Subject:
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RE: a couple of new-bot questions from a generally quiet lurker
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 20 Sep 1999 16:31:57 GMT
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Original-From:
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Steve Hassenplug <SteveH@mailcode.com>
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Viewed:
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742 times
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> =>From: "Stephen P. Gibbons" <steve@aztech.net>
>=>...
>=>My biggest gripe with this design [differtrans] is that there is no
>=>way to get all motors contributing to a single effort in one
>=>direction.
> Perhaps you could use two regular motors joined through another
> differential to provide drive, and a micro motor to provide turning?
> (I don't have a micro motor, so I don't know whether it's got enough
> torque to do any good. In addition, you'll probably waste a lot of
> power through all the gears you'd need to set this up.)
> I think the best idea I've heard for the differtrans is to build a
> regular, one-motor-per-wheel platform, but also drive the differtrans
> inputs from the wheel axles. Then, use a rotation sensor on the
> differtrans outputs to see whether the robot is turning due to
> different axle speeds. This is a win because you don't have to
> transmit any power through the (lossy) differtrans, you get both
> motors driving the robot, and you still know whether your robot is
> going straight. (I didn't think of this; somebody else on the list
> did. It was a while ago, but maybe you could find the message in the
> archives. Or maybe the originator will speak up and tell us how
> things worked out for that robot...)
I've just finished up a nice little bot. The only thing some people may
consider bad is that fact that I'm using two rotation sensors on it. (I
knew a week after I got my kit that I would need two of them.)
I have it set up so that there is one motor directly driving each wheel.
The motor and wheel both have the same size gears (I think ~24 teeth) so
it's a 1:1 ratio, and there is a rotation sensor on each wheel axle. There
is almost no gearing to add friction, and it is powered by two motors.
I like this system for several reasons
1) Like the single Rotation sensor system, you can monitor the
difference in wheels in forward/backward movement
2) You can monitor Forward/backward DISTANCE
3) You can monitor turning distance.
4) You can detect stalling. (if no pulses are coming in, the robot is
not moving, and something else must be done.)
5) You can calculate speed.
The other system will only allow #1 and somewhat allow #3
The big drawback is using two sensor inputs. (and rotations sensors)
My current robot design, which is actually my first design, uses this
system, and also has a light sensor/proximity detector in front multiplexed
with two touch sensors, which I have attached to the back so I can detect if
it has backed into anything. The touch sensors are not really necessary,
because it can already detect if it has stopped moving.
Some time soon, I want to get a picture of it that I can put up on the web,
because I like the design, and it's working rather well. The whole thing is
not much longer (two or three bricks longer) than the RCX itself. It's not
much higher than the RCX (horizontal) on top of two motors. It's biggest
dimension may be it's width. I'm using the fat tires that came with the
RCX, so it's as wide as the RCX + one tire on each side. (it also has the
smaller matching tires just in front of the big tires, which pivot for
turning.
Like I said, I need to get some pictures, so I can tear it apart and move on
to my next design.
</steve>
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