Mowing Mower deck hydraulic motor.

[ponytug]

While I wouldn't advocate removing a lovejoy coupler if you have one, there are new motors from Eaton and others that have the motor with built in shock absorption. (something about oil suspension and shock dissipation by design) I have no idea how effective the design is, but clearly the manufacturers think it improves the motor reliability. According to Terry, the 72" brush cutter on the 1445 is this design.

If you do put in a lovejoy, make sure that the two motor axis are aligned, and stay that way. Mis-alignment is the #1 cause of lovejoy coupler failures, and it can happen very rapidly. Bear in mind that it may be advantageous to reinforce the deck around the motor and coupling to get a stiff enough plate to align everything and keep it that way. Belts have the advantage that they do offer some shock absorption, jam protection, and reduce the alignment requirements enormously. They also open up your choice of hydraulic motors, because you can alter the pulley sizes to get the blade speed that you desire from any given motor speed.

I think that the engineering tradeoffs are complicated; clearly the existing design failed under your conditions. That at a minimum presents the question of whether direct replacement is the best thing for you. As they say, YMMV.

[Off thread comment:]

For those with curious minds, there is an interesting article on how an established computer graphics chip company made a connected series of engineering choices that has caused them widespread grief. I take it as a lesson of why wearing a belt and suspenders is sometimes a good idea, and a useful lesson on why it is a good idea not to lose sight of the big picture.
​

All the best,

Peter

Mith, the deck mounted hydraulic motor that came on my 48" brush cutter was a re-branded M+S Hydraulic MLHR 50 wheel motor. M+S Hydraulic is a Bulgarian company. The motor seized, and I replaced it with a Parker TJ0050US080AAAA wheel motor, which has roughly the same specs. The Parker was built to order for me. Nobody had them in stock.

I strongly suggest you do not directly deck mount the motor, as Power Trac is now doing with the 48" brush cutter. In my opinion, the shock loading is what caused my motor to fail very early in life. The older models have a different motor mounted on a bracket. The motor is coupled to a blade hub by a Lovejoy coupler. It provides at least some isolation from shock loads. The variant I have has none.

It is easy to find straight shaft motors of the right size for the old style brush cutters. It is very difficult to find tapered shaft wheel motors for the current models, other than the M+S model that failed, which is quite expensive. The Parker was much cheaper, but must be built to order, and most US suppliers don't catalog it.

I did not want to go with a larger displacement wheel motor, which are much more readily available, as it would have produced unacceptably slow blade speeds.

 

[SnowRidge]

I think that the engineering tradeoffs are complicated; clearly the existing design failed under your conditions. That at a minimum presents the question of whether direct replacement is the best thing for you. As they say, YMMV.

[

Not really. I offered the additional information (beyond the motor ID and specs) for Mith, as I thought it might be useful knowledge for someone who is in the process of designing a mower.

For me, there is no question that the design and fabrication time, energy, and costs to change over to an indirectly mounted motor would exceed the worth of the cutter. There is also the possibility that the failure was simply a bad motor, unrelated to Power Trac's design decision, and that any redesign efforts would be a waste of time and money. I don't think that is the case, but we won't know until like cutters accumulate more hours. If a lot of them start failing, then my theory will be confirmed. If not, that will be good news for myself and the other owners of these cutters.

 

[Mith]

Thanks for the replies guys, I didnt expect to recieve such a thorough response. I'm still digesting the information.

At this point I am seriously considering hydraulically running a 540rpm PTO. If I have a flow of about 18gpm @1500-2500psi (I prefer the lower pressures) then I believe I should get the power I want based on what you guys have running your direct drive mower decks.

Thanks again

 

[J_J]

Thanks for the replies guys, I didnt expect to recieve such a thorough response. I'm still digesting the information.

At this point I am seriously considering hydraulically running a 540rpm PTO. If I have a flow of about 18gpm @1500-2500psi (I prefer the lower pressures) then I believe I should get the power I want based on what you guys have running your direct drive mower decks.

Thanks again

You already stated that you had about 31 HP, and going from what you have stated, the pump will take 31 HP at 2500 psi to run a hydraulic motor at 540 rpm. With an 85% efficiency, that puts about 27.5 HP to the mower deck.
If you run it at 1500 psi, it will take 18 HP. So, based on this, you will have to size the bush hog accordingly. Some people seem to run the bush hog at lower rpm for whatever reasons. Perhaps someone will reply and state the advantages or disadvantages at running at lower PTO rpms.

 

[BobRip]

Some people seem to run the bush hog at lower rpm for whatever reasons. Perhaps someone will reply and state the advantages or disadvantages at running at lower PTO rpms.

One of my friends stated that with low RPMs the engine stalls easily if you hit something. Therefore there is less damage to the blade, etc. If you had a lot of rocks around this might be a good idea.

 

[SnowRidge]

A disadvantage is it won't work as well. It certainly won't cut stuff as thick as it would at full speed.

 

[MossRoad]

I run mine at full speed, all the time, for a couple reasons.

1. It has more power to blast through things initially.
B. If it does bog down, it will recover faster.
Third. The engine is designed to be run at 3600 RPM for proper cooling and lubrication. Brush hogging and mowing are the toughest jobs these things will do.

Click on my little animated tractor in my signature. That takes you to my PT425 website. On the videos page, there are several videos of the brush hog in action. All of them are taken with the engine at full throttle.

 

[ponytug]

If you are really cutting brush, I think that you need the rpms to cut, chop, pulverize, and remove the brush. Otherwise, you end up stalling the blade, and leaving large chunks behind. With high rpms, anything I can push over gets chopped up. If I could make two changes to the PT brush cutter, it would be a pushover bar connecting the front two wheels, and a debris guard at the back.

If you have lots of rocks, you might want to consider a flail mower, which are more forgiving of rocks. They aren't without their drawbacks, e.g. having to replace flails worn out by hitting rocks too often.

Good luck on your project.

All the best,

Peter

One of my friends stated that with low RPMs the engine stalls easily if you hit something. Therefore there is less damage to the blade, etc. If you had a lot of rocks around this might be a good idea.

 

[stray]

Don't know if it will help or not but here is the link to my side mower.

http://www.tractorbynet.com/forums/power-trac/64961-side-mower.html

 

[MossRoad]

Bumping this old thread for reference for another member.