DIY Home built compact tractor

[Cidertom]

About the driveline angle. For slow speeds, 27 isn't that much out of the envelope. But...
U joints are not constant velocity. If you drive a shaft at a constant velocity and vary the angle of the U joint you will see a variation (depending on the angle) in instantaneous speed of the driven shaft. The effect will be a speeding up and slowing down at the rate of twice the shaft speed. This sets you up for vibration and increased loading on the gears. If the second U joint had the same angle and the knuckles are aligned properly they will cancel each other producing mostly a constant speed to the differential.

27 degrees would be out of my comfort zone, I would try to get it under 20.

 

[GT2]

Great project and play by play reportage!
Have you thought about the non-motive aspects of this, like fenders and cowlings? Hard to imagine you will save any money, when the cost of materials and your time totals up... plus you are trying to do something that engineers at companies like Kubota have a history of having done hundreds of times, hopefully learning and improving every time. Still, this project is great training for... something.

Thanks, Its fun to share and get input.

If I keep it simple, how much sheet metal is there really? A hood, 2 fenders, some gearbox coverage and some kind of grill.
I've had my eye on some used rear fenders off a NH that are on e-bay, but they want $100 ea + shipping. I can buy plenty of alum sheet for that price.

Cost of my time? I never count time on my own projects!

I have no illusions what so ever that my design in going to be better than the factory stuff. However I'm very sure that I'm saving some money, how much Time will only tell.
This is just a fun project for me and hopefully will yeld a usefull tool when I'm done.
Cheers, Tim

 

[GT2]

About the driveline angle. For slow speeds, 27 isn't that much out of the envelope. But...
U joints are not constant velocity. If you drive a shaft at a constant velocity and vary the angle of the U joint you will see a variation (depending on the angle) in instantaneous speed of the driven shaft. The effect will be a speeding up and slowing down at the rate of twice the shaft speed. This sets you up for vibration and increased loading on the gears. If the second U joint had the same angle and the knuckles are aligned properly they will cancel each other producing mostly a constant speed to the differential.

27 degrees would be out of my comfort zone, I would try to get it under 20.

Hmm... I had planed to use cv joints at the gear box (that is what it is set up for) and a u joint at the diffs.
I could convert the diffs to cv joints as well.
Think I still need less than 27deg with cv's?
Thanks, Tim

 

[bx23barry]

You can just run the cv joint at the gearbox and tilt the diff up so the u joint runs straight/flat. That is what you need to/should do at both ends to not have vibration. Too bad you already welded the ends on the front because when you tilt the diff the castor will also change. It may not matter much at low speed but could be fun down the road. I wouldn't mess with putting a cv joint at the diff or worry about the front angle at the speeds you are planing (u joints are cheap and I have run them alot steeper than that). What size tires are planning on the front (front and rear need to be the same if you are using the same gear ratio in both)? Will they hit the frame at full lock? I think you are gon'na be pretty high geared for a tractor (should have crawl ratio in the 200s) but if you don't plan on alot of ground engagement it isn't a big deal. Otherwise it looks pretty kool. Who needs body parts?

 

[EddieWalker]

I'd get the engine as low as you can. The lower the engine, the lower your center of gravity, and the more stable it will be.

Are you going to have any sort of suspension? If the axle is just mounted to the frame, lift the axle up the the point of lining up straight with the engine. There's no need for it to be down below the frame.

Eddie

 

[Cidertom]

I forgot to ask..
Since the running gear is from a samurai and the engine is the same as a vw rabbit, does this make your tractor a samurai bunny?

 

[GT2]

Hi all, I've been held up a bit waiting for parts and such, but I got a little more done.
Here the tie rod is shortened. Cant shorten the drag link till I get the steering box mounted.

Here I've made the front axle pivot plate templates.

Heres the steel plates. I cant weld them to the axle till I get my pin and bushing material so I can drill the correct size holes.

 

[Renze]

GT2, is only the alternator in the way, next to the engine ? If you cab move it to a bracket somewhere else, the whole engine and tranny might be able to drop 10 inches lower into the frame, straightening out your drive axles and U joints ?

 

[GT2]

GT2, is only the alternator in the way, next to the engine ? If you cab move it to a bracket somewhere else, the whole engine and tranny might be able to drop 10 inches lower into the frame, straightening out your drive axles and U joints ?

I can lower the engine as is, the alt will clear.
I guess I'm going to lower it. I was trying to keep as much oil pan clearance as possible, but I guess that is what skid plates are for.

 

[john_bud]

I can lower the engine as is, the alt will clear.
I guess I'm going to lower it. I was trying to keep as much oil pan clearance as possible, but I guess that is what skid plates are for.

Clearance? Get taller tires!

What size tires are you going to get and what gear ratio in the diffs?

jb

 

[GT2]

Clearance? Get taller tires!

What size tires are you going to get and what gear ratio in the diffs?

jb

I'm trying to keep my low speed as low as possable using the VW trans., so taller tires are not an option.
I'm using 30" rear and 23" front loader tires.
I have a 5.38 rear and a 3.72 front diff. The trans ratio in low is about 14.30

 

[EddieWalker]

I can lower the engine as is, the alt will clear.
I guess I'm going to lower it. I was trying to keep as much oil pan clearance as possible, but I guess that is what skid plates are for.

Don't confuse off roading with tractoring. Oil pans rarely come into contact with anything when your on a tractor. It's always possible, but extremly rare to damage it, or puncture it.

But there's always an exception, and my Dad proved me wrong with my dozer. It's about as well protected as it can be. Much, much better then any wheeled tractor!!! He was pushing over some small pines and commited the cardinal sin. Never get on top of the debri!! He did, and then to make it worse, he changed directions and spun around on it.

A small pine that was about an inch think worked it's way through the belly plates and right through the oil pan. He also tore off two hydraulic lines and busted of the oil preasure sending unit. Dad is 70 years old and he tries, but this time he really screwed up. Oh well. LOL

My point is that anything is vulnerable, but in general, your oil pan is pretty safe on a farm tractor.

Eddie

 

[Renze]

My brother used to bust his oil pan frequently on his 1983 Mercedes 300 D, even if he did nothing unusual with it. On the 3 Volvo 440's i had, i lost all cover plastics that were mounted under the car within 3 weeks, by driving through the wheeltracks of a small farm road with a grass ridge in the middle, where no wheels come.

I gave all my cars the chance of an honourable death, (to "die in the harness") but i havent manage to bust one single oil pan on any of these in the woods. Some cars are more prone to busting oil pans than others, mostly because of the oil pan sticking out below the chassis parts. You dont need much metal to protect an oil pan, and they easier dent than bust anyways.
On your vehicle you've got a heavy axle to shave off any trees before they can hit the oil pan, so dont worry

If you have the chance i'd definately drop the center of gravity, you're going to get pretty high on 30" tires, plus you have narrowed the axles making it less stabile. even with double reduction, the thing is going to get quite speedy because of the big wheels i suppose.

I'm looking forward for more pics

 

[GT2]

Don't confuse off roading with tractoring. Oil pans rarely come into contact with anything when your on a tractor. It's always possible, but extremly rare to damage it, or puncture it.

But there's always an exception, and my Dad proved me wrong with my dozer. It's about as well protected as it can be. Much, much better then any wheeled tractor!!! He was pushing over some small pines and commited the cardinal sin. Never get on top of the debri!! He did, and then to make it worse, he changed directions and spun around on it.

A small pine that was about an inch think worked it's way through the belly plates and right through the oil pan. He also tore off two hydraulic lines and busted of the oil preasure sending unit. Dad is 70 years old and he tries, but this time he really screwed up. Oh well. LOL

My point is that anything is vulnerable, but in general, your oil pan is pretty safe on a farm tractor.

Eddie

Good point Eddy, I guess I had it in my mind that I would be clamboring over large rocks at some time. Thats not really the idea with a tractor? Clear/make a path.
Most of my experiance has been with skid steers. With thier flat bottoms you can slide over most anything.

 

[jimmysisson]

Hi all, I've been held up a bit waiting for parts and such, but I got a little more done.
Here the tie rod is shortened. Cant shorten the drag link till I get the steering box mounted.

Here I've made the front axle pivot plate templates.

Heres the steel plates. I cant weld them to the axle till I get my pin and bushing material so I can drill the correct size holes.

Is the C-shaped steel to be bolted to the frame, and to the diff, with the pivot near the plastic grip on the spring clamp? In that case the diff will swing side to side as one side goes up and down. I wonder what that does to the tire steering clearance on the low side? I'm sure you've got that all worked out but I wonder if it'll act squirrely. My tractor has the pivot gear centered on the front diff. (had to run out to check).
Maybe I am misinterpreting your mock-up. I love this project, keep sending photos!
Jim

 

[DieselPower]

Kind of have some questions about the front end myself. Anything to support it from twisting front to back? Anything to keep it level? Without springs you may find it tilts to whichever side is heavier.

I hyjacked your photo and added some things you might consider. Go to the junk yard and find a 70's to 80's Ford P/U and get the Radius arms and frame mounts and install them to add resistance to the axle twisting. You could also pick up a old coil spring, chop it in half and install on either side of the C mount you made to add some leveling support.

Added: Here's a link to a web page that shows what the radius arm is. Doesn't need to be as high speed as the ones pictured, a old set of factory ford ones would work fine. Ford Bronco Radius Arm Page

By the way, keep the pic's coming. This is a really neat looking project you have going there.

 

[GT2]

Is the C-shaped steel to be bolted to the frame, and to the diff, with the pivot near the plastic grip on the spring clamp? In that case the diff will swing side to side as one side goes up and down. I wonder what that does to the tire steering clearance on the low side? I'm sure you've got that all worked out but I wonder if it'll act squirrely. My tractor has the pivot gear centered on the front diff. (had to run out to check).
Maybe I am misinterpreting your mock-up. I love this project, keep sending photos!
Jim

The "C" shaped steel plates are welded to the axle assy only. The pivot will be just below the spring clamp, as low on the cross member as I can get it.Yes the whole axle will move slightly from side to side as it pivots. This will cause some bump steer, but I'm going to limit the amount the axle will pivot to a few inches. So I think the bump steer wont be a major problem.

 

[GT2]

Kind of have some questions about the front end myself. Anything to support it from twisting front to back? Anything to keep it level? Without springs you may find it tilts to whichever side is heavier.

I hyjacked your photo and added some things you might consider. Go to the junk yard and find a 70's to 80's Ford P/U and get the Radius arms and frame mounts and install them to add resistance to the axle twisting. You could also pick up a old coil spring, chop it in half and install on either side of the C mount you made to add some leveling support.

Added: Here's a link to a web page that shows what the radius arm is. Doesn't need to be as high speed as the ones pictured, a old set of factory ford ones would work fine. Ford Bronco Radius Arm Page

By the way, keep the pic's coming. This is a really neat looking project you have going there.

My understanding was that if the rear axle is solid mounted, then the front springs are not needed
I was hoping that my heavy steel axle pivot plates (one on the front and one on the rear of the axle) would be strong enough to resist axle twist.
However your radius rod arms idea makes sense. Maybe I can add them later if it needs it.
Thanks for the ideas!
Tim

 

[bx23barry]

I like the front pivot solution you came up with. I don't think you'll need "radius arms". Maybe a gusset or two.

 

[ZJ_HR]

If you have the chance i'd definately drop the center of gravity, you're going to get pretty high on 30" tires, plus you have narrowed the axles making it less stabile. even with double reduction, the thing is going to get quite speedy because of the big wheels i suppose.

30" mens outer diameter of the wheel, not rim only. Am I right?