Subject:
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Re: lego Technic "class"
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 29 Oct 1999 21:15:35 GMT
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Original-From:
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Stephen Unwin <STEPHEN@ELMSFARM.DEMON.spamlessCO.UK>
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Viewed:
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3817 times
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On Fri 29 Oct, Chris Phillips wrote:
> In lugnet.edu, Scott Arthur writes:
> > I've thought about using two motors for steering.
> >
> > Do they turn at exectly the same rate?
>
> Generally not. I've built robotic platforms that use a pair of motors to
> drive the wheels so that the robot can move "straight" or turn in place. I've
> found that the motors typically have large variations in speed that make the
> robot veer to one side or the other when it is trying to go straight. I've
> done experiments with angle sensors to try to detect navigation errors and
> modulate the motor speeds accordingly, but haven't had much success so far.
>
> The same motor also seems to run faster in one direction than the other. I
> think I've heard that this is due to the internal gearing in the motor, but I
> never quite wrapped my brain around how that could be... Anyway, most two-
> motor-drive platform designs that I've seen have the motors oriented 180
> degrees apart from one another, so in either forward or backward motion, the
> motors will be turning in opposite directions, and the gearing problem will
> drag you off course even with perfectly-matched motors.
*snip*
As a somewhat Bizzare experiment, I have run a LEGO motor from the battery box
controller as supplied with motor set 8735. The motor is placed next to a
Pick-up on an electric guitar plugged into an electronic tuner. With the motor
turning in the same direction each time I could not guarantee the same result.
The gearing in the motor is the same in both directions, and should have no
effect whatsoever. However, the brushes onto the commutator are roughly at
90 degrees and not opposite. The com. has 6 segments. If the brushes to not
line up exactly, then I would expect some difference in speed.
As an aside, has anyone had trouble with motors seizing up? I have had 4 of
the geared motors before the two in RIS and one in Cybermaster. One is ok, two
cannot be turned by hand and one has stopped altogether. Having completely
dismantled the seized motor I discovered a fine black magnetic powder inside.
Taking the motors apart is not to be recommended. Even popping the back off
carefully can make a mess of the case.
/////
< .. >
>
- stephen@elmsfarm.demon.co.uk
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Message has 2 Replies:
 | | Re: lego Technic "class"
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| In lugnet.robotics, Stephen Unwin writes: <...snip...> (...) I've never seen this, but I recall hearing somebody discuss this recently. It might be a quality control problem having to do with adhesive getting worn off and gumming up the gears. (...) (25 years ago, 29-Oct-99, to lugnet.robotics)
| | | Re: lego Technic "class"
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| Stephen, I have had one RIS motor fail shortly after first use, apparently developing a shorted armature winding. Symptom: hard to rotate fast by hand. OK very slow. Under power: ran rough and slow, made humming noise I suspect was once-per-motor (...) (25 years ago, 1-Nov-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: lego Technic "class"
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| (...) Generally not. I've built robotic platforms that use a pair of motors to drive the wheels so that the robot can move "straight" or turn in place. I've found that the motors typically have large variations in speed that make the robot veer to (...) (25 years ago, 29-Oct-99, to lugnet.edu, lugnet.technic, lugnet.robotics)
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