180 to 270 degree servo conversion

I have built a dashboard out of servos and an old Ford Expedition dashboard layout using an Arduino Mega and it works great. It is for American Trucking Simulator. The only problem is that the speedometer, because the servos only go 180 degrees, it cuts out at 81. When I go 85, it still says 81 because it cannot go any further. Now I have seen that it is possible to add a resistor to a 180 degree servo's potentiometer to make the servo turn more (essentially adding more resistance to the pot so it takes a lot more turning radius to get from point A to B on the servo). Is this possible? If so, is it feasable and how would you do it? How do you know what value resistor to add? Like I said...people say that it is possible, but provide no information on how to do it. Thanks!

I don't know that either, but how would you get by the mechanical end stops?

Maybe I can just cut them off? Would I need them though. I can keep the one stop for the 0 degree rotation but cut off the stop for the 180 degree point?

Do cheap servos have potentiometers that originally sweep some 300 degrees and they use only 180 degrees? If that's true, then it could be hackable. The optimal thing would of course be a servo which turns 180 degrees if it's supposed to turn 180 degrees, but the internal movement of the potentiometer sweeper would be 300 degrees, if that's what the potentiometer can perform. It would be achieved through the gears.

I think you are pursuing the wrong path.
Buy (or 3d print) some gears for your servo.
Make them of the ratio 3:2 or there abouts.
Big one on your servo. Little on on your object to be turned.
270 degrees of movement! :slight_smile:

While that would be a viable thing to do...if I can take the easy route (i.e. adding a resistor and cutting off the 180 degree stopper), then that is what I am going to do. I don't have a 3D printer, but my school does in stem class. I could print new gears, but adding a resistor and changing the code a little bit saves me a lot of hassle.

So you believe the servo uses only 2/3 or less of the built in potentiometer? And cutting the stopper will unleash the whole range? Are there two stoppers or is it the same stopper on some gear that rotates 360 degrees (minus the stopper) while the servo rotates 180 degrees?

Johan_Ha:
Do cheap servos have potentiometers that originally sweep some 300 degrees and they use only 180 degrees?

Who knows, for cheap people do whatever works enough, and don't provide datasheets, or guarantee later
versions behave the same as earlier versions.

Dashboard steppers are commonly available, such as the Switech X27, designed for this purpose.