Instructables

Mechanical Servo Hack.

Another servo hack, is this really necessary? 
Only, if it adds something new. I think this one does, but correct me if I'm wrong.

As a novice, at first I found it hard to understand the differences between the types of hacks. As far as I can tell there are 3 types: 
  1. Total rip out hack. In this type of hack, the electronics are ripped out, and the Gnd and +5V wires are reconnected. The result is a DC motor with no digital pin. Look at the I'bles of Robomaniac and Randofo.
  2. Fool the electronics. This involves de-soldering the potentiometer and replacing it by two resistors, hence fooling the electronics. Look at djsures or here.
  3. Fool the mechanics. This involves drilling out the gear so that it does not catch the potentiometer anymore.Look at the I'ble of Zeitron

This slideshow is a variation on the last type.
  1. Open the servo by unscrewing the bottom.
  2. Remove the main gear.
  3. Cut the stopper on the main gear.
  4. Take a set of sharp pliers and cut the potentiometer.
  5. Set potentiometer in neutral position and glue it tight. Let it really dry prior to assembling, else you will be glueing the main gear.
  6. Assemble the servo. Done.

Zeitron3 years ago
Well bertus52x11 if you found a modification that works for your particular servo then I'm glad. Also, if it's irreversible then you must be content with it's final state since there's no going back. As for my particular servo modification the Main Gear rests on top of the potentiometer shaft. This shaft provides support and cannot be cut off or altered otherwise my servos Main Gear would wobble within the case and not lock onto the secondary gear properly causing unnecessary vibrations and poor rotational force.

So the consideration of altering the potentiometer permanantly in anyway depends on the type of servo and how the parts (potentiometer and gears) are arranged within the case. What is possible with one servo might be impossible with another................
bertus52x11 (author)  Zeitron3 years ago
Thanks.
AndyGadget3 years ago

HI Bertus. I think you'll find that Zeitron's method is, in essence, exactly the same as yours.  The trouble with servos is that there are so many different designs in the way the positional feedback to the pot, the rotation limiting and the general layout are arranged.

The aim is to make a reversible geared motor which is speed controllable, using the existing servo electronics.  To do this you need to lock the pot (or replace it with fixed resistors) and remove the mechanical endstops.  Once modified, you can control the speed and direction with a normal servo pulsed signal but again, servos vary and some will go from stationary to full speed in 20 steps whereas others will take only 4 or 5.  Digital servos will usually give a higher number of steps than analogue ones.

(Some of the cheapy eBay servos will remove their own endstops if you drive them to the extremes of their travel - I found this out by accident #;¬)

Randofo's mod was a strange one and would only be used in certain specific situations as it's driving the motor hard against the endstops.  This method could easily burn out the motor or strip the gears.
bertus52x11 (author)  AndyGadget3 years ago
Thanks for your comment.