Differential

[Orrin]

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
cylinder block was an interesting bit, but I think it came out well.

I also added a spur gear differential to mine.

I have some old photos of it on my web pages, http://plsntcov.8m.com

One other note, Roger Mason modestly failed to note the original book
was written by L.C. Mason, his father. One of several books he wrote, a
major contribution to Model Engineering.

ron ginger

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.

I started to write up a description here, but it got to complicated. I'll try to photo the thing and post them to my site. It is a very simple design and works very well.

ron ginger

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

Basically, the two planet shafts provide the reversal of movement
which is achieved by the planet bevel gear on a bevel differential.

Jim Guthrie <[email protected]>

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

 

[cfellows]

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

 

[GailInNM]

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

 

[Noitoen]

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

 

[bob ward]

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.

 

[jack404]

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

 

[RonGinger]

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.

 

[bob ward]

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.

 

[Orrin]

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

 

[Brian Rupnow]

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

 

[Orrin]

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

 

[GailInNM]

One more spur gear differential illustration

 

[joeby]

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

 

[Noitoen]

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

 

[RonGinger]

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.