Quote:
Originally Posted by sircedric4
For those with electrical arm and elevator experience, how do you keep your arm or forklift in the position you want it without power. How do you make the up and down appear so easy and controlled?
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We have built a couple big arm bots and 1 forklift. There is a really good article with pictures of our 2007 bot in the Behind the Design book. It also discusses the controls. On both the 2005, and 2007 machines, we had a high axis arm with a large drive sprocket. We also used a 3-4" lever off the back of the arm and tied multiple loops of bungee. The bungee was very very tight. For 2005 there was approximately 200 lbs of downforce on those joints. make sure the bungee is fresh for that year (it degrades quickly especially if stressed). Also, when operating in cold environments, the bungee will stiffen. Warm it up to room temp before operating your arm otherwise funny stuff might happen.
The resolution with the shoulder joint was not the best due to the locking pins in the dewalt, and the use of FP motors which burn up in stall very easily. Because of this we had a forearm on both of those bots that would adjust relative to the shoulder position. Ideally you want angular feedback right at the actual joint for rotation. This will give you true position vs. using a sensor in teh chain loop that will have a little error from chain lash.
I don't remember what we used as the drum brake for our elevator in 2008. In fact, I am not sure that we had one.