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Horse power vs Man power...

Dave J

Cast Iron
Apr 11, 2001
Hammond IN
How do you convert manpower to horsepower ?

I would like to make a gas powered trailer dolly to move a large heavy trailer. This normally requires 5 or 6 men to move it. This doesn't have to be fast, so I will gear it down quite a bit. It will have to work on pavement or grass, and have enough power to pull up a slight incline (normal parking lot slope). Would a 4 Hp 4 stroke be enough ? Would a 30 or 40 cc 2 cycle be good enough ?

If anyone else has built or has plans, please feel free to share them. I would like it to have foward and reverse also.

Thanks !

Forrest Addy

Dec 20, 2000
Bremerton WA USA
A 180 lb man can push 60 lb for several minutes on good footing. Take it from there.

Looks like you need 400 lb traction with 800 lb surge. General aviation ramp service people use a factory made powered tiller bar on the nose wheel of airplanes they have to move around. You might use the same thing on the trailer tongue. I suggest you explore using a garden tiller modified with pair of 12" trailer wheels on the output shaft.

Lots of travel trailer places use a wheeled farm tractor with a three point hitch to move their stock around. I bet a little ATV would work as well.


Apr 25, 2003
Berkeley Springs, WV, USA
I worked at an equipment rental yard once. We had one of these little Clark aircraft tugs that was fitted wth a hitch ball that could raise or lower by hydraulic power.


Hot Rolled
Jan 23, 2004
Porter, Tx
I did a study on "horsepower" on windmills, horses and humans, for a history course...

a human can produce abotu 1/4 of a hp for VERY limited times, and generally 1/8 for extend (more than 15 mins) time.

The 2 stroke has no TORQUE at lower rpm which is what you are actually after, btw, as that is your speed control

a 5:1 or 10:1 gearbox, on a $200 4 stroke would jerk the back back teeth out of a bear. and still have some torque.

if you really wanted to make your life easy, get a 24v battery, a 1/4hp DC motor, a 10 or 15 to 1 gear box, and make a speed control... plug the batt into a charger once a week and be done with it


J Tiers

Power is the time rate of energy delivery. Techie talk meaning that the slower you move the load, the less "power" you need.

Therefore decide how fast it has to go.

The weight and lift give you the actual energy, and the time you lift it in (you said an incline) converts to power. The "horsepower" is 33000 foot-lbs per minute.

Then you have to discount for friction etc. On grass, there will be more friction, so I would derate at least 2:1.

If for instance it was 33,000 lb, you pulled it up one foot in height of incline, and had to do it in one minute, the theoretical frictionless HP with that formula would be 1 HP, given suitable gearing etc. Actual would be 2 or three HP, due to friction etc. Long trains of gears or belts lose power in a hurry.

Speed, weight, lift, pick two.

Bill D

Apr 1, 2004
Modesto, CA USA
I second the idea of a rototiller. many of them have drive wheels with forward and reverse. look at this one on ebay with hydralic drive or look at the barrito website.
A gravely two wheel tractor would be ideal but I think they go too high for such a simple use. look at BCS as they tend to go a little cheaper. Consider replacing the gas engine with a battery motor at any rate.
Bill D.
The quickest and least modifications needed would of course be to use a horse. Provides variable speed, power steering, collision advoidance sensors, fuzzy logic all right out of the box.

L Webb

Jul 28, 2001
Fullerton, CA USA
The pavement part is easy, the grass is tougher. For traction in the grass, the motive power will need to be heavier with more tire on the ground.

I have a friend, an engineer of course, who wanted a cheap efficient way to move his T-28 Trojan in and out of the hangar. The plane is a little heavy for the small hand tugs and there was a little slope to deal with. His solution was an electric pallet jack. He bought an old one at auction for cheap.
He made a fixture to pickup the nose wheel a little and he can move the plane anywhere with ease.

Come and rent my skid steer..
It will easily drag a dead horse.


Dave J

Cast Iron
Apr 11, 2001
Hammond IN
Thanks Guys, lots of great ideas !

I think D's website won me over to electric mover. Easy to reverse, reasonable light weight, compact size. I will try to copy this style.

Right now I am thinking a starter motor hooked up to a worm reduction (good reduction, and self braking), then a chain drive to get the final reduction dialed in.

MetalDoctor, I have moved dead horses, they aren't easy !

Sandman; What is that thing ? What does it move ? Looks like it uses a LOT of air !

I will post when this gets under way, I really need this, but my project list has numbers AND letters !

Thanks All !

Mike W

Jan 12, 2003
Central Kali.
Years ago I saw a small rig with an 8 horse Koler that was used to move mobile homes in a trailer park. I don't remember the details but it was pretty small.

motion guru

Dec 8, 2003
Yacolt, WA
Sandman - that looks like what a lot of paper mills used to move parent rolls around with or carts full of "broke" . . .

I have an employee who had a rototiller that threw a rod. He fished around in his pile of junk and found a 2HP single phase compressor motor and bolted that up with a tiny pulley on the motor. As long as he keeps the extension cord out of the tines, it is the cat's butt for tilling his garden.

That is a Ramrod, small skid steer with 36 hp Kawasaki or Koehler engine (your choice if you buy new) . These things are a tad pricy new, but you can get something like 36-40 different attachemtns for them. I have a 40" dirt bucket and a set of 48" pallet forks for mine. Tough little tractor. Has secondary hydraulic lines for running attachments.


[This message has been edited by TheMetalDoctor (edited 07-21-2004).]