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Technic - rotating a liftarm - ideas?

CCCCCC Member Posts: 20,526
I need to rotate a liftarm from a servo motor, in quite a small gap. Ideally I'd just attach the liftarm directly to the motor axle (I'm using a third party slimline servo, so can glue any connector onto the axle). However, using a friction pin is not going to allow enough torque in the rotation. What I really need is a liftarm with a x or + in the middle so I can use a + pin on the axle to rotate it. Has anyone got any ideas how to drive it. The best so far is to use a pulley wheel (with it's + hole) and connect the liftarm across it with two 1.5 length pins but this makes it a bit too bulky in the centre and obvioulsy increases the thickness. I've tried various combinations of thin liftarms too.

Any better solutions?

I really wish there was a liftarm with a + hole in the centre.

I know an alternative is to glue the friction pin in place, which is probably what I will end up doing.


  • datsunrobbiedatsunrobbie Member Posts: 1,817
    What's the part# for the liftarm that comes closest to working? A picture of your assembly using that part might help for figuring out how to piece together a solution.
  • CCCCCC Member Posts: 20,526
    It is a standard 1x15 liftarm (thick).

    I'm then using a pulley wheel 4185 which connects to the centre of the liftarm with two 3/4 pins 32002 (not the 1.5 as mentioned earlier, I refer to a normal pin as a 2 as it has two sides). This works perfectly, but I'd rather lose the large pulley wheel if possible. It connects to the motor spindle with an axle pin, the axle into the pulley and the pin side glued to the motor spindle.
    Comb wheel 6575?
  • CCCCCC Member Posts: 20,526
    I've found another solution to the problem. It is for a middle leg pair (pivoting legs) on an insectoid type robot, and I can get away with using a bent liftarm, rather than a straight one with right angle joints.

    I just wish they made stright versions of this, I cannot believe I am the only person that has ever wanted to spin a liftarm around an axle in a controlled way!

  • DaraghDaragh Member Posts: 363
    Would 6632 work, it's straight but would be offset on one side. 
  • graphitegraphite Member Posts: 3,275
    Its hard to offer solutions without seeing it, and how much room you have around it, but you said you tried a combination of thin liftarms.  Did you try creating a full 15L length out of just thin parts to line up an axle hole at the center?  Or did you use thin arms attached to the 15L to get an axle hole in place?
  • sid3windrsid3windr Member Posts: 1,460
    2711 not an option? I don't know what you need at the ends...
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