Differential

[Julian]

Hi All,

I need to build a simple differential for my traction engine. I am looking for something dead simple and easy to build. It needs to fit hopefully in the middle of my rear axle. The axle is solid at present but will bu cut to suit. One and of the axle is chain driven from the gears and needs to drive the diff to drive the other wheel. The axle is at the moment about 12mm dia and the length available is around 125mm.
One thought I had wasthe pic below. The red gear driven from one side of the axle drives the blue gear via the yellow set. The yellow ones are held together by a rod with a nut on each end. This allows them to be preloaded but to still turn independently. The strain of the wheels reacting to steering should allow them to roll around thus reducing the drive to the other wheel. All enclosed in the green case. Simple but may work.

Any ideas, views or suggestions please.

Julian.

 

[rleete]

R/C car guys have been using diffs for quite some time. You may want to search for their forums to see what they recommend.

 

[Jasonb]

Standard traction engine practice is to have a solid axle. One side of the diff is keyed to the axle and drives the wheel on the opposite side of the engine. The other diff wheel is fixed to the hub of the other wheel. The two pinions are set within the final drive gear, something like this

Quite simple really as it was the technology of 150yrs ago.

Jason

 

[ChooChooMike]

Here's a very popular R/C site you might want to check :

http://www.rcgroups.com/forums/index.php

 

[Brian Rupnow]

Julian---Why worry about a differential at all? What you have shown will work, and that is what is found in the differential of any rear wheel drive car. Its primary purpose is to allow one rear wheel to travel farther than the other when the car goes around a corner, without any slippage. However, even the lightest of cars weighs in at a ton, and travels at high speeds, where a tire "slipping" would wear out the tire and possibly lead to loss of control. Unless you are building an extremely large vehicle, which will travel at high speeds, why not take the go-cart approach. No differential. A light vehicle will let the outside wheel slip a little bit with no terrible effects.

 

[Stan]

Another approach is that used on lawn mowers, which is just a ratchet wheel or over running clutch in each hub.

 

[Jasonb]

A light vehicle will let the outside wheel slip a little bit with no terrible effects.

Actually if you have drive pins in the rear wheels then removing one of the pins will allow for tighter turns without making the engine prone to going round in circles, again standard TE practice.

As Brian says for a small engine a diff is not really needed, my 1" minnie turns OK without a diff.

Jason

 

[artrans]

just power one wheel and let the other wheel free wheel what size are we talking about here
model or ride on.

 

[Julian]

Ride-on. the rear wheels are 350mm diametre

 

[Jasonb]

If its a ride on then that back axle is a bit on the thin side at 12mm. The diff I pictured is for a 2" scale Fowler that I am building, that has 305mm rear wheels and the axle is 7/8" (22mm) and I will be on a driving trolly behind it.

Jason

 

[Julian]

Jason,

Yes I agree. My Axle same as yours 22mm. the 12 was due to the time 04:30am while the kettle boiled before work!
I will be on a trolley at the back aswell. We are both about the same scale but mine is scratch-built with no plans. May call it "Seat-of-your-Pants" when finished.

Julian

 

[Jasonb]

Are there any pic sof your TE? Always like to see what fellow TE builders are upto.

I assume the available space you have is between the hornplates, if the diff is as you show using 45degree bevel gears it will be quite wide and may make access to the firehole a problem, it is coal fired isn't it?

These are mine

Jason

 

[Noitoen]

Hi,

Speaking of differentials, do you know how they compensate the difference of travel in a locomotive? They have solid axles, travel different distances in turns but they don't "slip" their wheels I'll explain if you want.

Helder Ferreira

 

[artrans]

I will bite Noitoen how do they do it

 

[cfellows]

Bank the tracks?

 

[Julian]

I am looking at building and fitting a simple dif now while I can still get at it easily. It may not in the end need it but this is a more appropriate time to build and fit before other stuff gets in the way. Also I have some hand-built ali wheels I spent quite a time building that may or may not have tyres fitted. If not I don't want to damage them with the turns. Also its another bit on the engine that can work.

Julian

 

[bob ward]

If you have 125mm to play with, I imagine you could make a diff quite readily by using 'off the shelf' gears from a small car diff

 

[Julian]

Bob, Forgive me but its 125MM not CM. I would not be able to fit any car dif i know of inside 125mm (6 inches). It will be built from scratch.


Julian

 

[Dusty1]

My 1/2 scale Terning Case Engine has a John Dear differential in it.

The Quarter size has 5 home made bevel gears inset in the bull gear
or a total of 18 home made gears.

This engine was built from scrap in 1982 on a Logan 10" lathe, and Enco Mill drill.

Boston gear has/had a good selection of bevel gears that could be used.
These may be rather pricey these days.

If you are building a small engine, those old crank driven hand drills
have nice bevels in them. Find two of the same model and use those.

The Germans used some kind of differential made of hardened wedges
in WWII.

A little research here may find a drawing.

Kap

 

[Dusty1]

Hi,

Speaking of differentials, do you know how they compensate the difference of travel in a locomotive? They have solid axles, travel different distances in turns but they don't "slip" their wheels I'll explain if you want.

Helder Ferreira

Wheels are tapered 2 degrees 50 minutes.
Like a barrel rolling down a two railed ramp.

kap