Subject:
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Re: Converting servos + other stuff
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 23 Jul 1997 05:48:57 GMT
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Original-From:
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Chuck McManis <cmcmanis@netcomSPAMCAKE.com>
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Viewed:
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1259 times
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thehahns@nconnect.net wrote:
> I'm trying to find a good source for motors, but to no
> avail.Has
> anyone tried using modified servos, as described in 'mobile
> robots'(Jones
> and Flynn)? It seems kind of expensive, but these appear to be pretty
> good
> quality stuff. Opinions and helpwanted!
Servos work well, but are constrained to relatively light robots (less
thana three pounds. You can use them on heavier robots if you install a
bearing
axle for the wheels and just use the servo to drive the wheel. Basically
the
servo wasn't designed to take a much continuous side force as using it
as
an axle puts on it.
Generally I find it easier to buy the motors and then design the robot
because getting good motors can be so difficult.
> Also, I had an idea. How should you determine the amount of
> torque
> needed for a robot? I have a robot built alrealy:all it needs is
> motors. I
> came up with a method: please tell me if it will work or not.
Your idea (edited for brevity) is basically sound, however you need to
take the
"worst case" and compute for that. So consider perhaps that you want
your
robot to drive up a 15 degree incline with low batteries. When the robot
is
not level there is addition drag due to gravity. Ideally you take the
worst case
and double it, but sometimes you are stuck just designing to it. As your
torque requirement grows, so does the size/weight of your motor which
increases your torque requirement, etc. So you can in fact build a robot
that
it is not possible to drive with an on-board power source (remember the
batteries weigh a _lot_ and they add to the torque requirement too).
Using gears you can increase your available torque at the expense of
angular
velocity (raw speed). If you think about it you can look at gears as
round levers
with one end being one gear center and the other end being the other
gear center
and their relative diameters like the positioning of a fulcrum. So in a
lever if the
1/4 of the lever is on one side of the fulcrum on 3/4 is on the other
side, you
get a 3:1 advantage when you press on the long side,. when one gear has
three times
the teeth of the driving gear you get 3 times the torque and 1/3 the
speed. (the
laws of thermodynamics not withstanding)
--Chuck
--
--Chuck McManis http://www.professionals.com/~cmcmanis/index.html
All opinions in this message are those of the author. No warranty as to
the suitability or accuracy is stated or implied. Use at your own risk.
cmcmanis@netcom.com +1.408.524.4805
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Message is in Reply To:
 | | Converting servos + other stuff
|
| hello, Yall! I'm trying to find a good source for motors, but to no avail.Has anyone tried using modified servos, as described in 'mobile robots'(Jones and Flynn)? It seems kind of expensive, but these appear to be pretty good quality stuff. (...) (27 years ago, 23-Jul-97, to lugnet.robotics.handyboard)
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