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