Modifying a servo for continuous rotation

[robomaniac] shows us how to modify a standard servo to allow continuous rotation. This is a classic robotics hack and has been around for a while, but we really like the way he put this together. Although you may need some soldering and desoldering tools to open the servo up, the hack is a physical one. All you really need to do is cut off a plastic tab on one of the gears. If you want to see an example of a bot you can build with one of these CR servos, he just posted this one motor walker.


  1. Entropia says:

    Putting the bad English aside, I wouldn’t go about modifying a servo for continuous motion like that. You lose one kind of nifty feature by removing the whole controlling logic, which is the ability to drive it in two directions easily. Depending on the servo, you might also lose ability to drive it faster or slower in two directions.

    What I would do, is to remove the linkage between the gears and the potentiometer that senses where the gears are. Then remove the tab from the gears that is explained in the Instructables.

    Then set the potentiometer to halfway. When you command the servo to go to its maximum, it spins fast forwards (but never reaches the goal). Make it just a little bit over the halfway and it’ll crawl forward. The same applies for reverse motion as well.

  2. Jerome Demers says:

    It has been on hackaday, that is why I get more people visiting my servo modification instead of my one motor walker!


    Thanks for posting!

  3. h_2_o says:

    not sure if that post was directly stolen from the forums of the makers of phidgets, but the guys over there have had that mod up for quite some time now. i know at least 5 years.

  4. miked says:

    >not sure if that post was directly stolen from the >forums of the makers of phidgets, but the guys over >there have had that mod up for quite some time now. i >know at least 5 years.

    This is a common mod in the bot world. It is in a lot of places.

  5. MadEngineer says:

    I agree with Entropia. All that is required is to cut off the tab as per the last step. Don’t remove the electronics.

  6. Haku says:

    Servos can also make neat little rudimentary electronic speed controllers, for example I’ve modified a couple of small wired controlled toy cars in the past by making them completely radio controlled with fully proportional steering & driving.
    Basically you take out the electronics of a servo, keeping potentiometer & leaving the motor+case behind, then wire up the toy car’s (usually) 3v motor to the motor output of the servo.
    Et-voila, one rudimentary electronic speed controller, when you switch the transmitter+receiver on you’ll need to initially adjust the variable resistor so that the wheels don’t spin.

  7. Jerome Demers says:

    yes Haku!

    I have already done that with the old servo electronic.
    It been a while, back in 2001.
    You put 2,2k resistor or simply use the pot.

    That could be a idea for a other instructables…

    thanks man!


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