# Differential



## Julian (Jan 14, 2009)

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.


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## rleete (Jan 14, 2009)

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.


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## Jasonb (Jan 14, 2009)

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


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## ChooChooMike (Jan 14, 2009)

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

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


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## Brian Rupnow (Jan 14, 2009)

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.


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## Stan (Jan 14, 2009)

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


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## Jasonb (Jan 14, 2009)

> 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


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## artrans (Jan 14, 2009)

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


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## Julian (Jan 14, 2009)

Ride-on. the rear wheels are 350mm diametre


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## Jasonb (Jan 15, 2009)

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


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## Julian (Jan 15, 2009)

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


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## Jasonb (Jan 15, 2009)

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


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## Noitoen (Jan 15, 2009)

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


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## artrans (Jan 15, 2009)

I will bite Noitoen how do they do it


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## cfellows (Jan 15, 2009)

Bank the tracks?


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## Julian (Jan 18, 2009)

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


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## bob ward (Jan 19, 2009)

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


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## Julian (Jan 19, 2009)

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


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## metal mite (Jan 20, 2009)

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


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## metal mite (Jan 20, 2009)

Noitoen  said:
			
		

> 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


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## Orrin (Jan 21, 2009)

It is possible to build a differential without using beveled gears. The entire construction is with spur gears. 

I'll not be very helpful when it comes to describing the construction because I am having trouble visualizing how it works. Ron Ginger built one. Here's an old post I saved:



> I have a Minnie about 95% complete. I scaled mine by 125%, because I had
> a piece of 3" tube and the plans call for 2 1/2"
> 
> I did not use any castings- I carved it all out of the solid. The
> ...



Another Ginger quote:



> if anyone wants to see a photo of an all spur gear differential, as on my modified MINNIE, see
> 
> http://www.plsntcov.8m.com/differential.htm
> 
> Follow the link to MINNIE, then to the differential.



Another:



> I have photos of one on my web page ( http://plsntcov.8m.com ) but the
> photo is not good, and the design didnt work to well. It relied on an idler gear that was supported by a single bearing that was just the width of the bull gear thickness- less than 1/4" This was not enough support for the gear, and they didnt run smooth.
> 
> After building it I bought the CDROM of Traction Engines that was offered here a year or so ago, and in that found a much nicer drawing. I built a new one for my MINNIE, which I have not photographed.
> ...



Here's something from Jim Guthrie:



> A spur gear differential I have built was constructed with a spur on
> each of the input shafts.  These spurs meshed each with a spur planet
> gear on its own shaft, and the two planet gears mesh together.  I
> can't think of a way of showing this with ASCII art
> ...



I know this isn't much help, but I'm sure Ron Ginger would be able to point you in the right direction. 

Regards, 

Orrin


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## cfellows (Jan 22, 2009)

I looked at the links from Orrin's post, and one of the things that wasn't immediately apparent (to me) is that there are 3 spur gears on the side of the bull gear in the photo, but only 2 gears on the other side. It's hard to get my head around how this thing works.

Chuck


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## GailInNM (Jan 22, 2009)

Spur gear differentials were used on several early automobiles. Best known were the 1903-5 Cadillacs. They are still used today on some ATVs.
Primary advantage is that the input shaft is parallel to the output shafts. Most often they are chain drive, but they can be gear driven by driving a bull gear. 

On mechanically automated machinery they are used to adjust the phase relationship of two shafts, although most of the modern ones are turned inside out and made with a planetary gear system as it is more compact. 

Cheddar models used a variation of it to adjust the phase of an eccentric drive shaft by 180 degrees for reversing one of their marine steam engines.

There are several illustrations of the Cadillac differential on the internet, but I make a quick look for them and could not find one. 

Gail in NM,USA


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## Noitoen (Jan 22, 2009)

Here in Portugal they have a small 3 wheeled 50cc motorcycle with a small bevel geared differential. The geared centre is about 50mm (2") in diameter. Don't you have those in your country? You can also use some kind of "clutch slipping" mechanism on one of the wheels. One would have solid traction, the other could "slip" when required. 

I remember now that those 1:4 scale R/C cars also have nice difs 

Helder


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## bob ward (Jan 23, 2009)

Julian  said:
			
		

> 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.



Apologies, I didn't explain myself properly. 

Rather than use a whole back axle, I meant that if you open up the diff centre from a small dead car, you will find 4 small bevel gears, 2 of them already mounted on a shaft, and other useful bits and pieces.


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## jack404 (Jan 23, 2009)

G'day folks

heres jacks 2 bobs worth.

kubota make a small lawn mower/yard tractor called the yard boss and yard king for Oz and NZ dunno what they are called in the USA.

the diff is only 4" wide 3.5 tall and 4 deep on the yard boss (100 cc motor with 2 power take offs )

the king has 3 PTO and 150 cc motor and i dont have the sizes for that sorry

i dont have a web page but do have the user guide , service manual 

so if kubota make em i'm sure some of the US made one would have small size diffs 

cheers

jack


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## RonGinger (Jan 23, 2009)

I see Orrin has already posted some quotes and links to my spur gear differential made for MINNIE. I dont know where those were posted, but it was a long time ago, and I still have not taken better photos or updated that web page.

I did build a new differential and it works quite well, and looks fairly presentable.

I did make one big mistake. My wheel gears are 20 tooth. I decided to have 3 sets of the planet gears around them. I made all the gears, and drilled the holes, but when I went to assemble it I found the 3 gears did not mesh well on a 20t gear- as any dummy could figure 20 is not evenly divisible by 3. A 21 T gear would have been better.

I re-drilled the base for 2 gears, and I keep the other pair to show and explain how it works. I pretend I planned it that way 

I will try to get some photos and update that page.


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## bob ward (Jan 24, 2009)

FWIW, I'm reading a book on the Austin 7 at the moment and they use a spur gear differential. There is a standard crown wheel and pinion, and the differential action is obtained by using an arrrangement of 6 spur gears.


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## Orrin (Jan 24, 2009)

Ever since I read Ron Ginger's post to [email protected] regarding his Minnie engine, I've been trying to visualize how the spur gear differential (SGD)worked, but could never get it through my head. 

So, when this thread started I thought I'd do some "Googling." As it turns out, there are many more spur gear differentials being used than what we realize. Garden tractors and 4X4 ATVs are the main application, nowadays. 

Google Books came up with a number of good illustrations of early applications of SGDs in automobiles. Correct me if I'm wrong, but it appears as though the one pictured in Ron's Minnie can be thought of as being turned "inside out" when compared to the conventional type. 

Regards, 

Orrin


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## Brian Rupnow (Jan 24, 2009)

Orrin---I too am intrigued by the spur gear differential, and although I spent an hour searching the internet, I couldn't even find a picture like you did!!! I thought that if I could actually figure out in my mind how it worked, I would build a 3D cad model and post it here to simplify it for other folks---but I never did clearly figure out how it works.---Brian


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## Orrin (Jan 25, 2009)

Brian, here is another view that helps clarify things. It is very fuzzy and the text is illegible; but, that doesn't make any difference.

You'll notice that the long pinion gears mesh with the wheel gear on their respective sides; and, they mesh with the long pinion on the other side of the assembly. 

The shafts for the long pinion gears are fastened to the center section which could be either a gear, pulley, or sprocket. 

You'll see that this arrangement is slightly different from the spur gear assembly in my earlier post. To me, this fuzzy illustration is easier to understand; but, it should also help clarify the earlier drawing.

I hope this helps.

Orrin


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## GailInNM (Feb 4, 2009)

One more spur gear differential illustration


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## joeby (Feb 4, 2009)

If you happen to know the whereabouts of one of the older Allis-Chalmers or Simplicity garden tractors (A-C B-1, B-10, or the like), they had an interesting differential setup. It was entirely outside the transaxle on the right side, completely exposed. It was a spur gear differential driven by a hollow axle, the left side axle passed completely through the transaxle through the hollow right side axle, and into the differential.

 Very simple setup, just a stamped housing with spur gears and pre-load springs. I would think any old tractor service manual would have an exploded view and maybe a detailed description.

Kevin


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## Noitoen (Feb 4, 2009)

Interesting application of differentials invented by the Chinese a long time ago is this: http://www.stirlingsouth.com/richard2/south_pointing_penguin.htm and http://www.stirlingsouth.com/richard/Chariot.htm


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## RonGinger (Feb 4, 2009)

Reply 32 above is almost exactly how I built the differential for MINNIE. The only minor change is that I centered the hub on the bull gear instead of having it all on one side.

What may not be clear from that drawing is that the two center gears are the axel driving gears, each connected to its respective side axel.

The photo onmy web site and linked above, is my first attempt. It sed only one planet gear, and that was supported on a shaft through a hole in the bull gear. One one side was an idler to reverse its direction. It worked, but the center gear bearing was to short being only the thickness of the bull gear, so it tended to twist.


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