Thursday, December 20, 2012

Continuous rotation pan-servo hack

The ratchet pan system needed constant adjustment to keep operating so I decided to change to a continuous rotation pan servo with gearing.

Servos are designed to rotate +/- 30º to 45º but with a simple hack they can be made to rotate in either direction continuously. All that's required is to open the servo, cut out a couple of little plastic tags and drill out the inside of the lower part of the spline. Here's a full explanation of the hack from the KAPER e-magazine.

Gearing down is a good idea to reduce the speed of panning, so a large gear on the pan bolt is meshed with a smaller gear on the servo. This rig used 2:1 ratio but 4:1 is recommended.

One issue you may need to deal with is servo creep. Some continuous rotation servos will not stay stopped no matter how much you adjust the trim switches. James Gentles makes an antiCREEP unit that solves the issue for standard servos. It gives a wider "no movement" zone and slower rotation overall. Unfortunately I found the hacked Turnigy servos did not work well with antiCREEP. The "no movement" zone became too wide.

This three legged rig with continuous pan micro servo and standard tilt servo weighed 560g all up, but suffered from pan servo creep.

Another issue with continuous pan is that you can easily lose track of which way the camera is pointing unless you use a video downlink (extra weight and expense) or some sort of pointer on the rig that is visible from the ground.

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