Cheapest/easiest way to add linear motion to DIY gantry crane

Thread Starter

ryanjg117

Joined Nov 3, 2017
22
I've designed my own height adjustable, small gantry crane for my hobby shop, perfectly sized to collapse just small enough to get under my regular-car garage doors, and yet expandable up to 9.5 ft to utilize the full ceiling height of my shop. The design has been mostly dictated by materials I have on hand (which is why I'm going with pipe for the uprights and a 4x4 i-beam along the top).

I enjoy TIG welding, but this project is going to be pretty boring from that standpoint, so I thought it could be fun to try to build some power height adjustment into the sides.

The upper/moveable part of the crane will weigh about 150 lbs. The full height adjustment range is about 38 inches from lowest to tallest. I would only change heights when there is no load on the crane (beyond the weight of the upper assembly). Once I have the right height, I would lock/secure it with clevis pins as shown in the drawings. This crane will be limited to about 1,000 as that's the limit of my I-beam trolley.

What do you think would be the most effective and economical way to add power adjustability? I'm very new to robotics but have played around with servos and an Arduino. I thought maybe a planetary or offset motor on each side (mounted on the top structure pointing down), with a lead screw going through a nut welded onto the lower leg assemblies. Or is this just a completely ridiculous idea?
 

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I would think your screw idea would work out. Maybe like some 1" or so threaded rod, with a sprocket welded near one end. Between your sprocket and top plate you could put some sort of thrust bearing. You can find a 1" or 1 1/4" trailer wheel bearing at any parts store here (hopefully in your area also). I don't recall the diameter of the outside race, but I do remember they are a normal everyday fractional number that wouldn't be hard to find a hole saw or something to make a cup for them. A little chain and a motor and sprocket and both sides could be raised and lowered at the same time. Depending on how your trolley mounts you could keep the chain inside the I beam and get your full height, or loose a couple inches of height and put it over the top.

I personally have a few adjustable links I've made out of 5/8" threaded rod and 1/2" pipe that have held up with 75 - 100 pounds hanging on them and getting bounced around the yard. Other than a little too heavy weld getting too deep on one and binding things up they work good.
 
For the motor part you could probably use say an electric scooter motor and jack shaft set up. I don't know how to size the motor, but I'm thinking with some ratio changes between the motor, jack shaft, and final sprockets it wouldn't take much.
 

jpanhalt

Joined Jan 18, 2008
10,222
Screw will work. You might want to consider making the vertical pipe from cold drawn seamless (CDS) or drawn on mandrel (DOM) steel. The tolerances are pretty decent. Then make a telescoping "plunger" with an O-ring cap. Use air or oil as your working fluid. Since you are pinning it for safety once it is lifted, a little leakage won't matter. 2" diameter = 3.1 in^2. Lifting 200# would only require shop air of 35 psi on each side.

You will not want a really close fit on the plunger so it doesn't grab as it moves. The cap and O-rings, of course need to be a closer fit.

Another way is cables as are used for above the ground car lifts.

EDIT: BTW, for movement across the top, you probably should invest in a powered dolly. My non-powered dolly works (2T), but when loaded, positioning is not always easy.
 
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drc_567

Joined Dec 29, 2008
882
Another idea is to use a rack and pinion assembly, such as:
3368247-11.jpg
rack and pinion
This particular assembly is available as 1" wide by 4 ft. long.
The material is steel.
A gear motor drives the piniion, and clevis pins secure it in convenient !ocked positions.
The cost is certainly a design factor, however, the margin of safety may be more important.
 
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Thread Starter

ryanjg117

Joined Nov 3, 2017
22
Talking of safety, won't some diagonal bracing be necessary to prevent the crane going parallelogramatic?
Yep, that's a little downside I realized to using telescoping tubing. The only thing keeping it square will be the clevis pins, which I might size up (right now they're 1/2" diameter). I'll definitely want to lock all the swivel casters down before pulling out the pins and raising it.
 

dendad

Joined Feb 20, 2016
3,602
Have you looked at off the shelf electric sliding gate parts? That may be the easiest way to get the horizontal movement going.
 
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jpanhalt

Joined Jan 18, 2008
10,222
Yep, that's a little downside I realized to using telescoping tubing. The only thing keeping it square will be the clevis pins, which I might size up (right now they're 1/2" diameter). I'll definitely want to lock all the swivel casters down before pulling out the pins and raising it.
My gantry crane is a little bigger and made with square tubing (verticals are 6"). It has casters on all 4 legs. The wheel locks,but not the caster.
1593593469819.png

If I were to make it again, I would still have casters for easy movement, but I would either use locking casters or some way to put plates against the floor and raise the casters just a little. For the floor brakes, a pad on a screw or an over-center latch were considered. I just don't use it enough now to make the changes.

If you notice, I do not have tall side braces. That was purposeful so I could move in close to something and lift.
 

shortbus

Joined Sep 30, 2009
7,930
I thought maybe a planetary or offset motor on each side (mounted on the top structure pointing down), with a lead screw going through a nut welded onto the lower leg assemblies.

If going that route, how are you going to synchronize the movement? If one side moves faster than the other it will bind. While not a gantry crane, look at how wood working thickness planers or thickness sanders move the platen.

I have a homemade gantry(don't use it now that I have a cherry picker). It was made to fit the inside height of the garage/shop. You will have a chain fall or other lifting mechanism that takes the different lift heights so why the frame height change?
 
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