gear ratios

[jhtoy]

I am building a trans for a ford truggy project I just started.I am using the two metal gears from a scale hobby trans I had lying around.Basically from the top down I have an Integy 65t motor with a 14t pinion turning a 72t spur gear turning a 18t output shaft to the driveshafts.I will be running tlt axles with 2.2 tires.I understand basic gear ratios but the third gear(output shaft) kind of confused me!I am trying to use parts I have lying around to keep the cost down so any help on what kind of wheelspeed vs. torque this combo will produce is greatly appreciated!Thanks Jim

[Mechanicalbob]

If I understand you right you are going from the pinion, spur then the output? Like this?




I know the gears are not the size you are running but it is just a general referance. In the picture the red gear is not takin into effect as it is just an idler gear changing the rotaion direction. So you have a gear ratio of about 1.29 If you would like more help with this PM me and I will see what I can do.

Steve

[rash_powder]

I believe your ratio is 1 : 1.286

Formula source is:

http://en.wikipedia.org/wiki/Gear_ratio

Explanation:

If I understand your post correctly, your 14t pinion (a) drives a 72t spur (b) which then drives a 18t gear (c) on the output shaft. Gear ratio between a and b is 14/72 and the ratio between b and c is 72/18. Multiply those two ratios together, 14/72 * 72/18, which is the same as {14 * 72}/{72 * 18}. The 72's cancel leaving 14/18, which is .7777777778. That is a 1 turn in for every 1.286 turns out, 1:1.286

As far as wheel speed and torque, for crawling I would think a person would want a final ratio that is less than 1:1. That would give the motor a mechanical advantage and have the affect of multiplying torque; ie more torque and less wheel speed. A ratio greater than 1:1 will give more wheel speed with less apparent torque; the motor has to work harder to turn the wheels.

I find this stuff kinda complicated so I spelled it out for all to see how I got what I think is the right ratio. If I am wrong, let me know so that I can adjust fire.

rash

[jhtoy]

Thank you both for your explanations!Very informative.I am hoping I can run a small enough pinion gear to get the ratio down.Thanks Jim