02-10-2005 20:39

Re: pic: My wheel/leg design

GREAT! Just a thought ...
you'll need some pretty sophiticated stuff to be able to stop the robot.
In the show the robot kinda turn and difts to a stop

02-10-2005 21:30

Kevin Sevcik

Re: pic: My wheel/leg design

From a more practical standpoint, if you make that entire shaft spin, you'll be putting a terribly large load on the bearings and shaft. Ball bearings are intended to support mostly radial loads. With your current design, the shaft bearing at the top would see a large thrust load, which would drastically shorten the bearing's life if you don't over-spec the bearing by a lot. Also, keep in mind that flexible shafts aren't going to transmit much torque.

02-10-2005 23:15

greencactus3

Re: pic: My wheel/leg design

i think a simple doublewishbone idea of a suspension would work just as well and simpler.

02-10-2005 23:20

mechanicalbrain

Re: pic: My wheel/leg design

I specifically want a simple walking/rolling design.

02-10-2005 23:54

Re: pic: My wheel/leg design

Just wondering but, could you explain how it works? It look pretty cool

03-10-2005 00:19

mechanicalbrain

Re: pic: My wheel/leg design

Well the general idea is that their are four legs and the sit out at an angle from the robot. The entire leg can rotate on that gear (more symbolic of where it pivots then anything else). Also the rod is attached to that square coupler by a ball bearing and rotates. When it rotates the half sphere at the bottom acts like a wheel. Its just a conceptual design right now and not really possible due to the limits of last years kit but its a future plan. Not only could it have simple walking but the legs could start facing up and fold down to add significantly to the height of a robot. Basically I'm trying to come up with a simple walking robot that doesn't have the disadvantages of speed that most walking robots posses.

As mentioned its got a few engineering hurdles it needs to overcome but if i don't use something like this in FIRST then ill definitely do it privately because the idea has been bouncing around my head for quite some time i just never really developed it until now.

03-10-2005 09:16

phrontist

Re: pic: My wheel/leg design

In what way does this "walk"? Iit just a wheel at the end of a shaft? Or can it also swing the shaft some how...

03-10-2005 12:01

Kevin Sevcik

Re: pic: My wheel/leg design

It "walks" by whipping around that large gear the shaft bracket is attached to. Mind you, it'd walk better if the leg moved in and out as well as around or something similar. Perhaps instead of starting from scratch on both counts, you should find some simple leg joints that work for people and then figure out how to put wheels on them?

03-10-2005 19:31

mechanicalbrain

Re: pic: My wheel/leg design

Yes thats exactly how it works. As to the retracting part. It would have to involve a mechanical function so i can keep the motors to a minimum. I want it to come around back so it can clear stairs and such objects. Finally, If I added wheels to the end of legs it would need to be some type of pulley system and then again I run into having more then two motors a leg.

03-10-2005 19:48

artdutra04

Re: pic: My wheel/leg design

I you want to see a ton of different walking robot designs, check out this page. (You'll have to scroll down a bit.) I know that these are Lego creations, but the principles behind the walking robots can be adapted to a larger scale. IMHO, I would think that instead of rotating the entire leg around, do as Kevin Sevcik suggested, and make the legs go up and down, instead of in circles. Similar to this picture:


I know that it wouldn't be able to go up stairs, but it would have much less stress on the shafts.

Also, I am curious. What is the size of your leg?

03-10-2005 21:06

mechanicalbrain

Re: pic: My wheel/leg design

Thanks for the link! Ill go through it. You see the point is that Im TRYING to do a wheel/leg and not just a walking design. Your typical walking robot is very, very slow. I want to have some type of wheels to give it a good speed and then legs to give it the best climbing available while using a minimum amount of motors. In answer to that last question, I was looking at making the legs 1' - 1.5'. Thanks agian for the link.

03-10-2005 23:11

Matt Krass

Re: pic: My wheel/leg design

You may want to try a tri-wheel.

Essentially its three wheels centered around a point, 120 degrees apart at the center of each wheel. Two rest on the ground and all three spin. When you hit a stair well, the friction cause it to pivot around the center and climb up the step, in theory. I played with the idea but never built it, I'm gonna see if I can do it with the Vex kit I'm getting this weekend.

EDIT: I added a rough sketch.

04-10-2005 09:10

artdutra04

Re: pic: My wheel/leg design

I've built one of those before using Legos, and it worked pretty well. But there is one thing to remember when you build these. The wheels around the outside must spin faster than the center shaft. This will make the three wheels roll easily, but when an obstacle comes (like a stair), the force will then take the easier route and rotate the whole assembly (instead of the indiviaual wheels).

If you are interested, here is video of a Lego Tri-Wheel robot climbing stairs: http://www.visi.com/~dc/tristar/stairs4.avi

There are more pictures on this page:
http://www.visi.com/~dc/tristar/

06-10-2005 10:29

Travis Hoffman

Re: pic: My wheel/leg design

Got whegs?

http://www.chiefdelphi.com/forums/sh...ighlight=whegs

Courtesy of researchers at Case Western Reserve University in Cleveland, OH.

Have fun putting wheels on the ends of these things!

07-10-2005 09:42

Kevin Sevcik

Re: pic: My wheel/leg design

Finally getting around to answering this... You could obviate the need for tons of extra motors, pulleys, chains, flexible shafts, etc by going with a large, well designed leg, and then putting a motor/gear case/wheel assembly on the end of it. Using FIRST parts, it'd be some sort of sturdy leg system with a Nothin'-But-Dewalts motor assembly attached to a wheel at the end of the leg. There are trade-offs, obviously. This makes your leg much heavier. But on the plus side, electricity is an awful lot easier to bend around corners than mechanical rotation.

07-10-2005 11:08

mechanicalbrain

Re: pic: My wheel/leg design

Wait would it still have both leg and wheel motion? If you can, add a picture of the design. Thanks.

07-10-2005 12:01

Kevin Sevcik

Re: pic: My wheel/leg design

It's no design in particular. It's just an easier way of going about it. So no picture. Just imagine you have some sort of walking robot already. At the very end of each leg you put a wheel-motor assembly instead of a little rubber foot or what have you. Voila, a leg with a wheel on it.

It's not at all elegant, of course. But if you don't need a central engine driving the wheels, then it's a lot easier than the mass of U-joints, flexible shafts, or telescoping shafts you'd probably need otherwise. As a side note, if you're going to scale this up then at some point it becomes more efficient to use hydraulic motors to drive the wheels instead of electric ones. Though I'm not informed on the flexibility of high pressure hydraulic lines.