dmoseley
"Very" rookie team here. My kids are having a hard time getting our arm going. Are there any resources for some basics in robot arm designs? We are days away from practice and still have so much to do. Thank you. 
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dannyk
We're pretty rookie also compared to a lot of folks on this forum, but I have searched a long time for good references on how to do things like this and never found any. My first suggestion would be to call your Hub Director and ask if they have someone to mentor your team. If all else fails, I would be glad to help but it is hard to do by email or phone. We have used pulley systems with good success the last 2 years and are using the supplied gears this year. We like the Igus things for our axle. Counterweights are extremely important, pennies or bungee or both.
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dmoseley
Thanks for the input. We have made some progress with a pulley system and PVC. It's not finished, but we're getting there. 
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EvansPhysics
Just another idea... Depending on what your arm needs to do and is capable of... but if it has linear extension, then a very simple method is to used a winch and gravity to change its angle of inclination.  There are some drawbacks, but is is very simple and can be very strong.  (The black gear in the photo is used as an idler to change the angle of the string.)
Arm Example.jpg 
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jgraber
The simplest method to lift an arm is to tie a string to the far end, and wind up the string on pulley on the motor axle, such as 1/2" rod, or the drive pulley.
A slightly better method is to put a big string drum (eg 6-12" diameter) with the axle the same as the arm axle, and attached to the arm,
and use a small string drum (same as above) to wind up a string wrapped around the arm string drum.
arm_wheel.PNG 
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