The Jtrack

Subject: The Jtrack February 9th 2020, 4:30 am

Hello Everyone,
Time for a little write-up on the down n' dirty details of my hydrostatic half tracked heavy hauler, aka; The Jtrack. I'm writing this on my mobile and the text size looks a bit odd to me so I hope it formats ok.
I consider myself a pretty decent mechanic but this is the first time I've ever built anything track based or off of a lawn tractor style platform. Basically all of the inspiration came from all of you fine folks.

Background. We recently bought a house and I needed a small-ish UTV to haul rocks, blocks, dirt, firewood etc. I picked up a non running, no mower deck Craftsman lawn tractor for 50 bucks. Hydrostatic drive, 19hp Briggs oppy twin. It needed a starter rebuild and all of the snot cleaned out the carb. There was also a problem with one of the safety switches, dunno which one because I just went ahead and chopped 'em all out. Problem solved.

It came with a hood but I immediately got rid of that and built the flat bed for it.

I knew already that I was going to build a half track for it but I couldn't resist a little woodland baseline test romp, instant disappointment, open diff=no good.
I wanted to overhaul the transaxle because I didn't really know what the tractor had been through and hydraulic systems like to be kept clean. I took that opportunity to Lincoln lock the diff, reassembled and went for another test romp with much better results. I could see those 15/6/6 front tires were not gonna work but I had a plan.

I had watched a few videos on the googleTube where simple half track configurations had been built and I had a few ideas of my own so I got started building my swing arm out of some old ladder rack and swingset frame. The threaded track length adjustment is an oem style, spare tire kit scissor jack, it offers just over 4 inches of adjustment in it's current configuration but could easily be modified to get more if needed. The wheels are just mocked up in the pics but I think you can see things taking shape.

More to come, stay tuned.

Subject: Re: The Jtrack February 9th 2020, 6:19 am

Next I cut my tracks. I had some worn out E range truck tires laying around and I tried a few different ways but it turns out the best sidewall cutter is still the old fashion pocket knife. I wanted to leave a little sidewall to help keep the tracks on and cut triangular tabs out to help relieve the pinch created by forcing a round tire into an oval shape. Once I got the feeling back in my knife arm and my track length was known I could weld up an offset axle and mount it to the swingarm like so...

The axle is allowed to rotate freely, and tension of the tracks keeps the offset in the axle extended, if that makes sense... The reason for this is because as terrain changes the swing arm rotates up or down to keep maximum ground contact, because of where the swingarm is mounted the departure angle changes the distance from axle to axle. The offset rolls in as the tracks are forced up or down by terrain to keep the tension consistent. That is an important detail because the tension of the tracks and the geometry of the pivot and axle locations provides the downward force that keeps the tracks dug in as the ground level changes.
Another important detail is that the amount of air in the tires changes their outside diameter. The tires must have equal outside diameters right to left since the track tensions are not independently adjustable
Here it is after my track trial test romp. I had to play with the tension a bit but I'm pretty stoked that it performed as advertised.

Still to come,
Swapped the front axle for a much heavier simplicity axle
Direct steering
Front flatbed pivot actuated by deck engagement lever
Rear dump box actuated by deck hight lever
Stay tuned...

Subject: Re: The Jtrack February 9th 2020, 8:40 am

Sweet half track build! Looks like a lot of fun, and pretty hand with the flatbed up front. I like the tension adjustment setup too.

Did the half track with locked differential affect the steering much?

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Subject: Re: The Jtrack February 9th 2020, 10:29 am

The steering was affected but not as much as I thought it would be. When cornering the inside track hops and chews up the grass a little but that's the price we pay for traction I guess

Subject: Re: The Jtrack February 9th 2020, 3:37 pm

very cool man, talk about out of the box