Author Topic: Durable and Light Rotational Joint  (Read 929 times)

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Offline davidhere40Topic starter

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Durable and Light Rotational Joint
« on: January 28, 2012, 09:33:25 PM »
I'm researching how to make a durable, yet light rotational joint. I've managed to construct a joint on a 8 foot long robotic arm with horizontal-only freedom/motion. It uses two servos as the joint between two 4-foot-long square aluminum tubes. But, I don't think that's sufficiently durable. I plan to have multiple such joints and need it to hold a small payload on the end, like 0.5 kg or less, plus the ability to withstand a bit of tugging when the arm grabs something that is not free.

I'm thinking of separating the joint from the motor. But to do that I need some sort of bearing or something. It has to be light weight but rigid and durable. If it's heavy, then that means the motors will have to be heavier and more expensive.
There has to be a simple way of doing it such that it can withstand industrial usage without making it gigantic and heavy like most industrial robotic arms. Any pointers would be much appreciated! I'm just an individual building a prototype on my own, so I'm only looking to spend max $100 on any hardware for the joint. Hopefully a lot less if possible.


Offline georgeecollins

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Re: Durable and Light Rotational Joint
« Reply #1 on: January 31, 2012, 07:39:51 PM »
I would look at some of the hardware they have on servocity.com .  They have joints, bearings and couplers that are pretty sturdy.  Their hardware is generally designed to integrate with servos.  It's hard to know exactly what you need without a picture. 

What kind of servo did you use that could move an 8 foot arm?  I am guessing a pretty powerful one, but I am curious. 

Also, do you mind if I ask what the application is?  It sounds like an interesting project. 

Offline davidhere40Topic starter

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Re: Durable and Light Rotational Joint
« Reply #2 on: February 15, 2012, 01:16:58 PM »
Thanks for the reply. Sorry I didn't get back for a while. I've been completely swamped lately.

Well, I used a AX-18A Dynamixel. Which, worked, but because I was not using a good joint, it didn't work well at all (the joint was unstable and probably did a bit of damage to the motor, or at least damaged the bracket).

Since I'm an almost complete newb to robotics, I didn't know about bearings. Now I realize that whenever you need a strong, stable and durable joint, you use bearings.

But, since I had this idea, I decided not to use a rotational joint like that. I'm planning to use a jib arm instead. I'd like to say what the application is :) but I'm afraid it's probably a bad idea because it will be a new product, and I don't want to broadcast the idea.

Offline georgeecollins

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Re: Durable and Light Rotational Joint
« Reply #3 on: February 18, 2012, 07:38:21 PM »
A jib arm makes much more sense, particularly if you are going to have a counterweight.  An AX-18 has 18 Kg/cm of torque.  So if you had it act on an arm that is 4ft long ( or 121 cm) it would only have 0.14 Kg of torque.  That won't work for 0.5 kg load.  But a counterweight will make it much more manageable.   

Good luck! 

 


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