How much abuse can a slip clutch take?

[BrokenTrack]

It's a PTO generator. I didn't disclose that initially because I've discussed it online before and I know the direction the thread will take after I say what I'm about to say in the next paragraph. I'm not interested in trying to reason with anyone about whether or not the generator will work. I'll post the proof once I get it running.

The generator head is a 210kW Caterpillar SR4B that is designed to be mounted to a 300HP skid-mounted oilfield diesel engine. (Yes I know my tractor is only 40hp, doesn't matter). The rotor of the generator head is very heavy. I don't know how much but I think my estimate is reasonable.

I would have liked to use belts but I've done the math and the pulleys needed would be many, massive, and expensive. And I have zero of them. What I do have however, is a pile of gears I salvaged from an old transmission and transfer case, which give me just the right ratio. In using gears I miss out on the clutching action that belts afford, but I hope to regain it with the slip clutch.

I fully understand! (LOL)

You did not have to tell me if you did not want to. I was not trying to pry...

I got a thread going myself on a PTO Generator build, so I know what negative-nannies are like. It is just part of the internet age. Some float around and tell you it cannot be done, but that is all they ever do...be on the internet and tell everyone it cannot be done. There is some value in that, by kicking around ideas, but 19 out of 20 people will tell you it cannot be done, when a few of us actually make things in our shops instead.

I am a doer...

But by all means, disregard the belting idea, I was just thinking maybe you were building a homemade flail mower or something.

 

[strantor]

IF you don't service a slip clutch, it's NEVER going to work right!

IF you slip that clutch too much, it's NOT going to last very long at all!

Implements that have very heavy starting rotation loads, have a hydraulic motor to get things started moving and up to a certain rpm, THEN the pto kicks in and takes over.

SR

I was considering something like that; maybe a car starter or something to get it up to speed first. Do you have any examples of equipment which has this kind of starting strategy? I would like to look into one or more example cases to get a feel for what weights & RPMs are considered the entry point into the realm where this strategy is needed.

 

[Sawyer Rob]

The big Krone square balers have a hydraulic start on them.

SR

 

[ptsg]

I was considering something like that; maybe a car starter or something to get it up to speed first. Do you have any examples of equipment which has this kind of starting strategy? I would like to look into one or more example cases to get a feel for what weights & RPMs are considered the entry point into the realm where this strategy is needed.

It's usually done on bigger square balers, since they have a lot of stuff to be powered and a huge flywheel. The first one that comes to mind is the Krone balers but others use that also.

That starter idea might do the trick though. At least would get things moving and the tractor wouldn't have sustain all the load of trying to turn the thing from a complete stop.

 

[strantor]

Ok I've looked into the Krone balers with hydraulic start, and that big flywheel "looks" about the same weight as my rotor "looks" but it's more of a wheel than a drum, so probably has more inertia, however it's rotating at PTO RPM, not 1800RPM. So I think my application deserves a starting assist even more. That is going to complicate my build. I'm not happy about that. I'm tempted forego it, just try without it and "see what happens" - but the results could be destructive, maybe to the gearbox I'm building. I will stress about this for a while and then decide how to proceed.

 

[strantor]

I fully understand! (LOL)

You did not have to tell me if you did not want to. I was not trying to pry...

I got a thread going myself on a PTO Generator build, so I know what negative-nannies are like. It is just part of the internet age. Some float around and tell you it cannot be done, but that is all they ever do...be on the internet and tell everyone it cannot be done. There is some value in that, by kicking around ideas, but 19 out of 20 people will tell you it cannot be done, when a few of us actually make things in our shops instead.

I am a doer...

But by all means, disregard the belting idea, I was just thinking maybe you were building a homemade flail mower or something.

I saw your thread; seems more the opposite of a PTO generator thread LOL. I have two of the mondo generator heads. My other one is waiting patiently for eventual marriage to a propane forklift engine that is also patiently waiting, just a few yards away. I say patiently, maybe not; I haven't checked either for rust in nearly 2 years.

I'm a doer too, in fits & starts. More starts than finishes. I have enough projects started right now to keep me occupied for probably 5 years if I retired right now. But I have a few decades left before retirement. This is the one I've I've committed to finishing next. I started a couple of years ago and made a build thread. It's been collecting dust since then.

 

[Egon]

It all depends on how often and for how long the slip clutch is slipping! Just like most things they wear out if slipped.

 

[Fallon]

If you have a bunch of spare transmissions & parts, could you impliment a standard automotive clutch? Would be easier to replace than the internal clutch at least.

I had the slip clutch on my tiller smoking after about a minute or so when it wasnt tight enough & it survived. Not sure how long it would last if I did that often though. But it's meant to match up to a 40hp tractor. So it stands to reason it should hold up to occasional slipping at 40hp levels.

As others have said you need to service them anually if you want them to slip when they are suppose to. If I loosen the clutch on my tiller completely loose, it will cut a 2x4 I jam into the tines 75% of the way through. That's just with the rust holding it together. I do that every spring to free it up. Big bang when it frees up. I tighten things up a hair, slip the clutch for a few seconds then tighten it back up to spec.

 

[strantor]

If you have a bunch of spare transmissions & parts, could you impliment a standard automotive clutch? Would be easier to replace than the internal clutch at least.

I do have the clutch, as well as the flywheel that goes with the transmission. I have gone back and forth many times about using it or not, and how. If the transmission in its original configuration had a gear selection (1st gear) with a ratio of 3.33:1, then the challenge would be to make an adapter plate to mate transmission's bellhousing to the bellhousing of the generator head. The "plate" would need to be more than a plate; a 3 dimensional assembly of variable thickness. It's hard to explain why in text; it would be easier in video, but for now I hope saying "it ain't that simple" will suffice.

To make matters worse, the tranny didn't have a gear selection with that ratio; I had to to combine one gear pair from the transfer case and two gear pairs from the transmission to achieve the ratio. Further, I had cut up the intermediate shaft of transmission to rearrange the gears, so the transmission case is no longer suitable as my gearbox. I am making a new gearbox to house these gears.

So now the challenge would be:
(A) to design the same bellhousing adapter as before, and in addition design an adapter for other side of the bellhousing as well, to adapt my new gearbox to it. Or,
(B) design an entirely new housing for the clutch, possibly integrating it into my new gearbox design.

B is probably the simpler of the two options, but still not simple. The diameter of the flywheel and clutch is the thing making it hard. I dont have any capacity to machine things that big. It would have to be made up of many welded pieces. Trying to keep dimensions within necessary tolerances from start to finish of a welding operation like that is going to be just at, or past my skill level. Plus it would be very tedious and time consuming.

Another idea I am kicking around is to make my own manual clutch, using a PTO slip clutch as a starting point. Remove the preload springs and replace them with a throw-out assembly comprised of cam roller bearings. Or maybe instead of a slip clutch, a brake disk, brake pads, and maybe the caliper too... I need to go to sleep.

 

[BrokenTrack]

It sounds to me like you need a torque converter.

On my skidder (Clark 664D) it is an automatic transmission with a 453 Detroit, so 140 horse power. I am not sure if that is a little or a lot, but it has no brakes, so as I start down a hill, I will get partway down, throttle into it, and jam it in reverse. It immediately fetches up, and stops the tractor.

I logged all winter over a steep grade, perhaps 30 degree hill, and had to do that a few times on the way down. The torque converter can take the abuse. That is a lot of pressure as its big tires, with all that planetary gearing, gets transferred back to the torque converter.

But when starting out, I have to wind the engine up to get the machine to move. That is a lot of power and torque as it begins to move. You would do the same thing with your tractor and big generator.

Around here homemade tractors are made with two transmissions, that way there is a really double-low. The best homemade tractor I ever saw had (2) transmissions, but one was a manual, and the other an automatic. The guy would pick a manual gear, then as the tractor moved to certain speeds, the tractor would shift on its own. Or, he could drop the two transmissions manually by stick shift, into first gear, and get low granny gearing, but also shift into overdrive with the manual, then eventually get double-overdrives. It was really a capable homemade tractor.

You could do the same thing. Use a manual tranny to get the gearing you need, but the auto tranny would then give you the slosh drive buffer you need, but eventually shift itself into the right range depending on what the load was on the generator. It really does not seem that complicated to me...nor hard to do.