Supporting > Vehicles & Models
Cotta Transmission Cutaway Model
crueby:
Back in the shop again and ready for a new build, though a much smaller one than the last engine! This one is a cutaway model of a Cotta transmission, which is the type used in the Lombard tractor/trucks built early in the 1900's in Waterville Maine. I first got introduced to the Lombard line of vehicles years ago when I went up to the Maine Forest And Logging Museum outside Bangor Maine, and took tons of pictures/measurements of their steam powered Lombard Log Haulers so I could build a working model of one. Since then, I've been going up there several times a year to volunteer on their crew running one of the steamers and the two (about to be three) gas powered trucks at their annual events.
The gas powered trucks used versions of transmissions built by Cotta, a company that is still around making more modern transmissions. Terry, one of the gang up at the museum, got me copies of some of the ads for the transmissions, and I was able to find the original patents for them too. Here are a couple of pictures:
As the ads describe, they are a constant-mesh type gearbox, so no stripping of gears with bad shifting. They use sets of dog clutches sliding on the shafts to engage different sets of the gears for the different speeds. There were a couple different variants of these transmissions, so I picked one that I had the most documentation for, and will build that. It has three forward and one reverse speed. The transmission was modeled up in 3D CAD, and I've made up some spreadsheets for the gear ratios and spacings, picking a scale that would work out well on my lathe/mill for cutting the gears as well as using cutters that I had on hand. All the gears will be cut in Module 1 from brass bar stock.
The shop elves are back from their trip up North to help out at the big shop for Christmas. They brought me a picture of the shop up there:
Now that they are back, they have been playing on the bandsaw to cut me out the raw bar stock for the gears. Two sets, since I'll be keeping one model and sending the other up to the museum:
As you can see in the picture, some of the blanks are from hex bar stock - normally I wouldn't buy hex bar, but I got a huge deal on it as an offcut drop bar from the supplier. A quick rounding off on the lathe and they will be perfect for several of the gears.
So, next up will be to trim all of the blanks to length on the lathe, and bore center holes to hold them on an arbor (already made) to turn them mto final diameter before starting the gear cutting. Most of this project is an excercise in gear cutting, which will be done with a vertically mounted rotary table over on the mill with a set of M1 gear cutters. All the gears will fit onto 3/8" diameter shafts. The sliding clutches will be made separately, the moving pieces of those will be on square bar bored to fit over the main shafts. The case will just be a minimal base, enough to hold the shafts and the shifter.
RReid:
Getting all geared up to follow along. Love that shop picture. :popcorn: :popcorn: :cheers:
Kim:
How exciting! A new Crueby build. I'll get the popcorn ready! :popcorn: :popcorn: :popcorn:
Kim
steamer:
:popcorn: :cheers:
Watching along! But it needs an engine to bolt onto.....just sayin 8)
crueby:
--- Quote from: steamer on December 22, 2023, 06:23:53 PM --- :popcorn: :cheers:
Watching along! But it needs an engine to bolt onto.....just sayin 8)
--- End quote ---
Yeah, well, IC engines are not my thing. :shrug: These were very large T head engines. For this cutaway, the 'engine' will be a hand crank. I do have some RC truck differentials, going to put one on the output shaft of each model, with a sprocket on each side so you can see the speed/direction that the crank input gives on the output side. At least the hand crank can be made to look like the crank used to start the engines! These trucks did have starter motors, but also had hand cranks too - wouldn't want to be stuck out in the woods with a dead battery and no crank. That would make me cranky! :Lol:
And I DID contact the guys at the museum to double check which way those engines rotated, in the early days of engines they may not have been standardized on things like that, and I wanted to be sure I oriented the clutch jaws the right way.
Navigation
[0] Message Index
[#] Next page
Go to full version