Alt-BEAM Archive

Message #03152



To: Wilf Rigter Wilf.Rigter@powertech.bc.ca, beam@corp.sgi.com
From: Dennison dennlill@buffnet.net
Date: Mon, 10 May 1999 19:38:35 -0400
Subject: [alt-beam] Re: a useless idea


Actually, that's the same Idea that I use in my bot for chiu's contest. I
don't know if anyone got either other posting, but my bot uses the same idea
of inertia, or momentum, for locomotion. Using one motor, and a ordinary
bicore head, with a little modification, I have a bot that is phototropic.
The head not only points twards the light, but it moves twards it. Basically
the head swings a large weight around (not all the way around) a ceritan
amount, about 260 degres or so, and it produces a forward motion from the
angular momentum.

When the head swings and reverses direction, you get a tangential
acceleration found by

Acceleration-tangential = Radius * AngularAcceleration

From that we can calculate a rough idea of the force, given the weight of
our head, and the radius of the counterweight.

Force=Mass(weight)*Acceleration(tangential)

But what about the inertia?

Force = Mass * Acceleration

so then

Force = Mass * Radius * Angular Acceleration

But we need some more befor we can go on, Torque is Radius times the force
or

Torque=radisu*Force and we know what force is, so we get:

Torque = Mass * Radius^2 * Angular Acceleration (mr^2 represents the
rotational inertia)

To find the total torque, supposidly we need to calculate the torque for
every single particle. Atoms, quarks, etc.. But thats unnessesary for our
purposes.

So the Momenet of Inertia for our HEAD or mobile, or etc.. is

Inertia = Sumation( mass *radius^2)

Actually this is a little simplified. For a Bicore head, or the mobile
described, the shape of our device isn't a thin hoop, which the above
formula works for. The formula for the momenet of inertia for our devices
is: (1/3)Mass*Radius^2

When building a bot like this, this really isn't too important to know,
although you should understand it to produce good results, if you want more,
any good physics book will tell you how. There's also a bunch more to it.
Like calculating the friction between the head device and it's environment
and such. But it's fun stuff.

Dennison





>Inertial positioning!
>
>Useless???? You have practically invented a phototropic MOBILE ! This is
of
>course a brilliant (although perhaps not entirely new) idea ! A low
>friction bearing would permit the same mechanism to be used for standard
>head applications with a tripod support. While interesting for
>head/bot/mobiles that turn with respect to a fixed reference this idea is
>much more practical when used in referenceless application: Most effective
>in zero gravity applications (in space), it can also be used for zero
>bouancy applications in the air for example with helium filled spherical
>"AIRHEAD" or under water for example a cylindrical shaped or spherical 1
or
>2 DOF "AQUAHEAD" suspended in a transparent tank (aquarium) could use
this
>phototropic inertial positioning idea to follow a light.
>
>enjoy
>
>
> Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
> tel: (604)590-7493
> fax: (604)590-3411
>
>> -----Original Message-----
>> From: Wouter Brok [SMTP:w.j.m.brok@stud.tue.nl]
>> Sent: Sunday, May 09, 1999 11:33 PM
>> To: beam@corp.sgi.com
>> Subject: a useless idea
>>
>> Hello,
>>
>> Yesterday I thought up an weird hanging robot (well, you can hardly call
>> it
>> a robot, but it moves). I attached a scanned drawing to make things more
>> clear, and I will write down a couple of remarks below. Maybe somebody
>> thinks it is a funny thing to make (be my guest ... I would like to hear
>> about it) or maybe somebody can make a greater idea from it (... I would
>> like to hear about that too).
>>
>> In a hanging box (which could be made with PCB, with the components on
the
>> outside) a motor is fixed with a weight attached to the axis. When the
>> motor turns the box will turn around the line of the wire to which it is
>> attached. If the circuit is equiped with photodiodes it can turn itself
so
>> that these will keep pointing at a light source: the circuit will control
>> the motor in such a way that the side of the box with the photodiodes
will
>> keep pointing to the light-source (is it clear what I have in mind?)
>>
>> - it is not interesting from the practical point of view (at least I
>> wouldn't know an application which can't be done easier), but from the
>> physics and system-control point of view it is.
>> - it can be made with a bicore (which is a really cool circuit, for
>> refference see http://www.beam-online.com/Bicore_article/select.htm).
>> - the mass as drawn in the picture doesn't need to be excentric, as long
>> as
>> it is quite a mass compared to the overall mass.
>> - the box should be able to rotate freely around the point to which the
>> wire is attached, else the wire will excert a force on the box wich will
>> try to turn it; that only complicates things.
>> - a little friction however can be usefull because than the motion is
>> damped.
>>
>> What do you think?
>>
>> Wouter Brok
>>
>> PS: hope the file isn't too large
>>
>> << File: Idea1.GIF >>


------------------------------------------------------------------------
eGroup home: http://www.eGroups.com/group/alt-beam
http://www.eGroups.com - Simplifying group communications

Home