Hydraulic motor sizing - weird project

[oldnslo]

the very simplest control system for travel drives is closed loop hydrostatic drives. These provide forward reverse direction, braking, steering without any external valves and have option of proportional displacement control so they could be operated via wired pendant that you bring in the car or potentially a wireless remote control.

Basically a newer skid steer system since a good portion of these are now electro proportional control via a joy stick.

 

[ArlyA]

I'm waiting for photos of this project.

 

[cmaas]

the very simplest control system for travel drives is closed loop hydrostatic drives. These provide forward reverse direction, braking, steering without any external valves and have option of proportional displacement control so they could be operated via wired pendant that you bring in the car or potentially a wireless remote control.

Basically a newer skid steer system since a good portion of these are now electro proportional control via a joy stick.

Thanks, that sounds great. A quick search hasn't gotten me much closer to understanding what components are needed to make such a thing. A complete plug and play system would be ideal, but probably way over my budget - even if such a thing is available

 

[cmaas]

I'm waiting for photos of this project.

Check out the previous page.

 

[oldnslo]

cmaas,
Have you established or determine what size drive motors you will be using for the wheels? With this information we could then figure required pump flow and pressure to achieve desired torque and speed. From this information you could then start looking for pumps. Are there any repair centers for fishing trawlers in your area? The might have some pumps and motors used for winches but no clue if electrical - proportional control or manual control used on fishing trawlers.

Two major manufacturers of hydrostatic pumps are Sauer Danfoss and Rexroth. Both of these companies should have pumps that would fit in your application.

Eaton & Parker are two other companies but not sure if they would have hydrostatic pumps in the size that you are looking for.

 

[cmaas]

cmaas,
Have you established or determine what size drive motors you will be using for the wheels? With this information we could then figure required pump flow and pressure to achieve desired torque and speed. From this information you could then start looking for pumps. Are there any repair centers for fishing trawlers in your area? The might have some pumps and motors used for winches but no clue if electrical - proportional control or manual control used on fishing trawlers.

Thank you for that. I really appreciate your taking the time to advise me.

I like the idea of using hydrostatic drive, but, unless I am not understanding it right, I would need a hydrostatic pump for each wheel and a gear pump for the five wheel and ramp lifting cylinders. I'm pretty sure that will be too pricey for this hobby project. Especially since it has a good chance of being a failure.

I have two 28 cu. in. wheel motors now and I need about 600ft. lb. of torque per wheel to get me up my steepest hill. It's okay if I crawl up that hill at 2mph - the hill is very short.

Here is what I'm thinking might work, leaving out the minor details, like braking, for now:

- 2 28cu. in. wheel motors.
- 1 3.11 cu. in. gear pump. Belt driven w/electric clutch.
- 2 one spool directional motor control valve w/ flow control (It looks like a solenoid controlled valve would be too expensive, though I haven't actually found one yet).
- 1 proportional flow divider.

Any thoughts?

 

[oldnslo]

Cmaas
Yes those components will work
Question need for flow control on motor valves if you have a flow divider feeding them or did you mean a motor valve with good feathering for fine flow control for slow movement, steering, etc.

for braking look at dual counterbalance valves. These are designed to prevent runaway operations and typically work well. Size them as close as possible to full flow through the motor to large a valve and they do not control as well

sun hydraulics is the most common source for counterbalance valves in USA.

Rexroth - Oil Control is another source but as not as popular in the USA.

 

[MossRoad]

Thank you for that. I really appreciate your taking the time to advise me.

I like the idea of using hydrostatic drive, but, unless I am not understanding it right, I would need a hydrostatic pump for each wheel and a gear pump for the five wheel and ramp lifting cylinders. I'm pretty sure that will be too pricey for this hobby project. Especially since it has a good chance of being a failure.

I have two 28 cu. in. wheel motors now and I need about 600ft. lb. of torque per wheel to get me up my steepest hill. It's okay if I crawl up that hill at 2mph - the hill is very short.

Here is what I'm thinking might work, leaving out the minor details, like braking, for now:

- 2 28cu. in. wheel motors.
- 1 3.11 cu. in. gear pump. Belt driven w/electric clutch.
- 2 one spool directional motor control valve w/ flow control (It looks like a solenoid controlled valve would be too expensive, though I haven't actually found one yet).
- 1 proportional flow divider.

Any thoughts?

I have an all hydraulic machine. It has one wheel motor on each corner. There's one variable volume pump that drives two wheel circuits (right front is in series with left rear, left front is in series with right rear, then both of those circuits are in parallel). All 4 wheel motors get the same flow and steering is accomplished by articulation. So you could drive two wheel motors with one pump. That would control speed and direction. I'm not sure how you'd vary the flow to each wheel motor for turning. And yes, you'd need a gear pump for the cylinders.

They make the variable volume pump with one, two or more gear pumps piggybacked on to the VVP. That way only 1 driveshaft is required.

 

[cmaas]

Cmaas
Yes those components will work
Question need for flow control on motor valves if you have a flow divider feeding them or did you mean a motor valve with good feathering for fine flow control for slow movement, steering, etc.

I took flow control to mean variable speed control. It seems like without that motor directional valves are either on or off. Is that wrong? There are a lot more available valves if I'm not looking for the words "flow control".

"A little bit of knowledge is a dangerous thing". Designing hydraulic systems is just what that saying applies to. I read a bit here and a bit there. Often it seems like different terms are used for the same component. The latest thing I read tells me I should use "meter in flow controls". That way I don't need a case drain in the motor. Which my motors don't have.

I am thinking that with a pump that has a 35GPM max that each motor valve will only see 17.5 GPM so a valve that has a 18GPM capacity should work. My motors have a 23.7GPM max.

Sun Hydraulics want me to choose a "pilot ratio" for the counter balance valve. Any thoughts about that?

I guess it's a good thing that this barge is going to be slow. Otherwise this could all be pretty scary.

Thanks again for the help.

 

[cmaas]

I have an all hydraulic machine. It has one wheel motor on each corner. There's one variable volume pump that drives two wheel circuits (right front is in series with left rear, left front is in series with right rear, then both of those circuits are in parallel). All 4 wheel motors get the same flow and steering is accomplished by articulation. So you could drive two wheel motors with one pump. That would control speed and direction. I'm not sure how you'd vary the flow to each wheel motor for turning. And yes, you'd need a gear pump for the cylinders.

They make the variable volume pump with one, two or more gear pumps piggybacked on to the VVP. That way only 1 driveshaft is required.

That's interesting. I'm just starting to understand how the system I've got in mind is going to work so trying to figure out something like yours is making me a little crazy. I guess I could make my back wheels steer if I really wanted to but I'm not sure how the front drive wheels would do without a differential.

 

[MossRoad]

So how is it going to roll? Two axles, one front and one rear, or 4 independent axles, one at each corner?

I see you have two hydraulic motors.

If you go with two axles, one front and one rear, you could put one hydraulic motor on each axle to turn the differentials. Steer with the front or rear as you desire. Then you'd only need one valve to control forward, reverse on the variable volume pump, and one valve to operate a steering ram on the steering axle.

 

[MossRoad]

Hook the two hydraulic motors powering the two axle differentials in series. If one motor starts to slip due to the tires spinning, the other motor will stop it.

 

[oldnslo]

Cmaas
For Sun pilot ratio typically is 8:1 or 10:1 range for motor applications. The old printed books from the 90's had some helpful information in them in a section called technical tips. I suspect Sun put this information on-line for assistance in selecting the correct valve but I am familiar with their website.

The counterbalance valves will apply back pressure to the motors to slow or prevent running away down a slope so you may need case drain lines on the motors. If this is not possible you will have to look at some other form of braking or unwanted motion control.

A gear pump produces flow whenever it is turning and all of this flow is produced at the highest system demand pressure so you in theory can climb the hill using similar power at full speed Vs half speed and be more efficient at full speed since all the pressure is doing work across the motor Vs being bled off across some metering device or relief valve.

You can purchase directional valves with good metering over that flow range but they will not be inexpensive. Proportional Danfoss PVG is a very common valve in various sizes. If you get meter in and meter out style you might want to consider a 4 -ported counterbalance with spring chamber vented directly to tank. This eliminates the potential for valve back pressure causing the counterbalance to go unstable.

I know throwing lots of stuff at you but hopefully some of it is helpful and prevents an oh shucks moment.

 

[cmaas]

So how is it going to roll? Two axles, one front and one rear, or 4 independent axles, one at each corner?

I see you have two hydraulic motors.

If you go with two axles, one front and one rear, you could put one hydraulic motor on each axle to turn the differentials. Steer with the front or rear as you desire. Then you'd only need one valve to control forward, reverse on the variable volume pump, and one valve to operate a steering ram on the steering axle.

Have a look at the photo on page on page 4. Each wheel leg is independent and can pivot up out of the water.

 

[cmaas]

I know throwing lots of stuff at you but hopefully some of it is helpful and prevents an oh shucks moment.

Thanks, that's all helpful information. I am looking at Sun's Dual Counterbalance Assembly with Crossport Relief and Shuttle, 10:1 Pilot Ratio. It seems to be rated at 15gpm which is a little less than I can get from my pump's 35gpm intermittent capacity (after being split by the 50/50 flow divider). Not sure if that's a problem.

I've just had a look at Sun's video about choosing a counterbalance valve. Woah! That was mind bogglingly confusing! I knew I was getting in over my head with this hydraulic stuff but I had no idea just how complex the subject is.

 

[cmaas]

Cmaas
For Sun pilot ratio typically is 8:1 or 10:1 range for motor applications. The old printed books from the 90's had some helpful information in them in a section called technical tips. I suspect Sun put this information on-line for assistance in selecting the correct valve but I am familiar with their website.

I just received my Rexroth counterbalance valves from the Italian distributor. Those guys were great. Good price and got them here in about 2 weeks.
Can you tell me if they can be mounted 2' away from the motors? With hose rather than steel tubing?

 

[oldnslo]

You can mount them with hose but only concern is hose breaks you have lost your braking capability on that motor. Same if steel line breaks.

 

[cmaas]

Here's a dumb question - do C1 and C2 go from the counterbalance valve to the motor or do V1 and V2?

 

[oldnslo]

C1 and C2 go to motor
V1 and V2 go to valve

since counterbalance is more commonly used on cylinders C = cylinder and V = Valve

 

[cmaas]

Thanks.
I'm not sure what's happened to my thread here. I can't see some of the more recent posts.