor in series with the motor.

Here is the inside of an old Black and Decker cordless drill which you can't get the batteries for anymore. Someone threw it away. This has a very nice 7 volt DC motor and a very substantial gearbox reducer. As an added bonus, there is a variable speed circuit in the trigger grip which could be used to set any desired speed. Another bonus is the very nice tool-less Jacobs chuck which could simply be tightened onto the end of the drive screw. I couldn't figure out how to remove the torque limiter but it wouldn't be necessary to remove it. It could simply be left in the "drilling" position where the torque limiter doesn't act.

The whole reason for the gear motor is of course, the very slow speed of the sun across the sky. If the solar tracker drive operates too fast, the array will overshoot the position of the sun, go back, overshoot again, go back etc, etc. So the drive would be unstable and it would in effect, oscillate which is not desirable since it causes unnecessary wear to the whole mechanism and uses more power than it needs to.

So if you can't find a suitable gear motor, look around at your old cordless tools, or visit the local re-cycling center.

My friend in Mexico liked my suggestion and is now looking for a suitable tool to re-cycle for his solar project.

1 comment:

George Plhak said...

I recently found this video relevant to salvaging these very useful motors video on YouTube