Is 1/6hp at 2:1 1/3hp?

[rjwaldren]

Is HP output linear when geared? If I take a 1/6HP@3450 motor and gear it 2:1 will I get 1/3HP@1725. I realize there are other losses to consider also, but I'm trying to find use for some surplus items.

[cgallery]

I think you double your torque, but the HP remains a constant.

[LCHIEN]

Is HP output linear when geared? If I take a 1/6HP@3450 motor and gear it 2:1 will I get 1/3HP@1725. I realize there are other losses to consider also, but I'm trying to find use for some surplus items.

no its still the same amount of power. The torque is changed by gearing.
it'll move slower but push harder, net power is the same.

a 1 HP motor 1725 RPM will have half the speed, twice the torque, same HP as a 1 HP motor 3450 RPM.
Further gearing will change the torque some more but not the power.

Consider the old addage a washing machine motor properly geared down can move a freight train, but very very slowly, certaily not 80 MPH.

[cgallery]

Consider the old addage a washing machine motor properly geared down can move a freight train, but very very slowly, certaily not 80 MPH.

Did Mythbusters ever test that? Do you think it would really be possible?

[LCHIEN]

Did Mythbusters ever test that? Do you think it would really be possible?

oh yeah it would work.
the problem with doing it for TV is that one, to get enough traction to pull a freight train you'd need a lot of weight to get enough traction, so you'd either have to gut a locomotive or build a monster weighted sled to mount your motor on, both a rather expensive doing. They're not really well equipped or financed for doing things on that scale.
Second the rate of movement would be so slow as to make for lousy TV. I don't think it's likely you could discern movement, you'd have to come back hours later and see how many inches it moved. they'd rather blow things up, makes for better audience involvement.

[cgallery]

Second the rate of movement would be so slow as to make for lousy TV.

Lousy TV? You've never watched Gray's Anatomy (wife favorite show), have you?

You're right, though, I do think it would be complicated and require making some pretty large and expensive components to pull it off. Probably no sense in submitting the idea to them.

It would be sort of interesting to have an engineer outline the gearing necessary to do it, and then compute the maximum speed.

[crokett]

Hmm... a better one to submit to Mythbusters might be to have a washing machine motor move a car. Or maybe a tractor trailer? It might move a little faster then. If you used a Pinto you could get the explosion the audience likes.

[LCHIEN]

Actually, I'm going to answer this question in another way.
A 1 HP motor in use seldom produces 1 HP, except for certain constant load applications like compressors, pumps, fans where they are designed to use maximum power most of the time. I'm talking about power tool motors where the power they produce (or more accurately, convert) is proportional to the load up to the maximum power rating of the motor.

So a 1 HP motor on a big saw turning against a friction load might be producing 1/4 HP at a certain feed rate.
Now suppose we geared up the motor (gearbox, or change belts) so the blade spun twice as fast and the power consumed in friction would double, so would the work and hence the power consumed.
So in this case the motor would up its output from 1/4 to 1/2 HP, so yes, in this case the motor power would double.

But you cannot do this beyond the rated power of the motor. Once exceeding the rated HP of the motor, it will want to stall and eventually burn up. So no you cannot turn a 1 HP rated motor into a 2 HP motor by changing the gearing or pulley ratio!

[LCHIEN]

Lousy TV? You've never watched Gray's Anatomy (wife favorite show), have you?

You're right, though, I do think it would be complicated and require making some pretty large and expensive components to pull it off. Probably no sense in submitting the idea to them.

It would be sort of interesting to have an engineer outline the gearing necessary to do it, and then compute the maximum speed.

This loco is rated at 4300 HP, it weighs 408,000 lbs. Often used in tandem or triple configurations for large loads. Tractive effort is rated at 157,000 lbs at 12 mph and 191,000 lbs starting effort. Maximum speed is 70 MPH.

A quick look at washing machine motors yields power ratings of 40 to 250 watts. Lets use a big one, 250 watts, there's no point in skimping on power, now, is there?

So we have a 1/3 HP motor (approx 750 watts per HP conversion factor).
in order to get the same amount of starting torque (the largest torque will be getting the cars from zero speed to initially moving) we have to gear it
in inverse proportion to the power. So for a big train with three 4300 HP diesel electrics or roughly 13,000 HP we'd have to gear the washing machine motor approx 39,000:1

so that ratio drops 70 MPH to .03 inches per second or about .15 foot per hour.

P.S. like my choice of Loco livery?

[Wood_workur]

What kind of MPG would we be looking at with that setup?

[LCHIEN]

i don't think the train gets very many MPG, probably better measured in many gallons per mile so the washing machine motor, if it was hooked to a small gasoline generator would not do much better. Though slower, its doing the same amount of work - we're assuming for a train the air resistance isn't a big factor.

BTW that loco holds 4900 gallons of diesel fuel. And we're assuming there's three locos for this train.
Assuming that the engine has like a 500-1000 mile range (That's a good guess for how far it can go on a tank of fuel before needing refueling) then one engine gets .1 to .2 miles per gallon of diesel. Three engines pulling a 100-car train would get .03 to .06 miles per gallon. that's 16-30 gallons per mile. That's still better than 200 semi-tractor trailers put together.