Trailer mounted cranes can be useful in a variety of situations, and if you are adding a crane to your trailer on your own, there are several things you need to keep in mind during the project. Ultimately, whether you are mounting a jib crane, a mini crane, or any other type of crane, your final decisions depend on your preferences, your budget, and the materials you have available.
If you buy a crane designed to mount on your trailer, it likely contains instructions on the best places to mount it. However, if you are fashioning your own trailer crane, you need to choose your position carefully. The middle of the trailer is typically the most stable, but if you want to mount the crane near the back end or by the pull bar, you have to think about how the load on the crane is likely to affect the trailer. In most cases, these positions lower the total amount of weight you can lift without destabilizing the trailer.
Mounting the crane to the trailer is typically pretty straightforward. Ideally, you want to use heavy duty nuts and bolts to secure the crane directly to the frame of the trailer. However, in some cases, the trailer's frame isn't the right size to allow this. For example, when you line up one edge of the crane with the trailer, the other edge extends over empty air rather than reaching another part of the frame. In these cases, you need to make a solid platform on your trailer, and you can mount the crane to that.
In most cases, for your trailer crane to be effective, it needs to rotate, and with a DIY approach, there are a couple different ways you can facilitate rotation. You can fashion your own motorized rotating base using old hubs and rotors. However, you need to consider how well the hubs are likely to withstand the pressure that occurs when you have a large load swinging from the crane. Alternatively, you may want to consider using two tubes slipped over each other. In this case, one tube stays steady, but the inside tube is allowed to rotate.
Whether you choose one of these options or an alternative one, you should make sure that the components don't turn too easily. If there is no resistance, they may automatically turn unexpectedly. In particular, if the trailer is on uneven ground, and gravity is pulling the load one way, the crane may rotate in that direction.
The simplest option is to put on a crane that doesn't move up and down aside from the motions of the boom. However, if you want to be able to raise and lower your crane before using it, you may want to integrate a hydraulic jack into the design.
If you decide to use a jack, use a high quality one. An inexpensive jack may leak hydraulic fluid or may rust if you have to leave the trailer outside. Rather than using a jack, some people use removable pins so they can easily add or remove height to the boom as desired. This can also be a way to make the crane foldable.
Finally, consider the issue of power. This is especially important if you are trying to decide between a mechanical trailer crane and a powered winch. Unfortunately, powered items can drain your battery, and they are virtually useless if your battery is dead. With a manual crane, however, you can use it regardless of whether you have a battery or access to any power.