Custom Karts Forum

Guillermo, if you ever see this biplane flying overhead, I built it.
I sold it to a crop duster in Buenos Aires a couple of years ago.
dg

Hi Ernest,

Yes, that is correct.
This drawing is probably "a view of the mind" for understanding., I think high speed would be impossible ....
In fact, with straight gears, the rule is simple ! The number of contacts must imperatively be "odd"
In the drawing, only one "contact" and my prototype, three contacts !

Is there a rotational speed limit for balanced spur gear differentials that is lower than the common automotive design? In other words, in my use of the Snapper differential, I am planning to remove a chain & gear reduction gearing that will greatly accelerate the rotational speed of the spur gear differential itself. Is this a problem with the spur gear design in general?

Hi Ernest,

I do not have the technical skills to answer your question, I am only a handyman ....
But I think that the type of differential you have is likely to be difficult to "modify"
It is for similar reasons that I preferred, to design a complete model ...
In the past, I have tried to make modifications or adaptations, Some times it is simpler to start zero with its own drawing ....

Soon
Fabrice

From your posts so far, it looks to me like you are more than just a handyman. I need to take some more photographs of this differential I have, to show how I plan to modify it. With parts from the second one I have, I do not think that it should be very difficult. There is, however, one part I will need to have machined, because I do not have a metal lathe. But it is a fairly simple part, so it should not be too difficult to get someone to make it for me. This one part will delete or bypass two gear reductions, and allow for the large gear to be replaced with the piece from the other side, from the second differential I have. This will also remove a lot of extra weight. I can also use the two sets of spur gears from the second unit if necessary, but I don't know if it needs 4 sets, or if I am just adding weight.

Hi Ernest,

Small information if you change the number of sprockets
I had some problems when I wanted to add some sprockets! In fact I think there is a rule with this type of differential !!
This is what I believe... The number of teeth of the great sproket and of the small sproket must always be divisible by the number of contacts
To be clearer, because my English is lamentable .....
- Contacts: 3
- Large sproket: 27 teeth (divisible by 3)
- Small sprockets: 12 teeth (divisible by 3)

I tried with 4 and 5 contacts, and nothing worked ....

I went up to my shop to get some pictures to hopefully better explain it, but in its stock configuration it is geared way down. I have torn it down, and I can leave out two gearing reductions, a sprocket & chain set up reduction of 2:1 (17 cogs to 34 cogs), and a gear to gear reduction of 5.7:1 (input gear has 11 cogs, output gear has 63). This modification would also get rid of the direction reversal of the octagonal hollow shaft in relation to the axle shaft on which it rides.

Photo # 3511 shows the stock application. (This is looking from the bottom – the mower is set up on its rear end.) The mower had a vertical shaft engine positioned above the rear axle. I really dislike vertical shaft engines, and this configuration would also put a lot of weight up pretty high. This has to be changed anyway, to get rear suspension. You have probably seen set ups like this, but a 7” diameter disk is mounted to the engine shaft, and the rubber wheel contacts the bottom side of it. The rubber wheel is mounted on a sliding apparatus, that allows you to position the friction wheel at any place toward the outside of the rotating disk, or past center for reverse.

I have disassembled the entire unit, and the following pictures are an attempt to show how the differential is designed. It is a spur gear type, and this allowed them to stabilize the axles relative one to another by having the long axle shaft set into the large diameter shaft by about 6 inches (with brass bushings inside the larger hollow shaft). (See photo # 3516 in my post on page 1 of this thread)

The rotating disk turns the rubber wheel, which via the gear & chain set up in the sliding mechanism turns the octagonal sleeve which rides on the long shaft. The octagonal hollow shaft (or sleeve) has a gear on the end inside the main differential case, and a chain runs from that sprocket (10 cogs) to a larger sprocket (33 cogs). This larger sprocket has an attached meshing gear (11 cogs) riding on the main differential gear (63 cogs). This part of the mechanism reverses the direction of the axle in relation to the octagonal sleeve. This is the gear & chain mechanism that I will leave out. (I will just need to provide a 1 to 1 connection between the octagonal shaft and the main differential gear, which shouldn’t be too difficult. See Photo # 3514 in my post on page 1 of this thread, and Photo # 3517 & 3521 in this post.)

This increases the over-all gearing of this whole deal from around 32:1 (at top speed) to around 3.3:1, and makes the octagonal sleeve rotate in the same direction as the axle it is riding on. In fact, it will turn at exactly the same rate except when cornering (when the differential action is in play), instead of always turning in the opposite direction. Before anyone comes out of their nest about this ratio, I will mount this assembly so that the axles will function as dual jack shafts, with separate chains running to each real wheel. Because of an old back injury, I feel that I need a rear suspension, or this will not be fun to drive for me. The rear wheels will be mounted on separate trailing arm independent suspensions, avoiding the twisting action of a straight axle (which I’m guessing would throw a chain).

I might eventually consider getting a CVT as well, and mounting this as a way to have reverse gear, plus a sort of over-drive, but don’t have the funds available for that extra cost at this time. I am also not aiming for a high top end speed. I’ll be satisfied with around 25 MPH, because that will allow me to operate this legally on the roadway berm. (Because this is an area where there is lots of horse & buggy, tractor, and bicycle traffic, many of our roads have an extra wide shoulder to accommodate the Amish.)

Hi Ernest,

How fast does the engine work ?, I think + - 600 laps for the wheels is a good average for a 17 "and in your case, maybe simplify the gears to get close to that.

Fabrice

The original engine on the riding mower was an 11 horse, but I will use a 6.75 horse Briggs & Stratton. I am guessing that it runs at about the same speed as a 6.5 Honda or Predator. As I commented earlier, I do not like vertical shaft engines, but that is what I have, so I will use it, at least for now. (It was mounted on a torn up push mower that was abandoned in an apartment I cleaned out for the apartment owner. At first I thought it was worn out as well, and was planning to sell it for scrap metal, but after replacing the fuel line & going through the carburetor, it started right up.)

I had thought that I could turn this differential system on end, to use a horizontal shaft engine, but that would place the enclosed chain drive in an upright orientation, with the small sprocket directly below the large one, and I have read technical articles saying that that is the least desirable design, because it can allow the chain to jump on the smaller sprocket.

As far as final ratio is concerned, I think I should aim for around 9:1, which should give me a top speed of around 25 MPH. If it doesn't run much over that, it should be allowed on the road sides, with the SMV triangle & blinking lights on the rear. (SMV = Slow Moving Vehicle. It is used on horse-drawn buggies & wagons, and farm equipment. I am planning to use the sheet metal from an old tractor, so it should be accepted. The tractor was a FarmAll M, around a 1939 model.) I have to make this useful for more than just play, so I want to be able to pull a small trailer with it, around our orchard & garden area. Eventually, if I can afford it, I'll convert it to a regular cycleKart, but at first I guess it will be a "CycleTractor".

Hi Ernest,

I think 9/1 is still very correct !
You are very lucky to be able to ride with this SMV triangle !!
In France, the automobile belongs "to the Gods" and the slightest attempt to drive on the road is punishable !

Fabrice

Hello all,

Somme news of my DIY differential !

The attachment of the half-axles with squares of 22x22mm.
For the moment, + -950mm track !
The axle halves will not be fixed to the differential, but simply "entered" to the inside ! This will allow me to align the 4 bearings without the differential, and to place it afterwards.
The hole of the central ring, allows me to see when the axles are "end to end" and the hole also allows lubrication ...
Finally, for the fixation of the axles, simply "anti-return" rings in front of the bearings..
Maybe a bit odd as a concept, but I trust ....

Soon
Fabrice



Edited 2 time(s). Last edit at 2017-07-24 12:58 PM by Little French.

Superb work as always Fabrice, I'm following this with great interest. Are you going to put a sleeve around it to form a casing to contain lubricant?

Chris

Hi Chris,

Yes, I am preparing a waterproof case and I will use a thick oil, as for the rear axles of car !
If the operation gives me satisfaction, I would place the complete plan here! But I would like to do real testing before ....

Fabrice

Hi,

Some news !

Still some finishing before the tests...

Some Feature :
- Length : 185mm
- Diameter : 120mm
- Weight : 4.300kg
- Axles : 30mm
- Sprockets :
2x 27 teeth module 2
12x 12 teeth module 2

Fabrice

is that 4.3 kg with the axles Fabrice???

Denny G