Calculating gear ratios

[tkruger]

I am in the process of building a custom transmission. I know the ratio of the first to gears and the second two. How do I calculate the ration when these two sets of gears are combined? Am I correct that I just add the ratios of all the sets of gears and that is the final output? Finally what is the gear ration of the pede tranny so that I can compare.

[BENDER]

The pede tranny is 2.72:1

[Zuki Tyler]

Originally Posted by tkruger

I am in the process of building a custom transmission. I know the ratio of the first to gears and the second two. How do I calculate the ration when these two sets of gears are combined? Am I correct that I just add the ratios of all the sets of gears and that is the final output? Finally what is the gear ration of the pede tranny so that I can compare.

You multiply...

On a side note, how many gears are you using? Do you have any pictures?

I've been building quite a few transmissions lately...but frustration has finally set in (Dremel crapped out this morning)

[tkruger]

Originally Posted by Zuki Tyler

You multiply...

On a side note, how many gears are you using? Do you have any pictures?

I've been building quite a few transmissions lately...but frustration has finally set in (Dremel crapped out this morning)

Currently I just have drawings and ideas, nothing solid. I am also building the frame for the RC from scratch. I want the parts to work together so that I do not have to modify one to fit it in the other. At this time the first set of gears will be a GD600. Gives a good mounting point for the motor. The second set will be a pinion (size yet to be determined) and a 90 tooth or larger spur (48 pitch).

[Zuki Tyler]

A 90 tooth spur is huge, the radius on it would either set your driveshafts really high in the chassis, or the spur would be hanging way underneath.

When I built my MKI transmission (and the MKII re-work) I used several small gearsets to get the required reduction, with the final gear on the output shaft having a very small radius, allowing for better driveshaft angles, without sacrificing ground clearance

[tkruger]

Originally Posted by Zuki Tyler

A 90 tooth spur is huge, the radius on it would either set your driveshafts really high in the chassis, or the spur would be hanging way underneath.

When I built my MKI transmission (and the MKII re-work) I used several small gear sets to get the required reduction, with the final gear on the output shaft having a very small radius, allowing for better drive shaft angles, without sacrificing ground clearance

Thanks after looking at it you are right. Maby I should incorporate a transfer case of some type. Or maby a set of two part drive shafts with U joints in the middle. Just thoughts.

[Zuki Tyler]

Running a transfercase in addition to the transmission might raise the center of gravity quite a bit. I countered that by positioning my small motor at the very bottom, against the skid, then positioning the gears so that the reduction followed the path of an upside-down U.

I've pulled all of my gears out of radioshack trucks. So far, those gears are tougher than a TLT pinion's shaft, and they have small diameters too. You might want to consider buying 2 or so cheap RS trucks, just to pillage the gears and motors out of them. Doing that, you can create virtually any ratio you would need, it would all fit in a small area, and it's cheap.