Subject:
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Re: Expected battery life / motor differences
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 12 Jan 2000 17:48:20 GMT
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Viewed:
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496 times
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In lugnet.robotics, "ssweeney@sanders.com" <ssweeney@sanders.com> writes:
>
> What I find is that the bot will move nicely forward and bog down in
> turns. One motor will appear to stall. I have looked for any place
> the parts may be binding and have found none. I am wondering
> if this is just weak batteries. They are down to 7.8V.
If you're talking about the tank treads, those scrub a lot when trying to turn
in place. A line following bot would probably be easier to build with one of
the alternate wheelsets (and I don't mean the little feet!).
> How long do you normally get from a fresh set of good quality batteries?
Depends. If I'm just downloading programs to a stationary RCX it works fine at
pretty low voltages (though I've never gotten close to the low-battery warning
@ 6.3v). If the bot is motor driven there can be a big difference in speed at
lower voltages. The other night I made a stay-on-the-table bot which I thought
was getting better and better so I raised the speed to MAX/2 (from MAX/3).
Later I replaced the batteries and discovered that it was going too fast to
stop (splat!).
Now I'm using Rayovac Renewals. These are great rechargable batteries for an
application like this. Shelf life like regular alkaline and very similar
performance. Plus they recharge extremely quickly.
> Also, in building a simple two wheel and castor bot as per the instructions,
> the robot does not travel in a straight line as the instructions say it
> will. Is it possible that I have a bad motor?
I'm up to 7 new-style 9v motors, and no 2 are exactly alike. The tabletop
robot chassis happened to use my two most extremely different motors and drove
in a very noticable arc on a smooth surface. I ended up building a small test
stand with a differential: mount the diff so it can spin, connect each side to
a motor with an axle extender, connect the motors together with opposite
polarity, and then power them (a 9v battery box is fine). Two equal motors
will cause the inner diff gear to spin madly at the motor output RPM. If one
is faster, the diff cage will rotate slowly one way or the other. I picked two
more similar motors and my bot drives much straighter now.
What really concerns me is how the properties of motors might change as they
experience stalls and other loads during their lifetimes. Were all of my
motors once as fast as that one? I doubt it. But were they all a little
faster? Mmmmaybe...
--Ben
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Message is in Reply To:
 | | Expected battery life
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| Activate de-lurk and engage..... I got a RIS recently and am having great fun with it. I am working with the tank tread robot from the manual trying out the line following challenge. What I find is that the bot will move nicely forward and bog down (...) (25 years ago, 12-Jan-00, to lugnet.robotics)
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