Subject:
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Re: Fishing for a tasty linkage/gearing/robotic building thread...
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 13 May 1999 13:51:20 GMT
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Original-From:
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Paul Speed <pspeed@augustschell.SPAMCAKEcom>
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Viewed:
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1633 times
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S. Crawshaw wrote:
>
> On Thu, 13 May 1999, Paul Speed wrote:
>
> > Or third, a synchro drive constrained to a ninety degree
> > throw. This is simpler than the independent wheels since it doesn't • <snip>
> > The most complicated part of this will be getting the drive train
> > snaked through whatever rotation assembly you have. Most of the
> > synchro drives you will see examples of use the turntable pieces.
>
> Surely the only reason there's usually complication is that the assembly
> needs to be able to rotate any amount in either direction. If 0-90 degrees
> is the total range, then there are lots of really simple solutions.
True. The main complication I always had was somehow rotating
the assembly around the drive train. As far as I know there are only
three ways to do this....
>
> [This next bit is irrelevant to the 0-90 constrained synchro drive]
>
> > I do not have any of these so I have experimented with several
> > other linkages. I won't go into them here... they are an
> > implementation detail.
>
> That's a bit of an understatement - and I'd love to hear how many other
> ways you found to make a synchro drive: I've only heard of one way
> that doesn't use a turntable (uses a differential instead)
The three ways that I have found are the turntables(really
simple), the differential (and if you have enough of these then
you really should buy some turntables), or snaking the drive train
through an idler gear that is hard mounted to your assembly.
In the last case, you can rotate the assembly by driving
the idler gear, or rotate the drive train independently. In my
experiments I was ratcheting the idler gear to the platform so
that the assembly could only turn one way. Unfortunately, I didn't
have enough pieces to make more than one complete assembly.
>
> Incidentally, apart from Dacta and the (rather expensive) tow truck, where
> else can you get turntables?
>
> [Back on topic]
>
> > The other hardest part is usually getting the rotation linked. With
>
> Why link the rotation assemblies? So long as all the rotation assemblies
> _eventually_ get to either 0 or 90, before the drive is engaged, then it
> doesn't matter if they rotated at different speeds.
True, but I'm not sure how you would turn them separately
without a whole slew of motors. Besides, since we are only turning
90 degrees it's relatively easy just to link them all with beams and
have one of the beams driven by a large pulley or gear. Haven't
tried it yet though.
>
> Seems to me that the only problem is if the robot drifts slightly while
> the rotation assemblies are turning ...
>
> ... oops. Have spotted a flaw - if the synchro drive is constrained to
> 0-90 degrees, then it needs to turn *both* ways - so you would need a
> second motor to drive the wheels. (OK, I accept that you could use a
> mechanical solution to reverse the turn without reversing the motor *but*
> then you would need sensor(s) to know when to stop the turn)
>
> Sounds to me like you need two motors/no sensors or one motor/two sensors.
> But at least you don't need a rotation sensor.
Yeah, it would still take two motors, but it won't take
three motors. The solutions mentioned previously either used
a third motor or a rotation sensor. Well, to be fair the third
motor in the first solution could have been replaced with a complex
mechanism.
Hmmm... I hardly feel like I'm in the right list unless
I mention the word "firmware." :)
-Paul (pspeed@progeeks.com, http://www.progeeks.com)
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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