Subject:
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Re: moving in a straight line with two motors?
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 13 Nov 1998 16:39:02 GMT
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Original-From:
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Eric Brandwine <ERICB@MITRE.ORGnomorespam>
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Viewed:
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5290 times
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> > > > > "jsk" == John Scott Kjellman <jkjellman@ameritech.net> writes:
At one point, in the distant past, I saw plans for a gear box that
used either 2 or 3 differentials, I do not remember which.
2 motors were used, 1 to drive both axles, one for steering.
axle1 == motor1 + motor2
axle2 == motor1 - motor2
With motor2 off, 1 on, the vehicle (most likely treaded), will track
straight, in forward or reverse. With motor1 off, 2 on, the vehicle
will spin in place. Combinations of the 2 will do the obvious.
In order to regain the power of having 2 drive motors, you can run 2
motors off one output port, and couple the shafts together. Of
course, that brings the total motor count to 3, rather than 2, but it
still only occupies 2 of the motor outputs.
Any one know of this? The reason that I bring it up is that I do not
own a rotation sensor, and am too cheap to buy one.
I would rather use an R/C servo for steering anyway. I have just not
had time to hook my 'scope up to one of the motor outputs to see if
there is some simple way to decode the PWM. 8 power levels in 2
directions + stop == 17 possible states. Figure you need about
60degrees for useful steering, that gives you 3.5 degrees of
resolution. _Should_ work.
I already have servo code for a couple of microcontrollers, and a
couple of servos with epoxied on lego plates from an ill fated run in
with the Handy Board.....
ericb
jsk> Tim,
jsk> Instead of using the differential for angle sensors, why not use it to
jsk> allow a single motor to drive both wheels? Then a single angle sensor
jsk> coupled with a motor could drive the steering mechanism. This setup
jsk> would be very similar to a radio controlled car.
jsk> Just a thought.
jsk> KJohn
jsk> Tim Rueger wrote:
> >
> > Hi,
> >
> > One of the first things I ran into when making a mobile 'bot using one
> > motor for each of two drive wheels was the mismatch in their speed.
> > Needless to say, it's a nice way to make curved path. Not what I want.
> >
> > So I've got one of those nifty angle sensors. I'd like to use it for
> > feedback from the wheels to tell a motor to slow down when it gets too
> > far ahead of the other one. An obvious thing to do is to use two
> > angle sensors and subtract them, but I'd like to do it with one sensor,
> > given there are only 3 sensor inputs.
> >
> > A simple mechanical way to do this is to use a differential gear,
> > driving it backwards. One input gets the rotation of one wheel, and
> > the other input gets an inverted rotation of the other wheel. With
> > equal wheel rotations, there is no movement of the differential
> > housing.
> >
> > Unfortunately, gear slop keeps this from working well for me. Any
> > suggestions?
> >
> > Thanks,
> > -Tim
> >
> > --
> > Tim and/or Shelley Rueger - rueger "at" io.com
> > WWW page: http://www.io.com/~rueger/
--
Eric Brandwine, Systems Engineer | What is the definition of an engineer?
EricB@Mitre.org | Someone who solves a problem you
MITRE Corporation, McLean VA | didn't know you had in a way you
(703) 883-3319 F: (703) 883-1917 | don't understand.
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Message has 1 Reply:
 | | Re: moving in a straight line with two motors?
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| -- ===...=== Don Forth ( Klaatu ) email: dforth@caro.net Home Page: (URL) Brandwine wrote in message ... (...) Check out - (URL) has an example of a treaded vehicle that uses this type of system one motor for forward and backward motion and one for (...) (28 years ago, 14-Nov-98, to lugnet.robotics)
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Message is in Reply To:
| | Re: moving in a straight line with two motors?
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| Tim, Instead of using the differential for angle sensors, why not use it to allow a single motor to drive both wheels? Then a single angle sensor coupled with a motor could drive the steering mechanism. This setup would be very similar to a radio (...) (28 years ago, 13-Nov-98, to lugnet.robotics)
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