Boat/caravan trailer mover

[CR1]

Hello,
I'm poised to ask a question which is probably easy to answer. For my college project, I have to research and design a trailer mover which can pull a weight of upto 3000kgs.

However I have been looking into a DC motor that can accommodate a peak torque of 250Nm. This has lead to a few slight problems, there isn't that many DC motors that can accommodate this kind of torque and the ones that do really aren't in my price bracket.

So my question; Does it really matter about the torque? If high RPM = Low torque, then using a particular gearbox shouldn't I be able to use a High RPM Motor connected to a planetary gearbox or something and produce the torque I need?

 

[Danger]

You can do that, but I suspect that there's a limit to how much reduction you can use before frictional losses in the gearbox become a serious problem. I don't, for instance, believe that it would be practical to gear a Dremel tool down 10,000:1. On the other hand, some high-torque motors can't handle more than a very limited duty cycle. An automotive starter would probably burn out after a few minutes of constant use.
One thing that you didn't mention is what sort of power supply is indicated. I've been assuming 12-24 volts for portability, but there are a lot of high-voltage DC motors that might be better suited to your needs if more power is available.

 

[berkeman]

Can you use an internal combustion engine for the power source? Maybe something like an inexpensive chainsaw engine?

 

[CR1]

The power source will need to be electrical, si I can't use combustion engines, mainly because they are noisey and the continued rise in fuel cost is expensive. 12v is ideal, as car/leisure batteries are usually sourced at this voltage. 24v is a little high, though I understand the higher voltage I use the more selection I will have to choose from in terms of DC motors.

Is there a limit on the number of motors that can be used?

 

[FredGarvin]

As a comparison, take a look at a company called "Robotow." They make a cordless tow bar used on aircraft. While it is moving less weight, I would think it may be a good starting point to see one that is already made.

http://www.sportys.com/acb/showdetl.cfm?DID=19&Product_ID=6433
www.robotow.com

 

[Q_Goest]

Hi CR1

So my question; Does it really matter about the torque? If high RPM = Low torque, then using a particular gearbox shouldn't I be able to use a High RPM Motor connected to a planetary gearbox or something and produce the torque I need?

Correct. The motor need not be high torque, you can use a gearbox to increase torque of the motor to the wheels. The power of the motor only needs to be sufficient to move the trailer at the speed it needs to be moved. How that power gets to the ground (through a gearbox to increase torque and reduce speed) is up to you to determine.

 

[brewnog]

These units are already available commercially. I'm sure ten minutes on google will be fruitful.

 

[CR1]

Thankyou for the many replies. I have searched on google and not found the 'Robotow' before, thankyou very much for this entry. There are simliar devies such as the powrtouch. However I have only a couple of months to produce something, and most of these companies they probably spend 12months+ research, so perhaps this project was a little more technical than I should have taken on. However I may be able to use this in University. So not all bad.

The technical details on the motor however I am still not competent so I will be researching for some time to come.

 

[Danger]

I tried to post this days ago, but kept getting an error message. What I was going to propose, if it isn't too late, is to look into electric pallet jacks and forklifts. They have huge lifting capacity, long duty cycles, and are battery powered.