one motor or two to raise/lower a platform ?

On my new bot I plan to have a horizontal aluminum bar that raises and lowers, perhaps by lead screw(s) or twin lines over pullies. Other items of
significant weight may at times be attached to the bar. The bar would be stabilized by riding between two upright tubes or rails, with appropriate bearings/guides.
Assuming motor weight is of no concern, what is best solution if there are 2 screws or 2 lines: one motor to work the screws or lines; or two ? I assume the hardest part with 2 motors is to get them to sync up and turn at the same speed simulatenously;
Would a single motor capable of handling the load use more power/current than two motors doing the same work ?
Thanks !
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    --How far is the distance you want to move them? Lately I've come across some interesting off the shelf solutions for moves of 18" or so, in the form of powered trailer leveling jacks, which come in electric and electro-hydraulic versions.
--
"Steamboat Ed" Haas : Bummed to be living in the
Hacking the Trailing Edge! : Golden Age of Bullshit...
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Hi.
Travel will be about 36 to 48 inches max. Must be able to lift about a maximum of 20 lbs in cargo, and most likely will usually be around 10 lbs. Doesn't need to be extremely fast, but should be able to do max travel in about 2 minutes or less.
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Given the other questions you're asking, you're probably better off with two leadscrews connected by a chain and sprockets, driven by one motor. Get a Berg catalog for small chain and sprockets, if bicycle parts are too big. Berg also has good leadscrews, although they're not cheap.
Multiple synchronized servomotors would work fine, but would cost more. You can easily put two Galil controllers in "software gearing" mode. But it will cost you.
            John Nagle
Pogo wrote:

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John Nagle wrote:

I agree on the two leadscrews and one motor being the best approach for both electrical efficiency and simplicity. Enco sells Acme thread rod in six foot lengths and nuts pretty reasonbly. (www.use-enco.com)
Central Surplus has a good suppy of chain and sprockets in many sizes and very good prices.
Good Luck, Bob

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Pogo wrote:

Why not use a scissors jack arrangement with one motor?
Steve
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Hmmmm ... not a bad idea, and one I hadn't even thought of. Ideally, though, I'd like for the opening between each guide rail to be open, and not taken up by the scissors jack arrangement. Assuming I'm willing to forgo that, however, what are the pros and cons of a scissors jack arrangement vs. a single lead screw in the middle of the crossbar ?
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though,
If you don't need to power the bar downward how about using a winch/crane assembly using a single motor, gearbox and a pully at the top of your structure. If you need more lifting capacity try a block and tackle approach. This has the benefit of allowing any reasonable lift height so long as the weight of the bar and payload is sufficient to lower itself downward.
Or you could opt for a cable/rope/wire to pull the bar downward in a full loop like a belt (think fan belt or conveyor belt approach).
thegoldbug
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Both of these assumptions are accurate.

Yep - I think this is the approach I am going to plan on for now. Thanks for the help !
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