DC Motor and Gearing

[A_Reed]

Originally Posted by Vikesrock

Don't gear ratios multiply?

Yeah they do, lol.

3:1 and 3:1 is 9:1

[Red-Rx7]

I did some quick research, and the gear stages do multiply.

I found an online calculator which can compute up to three stages:

http://www.technobots.co.uk/Technica...Calculator.htm

Playing with the User Defined section, I can come up with a few wild teeth combinations to equal what I need. I was browsing SDP-SI for parts, and found a simple combination of:

- 14 tooth on the motor shaft
- 50 tooth and 14 tooth on shaft # 2
- 32 tooth on the starter shaft.

This would mean that the 14 tooth on the motor would turn the 50 tooth, which would rotate the 14 tooth also on the same shaft; which is connected to the 32 tooth on the starter shaft.

This would create an 8.16:1 ratio.

Until I design it all with the actual gear sizes and such, I don't know what exact formula of gear teeth I will use. But, this is an example of something that I could use. That calculator comes in handy.

Next question:
- How to secure the gear shafts to the bracket plate?

For some reason, I am having a blonde moment here... I cannot figure out how the shafts that the gears would be secured too would attach to the bracket itself.

My original planned design was to take two aluminum plates to create a "top" and a "bottom" for the gearbox. I was going to put studs on each of the 4 corners to create the box. I was then planning on having the aluminum plates drilled out in the exact same spots with flanged ballbearings placed in them. Then, I was going to place the gearshaft in these bearings with the gears attached to the shaft. But... what prevents the shaft from just falling out (other than the gear being screwed to the shaft, and the gear resting on the aluminum plate)? Or is this how it is suppose to be held together?

Does that make since?

[DonRotolo]

Edit: Yes, gear ratios multiply.

Let's say you have a 1 to 4 reducer - 1000 RPM gets reduced to 250 RPM, right? Now, the second reducer is also 1:4, so 250 RPM gets reduced to 62.5

1000 / 62.5 = 16, so two stages of 1:4 is the same as 1:16

In this case, for 1:8 you'd want 1:4 and 1:2

Don

[Dad1279]

Having flown gas models in the past, I think you will find the starter motor required to be too large. Since you only need a few revs to start the engine, perhaps a smaller motor to wind a spring, with a latch to release. (like the old .049 airplane engines)