Subject:
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Re: New MOC: RoboArm I
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 10 May 2002 23:14:06 GMT
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Original-From:
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Steve Baker <sjbaker1@airmail%Spamcake%.net>
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Reply-To:
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SJBAKER1@AIRMAILnospam.NET
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Viewed:
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1875 times
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Bob Fay wrote:
> I am not a big fan of Lego pneumatics either, but they are so light weight
> and a perfect solution in your application. The micromotors have so little
> power, that you would have to gear them down to get any holding power for
> your grippers. Then opening and closing would be very slow and boring.
Yes - I agree.
I'd avoid using micromotors anyway because of their tendancy to lock up
when you put any kind of strain on them. Micromotors are good for little
decorative features or small one-time operations that don't need much power.
So what works?
I have a couple of those long bendy axles that came (I think) from a ZNAPS
set. They have short, white Technics axles on the ends and a long bendy
section in the middle. You can bend them through a right angle and
still drive them with little loss of power.
With these, you can mount all the motors in the base of your arm (with
appropriate gearing to transfer power at the elbow). This gives you
very lightweight joints and lets you use whatever motor(s) you need for
the speed and power you want without concern for the weight and bulk.
The only problems I've seen is that:
1) They introduce a little backlash and flexing that has to be taken
out with a worm gear.
2) They only come in one length - so you have to design the robot around
the drive mechanism instead of the other way around!
3) Unfortunately, I've *only* seen these in ZNAPS sets - and those are
not made anymore.
Is there any other source of these parts?
I agree that pneumatics is a good choice for the final gripper - once
again you can mount all the heavy stuff in the base - but you also get
the benefit that you won't stall any motors when the gripper finally
grabs hold of something. Eliminating limit switches and clutch gears
from that end of the arm is another good design thing. You can't really
use pneumatics for the wrist and elbow joint because they are rather
all-or-nothing devices - it's virtually impossible to extend a piston
just half way or whatever.
Really, the lessons I have from my occasional arm design efforts are
all to do with:
1) Keep the weight as close to the shoulder of the robot as
possible.
2) Keep everything stiff and eliminate backlash.
Those tend to be somewhat contradictory goals.
----------------------------- Steve Baker -------------------------------
Mail : <sjbaker1@airmail.net> WorkMail: <sjbaker@link.com>
URLs : http://www.sjbaker.org
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Message has 1 Reply:
 | | Re: New MOC: RoboArm I
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| I don't know of any other source for the flex axle. I found that they did not turn smoothly. Tend to loft. Maybe they can be contained at several points to stop the whipping action. Micromotors seem to work well in pairs, I guess they unlock each (...) (23 years ago, 10-May-02, to lugnet.robotics)
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Message is in Reply To:
| | Re: New MOC: RoboArm I
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| I am not a big fan of Lego pneumatics either, but they are so light weight and a perfect solution in your application. The micromotors have so little power, that you would have to gear them down to get any holding power for your grippers. Then (...) (23 years ago, 9-May-02, to lugnet.robotics, lugnet.technic, lugnet.build)
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