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Topic: Lifting up to 100 pounds with motor (Read 4311 times) previous topic - next topic

arduinoPi

I have a large robot and it has a wooden lid that weighs 5 pounds. The lid will be used like a dump truck and I'm am hoping for it to be able to "dump" up to 100 pounds. I found this motor http://www.servocity.com/html/0_5_rpm_gear_motor.html since I don't care about speed I chose this motor.
My question is will this motor be okay if the motor's shaft is holding the 100 pounds up? Is there something mechanically that would reduce the stress?
Should I go with a completely different design? All feedback is appreciated.

Jimmy60

I think I'd be looking for a way to give the motor a big mechanical advantage for both opening and holding. Something like a scissor jack or counter weights. Hard to say without seeing the whole setup.


johnwasser

"619* oz-in." of torque.  That means to lift 105 pounds (1680 ounces) the load has to be less than 0.36" from the center of the axel.  I don't think that's going to work.

If you want to tilt a 2'x2' platform weighing 105 pounds (loaded) you will need at least a 105 foot-pounds (20,160 oz-in's) of torque.
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PeterH

I don't know how much of that 100 pounds would actually need to be supported by the motor. If the dumping assembly is hinged, it may not need to lift all of it. If it's hinged somewhere near the center of gravity, it might not need to lift very much at all. You need to design the tilting assembly and decide how much force you need to generate to tilt it, worst case. That motor has a maximum torque of 619 oz-in which means it would theoretically be able to support 100 pounds at a radius of about 0.4". Given that it has a maximum speed of 0.5 RPM and will probably be *much* slower than that under load, you could be looking at a speed of fractions of an inch per minute. You say you don't care about speed, but presumably you have *some* expectations about how fast this thing will be. Lifting 100 pounds with a motor that only uses a couple of Watts is going to be slow, whatever way you do it.

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arduinoPi

wow thanks for the quick informative replies. What do you guys think I should do. The lid would be hinged and would be 2' by 3'. The lid would have to be flat initially and turn until it is at a 60 degree angle. Can any one recommend and procedures or products for going about doing this? if needed the load can be 30 pounds and not 100 pounds.

PeterH

It's not really possible to say without knowing more about the physical constraints you're working within. Where is the hinge, relative to the center of mass. Do you have any scope to move it? What are you going to mount the drive mechanism on? Do you really not care how fast this thing goes? It could realistically end up taking hours, the way you're specced it currently.
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johnwasser

I think your best bet is a "linear actuator" to lift the back side of the tilting platform.  It's a combination of a DC motor and a screw thread that acts like an electric piston.
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zoomkat

The below can lift ~675 pounds. Bottom is a listing of smaller actuators.

http://www.northerntool.com/shop/tools/product_200333245_200333245

http://www.firgelliauto.com/show_info.php?page_id=35
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Chagrin

Cheaper options for linear actuators.

If you're looking to jury-rig something take a look at a scissor jack for inspiration. The design keeps all of the weight off the gearmotor and avoids worrying about thrust bearings or such. For a dump mechanism it also has the advantage of a faster rate of extension near the end of its travel (when all the weight has been shifted to the platform's hinge).

PeterH


Cheaper options for linear actuators.

If you're looking to jury-rig something take a look at a scissor jack for inspiration. The design keeps all of the weight off the gearmotor and avoids worrying about thrust bearings or such. For a dump mechanism it also has the advantage of a faster rate of extension near the end of its travel (when all the weight has been shifted to the platform's hinge).


That advantage is also a disadvantage, though - it has a hideous leverage in the lowered position which means you need a bigger motor or lower gearing which is then redundant in the higher positions. In general I think it'd be better to have a constant leverage.
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Chagrin



Cheaper options for linear actuators.

If you're looking to jury-rig something take a look at a scissor jack for inspiration. The design keeps all of the weight off the gearmotor and avoids worrying about thrust bearings or such. For a dump mechanism it also has the advantage of a faster rate of extension near the end of its travel (when all the weight has been shifted to the platform's hinge).


That advantage is also a disadvantage, though - it has a hideous leverage in the lowered position which means you need a bigger motor or lower gearing which is then redundant in the higher positions. In general I think it'd be better to have a constant leverage.

Yes you're right - I stated that backwards. The rate of extension is actually faster at the start of the lifting and thus would have less leverage.

Had to break out the spreadsheet to doublecheck that ;)

arduinoPi

What other methods can I used besides a scissor lift? I would like something simple like linear actuator but they are really expensive and usually don't go more than a foot (I am looking for about 2.5 feet). Is there any cheap alternative?

dhenry

Quote
I don't think that's going to work.


It can be made to work, with sufficient gearing.

PeterH


What other methods can I used besides a scissor lift? I would like something simple like linear actuator but they are really expensive and usually don't go more than a foot (I am looking for about 2.5 feet). Is there any cheap alternative?


There are plenty of alternatives, but without any idea what your physical setup is, it's hard to know which ones are applicable.

Ultimately, with sufficient gearing, you can produce any arbitrary force from a given motor. But the lower the gearing, and the higher the losses resulting from that gearing, the slower it will move. What are you trying to lift? What are you trying to lift it against? How much force has to be generated to lift it? How far do you need to lift it? How long are you prepared to wait for that to happen? How big can your lifting mechanism be? Do you have an unlimited power supply for your motor? Are you constrained to use that motor, which appears hideously underpowered for this applications, or can you consider getting a more suitable motor?
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arduinoPi

I have a pretty good amount of space and am using a 12 volt lead acid battery at 24 amps an hour for a power supply. I can use any motor and anything mechanically. The robots total size is 3 feet by 2 feet and 3 feet high. My only constraint is it has to be cheap preferably under $100.

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