Introduction

In this post we are going to look in detail at the height adjustment mechanism for my DIY Gantry Crane, and the problems incurred. If you haven’t looked at the design process, please do so. Another helpful post is about finding the right beam for your project.

Finding The Right Beam For Your Project
DIY Gantry Crane – Design

Do You Need To Change Height?

Changing the height of the gantry crane is not always necessary. If you have a crane built for a specific task and it is used only for that task, then adjusting the height may not be necessary. To be clear, we are talking about adjusting the height of the main beam. The load height is adjusted through the hoist and that is very necessary!

I chose to make my crane adjustable in height. The reason for this is because I need it to be as versatile as possible to handle whatever task that comes my way. I may be lifting tall objects onto or off of the bed of a semi truck, or I may need to transport it to another place to help load something. So my design features a maximum height of 12 ft (bottom of the beam) and a minimum height of about 7.5 ft.

The height adjustment happens at the two telescoping posts. The inside shaft of the post has holes drilled every 6 inches for a 1 inch diameter pin to fit through and hold the shaft at the designated height. The problem with cranes like this, is that the structure that needs to be lifted is very heavy.

Common Lifting Mechanisms for Gantry Cranes

There are a few common lifting mechanisms for home gantry cranes. One is a manual lift using a bar to apply leverage to a pin to lift it. This is a manual process that requires the operator to lift one post and then move to the other side and lift the other post. That process would have to be repeated until the desired height is reached.

Some DIY Gantry crane designs have either hydraulic or manual scissor jacks to lift the crane in increments. This also requires the operator to move between posts to lift each side. There is an added step in that once the jack is at its max stroke, The crane has to be locked in place and the jack retracted so the lifting pad can be moved. Or, the crane may only have a small adjustment window.

Another common lifting mechanism is to use a winch. These can be manual winches, like what you would find on a boat trailer, or they can be electric winches. With the manual winches, you would likely have the same problem as the other lifting options, going back and forth between the two posts to lift it evenly. Electric winches would be easier to synchronize the lifting.

Design Goals

The design goals for my lifting design are to be cost effective (cheap), and to be able to lift both posts evenly without having to travel back and forth. This eliminates the leverage idea and the jacks. What it leaves me with are the winch ideas. Electric winches are not particularly cheap and they also require batteries or the ability to plug them in for them to work. That may be a future upgrade, but for now I want something manual.

That leaves me with the manual boat winch. The problem with this option is that it does not lift both sides at the same time. So I will need to create a solution to this problem.

The Synchronization Problem

If I was going to be able to synchronize the lifting, I had to physically tie the two winches together. When I turned one winch the other needed to turn. In order for this to work, I had to line them up perfectly so that their cranking shafts were lined up. I took great care in making sure the mounts for the winches were perfectly aligned.

Hardware Modifications

When I received the winches, I knew I had to make some adjustments. The first was that one of the winches needed to have the hardware reversed so that the handle was on the outside of the posts. The second was that both winches had to perform the same operation in the same direction. Which meant that if the handle was rotating in one direction, both winches had to be either lifting or lowering the gantry. This was not the case. I had to unspool the cable of one winch and then wrap the cable in the other direction. I also had to make sure that the selector switch on the winches (extension and retraction) each selected the same function in the same position. Up to retract, down to extend (cable).

Bushing Modifications

The next piece of hardware to modify were the bushings. The cranking shaft has a spur gear that is welded on near the handle. Then there were two bushings that held the shaft in the frame and allowed it to turn. I needed to make a connection point so I decided to modify the inside bushing (opposite of the cranking handle).

The original bushing allowed the shaft to rotate inside it. To make my design work, I would have to lock the bushing to the shaft so that it rotated with the shaft. This makes it less of a bushing and more of a coupler, but it still acts as a bushing between the shaft and the winch frame. Next, I drilled some holes through the coupler and a half inch rod that will act as one of the connecting shafts.

Middle Coupler

The distance between the two posts on the gantry crane is just over 10 feet. To connect the two winches I needed a shaft to go between them. However, I did not want a single 10ft pole as that would be hard to store when not in use. Instead, I elected on making two poles that connect in the middle.

This design is not without its problems. First, the two shafts need to have a bit of a gap between them when completely installed, otherwise I would never be able to insert them in the couplers at the winches. But they still needed to connect and provide a path for the torque to travel.

I decided to make a three part coupler. Each shaft would have a coupler welded to the end, and a sleeve that slipped over each end would connect them, with pins holding them in place.

Connecting The Cable To The Crane

All of this work is useless unless I connect the cable to the crane in a way to transfer the lifting force of the winch to the telescoping frame. Again, this is another area where I had to design on the fly.

The crane has a 1 inch diameter steel round bar connected to the base plate just under the main beam. At the bottom of that bar is a shackle where the winch cable will attach. I mounted the pulley up high. I also tried my best to make sure the cable coming off the pulley down to the shackle was vertical so that it didn’t introduce any twisting motion during the lift.

The pulley has a load capacity of 420 lbs, so between the two pulleys, it should be capable of handling 840 lbs. The main beam weighs 170lbs with the telescoping uprights in the neighborhood of 100 lbs each. That give a total of 370 lbs of steel to lift, so one pulley could handle the load by itself, albeit with a narrow margin of safety.

We Have A Problem

With everything connected and installed, the crane is complete. Unfortunately, I do have an issue with one of my two winches. The right side winch lifts beautifully, but the left side cannot lift higher than the right side. In fact, it only works if the right side is higher than the left. I was able to put a floor jack under the left side telescoping post and raised it smoothly. But when I tried to use the cable to pull it up, it would not move.

Understanding The Problem

I knew that the method I chose for lifting the crane would produce some torque on the system. Meaning, that it would tend to lift crooked because the force applied is slightly off the axis. However, I do not believe that this is the sole reason for the binding. Either the guide tube I welded on may not be in alignment, or the lifting bar itself may have a very slight bend. I did test the function of the left side prior to installing the beam and everything worked. I suspect that without the beam, the tube was able to rotate slightly to accommodate for the misalignment. But with the beam installed, it can’t self-adjust.

The next week will be spent diagnosing the problem and building the load leveling beam. I was able to lift the crane to a height of 10 feet, which should be plenty to start testing capacity.

Alternative Methods

If for some reason the winch problem cannot be solved, then the alternative would be to switch to a electrically actuated system. I would attach electric motors to the bottom of the frame and using a lead screw, lift the posts directly underneath to keep alignment. I’m not ready to move to this method yet, because lead screws and motors are expensive.

Thank You

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