Kubotasaurus, a home built micro tractor

[chaffe]

Are you serious dude, that thing is awesome. I just noticed the rear differential. That's a pretty big pumpkin. What did it come off of, and how did you mod it to work?

lol, it is off a 1990's ford transit van! I dont think it will break! :thumbsup:
What i did was cut the axle tubes down to length with a grinder, removed the half shafts, cut the halfshafts shorter and welded them back together (they are 1 1/4" dia, with a good weld prep on them too) so plenty of strength in them for this garden tractor! I then made some steel bushes for the shafts to run on, with brass bushes and a grease nipple, and welded a sleeve on the halfshaft (to stop it comming out) before welding the bushes onto the end of the axle tubes. Quite simple, but effective. I dont think wear will be a problem on this thing! and if it ever did wear i can always re-bush :thumbsup:
The diff is packed with grease, and there is a grease nipple on top to add more as and when required.

 

[davygp38]

Very nice, I can't wait to see more.

 

[chaffe]

Very nice, I can't wait to see more.

Thanks for all the possetive comments guys! I too cant wait to see more! I simply love small usefull things like this! tonight I am going to start on the rear lift arms (the top ones) with their hydraulic ram and bearings, once that is in place i can fix the seat (as the position of the seat mounts will be very dependant on the ram/lift arms. Then i need to look at foot plates and a pedal and linkages to operate the spool valve for farward and reverse. And i think i will make my own rear linkage as any ive seen are too big for this thing, please bare in mind it is only about the size of a cub-caddet!. :tractor:

 

[20 20]

thanks for sharing, now we need a video of it running

 

[chaffe]

thanks for sharing, now we need a video of it running

well, that will be coming soon, i hope to get the seat on and make it more "drivable" before i make a video! (not wanting all you lot laughing at me falling off the back!)

 

[J_J]

Can you explain what a hi-low hyd pump is? Is it a two stage pump? What is the displacement and pressure? Are you using motor spools? Any detents on the valve? How do you control fwd and rev speed?

 

[chaffe]

Can you explain what a hi-low hyd pump is? Is it a two stage pump? What is the displacement and pressure? Are you using motor spools? Any detents on the valve? How do you control fwd and rev speed?

Hi, the pump is a hi flow low pressure pump that changes flow when the pressure goes above 50 bar (although it is adjustable) to increase the pressure upto 200 bar, with much less flow (this stops the engine from stalling) very similar to what is on most log splitters, this pump is matched to my 5.5 hp engine, with around 26 litres/min on low pressure (where it spends most of its time)
I am using a 3/8" conventional spool as it was the best price possible (free) should i be using anything different? it seems to work well with this application. FWD and REV will be on a pedal as said previously, the speed is pretty much constant, at a walking pace. I could always have a throttle from my engine if i ever needed to speed up or slow it down, but this pace will be suitable for most things, thanks for the intrest, chaffe.

 

[chaffe]

Just had a thought, JJ if you are suggesting my 3/8" spool maybe a restriction? it could be, the specs on the pump are around 290rpm, and it does about half that, but the engine still loads up even if the hydraulic motor is in free air, so this could prehaps point to the valve block being a restriction, prehaps i can use two spools to drive the motor and use it as 2 speeds?!

 

[J_J]

There are times that you might want to go real slow, and you can do that with a regular valve, but you have to hold the lever. If your valve had three position detent, you could put it in fwd or rev detent and vary the engine rpm. If you want to use something like the valve below, you can vary the speed from 0 rpm to max rpm. Any excess fluid not used by this valve is sent back to tank. If you put a spring on this valve, you could have foot control for speed, and remove your foot and you have hyd brakes.

https://www.surpluscenter.com/item.asp?item=9-064-38&catname=hydraulic

I use one of these to vary the speed on my hyd PTO.

I am curious about the torque to the hyd motor, as the two stage pump only puts out about 650 psi in the high mode, and max GPM. If the tractor needs more go torque, the GPM's decreases, and the pressure goes to about 2500 psi.

What happens with this type of drive, is that you go from fast speed, little torque, and when the load/resistance increases, the pump shifts automatically to the lower speed, high torque mode.

Your system will work with a log splitter, but you really need a log splitter valve with reverse detent.


If what you have works for you, fine. These are just some thoughts I had

 

[chaffe]

The main points are as follows; 5.5hp honda powering a matched hi-lo hydraulic pump, two gallon hydraulic resevoir, bank of four spool valves (one for forward and reverse, on a pedal, one for rear lift and the other two for extra services) A hi-torque hydraulic motor drives the rear axle via a heavy duty chain. .

I was thinking of using the sprung to centre spool on a pedal, that way i can vary the speed and direction on one pedal :thumbsup:

There are times that you might want to go real slow, and you can do that with a regular valve, but you have to hold the lever. If your valve had three position detent, you could put it in fwd or rev detent and vary the engine rpm. If you want to use something like the valve below, you can vary the speed from 0 rpm to max rpm. Any excess fluid not used by this valve is sent back to tank. If you put a spring on this valve, you could have foot control for speed, and remove your foot and you have hyd brakes.

https://www.surpluscenter.com/item.asp?item=9-064-38&catname=hydraulic

I use one of these to vary the speed on my hyd PTO.

I am curious about the torque to the hyd motor, as the two stage pump only puts out about 650 psi in the high mode, and max GPM. If the tractor needs more go torque, the GPM's decreases, and the pressure goes to about 2500 psi.

What happens with this type of drive, is that you go from fast speed, little torque, and when the load/resistance increases, the pump shifts automatically to the lower speed, high torque mode.

Your system will work with a log splitter, but you really need a log splitter valve with reverse detent.


If what you have works for you, fine. These are just some thoughts I had

The spool i am using will give me hydraulic brakes and also dumps back to tank the excess i am not using, and is sprung to centre, prehaps I already have the exact same thing you suggest? I do not have any detented spools.
The good thing about the hi-lo pump is that it automaticaly "drops" downd a gear when the load increases on the transmission, quite ingenious if I may say so (and just lucky!) i hope this clarifies what i am trying to achieve, and thanks for the intrest again, chaffe

 

[chaffe]

also i looked up the specs on my motor, 700 n/m at 2500 psi, plenty of torque available, especially as it goes through a 4:1 reduction in the diff :thumbsup:

 

[chad22]

well, that will be coming soon, i hope to get the seat on and make it more "drivable" before i make a video! (not wanting all you lot laughing at me falling off the back!)

Come on now. We'd all love that video of you falling off the back. :laughing: "As long as you don't get hurt in the process".

Can you drive it standing up to the side? I used to do that when I was a kid. I'd stand on the side of the lawn tractor and drive it. "And no not while the blades were engaged". Now that would be dumb.

I fell off once too and I wish I had caught that on video. lol

When I was about say 10. I was towing a friend "he was 8" on another broken down lawn tractor. We were going up a curb and I had told him not to try to ride the side of the curb or he'd flip it. What da ya know. I got caught on the side of the curb and ended up flipping mine.

Luckily I didn't break anything, or worse.

Chad

PS. Sorry for going off topic. I'll quit rambling. lol

 

[chaffe]

ramble away chad! I did fall off yesterday lol, its quite "touchy" on the hydraulics when you are steering with one hand and holding on for grim death with the other, on the hydraulic lever! :laughing:
Never did much tonight, working 10 hour shifts and driving another 2 hours on top of that fairly makes me tired! but here is the result of an hour in the garage;

Ill get the seat on now, going to use two bits of 2" box at a slight angle to the rear for that, all will be reveiled soon!

 

[dfkrug]

The good thing about the hi-lo pump is that it automaticaly "drops" downd a gear when the load increases on the transmission, quite ingenious if I may say so (and just lucky!) i hope this clarifies what i am trying to achieve, and thanks for the intrest again, chaffe

Nice work, CHAFFE.

A 2-stage hyd pump is a great way to go with these small engines. I wish
I had one when I built my CADDigger years ago. Even with a 10hp engine,
the cylinders moved slower than I wanted in low-load situations.

The reason you want a "motor spool valve" is to avoid the large pressure
spikes that you get when braking, esp when you have a lot of momentum
to stop. The M-S valve will allow the drive to free-wheel a bit when you
return to neutral. Some have adjustable reliefs, but you can also install
an after-market relief valve in the system to avoid problems. You also
may want to have additional brakes as this will limit your hydraulic
braking action.

 

[chaffe]

Nice work, CHAFFE.

A 2-stage hyd pump is a great way to go with these small engines. I wish
I had one when I built my CADDigger years ago. Even with a 10hp engine,
the cylinders moved slower than I wanted in low-load situations.

The reason you want a "motor spool valve" is to avoid the large pressure
spikes that you get when braking, esp when you have a lot of momentum
to stop. The M-S valve will allow the drive to free-wheel a bit when you
return to neutral. Some have adjustable reliefs, but you can also install
an after-market relief valve in the system to avoid problems. You also
may want to have additional brakes as this will limit your hydraulic
braking action.

Thanks, And yes the 2-stage pump works very well in my experience. It makes the best of a not ideal situation.
Interesting that you mention the shock when the drive is halted, it skids the wheels very easy, although there is not much speed involved it still might make a mess of the grass if im not carefull with the drive pedal. I had thought of some kind of relief valve or "run on valve", or prehaps even a damper on the footpedal so it can only return slowly. I would be quite interested in any more information you may have about relief valves in the drive (i dont really want to change my spool), thanks Chaffe..

 

[dfkrug]

I would be quite interested in any more information you may have about relief valves in the drive (i dont really want to change my spool), thanks Chaffe..

I understand that you don't want to buy a different valve.

If you put a separate relief valve, connected between the 2 work ports
of the spool valve, this would provide a path for the oil when the
pressure spikes as you release the lever to neutral. You will also want
another RV, connected in the reverse direction, to handle the reverse
flow. You can use adjustable RVs, but you don't really want
to set them below your working pump output pressure. Not as good
as a motor-spool valve, but better than nothing.

I would also put in a control lever damper, as you suggested.

Note that in a hydrostatic transmission, the pressures are much higher
so the pressure spikes are not the same kind of problem that you have
with a gear pump and hoses.

 

[chaffe]

DFKRUG, thanks for the advice, i will certainly look into something of this nature.
Here are some high quality pictures of it with the seat on, this is essentially finished now bar the footplates. I can now count the lift linkages as seperate projects, the first thing to do is look at mounting my mower deck, as that is of primary importance this time of year!

thanks for looking :tractor:

 

[Johndeere3720]

DFKRUG, thanks for the advice, i will certainly look into something of this nature.
Here are some high quality pictures of it with the seat on, this is essentially finished now bar the footplates. I can now count the lift linkages as seperate projects, the first thing to do is look at mounting my mower deck, as that is of primary importance this time of year!

thanks for looking :tractor:

Looks like the real thing, only smaller. :thumbsup:

 

[Petroman1]

That is AWESOME!!! :thumbsup: Great job.

 

[J_J]

Have you considered the fact that a fully functional mower deck, one two or three bladed, will take just about all of the HP that the engine has.

A lot of single bladed lawn mowers have up to 6.5 HP available. .