Yet Another Hip Rotation Idea

[gdubb2]

Hivemind,

When you did the mods to your RN, did you experience the same kind of stability problems that I did?? I tried it with angle brackets like Ohms black one, and again with straight brackets like yours. most of the instability was in the lashup to the top leg servo just before the rotating one. Everything was just so wobbly it wouldn't do much of anything.

I agree that more torque would be nice. A lot more would be even better. I wonder if the gearsets from the new (unavailable) servo (5498 I think) would interchange with the 8498???

Gary

[hivemind]

I definitely apologize for 9x the negativety!

As for stability, yes, I did have some issues there, which is why I havent posted videos of Modi, I am redesigning him to get weight down, and trying to stabalize... If you have seen the most recent pictures I have pretty stable hips on him, but the height kills me, so I am going to reduce that and see what I can do then.

What is it that you are making your parts out of? I can give you some help with figuring out design if you ever need help... and choice of aluminum, and the stuff I am using is amazing (and cheap!). Email me or PM me if you want to try to sit down and work out a new design with me (taking into account weight conservation and zgp).

-Hive

[gdubb2]

Hi Hive,

This is definately worth persuing more.

The aluminum I'm using for brackets is .050 6061-T651. I have a bunch left over from some combat robot stuff. The stock brackets are .040 whatever alloy. The 6061 is easy to work with. I cut it on a band saw then bend it with a small cheapie break.

I also made thrust washers from a teflon like material to try to eliminate flexing. Metal servo horns would probably help as would higher torque.

I guess a guy could maching brackets from plastic. I have a lathe and mill, but they are not CNC.

Gary

[zaboomafuu]

After my last bad attempt at hip rotation, This morning another idea came to me.

Instead of adding extra DOF to the legs, simple rotate servos 4 and 22 in the hips to point down instead of front to back, but DO NOT add the servos below to replicate the original hip movement. You would lose the ability to kick out the side, but could replicate that movement by rotating the leg 90 deg and kick straight.

What do you all think??? Has it been tried before??? Good..Bad.. Really Bad...I dunno..

Gary

I was thinking about that would it work if you just made him walk a lil pigeon toe'ed lol? kinda have the feet like this walking up page / \ ? it would give you your side to side motion and still have your forward back too he would look kind of short buss but it might work lol

[Widgits]

I would worry about the T6 temper on the 6061 aluminum
This temper has a tendancy to crack at the outside line of a 90 degree fold
Typically most sheet metal shops run a 5052 grade that has a T3 temper
But this makes the aluminum soft and gooey and it has a noted problem with piling up the material on cutting tools
Punching and shearing work fine but machining it can have problems even with lubricants (Kool mist, tapmagic, kerosene etc.)

An old machinists trick is to cut the parts out of 6061T6 and then before you fold these bends put the parts into sudsy water made with clothes detergent
Heat them up with a propane torch very slowly until the soap film starts to turn color, and then let it slow cool back to room temperature
This changes the T6 temper down to a T3-T4 and still give you the better machining qualities of the 6061 grade and prevents this cracking problem
when you brake the metal
However if the material is thin enough this cracking problem might not happen to begin with, Check the outside corner with a loupe real close
Cracking is hard to see
But just in case it does here's an option for you
Widgits

[gdubb2]

Zaboom... I tried the walk cycle without using the hip servos. It works, sort of.. by just using the foot servos to shift the weight, it is quite unstable, and choppy. I finally gave up on that idea..

Widgets.. Thanks for the tip. I have been using 6061-t6 for quite a while, and have had very few problems with the bends. I think it is because my break is VERY cheap and cheesy, and I make fairly large bend radius'. When I try to bend it to tightly, it does indeed crack... Large radius bends aren't as good looking, but they work.

Gary