Moving heavy objects

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Moving heavy objects

Postby circuitmage » 21 Nov 2013, 17:45

I have a project I'm working on that requires rotating a small 3-5 lbs object and I'm looking for suggestions or examples of ways the NXT (motors) can handle that.

Since I don't have to actually grab anything, it seems like a simple project, but have found a few issues. Mainly handling the weight is the problem.
I have built a basic frame for what I need, and have revised it several times already. Sorry, cannot go into detail as I'm hoping I can use this at work.
But some basic concepts I am using / coming to grips with are;

* Center of gravity. Keeping item centered to avoid balance problems.
* Using more than 1 motor. Already having issues with controlling power with 1 motor.
* Rotational momentum. Think I need to gear down to control this. I'm at 1:2.33 now, and still have issues. More than 1 motor may solve this issue.
* Holding item down? I'm hoping gravity will do the work for me. Some rubber parts should keep the thing in place.
* Struts/caster supports. I have some good struts in my frame, but may need additional support for the weight. Thinking about adding casters the the bottom to keep it level...

Any examples/ideas along these lines would be great.
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Re: Moving heavy objects

Postby circuitmage » 22 Nov 2013, 14:46

Ok...so after more research, and build revisions I have found the following;

~40lbs movable on lego bearings on youtube.

I added a 2nd motor to my turntable and run both at 50% power. Seems to work well for 3lbs.

I still have some work to do on my frame, and this will take some time....
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Re: Moving heavy objects

Postby h-g-t » 22 Nov 2013, 16:59

If it is acceptable why not wrap a Lego chain round it and drive that using a standard gear?

I
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Re: Moving heavy objects

Postby circuitmage » 22 Nov 2013, 20:02

I am considering something along those lines. The object is cylindrical and smooth, so I could use a couple rubber treads to grab onto it. My only concern is if it slips. Since the object is smooth it is susceptible to slipping and as I am moving it frequently, any loss of movement is unacceptable.

So right now I have it balanced over two large wheels about 3 inches apart which are directly driving the object. This is working OK, but because of the weight of the object I need to support the entire assembly a little more.

I have also considered "clamping" down on the object to keep it in place, but I am still hoping gravity will do that work for me.

I am concerned about the long-time wear on the plastic gears. With two motors driving 24t gears to a turntable (56t) at 50%, I think it is OK.

I am also concerned about direct drive on a 3-6 lb. object (just spinning it). But so far, the two large wheels are doing it. If I can take more pressure off the wheels (and motor in return), then it should help.
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Re: Moving heavy objects

Postby h-g-t » 22 Nov 2013, 23:51

I had a similar situation although the forces involved were not nearly so great.

I rolled out some BluTak into a long worm about 3-4mm diameter and applied that to the surface, then squeezed Lego chain down over that.

The chain was driven by a standard gear which was turned using a worm drive, giving a very low gear ratio so it may be too slow for your purposes.

To minimise wear, I applied graphite grease to the worm drive, but this runs only intermittently so I don't know how long the gears will last.

To avoid over-straining the chain, the speed could be ramped up slowly.

If non-Lego parts are acceptable, there are a variety of metal or heavy duty plastic chains available, for instance.

http://www.smallparts.com.au/search/res ... 3A11&hl=en

I also saw a device where a Spanish Windlass was used, i.e. a long string wrapped round the object and a small axle. The tension helps to keep the string from slipping.

That device used a circular wooden turntable resting on 3 wheels for support.

String went round a groove in the edge.
A sophistical rhetorician, inebriated with the exuberance of his own verbosity, and gifted with an egotistical imagination that can at all times command an interminable and inconsistent series of arguments to malign an opponent and to glorify himself.
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Re: Moving heavy objects

Postby datbikerguy » 14 May 2014, 16:24

I agree with h-g-t. If you can use non-Lego parts. I would definitely go with metal for the gears and chains.

I am not exactly sure how you are trying to shape your robot but I would look at this framing.

http://www.nxtprograms.com/trailer_pull/steps.html

(One problem is that this robot cannot turn. But it can be modified to turn.

Hope that helps.
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