Homemade tractor (in aus)

[Vigo327]

Depending on the size of engines you're talking about you probably don't need 2 separate engines unless you're running a power hungry pto implement.

For example, if you look at the size of engines they put on small tillers it is well within the wheelhouse of a large riding mower engine to run one of those AND push a small vehicle at tilling speeds (probably requires ~2hp).

Stock riding mower transaxles are said to only be able to use about 2hp for propulsion. If you build a heavier vehicle that is much harder to roll that power requirement will be higher, but still low single digits hp, and you're unlikely to ever max out your 'propulsion' and 'pto' power requirements at the same time. So don't write off a single large (>500cc) riding mower engine of say 16+hp. My B6100 kubota does just fine with 600cc and 12hp. It can run 4ft wide pto attachments and push and pull plenty hard.

 

[tractor-mower project 1]

Depending on the size of engines you're talking about you probably don't need 2 separate engines unless you're running a power hungry pto implement.

For example, if you look at the size of engines they put on small tillers it is well within the wheelhouse of a large riding mower engine to run one of those AND push a small vehicle at tilling speeds (probably requires ~2hp).

Stock riding mower transaxles are said to only be able to use about 2hp for propulsion. If you build a heavier vehicle that is much harder to roll that power requirement will be higher, but still low single digits hp, and you're unlikely to ever max out your 'propulsion' and 'pto' power requirements at the same time. So don't write off a single large (>500cc) riding mower engine of say 16+hp. My B6100 kubota does just fine with 600cc and 12hp. It can run 4ft wide pto attachments and push and pull plenty hard.

Sadly I'm most likely needing two, as otherwise the drive system will be a PITA, and for lawnmower transmissions, from what I've heard unless you use a k66 or more (which even then isn't recommended) since they can burn out really easily with alot of strain being put on them. Granted my solution is using belts, which argue will be even worse but eh lol. I'm definitely not looking forward to using 2 engines, however I'm already using an old lt1042 so if I can find the same engine then hopefully it'll work fine. My biggest concern now is just the lack of HP, as a 20hp 3 cylinder diesel and 20hp single cylinder petrol will make massively different amounts of torque, so I'd need atleast 2 to be similar to the diesel. Plus tracks are absolutely miserable in the drivetrain, and are far harder to roll, so overall it could work but would be really hard in the engines

 

[Egon]

Rather than two engines consider one at around 25 hp. With an hydraulic pump. Use variable speed hydraulic motors for the drive And PTO. That might make all the hookups quite simple as well as easy control

 

[Vigo327]

I was only bringing up riding mower transmissions to point out that it only takes 2hp to move something of that size and 'rolling resistance' at 5mph. So the majority of your engine power is available to your PTO and there is not as much tied up in vehicle propulsion as you might expect. But yes, a heavier tracked vehicle will still have a much higher power requirement to go the same speed, and it's always good to design 'pessimistically' and over-deliver in the end, as long as it doesn't cost you too much time and money to do so.

Horsepower is Horsepower. If a small gas engine and a larger diesel say they make the same HP, then.. they do! In the 'small engine' world the gas engines are usually even spinning a similar rpm to the diesels while doing it, as well. But the difference you may be referring to can come from a couple of other things:

One is simply momentum, or inertia, in the rotating assembly of the engine. The other is how the engines are 'fueled'. As far as momentum, if 2 engines make the same power but one is 'storing' a lot more energy in its own parts because it weighs more, it will seem to react better to the same load being applied to it, than the other one. It is not making more torque, but it can apply more torque to the load because of its stored energy. It just has more momentum to 'soak up a hit'. This would definitely be the case between, for example, a ~500cc single cylinder briggs in a Craftsman DYT4000 riding mower i have, and the 600cc 3cyl diesel in my Kubota B6100. BUT.. it's just weight. You can add flywheel weight reasonably easily if you desire to. For example, I put a ~120cc push mower engine on one of those Craftsman DYT4000 riding mowers (have 2) to make room for a tiny crane on the front (yup..) and noticed that without the 'flywheel effect' of the 22" blade, the engine was extremely easy to stall with a load and did not like to run smoothly at anything lower than the governor rpm of 3000-something. I added a hydraulic fan clutch from a car (with no fan on it!) to the bottom of the crankshaft, and that spinning weight made the engine run a WHOLE lot smoother at low rpm, and you could apply a load to it a lot quicker without stalling it. So just adding flywheel weight is one option.

The other difference is not easy to change or improve, which is just a difference in how diesels and gas engines receive and use their fuel. A diesel engine sitting at a steady rpm with no load is basically using 100% of the fuel you're giving it. If you give it 4hp of fuel, it will rev up and up until it has 4hp of frictional losses, and then it will sit there at that rpm just 'breaking even'. If you apply a load and drop its rpm quickly, even before the injection pump has time to physically react, you're now receiving 4hp of fuel but only using 2 or 3 of it to overcome the engine's frictional losses, so the amount of power available to go out the end of the crankshaft goes up automatically! And then the injection pump guts shift a little and give more fuel. That's an oversimplification, but by nature a diesel has some amount of 'automatic, instantaneous load compensation' that doesn't require ANY of its parts to move or shift, and that in combination with them usually having more rotating weight for the same power level makes them feel like they struggle less when you apply a load.

I'm not against using 2 engines if it's justified/cheap/easy enough! But you may also consider adding some flywheel weight or at least leaving yourself the room to do so in the design.

But belts themselves are perfectly sufficient for these <15hp applications. You may have noticed most of the small engine equipment using belts in that ~15ish HP range are using 5/8" belts rather than 1/2" belts you would typically see on old cars and stuff, and if they go much into the 20s hp they'll usually be running TWO belts, but yeah properly sized the belts are not an issue and give you a nice built in 'slip clutch' or 'fuse' in the design.

 

[tractor-mower project 1]

I was only bringing up riding mower transmissions to point out that it only takes 2hp to move something of that size and 'rolling resistance' at 5mph. So the majority of your engine power is available to your PTO and there is not as much tied up in vehicle propulsion as you might expect. But yes, a heavier tracked vehicle will still have a much higher power requirement to go the same speed, and it's always good to design 'pessimistically' and over-deliver in the end, as long as it doesn't cost you too much time and money to do so.

Horsepower is Horsepower. If a small gas engine and a larger diesel say they make the same HP, then.. they do! In the 'small engine' world the gas engines are usually even spinning a similar rpm to the diesels while doing it, as well. But the difference you may be referring to can come from a couple of other things:

One is simply momentum, or inertia, in the rotating assembly of the engine. The other is how the engines are 'fueled'. As far as momentum, if 2 engines make the same power but one is 'storing' a lot more energy in its own parts because it weighs more, it will seem to react better to the same load being applied to it, than the other one. It is not making more torque, but it can apply more torque to the load because of its stored energy. It just has more momentum to 'soak up a hit'. This would definitely be the case between, for example, a ~500cc single cylinder briggs in a Craftsman DYT4000 riding mower i have, and the 600cc 3cyl diesel in my Kubota B6100. BUT.. it's just weight. You can add flywheel weight reasonably easily if you desire to. For example, I put a ~120cc push mower engine on one of those Craftsman DYT4000 riding mowers (have 2) to make room for a tiny crane on the front (yup..) and noticed that without the 'flywheel effect' of the 22" blade, the engine was extremely easy to stall with a load and did not like to run smoothly at anything lower than the governor rpm of 3000-something. I added a hydraulic fan clutch from a car (with no fan on it!) to the bottom of the crankshaft, and that spinning weight made the engine run a WHOLE lot smoother at low rpm, and you could apply a load to it a lot quicker without stalling it. So just adding flywheel weight is one option.

The other difference is not easy to change or improve, which is just a difference in how diesels and gas engines receive and use their fuel. A diesel engine sitting at a steady rpm with no load is basically using 100% of the fuel you're giving it. If you give it 4hp of fuel, it will rev up and up until it has 4hp of frictional losses, and then it will sit there at that rpm just 'breaking even'. If you apply a load and drop its rpm quickly, even before the injection pump has time to physically react, you're now receiving 4hp of fuel but only using 2 or 3 of it to overcome the engine's frictional losses, so the amount of power available to go out the end of the crankshaft goes up automatically! And then the injection pump guts shift a little and give more fuel. That's an oversimplification, but by nature a diesel has some amount of 'automatic, instantaneous load compensation' that doesn't require ANY of its parts to move or shift, and that in combination with them usually having more rotating weight for the same power level makes them feel like they struggle less when you apply a load.

I'm not against using 2 engines if it's justified/cheap/easy enough! But you may also consider adding some flywheel weight or at least leaving yourself the room to do so in the design.

But belts themselves are perfectly sufficient for these <15hp applications. You may have noticed most of the small engine equipment using belts in that ~15ish HP range are using 5/8" belts rather than 1/2" belts you would typically see on old cars and stuff, and if they go much into the 20s hp they'll usually be running TWO belts, but yeah properly sized the belts are not an issue and give you a nice built in 'slip clutch' or 'fuse' in the design.

ahh I understand what you mean now, in regards to the transmission. Hopefully I'll have the extra HP available just Incase, ie bog down ect. But nonetheless it will be very nice having a high pto HP amount, especially with running a tiller ect.

ascfor HP, I must remember to start writing torque instead lol, but I guess that's what having to explain the difference 1000 times does to a man. Regardless you make very valid points about the weight argument, and that is something I actually haven't even considered, yet very much will now. So thankyou greatly, I assume a large counterweight added onto the engine will be more than enough, since I assume that with running a tiller behind I'll end up needing that extra give before the engine stalls,Incase I hit something ect.

as for the twin engine, my main reasoning is already owning a lawnmower (that we don't use) and I'm able to buy another for 1500aud very easily,

whereas to buy a 30+HP one is atleast 4000$+, however I won't rule it out in future for sure,since it would probably be alot nicer.


as for the belts, lll most likely be running 2 per axle, and for the pto, I'll either go chain or just hope that the belts will grip enough to not slip and actually run enough and give enough grip to run through the ground

 

[Vigo327]

I don't know your local conditions but around here 'good' riding lawnmower engines are practically free, you just have to harvest them from non-running riding mowers. I have fixed up maybe half a dozen free or nearly free riding mowers and it seems that 95% of the time, they only stop running because of fuel system issues which are VERY cheap to fix.

 

[stephanadams]

Hi all, after consulting my wife on buying a SCUT/CUT she has, well firmly disagreed with the idea. However my dilemma is that I am wanting to create a garden/planting area, and due to our soil being 99% clay, I've had to approach the costly territory. So what I want to ask is:

Out of these three, what would be best
1. 7hp rear tine Chinese tiller
2. Tea20
3. Homemade tractor
Speed Test

Now I am limited to around ~5000aud or 3500-4000 usd. anything newer than an old Fergie is too expensive, and anything larger is a no due to size. (Well the fergie is already much too big but it's the smallest I can find).

I was initially planning on building a small wheeled tractor, with most likely a very low geared 19hp lawnmower engine, and another to purely drive the pto. This would allow me to build to the size I require, aswell as using mostly cheap or readily available parts. The issue I ran into was:

A hydrostatic off a lawnmower would burn out long before the tractor could much of anything, and the rear pto gives me some concern about HP/torque.

So my option now is to take a small car engine, detune it massively and run the entire system off of that. But that would require a transmission, which I would have to gear down myself, and the engineering for the pto would be far harder.


The other option is to build a tracked vehicle, as thatway I would have cabin AC, better traction, better stability , and tighter turns (a big must). However I'm completely lost on what to do in terms of transmission type, how to get said transmission to work. I was thinking clutch and brake but I would need to learn fully how to assemble that.

I do want a small as possible tractor due to size issues, imagine Kubota BX/b7000 series size. Hence why as the only small high hp second hand tractor in aus is a tea20. So what would I be best building? A small tracked homemade 2wd, or a smidge larger tracked vehicle? And what improvements would you make?

What sort of work would you be doing with the tractor? We don't have clay soils here, it's more the opposite. But I can't imagine plants growing well in pure clay. You'll likely need to amend the soil. Maybe it would make sense to hire a tractor to break up the clay with a sub soiler or similar for drainage and truck in some topsoil. Then you can work that by hand or with a roto tiller.