Lift Problem

[IronRooster]

I'm in the process of designing an automated carrying device. I want it to have the ability to lower and lift a max of 200lbs. Imagine a square robot with a basket on top. I am having trouble with the lifting system. I need it to lift the weight 2' into the air. Any ideas on how to do this mechanically?
PS I have access to strong servo motors.

 

[picbits]

Screw threads ?

Maybe some 10mm threaded rod with matching M10 nuts on the platform. Spin the thread and whatever the nuts are attached to will move.

 

[Hank Fletcher]

That's a good description to begin with, but there are still a lot of ways to do this depending on what the priorities of your design and what you're trying to accomplish are.

What's the nature of this heavy object? Is there a handle, or a hook, or spaces to insert forks like a fork-lift?

Is it something that's already part of the robot, or is it something extra that's being picked-up from the floor?

Does the robot have to move with the object after picking it up?

A picture's worth a thousand words, even one scribbled in MS Paint. Maybe you could post something with further description?

The only way I can envision lifting that much weight that high without having a really heavy robot is to have a strong frame on a robot that somehow lifts the weight from somewhere inside the frame. Would something along the lines of the lifts they use for moving yachts about on land work (see photo)?

**broken link removed**

 

[Krumlink]

A HEAVILY Geared window motor may do the job of lifting weight.

 

[IronRooster]

The weight is inside of a basket. A person puts the weight in and take it out. The robot is just lifting the basket. The only solution I can think of at low cost is a small scissor lift driven by a servo motor that controls a screw.

 

[IronRooster]

Picture of idea

This is really basic

 

[Hank Fletcher]

Is it not acceptable to have part of the robot extend above where the object is, as in the yacht lift? If that's okay, it gives you more options, I think. I'm thinking four pulleys, 8" diameter, each on one corner of the crane, with aircraft cable or even just strong rope (200lbs/4 posts = only 50lbs per post and pulley).

How much is speed (how fast the robot lifts) an issue? Maybe you could work something out by connecting a motor to a hydraulic jack?
**broken link removed**

I think it's rated for two tons, which might seem overkill, but could be quite close to what you need once you lever it to get your 2' requirement. $15 and for sale here:**broken link removed**

 

[Hank Fletcher]

After reading the reviews on that jack, I see someone recommended this one:
**broken link removed**

**broken link removed**
It's $25, but given your design might be more along the lines of what you need. Ooo... apparently the range is closer to what you need, too! In the Q/A, someone suggests that it has an extension of 15". Not quite what you need, but definitely something that'd be leverable for more range vs. weight.

 

[Hank Fletcher]

Here you go, 24" pre-fab. For about 4x my last suggestion, might be worth the time in labour to you, depending on your design. I'm beginning to see how using a single hydraulic cylinder with a couple scissor supports might work for you. How's this all working out in your design/cost plans? Is the retracted cylinder length of about 3' acceptable?
**broken link removed**

 

[IronRooster]

Thanks for all the help. I'm going with a car jack driven by a servo motor. It has the power and is easy to attach.

 

[blueroomelectronics]

A typical servo motor has no where near enough torque to turn a car jack.

 

[Hank Fletcher]

A typical servo motor has no where near enough torque to turn a car jack.

Blueroom's got a point, although I think that you could get a high-torque servo for under $50 that'll do the job just fine.

That said, personally I don't think I'd used a servo at all. I'd use a large motor, slightly geared - you really don't need that much torque at all to run the jack, but probably more than a little hobby servo. I'd find some other method of position feedback rather than monitoring the motor turns, if it were me. But then, I'm not privvy to the nuances of your design.

 

[blueroomelectronics]

Look at the size of the motor on this car jack
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[IronRooster]

Blueroom, where did you find that carjack and how much was it?

 

[picbits]

Might help if you post your location - the world is a big old place for sourcing stuff like this

 

[blueroomelectronics]

Just did a Google search for "motorised car jack" seems to be about $80 US.

 

[Hank Fletcher]

Look at the size of the motor on this car jack

It's a biggie, to be sure, but remember the jack (and motor) are probably designed to lift two tons at least, possibly even as much as four tons. The OP only needs to lift 200lbs. Even considering he might lever it for more stroke vs. force, that's still presumably only a modification factor of two, or the equivalent of 400lbs that he's meaning to lift. For that reason, he could get by with a smaller motor, presuming the same jack was for sale with a choice of motors

He still hasn't mentioned to what degree speed is a factor, which means quite a small motor could do, hypothetically, it just depends on how long he wants to wait around for the thing to lift. Watch this guy using a hydraulic jack - you can see that it's not taking him much effort at all to lift the car. They have a fancy name for the jack, but it's still just a basic hydraulic jack like the first one I posted from Canadian Tire.
https://www.youtube.com/watch?v=jQpeEXIC3JI

edit: on closer inspection I notice he's not lifting the car in the video, just bracing the trunk assembly. Still, there is/can be considerable force on the jack, but it's still very easy to manipulate the pump. I remember my Dad using one of the first Canadian Tire versions I posted to quite easily force up the corner of a large gazebo while he fitted a new permanent post - lifting it was a snap, it just took a lot of pumps. By "pumps" I mean pumping the jack - only one cylinder was used in the gazebo project.