Biped Construction

[Rolf]

Hello.

If you don’t want to read my full post, my question basically is:
How do I build the legs for my servo-based biped?

---full post---
I am quite new to robot-building, but I have recently built my first robot; an obstacle avoiding two-wheeler. Now I want a bit of a more challenge, and have decided to build a Biped. I have searched the Internet for a long time to find out how to do this. I then ordered eight standard-servos, a servo-controller, an accelerometer and an AVR Controller Board.

What I think will be the biggest challenge is constructing the legs. I think making them out of acrylic glass might work. Does anyone have experience on doing this? Maybe there is a web-site explaining how to build biped-legs with easy-to-get materials?

When I get my biped walking, I will add sensors to it; the accelerometer to make it balance, IR-sensors for range detection, and so on. I just have to overcome the problem of building the legs…

Thanx for helping me!
Robots are fun 

[ed1380]

[ shaped brackets

Thats what all the sevo controlled bipeds look like (the ones I've seen at least)

[Somchaya]

[ shaped brackets

Thats what all the sevo controlled bipeds look like (the ones I've seen at least)

Hmm, can you go into a little detail about this? I'm also pretty interested in learning it for fun..

[ed1380]

http://images.google.com/imgres?imgurl=http://www.alberts-equation.net/ZyRoQ.jpg&imgrefurl=http://www.alberts-equation.net/Robotics.shtml&h=543&w=550&sz=66&hl=en&start=11&um=1&tbnid=UW72TvQvxemV5M:&tbnh=131&tbnw=133&prev=/images%3Fq%3Dservo%2Bbiped%26svnum%3D10%26um%3D1%26hl%3Den%26rls%3DGGLR,GGLR:2006-48,GGLR:en%26sa%3DN

[Somchaya]

Ooh sweet, thanks For some reason, when I think of bipeds, using [ brackets in that way never came to mind, but it looks like it's a great way to do it..

[ed1380]

This site looks great http://www.pages.drexel.edu/~pyc23/bi_Pedal_Robot.htm

[Rolf]

Thanks for all the replies!

Making the brackets out of aluminium looks great, but I’m not sure I have the tools required. That’s why I want to make them out of acrylic plastic. I guess the problem with acrylic plastic is that you can’t bend it. Has anyone built biped-legs from acrylic plastic?

I could also buy the brackets from a web-shop, but the ones I have found is quite expensive. http://www.lynxmotion.com/ has great brackets, but buying two biped-legs there would cost more than 100$ with shipping.

[JonHylands]

Unless you've got a milling machine, your chances of being able to build biped leg brakcets that actually work is next to zero. Heat and bend works great when you're vacuum forming against a mold, but with servo brackets you need to have holes end up in the "right" place.

The other problem with acrylic is that it is very brittle - you drop your biped from any height and its going to break, pretty much guaranteed. The Bioloid kit, which I use, has plastic brackets, but they are a form of fiberglass-reinforced ABS which is very tough and a little bit flexible.

Its a hard problem to solve...

- Jon

[Rolf]

When the parts I ordered arrive, I think I will try making the brackets myself. I can maybe use thick acrylic plastic, and epoxy or melting to connect the parts. If I manage to get my brackets working, I will be sure to tell you, Jon 

If this does not work I might end up having to buying my brackets, making my robot more than twice as expensive as planned.

[dunk]

i'd recommend polycarbonate over acrylic. it's far stronger than acrylic but still easy to work with.

i have had some limited success bending 2mm polycarbonate in a domestic oven. the trick is to make a metal jig and experiment with your oven a bit to find the right temperature. between 180 and 200C is about right. if you start getting bubbles forming it's too hot.
you will need to design your jig so you can really clamp the poly carbonate in there.

the professional way of doing it is to use a strip heater which softens a line in your sheet plastic. because the plastic on either side of your melted line is still solid it makes for a nice clean fold.

i never got as far as building a strip heater.
clamping the polycarbonate in a jig gave me fairly accurate results 2 attempts out of 3.
good enough as i was only making 4 components i just kept going until i had enough of them that were accurate enough for my purpose.

dunk.

[Hal9000]

There is a really old book I have where the biped is made from wood and servos, but it has a really basic name I think (like "introduction to robotics")..........so it's hard for me to search on amazon for it, since I left it at Uni.

It has the robot on the front cover.......well, if you are still wanting to know, I go back to uni in about 4 days.

Also, if anoyone else knows what i'm talking about feel free to tell thus dude what book it is, as it could be just the thing?!?

[Hal9000]

ET VOILA!

http://www.amazon.co.uk/Introduction-Robotics-H-S-Sandhu/dp/1854861530/ref=sr_1_4/203-0397821-4676762?ie=UTF8&s=books&qid=1177084425&sr=8-4

[Hal9000]

Plus also:

http://www.amazon.co.uk/Build-Your-Humanoid-Robots-Robotics/dp/0071422749/ref=pd_bxgy_b_text_b/203-0397821-4676762?ie=UTF8&qid=1177084425&sr=8-4

Although with TAB robotics books they normally try and make you buy their stuff, so, unless it is a genreal book by TAB (electricity & electronics etc etc) then I wouldn't advise this.