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Ankle control for 2-3-2 idea
#1
I have been looking at the 2-3-2 transitions as implemented on other people's builds and the ones that look the most impressive use individual control of the ankles and shoulder joints. This, coupled with a fast center leg deployment lets you do a more dynamic transformation.



I am wondering if you could implement something similar in a 3D printed droid by modifying the legs to control the ankle push rods with some sort of linear actuator instead of running up to the shoulder.
1
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#2
Michaels original 2-3-2 implementation had a rod that ran from the should to the ankle - this would put the ankle in the correct position. I'm sure he'll have something similar in the next version (the legs have the slot for it).
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#3
Yeah that is Drew's R2 (Dwarf on Astromech). His is a really nice implementation, he also has his R2 running all-terrain, grass, gravel, roads.

It's a pretty simple solution, I think it used an electric windows motor from a car to throw and retract the third leg. He uses a piece of steel pipe to connect the two shoulders at the top of the legs for strength, it just runs straight through the body, so there is basically no body stress at all.
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#4
(08-28-2018, 04:38 AM)LarryJ Wrote: Michaels original 2-3-2 implementation had a rod that ran from the should to the ankle - this would put the ankle in the correct position. I'm sure he'll have something similar in the next version (the legs have the slot for it).

The linkage between the ankle and shoulder stops you being able to move them independently.

Dwarf's impressive (movie accurate) lunge onto the center foot is achieved by leaving the ankles fixed until the shoulders and center leg are in place. He says his 2-3-2 transform is acheived by:
Quote:Controlled by 1 relay, and several micro-switches (limit switches)
When "ON", it powers Center Leg, and shoulders
When center leg is extended (hits limit switch), power ankles.

When "OFF", it powers Shoulder & Ankles.
When Ankles hits limit switch, power center foot.
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#5
(08-28-2018, 06:04 AM)Martyman Wrote:
(08-28-2018, 04:38 AM)LarryJ Wrote: Michaels original 2-3-2 implementation had a rod that ran from the should to the ankle - this would put the ankle in the correct position. I'm sure he'll have something similar in the next version (the legs have the slot for it).

The linkage between the ankle and shoulder stops you being able to move them independently.

Dwarf's impressive (movie accurate) lunge onto the center foot is achieved by leaving the ankles fixed until the shoulders and center leg are in place. He says his 2-3-2 transform is acheived by:
Quote:Controlled by 1 relay, and several micro-switches (limit switches)
When "ON", it powers Center Leg, and shoulders
When center leg is extended (hits limit switch), power ankles.

When "OFF", it powers Shoulder & Ankles.
When Ankles hits limit switch, power center foot.

You have to see Michaels old design. The rod would allow the ankle to go to the correct 16 degree angle but allow the body to be at the full 32 deg angle - I believe it was modeled after one of Dwarf's earlier designs.
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#6
I was actually looking at a droid this weekend that uses pretty much the same setup that Dwarf uses. It is cool, but it seems too fast / abrupt to me. I wouldn't trust activating it unless right next to the droid (as it may tip over from the force).
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#7
With Dwarf's design there is no way it would tip over during the process, but it does startle kids if close by. It is the same speed as on-screen R2.
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#8
(08-28-2018, 08:49 AM)Laserman Wrote: With Dwarf's design there is no way it would tip over during the process, but it does startle kids if close by. It is the same speed as on-screen R2.

It's when it goes from 3 -> 2, the force coming up is the same as it is going down - when the droid comes up on two legs, the natural force is to pitch it forward. The guy I was with this weekend has had his do it many times - so much so, he won't go from 3 -> 2 without being next to it. He has more than a few dents and scratches to show why.

There have been many debates, on the R2 forum, about the speed seen in the movie and that it would be too hard on a droid if it was done all the time.

You also have to remember, the movie droid was designed only to do that one scene - our droids do the work of 10 movie droids.
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#9
The idea of independent ankle control has advantages beyond just the change between 2-3-2, while in the 2 mode the droid is less stable, this is an inherent design issue, with all the stability in the forward and back direction being relatively small compared to the height of the droid.

If the ground the droid in not level, then is very possible for R2D2 to fall over with very little helping it.

One solution to this is active balance control, using an Inertial Measurement Unit (IMU) to report to a controller its current angle relative to the ground and the direction it is moving. With that information the drod could alter the angle of the ankles to counter any falling movement and to level the droid feet so that the droid remains upright even if the ground has a small slope to it.
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#10
I couldn't push that one over, so maybe it had a lot more weight in the bottom end?

Also, you could design it so that the retraction was slower than the extraction.
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