Subject:
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2 Motors -> 1 axle
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 7 Jan 2000 16:30:53 GMT
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Viewed:
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593 times
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After the good suggestions from folks (see the Balancing Bots thread) I
did some experiments with using 2 motors to drive one axle (to double the
power to the axle) and thought the results might be of interest to others.
I first tried having the motors separately drive the same axle. That is,
the motors weren't directly connected to each other at all, except
through the axle. Each motor drove a 24t crown gear, and each crown gear
drove a separate 24t gear on the axle. The idea was that even if the
motors weren't matched exactly, there would simply be a bit of a load on
the "fast" motor.
Unfortunately, the motors were different enough that the gears actually
skipped teeth occasionally. Running in one direction would probably be
OK, but in this application I'm switching direction constantly, and it
didn't work. Also, even if the gears remained meshed, it's not an
effective use of the power in the motors: one of them is always pulling
the other one along, robbing the whole system of power.
Then I tried using a differential "backwards": I used a motor to drive
each of the outside axles, and the body of the differential to drive the
output. MUCH better, though bulkier. In this case, each motor contributes
what it can, and any difference between the motors just means the middle
gear in the differential spins a bit to absorb the difference, but no
power is lost fighting a mis-matched motor. I think this is the way to go.
Now if I could just figure out how to stiffen the axle torsionally. I
need a wide base for stability, but the long axle means that the wheels
aren't locked together very well, there's lots of springy torsional
wiggle between them, which twists my bot around a lot when it's whipping
the wheels back and forth. I'm thinking maybe a tripod base with only one
drive wheel would be good, or maybe treads. Or maybe I should just bug my
machinist friends to carve me some steel axles :-)
Dave Johnson
Still trying to balance
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Message has 4 Replies:
 | | Re: 2 Motors -> 1 axle
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| (...) One way to make the axle stiff is to use mutiple axles. For example, get one long axle and four equal length shorter axles. Use the four shorter axles to join two of the largest gears together, using the axle shaped holes that are off-center (...) (25 years ago, 7-Jan-00, to lugnet.robotics)
| | | Re: 2 Motors -> 1 axle
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| Instead of trying to connect two motors to the same axle using the crown gears, why not attach the two motors to the same axle using axle connectors. This would avoid the slipping problem that you mentioned and should have less frictional losses (...) (25 years ago, 7-Jan-00, to lugnet.robotics)
| | | Re: 2 Motors -> 1 axle
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| Dave Johnson <djohnson@sirius.com> wrote in message news:0FNZ00JD94JH7Y@...pbi.net... (...) I think you are drawing entirely the wrong conclusions. As others have said, your mechanical connection is at fault, not the differences between motors. Two (...) (25 years ago, 7-Jan-00, to lugnet.robotics)
| | | Re: 2 Motors -> 1 axle
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| (...) What an idea! This might be something we all could use! Think about it... Aluminum axles! Stronger than the plastic and just as light. Maybe an alloy would work better. Of course, we're talking _precision_ machining here, but it's possible... (...) (25 years ago, 9-Jan-00, to lugnet.robotics)
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