Alt-BEAM Archive
Message #03191
To: Dennison dennlill@buffnet.net, Wilf Rigter Wilf.Rigter@powertech.bc.ca,
From: Sharon Williams swilliam@cadvision.com
Date: Tue, 11 May 1999 07:41:19 -0600
Subject: [alt-beam] Re: a useless idea
why not just place a two DOF head inside a sort of gyro (like those rides
that you are straped in and the operator spins the two rings up and down
etc.) and place that in a MINIBALL sphere. An activly phototropic
miniball???????????
-Jeremy Williams
At 07:38 PM 5/10/99 -0400, Dennison wrote:
>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 >>
>
>
>
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