What is torque?

[AmericanWeiner]

I get that torque the force being put out by an arm.

I'm just that type that has to REALLY understand something before I accept it. So here's what I think it is- please add on or correct me.

Let's assume we're in a vacuum, and things work as they ideally would.

First question- I have a 4" gear spinning at the engine, and a 1" gear spinning at the wheel... is that a 4:1 ratio or a 1:4 ratio?

Secondly...let's assume that the 4" gear is spinning at 200rpms. The 1" gear (if they are the only two gears in the machine and are connected) will be spinning at 800rpms, correct?

Third question (I really would like to get this; also, any rpms reffered to here are the rotations of the wheel gear)- A 4" engine gear leading to a 1" wheel gear will put out less torque, but more rpm's than a 1" engine gear leading to a 4" wheel gear, right? So...I'm not sure how to word ratios yet...but assuming it's engine:wheel, a 4:2 puts out more torque, but fewer rpms than a 4:1, correct? Conversely, we might switch it to 1:4 if heavy lifting, and not speed, was the goal, correct?

I might be completely wrong- I've never understood this my whole life..and I'd like to start sometime soon.

[ZooTech]

First question- I have a 4" gear spinning at the engine, and a 1" gear spinning at the wheel... is that a 4:1 ratio or a 1:4 ratio?

Not enough information. Are the gears 4" and 1" in diameter, or is that the circumference? A better way to ask would be, "I have a 40-tooth gear and a 10-tooth gear..."

If you have an engine spinning a 40-tooth gear and it's attached to a 10-tooth gear (via timing belt) then you would have a 1:4 ratio. That is because for every time the drive gear rotates once, the driven gear rotates four times.

Secondly...let's assume that the 40-tooth gear is spinning at 200rpms. The 10-tooth gear (if they are the only two gears in the machine and are connected) will be spinning at 800rpms, correct?

Correct.

Third question (I really would like to get this; also, any rpms reffered to here are the rotations of the wheel gear)- A 40-tooth engine gear leading to a 10-tooth wheel gear will put out less torque, but more rpm's than a 10-tooth engine gear leading to a 40-tooth wheel gear, right? So...I'm not sure how to word ratios yet...but assuming it's engine:wheel, a 4:2 puts out more torque, but fewer rpms than a 4:1, correct? Conversely, we might switch it to 1:4 if heavy lifting, and not speed, was the goal, correct?

Try to think of it using truck rearends. If fuel mileage and lower engine RPM's at speed are your biggest concerns, you might opt for a 3.42:1 rearend, which means the driveshaft has to rotate 3.42 times to rotate the tires once. Now, if you have a dually and plan to tow a large trailer and torque is your biggest concern, you may go with a 4.10:1 rearend which means the driveshaft will have to spin 4.1 times for each rotation of the tires (.68 times more than the 3.42 rearend). That means the gear in the differential is much bigger in diameter, with more teeth on it than the one in the 3.42 rearend, so it offers more leverage when attempting to spin the rear axle and move the truck forward.

[rapidblue]

edit beat me to the puch but i'll leave it up anyway

the "easiest" way to think of it is like this:

lets replace the 4" gear with a 40 tooth gear and the 1" gear with a 10 tooth gear.

if you spin the 40 tooth gear one revolution 40 teeth will go around, but if you spin the 10 tooth gear once only 10 teeth will go around. so for the 10 tooth gear to keep up with the 40 tooth gear it has to pass 40 teeth or 4 revolutions. Technically it is a 4:1 and a 1:4 ratio. The difference in the wording is based on which gear is the "driver". In your case the 4"(40 tooth) gear is the "driver" since it is where the power is applied at. The 1"(10 tooth) gear is the driven. Thus you would have a 4:1 gear reduction ratio.

So if the 40 tooth gear is spinning at 200 rpm the 10 tooth gear has to spin four times as fast (4:1) to keep up to the gear or 800rpm.

As for torque...

if you have a 1ft bar and put a force of 100lbs on the end you get 100ft*lbs. A 50lb force on a 2ft bar will yield the same result 2*50=100ft*lbs or 200lbs on a 6in bar.

In a vacuum with no power loss, Power remains constant through a gearset.

TorquexSpeed=Power.

Therefore if you put 100ft*lbs through the 40 tooth gear the toque would only be 25ft*lbs because of the 4:1 gear ratio. As speed increases, torque decreases and vice-versa.

Hopefully I made it a little clearer, if not, sorry.

[AmericanWeiner]

Thanks for correcting and confirming my information guys. My only experience with motor and gears is from tooling around with my brother's Lego Mindstorm set.

I figured I was wrong about the ratios but didn't want to sound too stupid.

Basically, then, the engine creates the same force and the machinery puts it into a smaller place on a larger ratio, correct? And conversely, on a smaller ratio, the machinery spreads the force out over time (because less is required)?

EDIT: Now that I'm thinking in successive gear sizes...what's the common progression from 1-5 gear? Does it go small to high or high to small?

[High_Side]

Open the throttle on one of these at 3000rpm and you will know

[Skier]

An old car adage:

Horsepower is how fast you hit the wall. Torque is how far you take the wall with you.