# Compound gear train question.

1. Jan 22, 2010

### pest2u

Hi I hope someone can help.

I am working on a gear train with an electric motor which was burnt out and I'm trying to find the ratio and gear size without haveing to use a cutting torch to cut it up to get it out where I can work on it to measure the gear size. the gear on the motor (a) spins 1200 times to get the last gear in the train (d) to spin 1 time in between between (a) and (d) there are 2 compound gears (B) and (C) I can't get a measuring tape in the space to measure (B) and (C) but they seem to be the same size both the big gear and small gear on both

(A) is 5'' from tooth tip to tooth tip
(D) is smaller then (B & C) by a good bit and is probably 18''
the small gears on (B & C) look a little bit bigger then the gear on (A) but not buy much

How much torque comes out of (D)?
is there a mathematical formula for figureing the probible size of of ( B & C )?

thanks if you can help if not ill just have to cut it out Monday and measure before putting it back together

side note we tried to turn (D) to get (A) to spin and it wouldn't budge even after we disconnected the load on (D)
it is a small suger cain mill here in Louisiana
the use of this machine is to move old cain husks after there processed and they want it to move faster

Last edited: Jan 22, 2010
2. Jan 22, 2010

### Zula110100100

Do you have any more info? Like maybe a maximum size of the big part of B and C?

I think if they were like 42" big part and 6" small part if the others were 5" and 18" you'd have like 1,235 to 1...

And do B and C look like the same size I guess?

3. Jan 23, 2010

### pest2u

It's 1200 to 1. Had a fun time figureing that out
at what point do you measure a gear to tooth tips or mid point between the tooth tip and where it starts or from the base of the tooth?

4. Jan 25, 2010

### gmax137

I think you can say torque x rpm is a constant. so if the gearing results in a speed (rpm) reduction of 1200, then the torque is multiplied by 1200 (neglecting friction losses in the gear train)

You figured that 1200 out by counting teeth, right? That would be more accurate than by measuring gear diameter or circumference.