ive been thinking of incororating a different type of joint in the ankle and the hip, it complicates IK calculations but i should be able to get away with only three high torque servos per leg. i have the design in solidworks and i have a couple of renders of just the ankle that ill put here.
it a little hard to make out, but you have one servo mounted on the foot that rotates the foot assembly through the belt drive, the next servo is hight torque, does the bending and carries most of the load. the top servo is rotation and moves the whole setup. all three axes coincide at one point which is a big plus and the only other high torque servo is in the knee.
i believe the moments applied to the two rotation servos are orders less the that applied to the bending servos, though i might be missing something
just looking for some thoughts, opinions, and insights.
nick
if anyone has the SW or the viewer and would like the file just let me know.
interesting idea but I can see how not having a servo to lift up the foot could be a problem. Everything looks like it rotates which is fine but I would think you would need something in order to lift the assemly when taking a step. Otherwise it just seems like it will move like one of those foot dragger bipeds.
any chance you can upload a file for one of those servos? they look very well done and would really save me some time.
Hi Nick, I made the foot rotation axis using our Servo Erector Set. I varied from your design a bit, as I was going from memory. But I am pretty sure it can be done the way you designed it. I had to add a spacer to the foot th lift the gear enough to clear the bends on the foot. I am not a big fan of the vertical foot rotation design, but as you can see, it’s certainly do-able with off the shelf components. (Note: some of the parts aren’t actually on the shelf yet. )
I will be posting images of the custom ball bearing assembly, which is part of the low profile servo axis part, in the Servo Erector Set forum.
SN96 I think the basic solid works package(excluding COSMOS, Edrawings, and Conversion Wizard, etc.) starts at around $13,000. I could be wrong but I think thats what the 2003 cost was but 2006 is probably more. If you want it your best bet is to get a student version($200 I think) or the “special” version which I probably cant talk about on this board.
always amazed at the versitility of the erector set, but im curious about the gears. i was wondering how accurate the gears were, i went with the belt to try and avoid some of the inherant gear slop i have typically found.
nate, yes they are on the same axis, but only so long as the joint is vertical. once the ankle is bent each servo has a different affect on position. in all actuallity the foot servo is only required to maintain the foward orientation, if the foot was symetrical it would not be required. it does however increase the ability for the bot to rotate on a single foot.
nick
topher, file was sent. let me know how it works for you
Hi Nick!
The servo side of the assembly has about 30 thousandths adjustment each way, so you can ensure they mesh well. I believe any slop is inperceptable or at least negligable.
well after 20 some odd redesigns, and another 30 odd models for Jim; i have finally finished the solidworks model of my 7 dof leg. i has way to many mates which makes moving and animating a pain in the a$$, but i was able to get one video before i got too frustrated.
the video cuts right before the leg assembly rotates 180 degrees while the foot and make shift body(ie bar) stay pointing foward. which effectively gives the bot a reversed knee reminiscent ED 209. when the leg turns past 90 degrees the mates get confused and you end up with a bunch of broken parts
once you have all the parts modeled it pretty quick, putting it together was maybe 30 min and then an hour or so trying to get a vid. if the assembly is simple it can take as little as 5 min.
im not yet very good with simulation, but i was able to simulate Jim’s low profile bracket with accurate gear mesh. and that took maybe 10 min
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