Any simple collision detection ideas?

Posted by mikael on November 15, 2006, 6:11 pm

hello people

I am trying to build a foot touch sensor mechanism for my hexapod
walking robot using force sense resistors. The plan so far is to make
something simple like this: http://mikael.geekland.org/foot_idea.png As
you can (hopefully) see, it has only downward force detection..

But i would like bump sensing as well (for stair climbing etc)... I
only need a simple bump/no bump signal but it has to be detectable from
any angle and at least be near the foot/base of the leg (though
preferably apply to a fair length of the leg).

I've come up with a number of ideas involving such things as using the
aluminum leg's conductivity as part of a switch OR even moulding the
foot in such a way, producing a twist force on the FSR's upon object
collision BUT I can't seem to come up with anything practical (easy to
make and wont break) and cheap enough!

So I was just wondering if anyone here had any general thoughts or
ideas or has done something similar in the past. Any ideas would be
appreciated!

Mikael

Posted by Joe Strout on November 15, 2006, 6:37 pm

> But i would like bump sensing as well (for stair climbing etc)... I
> only need a simple bump/no bump signal but it has to be detectable from
> any angle and at least be near the foot/base of the leg (though
> preferably apply to a fair length of the leg).

Just brainstorming here...

What if each leg were dressed in a conductive (e.g. thin aluminum or
copper) "sleeve", attached at the top via a short cylinder of foam, so
that under normal circumstances it doesn't contact the leg. But when
you bump into something, contact is made with the leg, closing a
circuit. It's the same idea as a bumper skirt, but applied to each leg.

Another idea, if you have force feedback on your servos (e.g. you happen
to be using Robotis Bioloid servos), is to just detect when the knee
servo is registering unusual force. That probably means the leg is
running into something.

HTH,
- Joe

Posted by Curt Welch on November 15, 2006, 6:40 pm

> hello people
> I am trying to build a foot touch sensor mechanism for my hexapod
> walking robot using force sense resistors. The plan so far is to make
> something simple like this: http://mikael.geekland.org/foot_idea.png As
> you can (hopefully) see, it has only downward force detection..
> But i would like bump sensing as well (for stair climbing etc)... I
> only need a simple bump/no bump signal but it has to be detectable from
> any angle and at least be near the foot/base of the leg (though
> preferably apply to a fair length of the leg).
> I've come up with a number of ideas involving such things as using the
> aluminum leg's conductivity as part of a switch OR even moulding the
> foot in such a way, producing a twist force on the FSR's upon object
> collision BUT I can't seem to come up with anything practical (easy to
> make and wont break) and cheap enough!
> So I was just wondering if anyone here had any general thoughts or
> ideas or has done something similar in the past. Any ideas would be
> appreciated!
> Mikael

I don't know anything about that "force sense resistor" you are using, but
maybe you can just put the resistor at the top of the leg and attach the
lower leg to the resistor. Any bump or force on the lower leg should then
cause a detectable change in the resistor.

--
Curt Welch http://CurtWelch.Com/
curt@kcwc.com http://NewsReader.Com/

Posted by Frnak McKenney on November 16, 2006, 9:08 am

> hello people
>
> I am trying to build a foot touch sensor mechanism for my hexapod
> walking robot using force sense resistors. The plan so far is to make
> something simple like this: http://mikael.geekland.org/foot_idea.png As
> you can (hopefully) see, it has only downward force detection..
>
> But i would like bump sensing as well (for stair climbing etc)... I
> only need a simple bump/no bump signal but it has to be detectable from
> any angle and at least be near the foot/base of the leg (though
> preferably apply to a fair length of the leg).

Mikael,

Have you considered a pneumatic approach? You'd need an air-pressure
sensor, some tubing, and an air-filled ball, tube, or even an

irregular shape (e.g. an inflated dishwashing glove <grin!>).

As long as the air-filled "cushion" gets deformed far enough before
your robot damages itself (or the wall, or the furniture, or a
small pet or three) this should give you a remarkably flexible (in
several senses) and omnidirectional "bump sensor".

This would probably be difficult to use on a really light robot, but
I'd think anything that carried a reasonably hefty 12V battery would
have enough mass to make this work.

Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)
--
"He can compress the most words into the smallest idea of any
man I ever met." -- Abraham Lincoln
--

Posted by DragonSt0rm on November 16, 2006, 9:49 pm

mikael wrote:

Just brainstorming ....

You have to ways to detect a colision:
a) sensor on your skin feel the presure from the object
b) your muscles get suddenly and increase in tension while not advancing

For a) you can go with various solution, others already gave you some ideas.

For b) however, you can figure it out from 2 hints:
- the position (angle) transducer stop advancing
- a sudden increase into the power ( amperage) consumed by motor

This 2 facts simultaneously tells you that it bumped into something, so your
software can figure that out without need for "skin".

Just a thought...

MTM

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