Help requested improving side dump mulch applicator

[clavius]

So once again I will preface all this with the comment that I am not a pro with this stuff but have had some significant exposure. But please DO NOT take my advice as as any sort of last word. I am sure there are a lot of details I am overlooking here. You have some homework to do.

With that said, here is my take. You can make a hydraulic motor run at any speed you want. Think of a machine like a skidsteer Bobcat that utilizes a hydraulic drive. . The engine is running constant speed at maybe 2000RPM driving the pump, but the hydraulic motors can be driving the wheels at just a few RPM if you are creeping it along.

To get the required pressure and flow, the pump needs to turn at some specified speed that is determined by the design of the particular pump.

So long as the pump is supplying enough flow & pressure, you can vary the flow to control the speed of the motor. That is essentially what the hydrostatic drive on a tractor does. The pump runs continuously at whatever speed the engine is running, and you vary the flow to the hydraulic motor to control the speed of the tractor. More flow = more speed. Because the pressure is always pretty much the same, the torque you supply will remain the same as well. So in theory, you can have full torque at zero (or near zero) RPM. Of course theory and the real world are not quite the same thing, but it's pretty close to that. This is why things like skid steers and tractors use hydraulic drives. It gives you the ability to control lots of power quite precisely. The hydraulics serve as the gear box, essentially.

There are subtleties involved of course. You can't just valve off the flow from the pump, it is either diverted or you need a variable displacement pump, etc.

I think that what you want to do should be within your capabilities with a bit of research. I don't know what would be better, the small engine or a hydraulic drive. Like any engineering decision, it is a series of tradeoffs. No doubt either approach can be made to work well, they each have different strengths and weaknesses. The application and your preferences will dictate which strengths and weaknesses are most important.

You may want to take a look at the surplus center website (I think someone may have mentioned this already) at their technical info page here:

https://www.surpluscenter.com/Tech-Help/Tech-Help-Home/

They link some helpful videos and have calculators about hydraulics to help with the design work. Lots of other info on the web as well. If you prefer to read a book, this is a decent basics book that will get you in the ballpark:

https://www.amazon.com/Hydraulics-ro...p;qid=&sr=


I am sure there are lots of similarly good books out there. Hope that helps a little.

[clavius]

Amazing! I guess if you lower the rpm of a motor by a factor of 1 or more thousands you must really increase the torque!!!

This is exactly right. If you are using a gearbox to decrease the speed by a factor of 100, then (ignoring losses) you INCREASE the torque by the same factor of 100. There are always losses of course, how large those are depend on how much reduction you are doing and what mechanisms you use to achieve that reduction.

[ibdennyak]

the gerotor type of motor is a high torque/low rpm type of motor. Gear and vane types are generally more high speed. If you know what the flow rate of you tractor is, you could determine what the output speed would be. Of course the only way to vary the speed is to change the rpms of your tractor. You could plumb in a speed valove that diverts a portion of the flow back to the tank, but that will add extra cost and complication.

A hydrostatic transmission would be another good choice. Usually readily available in lawn equipment, and that would give you variable speed and even reversing. It would still more than likely require additional gear reduction.

One thing I didn't think of earlier is that any ground driven spreader I've ever dealt with (yeah, I'm that old) has a variable speed built into it. Usually there is a ratchet system that changes the number of teeth picked up by each ratchet motion. Might want to look your mechanism over a bit closer. Your answer may be ri8ght there.

[jedidiahwiebe]

Clavius. Really helpful. This is great. This is what I was hoping to get an understanding of. I like what you said about what I should do should be within my capabilities. Truly installing a gasser motor and some gearboxes + pulleys is well within my capabilities. However the other option may not be. To be honest I usually do get a kick out of taking on projects that are beyond my capabilities. It's generally an anuual event here. But I just got a call back from Kubota and they claim that installing rear remotes (or accessory valves whatever kubota calls them?) will run me 1100 canadian dollars. Yuck.

I'm making progress tho. Have made contact with various salvage guys... gonna see what they've got for gearboxes and pulleys.

[jedidiahwiebe]

ibdennyak Thank you this is also very very helpful. It is feeling so much closer within my grasp now. Actually variability in tractor rpm might just give me enough variability of flow rate. I still have to price out both possible system designs.

Yes my ground driven spreader does have the ratchet system. I am quite familiar with that part of the maching. However even at max speed it's slightly less than half the rpm I need on the apron chain driveshaft.

[ibdennyak]

Would it be possible to speed it up somehow? Either change a few sprockets, or increase the stroke of the ratchet????? Just spitballing here.....been a while. That might be cheaper and easier than anything else.

[jedidiahwiebe]

Wouldn't that be great. I have wracked my brain for a few years tryin a figure that out. I'll post a pic for you see if you see any way to speed it up.

[jedidiahwiebe]

Here's a vid of the ground drive system

[clavius]

If doing it with an engine and pulleys is the approach you are most familiar and comfortable with, then that is a perfectly good reason to use that approach. The cool stuff about these projects is that there are lots of right answers and you pick the one that works best for your situation.

A few other thoughts:

The suggestion made by ibdennyak of using a hydrostatic transmission from an old lawn tractor is a really good one. If you drive that with your gas engine (which is what it was designed for in the first place anyhow) the output side will give you variable speed and chances are good that the speed range will be much closer to what you want for your feeder anyhow. You can tweak the final speed range with pulleys, etc. Excellent suggestion I think.


Thanks for the video of how the wheel drive works. Interesting mechanism, thanks for educating me on that.

As for the three lobed cam on the wheel drive setup, rather than making the ratchet move more teeth each throw, could you make that into a six lobed cam so it moves twice as often? Or maybe move the cam off of the wheel axle onto its own shaft that is chain driven off the wheel at twice the speed? I suppose you could add levers to make the throw twice as long, not sure how easy that would be.

You could always cut some scale linkages out of cardboard, nail them to a piece of wood and try adding stuff to mess around with different arrangements. Sort of a backyard CAD system.

Fun stuff just to think about.

[jedidiahwiebe]

This is the most astonishing thing about asking for help in these kind of forms. I never would have thought of that!