What is the typical resistance range of a Servo POT ??

[CATPart]

I want to add an external POT to a servo. Is their a typical range of resistance I should be looking for? I know I could measure the pot in a particular servo, but I wonder if they all are pretty much te same or not.

Thanks,
CATPart

[Rodney]

5K on most.

[earlwb]

Yup 5k is about what most all the servos use. But there are some exceptions.

[rich smith]

Like the gang says 5k on most but I've noticed anything from 1k-100k works.

I want to add an external POT to a servo. Is their a typical range of resistance I should be looking for? I know I could measure the pot in a particular servo, but I wonder if they all are pretty much te same or not.

Thanks,
CATPart

[gobigkahuna]

Do you happen to know if the pots a DX5e are also 5k? I tried measuring them while still wired in place but that didn't work. And another, probably stupid, question: I'm a bit rusty on my electronics but if a joystick is centered and the pot is 5k ohms, then the resistance from the center connector to either side connector should be 2.5k and across the two outside connectors 5k, right?

[rich smith]

Most TX use linear pots so that should be true. I've replaced noisy ones in a few of my TX and, like with servos, the value is non-critical because we're dealing with ratio instead of absolute resistance.

Do you happen to know if the pots a DX5e are also 5k? I tried measuring them while still wired in place but that didn't work. And another, probably stupid, question: I'm a bit rusty on my electronics but if a joystick is centered and the pot is 5k ohms, then the resistance from the center connector to either side connector should be 2.5k and across the two outside connectors 5k, right?

[CATPart]

...the value is non-critical because we're dealing with ratio instead of absolute resistance.

Ahh...thats good news, should make it an easy choice then.

[earlwb]

Actually the center on the proportional servo's pots are slightly off to one side, so instead of being 2.5k, it is more like 2.3k or 2.4k. A old robotics trick to make servos into gear motor drives, was to configure the servo to rotate continuously. usually you could remove a little plastic clip or part that connected the potentiometer wiper arm shaft to the output arm on the servo. Then you could program your micro-controller to output the 1.2ms to 2ms pulses to the servo and the output arm would rotate. At center it would stop, and slightly off to one side or the other the servo would rotate slower. So you had a simple motor speed control setup with gear drive. Usually you could use a small jeweler's screwdriver and center the pot on the servo through the hole in the center of the output arm. On the robots they mount a wheel of course.

Now to use this with an actuator, you disconnect the motor from the servo and keep only the servo electronics and put in a small circuit board pot or a couple of resistors like 2.2k for example in place of the pot. Then you hook the actuator up to the motor wires, and you are in business. You have a simple actuator controller for a regular radio control system.

When i think about it, in place of the actuator you could use the same setup to power a motor to drive a propellor too. You can use the servo motor as the drive motor on a small airplane. In this case you set the center all the way off to one side so you have only one direction control of the motor. But with some new 3d airplanes they are doing reverse hovering and flying backwards too, so maybe this might be the just the ticket too.

A long time ago, i used to modify servos to use a 10 or 20 turn potentiometer so i could use the servo as a sailboat winch system for the sails too.

Not all servos are suitable for modifying to continuously rotate. it depends on how they designed the main output gear and how they control the pot shaft. In some servos you have to cut away a output shaft part that prevents the output arm from rotating 360 degrees. On some servos the output arm is the pot shaft, so you may be stuck in some cases.

A good source for servo parts is when other modellers crash a airplane and trash a lot of parts, the servo guts are usually still salvageable.

[gobigkahuna]

Oops. I just realized I misread the title of this thread. My apologies for diverting the thread in the wrong direction but thank you anyways for your answers.

[CATPart]

you guys think this is one might work?

http://www.etisystems.com/EUP1100.asp
• Thermoset plastic housing. brass plated terminals.
• Nickel plated brass bushing and shaft
• Wirewound Resistive Element
• Electrical Angle: 270 degrees
• Life Shaft Revolutions: 100,000
• Resistance Tolerance: ±10% Linearity: ±1%
• Operating Temperature Range: -35°C to +105°C
• Power rating: 1 watt
• Insulation Resistance: 1000 Megohms @ 500 VDC
• Dielectric Strength: 1000 VAC
• Starting Torque: 1.0 oz. in. maximum
• EUP1100: 285 degree mechanical rotation (end stops)
• EUP1125: Continuous mechanical rotation

[CATPart]

or maybe this one? http://www.etisystems.com/mw22.asp

[CATPart]

.....with a Hitec HS-635HB servo?
http://www3.towerhobbies.com/cgi-bin/WTI0001P?I=LXFRS6&P=8