Hydraulic motor sizing - weird project

[Industrial Toys]

I'm guessing that the wheel motors off most equipment would be a sought after scrap item.

 

[oldnslo]

Thank you for those calculations oldnslo. That is very helpful. Boy do I know there's a lot to think about with this project. Fortunately most of it I am qualified to figure out. Hydraulics is not one of those things.

So would I need a 40gpm pump to power those motors if that was its only task? Would that require a 50 gallon reservoir? That is more weight than I had hoped to carry. . Is there a way to cool the fluid other than that mass of fluid?

I am thinking the steering would be similar to a zero turn mower. And that the wheel motor speed and rotation direction would be controlled by flow control motor valves.

Do I need brakes? Or will reducing flow to the motors work?

With the 1000 cc motors you would need approx 16 GPM to operate at 60 RPM. You might want to consider a double pump so you have one for each wheel. This ensures that you have power to both wheels and eliminates the need for some type of flow divider.

For steering you have to limit flow to one wheel. This can be done via a good metering directional valve the twould allow you to control both forward and reverse directions.

Yes you will require hydraulic dynamic braking. With hydrostatic drive the drive system is also the braking system. With open loop (gear pumps)This is typically performed with counterbalance valves. These valves are designed to prevent loads from running away.

There are some companies that build planetary drive assemblies that incorporate the motor, counterbalance, gear reduction, and parking brake all in one package. I think PMP is one of these companies but have zero experience with them. I believe that there may also be some options for counterbalance manifold that mounts directly on some wheel motors. Again no experience with these either.

Oil cooling. How long will you be driving this on land. If just short time cooling may not be to much of a concern.

Reservoir sizing: Again lots of factors like drive time, heat generation from pressure losses, etc.

Hopefully this info makes sense and will help you decide on a system.

 

[cmaas]

Thanks. I like the idea of looking for salvaged parts. Around here anyway people seem to think those little excavators are made of gold so I imagine parts will cost more from them than new stuff from Surplus Center. I'll keep an eye out though. Good idea.

I壇 look for a scraped mini trackhoe, manlift, or tracked skid for donor motors. They値l already have a planetary and be plenty strong enough. It might be easier to get a truck rear and and drive the yoke with either a single electric or hydraulic motor.

 

[MossRoad]

I plan to build a amphibious barge to transport an electric car (Fiat 500). The car's 110hp electric motor will provide the motive power to the water propeller (sterndrive) and to the land drive wheels. I want to run the drive wheels with two hydraulic wheel mounted motors and am having trouble figuring out how to size them. Online calculators are just confusing me at this point so I'm hoping someone here can give me some advice.

I would like this thing to travel at about 4mph up a 23% slope. The complete package will weigh about 5,500 lbs. My engineering student friend tells me it will take 1,420 ft. lbs. of torque just to hold my place on the hill so I will need some amount more to actually move.

I plan to use 22" diameter tires which I think means they will rotate at 25rpm to travel 4mph.

What I don't understand is how to get that high torque and low rpm from a wheel motor? I mean if I have a motor with a rated torque of 1,400 in. lbs. at 500rpm does the torque go up as load increases and rpm decreases?

Thanks for any help. I imagine this falls under the stupid question heading but I am just not grasping it.

How are you planning to transfer the power from the electric car to the stern drive unit and the land drive wheels?

 

[cmaas]

The short answer is that the electric car drive wheels will turn 12" dia. rollers that are mounted to a 4:1 gear ratio differential. The differential input shaft turning up to 4000rpm ( and welded solid) will drive the sterndrive and maybe the hydraulic pump. Or the hydraulic pump might be driven by the diff output shaft - the old diff axle - if I use a 1000rpm PTO mounted pump. That's the basic idea anyway. The devil is always in the details though and that's why I'm here.

How are you planning to transfer the power from the electric car to the stern drive unit and the land drive wheels?

 

[MossRoad]

The short answer is that the electric car drive wheels will turn 12" dia. rollers that are mounted to a 4:1 gear ratio differential. The differential input shaft turning up to 4000rpm ( and welded solid) will drive the sterndrive and maybe the hydraulic pump. Or the hydraulic pump might be driven by the diff output shaft - the old diff axle - if I use a 1000rpm PTO mounted pump. That's the basic idea anyway. The devil is always in the details though and that's why I'm here.

I'd guess you'd be way better off financially and mechanically less complicated to just use a small engine powering one variable volume pump that provides power to two wheel motors that drive the two ground tires, and with diverter valves, power the stern drive with the same pump and a smaller hydraulic motor.

 

[cmaas]

That makes perfect sense, thanks. So those counterbalance valves will act as brakes but since the motors can still leak they won't work as parking brakes? That would be okay because "parked" means the front of the barge is lowered to the ground and it's not going anywhere. Do I look for counterbalance valves that handle flow in two directions? Or do I need two valves per motor?

About cooling -the land motors will usually run for about 5 minutes per trip but it would be good to be able to run for 15 minutes or so at times.

I'm going to add a new element now and say that I would also like to run cylinders off of my pump(s) that control raising and lowering the wheel legs and loading ramp. Those cylinders are not actuated while the motors are running and since they are not all that big I figure the pump sized for the motors can easily handle them.

I read that a gear pump idling will consume about 5% of its full rated power. Since I'm running on a limited battery supply I wonder if it is worth disengaging the pump when it's not being used? The pump is not being used for about 30 minutes of each trip.

With the 1000 cc motors you would need approx 16 GPM to operate at 60 RPM. You might want to consider a double pump so you have one for each wheel. This ensures that you have power to both wheels and eliminates the need for some type of flow divider.

For steering you have to limit flow to one wheel. This can be done via a good metering directional valve the twould allow you to control both forward and reverse directions.

Yes you will require hydraulic dynamic braking. With hydrostatic drive the drive system is also the braking system. With open loop (gear pumps)This is typically performed with counterbalance valves. These valves are designed to prevent loads from running away.

There are some companies that build planetary drive assemblies that incorporate the motor, counterbalance, gear reduction, and parking brake all in one package. I think PMP is one of these companies but have zero experience with them. I believe that there may also be some options for counterbalance manifold that mounts directly on some wheel motors. Again no experience with these either.

Oil cooling. How long will you be driving this on land. If just short time cooling may not be to much of a concern.

Reservoir sizing: Again lots of factors like drive time, heat generation from pressure losses, etc.

Hopefully this info makes sense and will help you decide on a system.

 

[ericm979]

Seems like it'd be simpler, cheaper and more efficient to skip the hydraulics and make it purely mechanical.

Use the roller drive diff output to turn a salvaged automatic transmission (for the torque converter to act as a clutch) which operates the front drive axle.

Also if there's not enough weight on them you might have traction problems with wet front tires on a 23% slope.

 

[MossRoad]

I'd also be leery of casters on a +5000# vehicle, weight balance, and the ability to get enough weight over the casters to provide steering force VS sinking into soft ground.

 

[MossRoad]

That makes perfect sense, thanks. So those counterbalance valves will act as brakes but since the motors can still leak they won't work as parking brakes? That would be okay because "parked" means the front of the barge is lowered to the ground and it's not going anywhere. Do I look for counterbalance valves that handle flow in two directions? Or do I need two valves per motor?

About cooling -the land motors will usually run for about 5 minutes per trip but it would be good to be able to run for 15 minutes or so at times.

I'm going to add a new element now and say that I would also like to run cylinders off of my pump(s) that control raising and lowering the wheel legs and loading ramp. Those cylinders are not actuated while the motors are running and since they are not all that big I figure the pump sized for the motors can easily handle them.

I read that a gear pump idling will consume about 5% of its full rated power. Since I'm running on a limited battery supply I wonder if it is worth disengaging the pump when it's not being used? The pump is not being used for about 30 minutes of each trip.

If you pursue that route, I'd definitely find a way to disengage any hydraulic pumps when not needed. It's unnecessary parasitic loss on your batteries.