I’m having trouble with on of the gauges that are driven by a geared HS-55 servo controlled by a Mini Maestro 12 channel card. This particular gauge has a pointer that almost makes a 360 degree turn to get from 0 to 10 (faceplate of the gauge). With the Pololu control panel I can enter min and max values but I do not get the dial to stop at the ends. Either the given value is too less/much to make the pointer reach the 0 position or the 10 position or when further lowering or enlarging the value the pointer passes slowly the 0 or 10 position and starts continuously rotating. It also seems that when stopping the rotation by pulling the slider back from either the extreme position on the Pololu control, the servo has ‘forgotten’ where its middle position etc. was.
Is this a hardware problem or software? Any ideas how to solve this?
From a brief Internet search, it looks like that servo might not be capable of 360-degree rotation. For example, ServoCity lists it’s maximum travel as 203 degrees. You can try following the method described in the “How do I use my Maestro servo controller to get the maximum possible range of motion from my servo?” FAQ on the Maestro’s product page to see what you can get from it.
Commanding it beyond it’s limits could result in some of the unexpected behavior you are describing. If you need to replace it with something capable of more travel, you might try searching for a 1-turn (sometimes called “sail winch”) servo, so you know it is able to travel the distance you need.
thank you. To add some info, I had to replace a few broken servos and discovered that they probably have been altered by the manufacturer of the gauges. The physical stops have been removed. I guess this is because most of the gauges need a larger travel than the HS-55 can offer (like you described). Maybe I can do something with other gear wheels. Or another servo. But then again, how to get it stopped at the right places?
As I mentioned in my previous post, you might try looking for a 1-turn “sail winch” servo. Those specialty servos typically travel a full 1-turn over the typical 1ms-2ms pulse width range. Using some kind of external gearing to increase the range of motion like you described could be a possible solution as well.
