I was brainstorming with JP Brown, who I had a chance to meet in person. He wanted a biped that had fast leg recovery. I'm not exactly sure what he meant by that. Typical bipeds have their two legs 180 degrees out of phase of each other at any point in the walking cycle. I presumed he meant something other than that.
A few months later it dawned on me that I could use a differential to meet JP's challenge. I knew it would not fit well into my usual motor driven biped designs, but I thought it might work well on other kinds of walker designs. I decided to use Miguel's DDK walker design because I thought it looked very stylistic.
I replaced Miguel's single worm gear driven by a MicroScout, with a Mini-Motor driving a differential, driving two worm gears, each driving two 40 tooth gears. By inserting the differential into the drive train, each foot was able to move independently.
Moving independently is nice, but I needed to make sure the feet movement was coordinated. I used a pin and a lever to slow one foot when that foot was in the middle of its weight bearing part of the leg movement cycle. This let the motor drive the other leg, while holding the weight bearing leg in place. The legs take turns bearing weight, while the other leg recovers. The basic result of this is that most of the time, only one leg is moving.
On a heavier biped I could imagine elimintaing the pin and lever, and having the pressing down of the soon to be weight bearing foot transfer energy to the foot that was already weight bearing. With the proper load transfer, this could have the weight bearing leg go slow and the recovering leg go fast. Someday I may try to make one of these.
The design is very simple, so I have not bothered to make an MLCAD design of it. Contact me if you want one. I made a but it is quite large at over 5MB. I'm running out of space on my website. If you want a copy of the movie just email me. If anyone has suggestions on how to decrease the resolution or size of the movie, please drop me a note.
