Hydraulic Dune Buggy Design: Is My Math Correct?

[drankin]

What do you think our chances are of properly making the pump work without any additional data? A comparable pump locally is about $3800. We could buy three of the surplus pumps and still have money left over in comparison. Do you think we should think about trying it, or would that be opening a can of worms?

Do we want to use a single joystick to run both the steering and pump swash plate? That's the first thing to consider. With the EDC we will need some data on how to drive it. We wouldn't be able to use the rexroth joystick for pump control. Basically, we need to decide on how we are going to interface the controls to it.

If using different pumps they need to have the same interface specs. Pump flange, shaft style, rotation, etc. Not to mention the pump controls.

 

[larkinja]

Do we want to use a single joystick to run both the steering and pump swash plate? That's the first thing to consider. With the EDC we will need some data on how to drive it. We wouldn't be able to use the rexroth joystick for pump control. Basically, we need to decide on how we are going to interface the controls to it.

If using different pumps they need to have the same interface specs. Pump flange, shaft style, rotation, etc. Not to mention the pump controls.

So with the electronic control, does that mean that whatever type of control is used would be all electrical? I guess I am not sure exactly what that means. Would it be some sort of control that increased voltage as it moves further? If so, is there some sort of electic joystick that could be used, or maybe a foot pedal that is electrically controlled. I guess I need some advise at this point. I really would like to use the cheaper pump if possible.

 

[drankin]

So with the electronic control, does that mean that whatever type of control is used would be all electrical? I guess I am not sure exactly what that means. Would it be some sort of control that increased voltage as it moves further? If so, is there some sort of electic joystick that could be used, or maybe a foot pedal that is electrically controlled. I guess I need some advise at this point. I really would like to use the cheaper pump if possible.

The Sunstrand pump is electronically controlled, proportional over hydraulic. We need documentation so we can interface with it. We may be able to bypass the EDC and drive it with the joystick hydraulically. If we can't then we will need a separate electronic joystick or foot pedal. For steering it would be ideal to use the hydraulic joystick or a hydraulic steering wheel. If you really want to use that pump and we can't bypass the EDC it would probably be better to go with an electronic footpedal and a hydraulic steering wheel assembly.

 

[larkinja]

The Sunstrand pump is electronically controlled, proportional over hydraulic. We need documentation so we can interface with it. We may be able to bypass the EDC and drive it with the joystick hydraulically. If we can't then we will need a separate electronic joystick or foot pedal. For steering it would be ideal to use the hydraulic joystick or a hydraulic steering wheel. If you really want to use that pump and we can't bypass the EDC it would probably be better to go with an electronic footpedal and a hydraulic steering wheel assembly.

So basically buying the pump would be a bit of a gamble, but if it works, would pay off big. Steering is a little less of a concern for me. I like the joystick idea, but at worst case, we have other options. One, we can use a orbital valve and a steering wheel. We can also use a traditional steering column and rack and pinion. So we have options there.

Doing it all with a joystick just seems like such a cool idea. Although I still don't know how it would be to drive. I think about when you go over a big bump, normally you hold on to the steering wheel pretty tight. With this, that won't be an option. Obviously we will be strapped in with a 4 or 5 point harness, but we won't how it would be to drive till we try it.

 

[larkinja]

So basically buying the pump would be a bit of a gamble, but if it works, would pay off big. Steering is a little less of a concern for me. I like the joystick idea, but at worst case, we have other options. One, we can use a orbital valve and a steering wheel. We can also use a traditional steering column and rack and pinion. So we have options there.

Doing it all with a joystick just seems like such a cool idea. Although I still don't know how it would be to drive. I think about when you go over a big bump, normally you hold on to the steering wheel pretty tight. With this, that won't be an option. Obviously we will be strapped in with a 4 or 5 point harness, but we won't how it would be to drive till we try it.

I posted at new topic on a different forum for more info on the pump. There have been some helpful answers already. Take a look and let me know if this is helpful. Looks like the specs we are going off may be wrong too according to one person. Looks like not a big deal though.

http://forums.hydraulicspneumatics.com/eve/forums?a=tpc&s=4721063911&f=8621030121&m=863102353&r=421104353#421104353

 

[larkinja]

Also, I talked to an engineer at Sauer Danfoss today, and it sound like he has everything we need. He is going to send me an email with some info. When I get that, can I forward it on to you, or maybe you can tell me what questions I need to ask.

He is also going to spec an equivalent pump for us as well. He said the pump we are looking at is closest to their Series 90 pumps. The pump we are looking at has a packard connector, and has an input on 11mA.

 

[drankin]

So basically buying the pump would be a bit of a gamble, but if it works, would pay off big. Steering is a little less of a concern for me. I like the joystick idea, but at worst case, we have other options. One, we can use a orbital valve and a steering wheel. We can also use a traditional steering column and rack and pinion. So we have options there.

Doing it all with a joystick just seems like such a cool idea. Although I still don't know how it would be to drive. I think about when you go over a big bump, normally you hold on to the steering wheel pretty tight. With this, that won't be an option. Obviously we will be strapped in with a 4 or 5 point harness, but we won't how it would be to drive till we try it.

I agree, I don't think a joystick would work as well in a fast moving, bumpy vehicle.

 

[drankin]

Also, I talked to an engineer at Sauer Danfoss today, and it sound like he has everything we need. He is going to send me an email with some info. When I get that, can I forward it on to you, or maybe you can tell me what questions I need to ask.

He is also going to spec an equivalent pump for us as well. He said the pump we are looking at is closest to their Series 90 pumps. The pump we are looking at has a packard connector, and has an input on 11mA.

The 90 Series hydrostatic pumps are top notch. I've used these once before. There is an option for hydraulic control of the swash plate. This is preferred.

But we will have to upgrade the drive motors as well. Sauer also offers a 90 Series motor that can work at the higher pressures. With higher pressure we can go with lower flows, smaller displacement components.

 

[larkinja]

I think I am going to use series 2000 motors model 105-1002-006. These are wheel motors. We are going to build them into the a-arms and trailing arms, and get rid of the axles altogether. They have a max pressure of 4500psi, so should be better overall in performance. There going to cost more, but I think its worth it.

I have been doing a bit of thinking on our circuit. The idea of a high speed circuit seems to be making less sense to me. Even in the 4 wheel drive mode, the speed is simply going to be limited by the rpm limit of the motor I think. So dumping more flow to just the backs really isn't going to do anything is it? The pump is capable of producing enough flow to drive all 4 motors to their max rpm right? If that is true, then it seems there is no point in the circuit.

I am also theorizing a little here, but if all 4 motors were simply put in parallel, with no flow dividers, the fear was that in low traction only 1 motor might be spinning. Here is my question. If the pump is trying to push 80gpm into just 1 motor, and that motor is only good for about 20gpm, what is going to happen to the rest of the flow? I understand that there is a relief in the motor, but wouldn't some of that flow want to go to the other motors before being forced through the releif port. Would this naturally give us a limited slip effect?

Let me know what your thoughts are on this. I am realizing how much these rotory flow dividers are going to cost that can handle the flow we need, plus on top of that all the valves and the custom manifold. I haven't come up with an estimated cost for all this yet, but it is looking like several thousand dollars, and I am just wondering if it is worth it. Part of me is thinking let's just hook it up in parallel, and see what happens, then adjust from there.

What do you think?

 

[drankin]

I think I am going to use series 2000 motors model 105-1002-006. These are wheel motors. We are going to build them into the a-arms and trailing arms, and get rid of the axles altogether. They have a max pressure of 4500psi, so should be better overall in performance. There going to cost more, but I think its worth it.

I have been doing a bit of thinking on our circuit. The idea of a high speed circuit seems to be making less sense to me. Even in the 4 wheel drive mode, the speed is simply going to be limited by the rpm limit of the motor I think. So dumping more flow to just the backs really isn't going to do anything is it? The pump is capable of producing enough flow to drive all 4 motors to their max rpm right? If that is true, then it seems there is no point in the circuit.

I am also theorizing a little here, but if all 4 motors were simply put in parallel, with no flow dividers, the fear was that in low traction only 1 motor might be spinning. Here is my question. If the pump is trying to push 80gpm into just 1 motor, and that motor is only good for about 20gpm, what is going to happen to the rest of the flow? I understand that there is a relief in the motor, but wouldn't some of that flow want to go to the other motors before being forced through the releif port. Would this naturally give us a limited slip effect?

Let me know what your thoughts are on this. I am realizing how much these rotory flow dividers are going to cost that can handle the flow we need, plus on top of that all the valves and the custom manifold. I haven't come up with an estimated cost for all this yet, but it is looking like several thousand dollars, and I am just wondering if it is worth it. Part of me is thinking let's just hook it up in parallel, and see what happens, then adjust from there.

What do you think?

The motor will rotate beyond its rpm rating. This will shorten the life or damage the motor. If you run on anything other than a flat surface you are going to have a heck of a time getting around. As soon as one wheel is off the ground you will lose power to the other three wheels and over-speed the one motor.

Maybe consider getting a smaller pump. Then for lower speeds you have 4WD where it's needed. At higher speeds you would only need 2WD.

Also, you could look at a series/parallel circuit. Run the right rear to the left front and vica-versa. Then the motors themselves act as a flow divider. you would need both corner wheels to lose traction in order to have a runaway condition. It's not a perfect setup flow wise because there is some loss of fluid to the case drain for each motor and the rear wheels will tend to push the front but it would work with minimal hydraulics. You will still need some check valves in between to protect the front motors from cavitation.

 

[larkinja]

How does series work in a hydraulics? If two motors are put in series, do the motors still put out the same amount of torque and rpm. Would it be possible to have the two rear motors in series creating a posi effect on the rear, and then have the front 2 in parallel giving a open differential effect?

Any chance you could give me an idea of what all the components should cost, the way you have it drawn?

 

[larkinja]

Actually torque would be half or rpm doubled wouldn't it?

 

[larkinja]

Also, you could look at a series/parallel circuit. Run the right rear to the left front and vica-versa. Then the motors themselves act as a flow divider. you would need both corner wheels to lose traction in order to have a runaway condition. It's not a perfect setup flow wise because there is some loss of fluid to the case drain for each motor and the rear wheels will tend to push the front but it would work with minimal hydraulics. You will still need some check valves in between to protect the front motors from cavitation.

How would this be plumbed?

 

[drankin]

How would this be plumbed?

There are trade-offs when you try to cut corners. Your power to the drive motors would be half and the max speed would double in this configuration with a given size pump.

One side of the pump goes into one motor, from that motor to another motor, out to the other side of the pump.

 

[drankin]

To compensate, you would double the motor size.

 

[larkinja]

would it be possible to put all 4 motors in parallel with a flow control at each motor. Could this limit the flow to one individual motor, forcing the remaining flow to the rest of the motors?

Just a thought, trying to come up with some alternatives.

 

[drankin]

would it be possible to put all 4 motors in parallel with a flow control at each motor. Could this limit the flow to one individual motor, forcing the remaining flow to the rest of the motors?

Just a thought, trying to come up with some alternatives.

You'll never get them all set exactly. It will make the system very inefficient and possibly give you a heat issue,.

 

[larkinja]

You'll never get them all set exactly. It will make the system very inefficient and possibly give you a heat issue,.

Do you see any possible alternatives, or should we just continue the way we had planned? If so, do you have some examples of the flow dividers, and the valves used in the circuit so I can start pricing them out?

What else has to be put into the circuit yet?

One other question. Is the pump going to control the direction of the motors, or are you talking about using controls outside the pump to control the direction. Do rotary flow dividers work in 2 directions?

 

[larkinja]

Here is a picture of the frame the way it sits. Haven't done much to it till we figure out what components we are using. Once we figure out the hyd motors, we can build the suspension.

 

[drankin]

Do you see any possible alternatives, or should we just continue the way we had planned? If so, do you have some examples of the flow dividers, and the valves used in the circuit so I can start pricing them out?

What else has to be put into the circuit yet?

One other question. Is the pump going to control the direction of the motors, or are you talking about using controls outside the pump to control the direction. Do rotary flow dividers work in 2 directions?

Google "hydraulic gear flow divider". Casappa has a good selection in our flow range.

Typically there is a hot-oil "flushing" circuit that circulates oil thru the pump case. I haven't added that yet. Usually you include the motors in the flushing circuit too but I think we can go without that.

The pump controls the oil direction as the swash plate is tilted. Max tilt is max flow in one direction then as it tilts toward zero flow is reduced until it crosses 0deg then flow begins to flow the other direction while flow enters the pump from the opposite port (from the motors). The pump swash is controlled by the pilot valve. In this case the pilot valve would be a joystick or footpedal.

The gear flow dividers are bidirectional (typically).

 

[drankin]

Here is a picture of the frame the way it sits. Haven't done much to it till we figure out what components we are using. Once we figure out the hyd motors, we can build the suspension.

Nice looking frame! How much does the engine weigh?

 

[larkinja]

Nice looking frame! How much does the engine weigh?

Thanks. The engine fully dressed weighs about 500lbs. The pump 220lbs, total of 4 motors, 84lbs. Wheels and tires, 120lbs. Frame so far weighs 180lbs but that will go up. Originally we planned 2000-2500lbs with 2 adults, so we'll see how close we come.

 

[drankin]

Thanks. The engine fully dressed weighs about 500lbs. The pump 220lbs, total of 4 motors, 84lbs. Wheels and tires, 120lbs. Frame so far weighs 180lbs but that will go up. Originally we planned 2000-2500lbs with 2 adults, so we'll see how close we come.

Do you use any 3D CAD softwares?

 

[larkinja]

Do you use any 3D CAD softwares?

No, not yet. I have autocad inventor on my laptop, but haven't tried anything with it yet. I own a sign company, and do most of the designing here, so I am pretty good with design software, I just need to take some time and learn autocad. Pretty much all of the concepts, I sketch out on paper, and some parts I draw in CorelDraw. When we have parts laser cut, I use Corel, and convert to a dwx.

 

[drankin]

A manifold example.

 

[larkinja]

A manifold example.

Gotcha, now the flow dividers will be part of that, or the output of the flow dividers will go into the manifold?

 

[drankin]

Gotcha, now the flow dividers will be part of that, or the output of the flow dividers will go into the manifold?

Yeah, we could make the manifold attach to the flow divider with short sections of tube or flange adapters.

 

[larkinja]

Do you think this could help us in any way? Looked interesting. Didn't know if it could simplify our design in any way. It can handle 52gpm and 6000psi.

 

[drankin]

Do you think this could help us in any way? Looked interesting. Didn't know if it could simplify our design in any way. It can handle 52gpm and 6000psi.

That's a neat circuit but since we are running four motors in parallel we would need 3 of them in a cascaded arrangement. And you wouldn't be able to switch it on the fly. It would be like an older 4wd pickup to where you have to come to a stop, switch it, and then run. And then keep your speed low and watch your fluid temperature.

Looking at this did give me some ideas on how to restrict a runaway wheel without using a flow divider and still run all motors in parallel. We could use pressure compensated flow controls on the motor outlets that are set very high to where they don't engage unless the flow is excessive. The issue is that the dynamics will be unpredictable and that can be scary at high speeds. There could be some pressure spiking and lurching of the wheels as the system tries to stabilize causing a loss of traction and control.

A gear flow divider is the best way to go in my opinion.

 

[larkinja]

That's a neat circuit but since we are running four motors in parallel we would need 3 of them in a cascaded arrangement. And you wouldn't be able to switch it on the fly. It would be like an older 4wd pickup to where you have to come to a stop, switch it, and then run. And then keep your speed low and watch your fluid temperature.

Looking at this did give me some ideas on how to restrict a runaway wheel without using a flow divider and still run all motors in parallel. We could use pressure compensated flow controls on the motor outlets that are set very high to where they don't engage unless the flow is excessive. The issue is that the dynamics will be unpredictable and that can be scary at high speeds. There could be some pressure spiking and lurching of the wheels as the system tries to stabilize causing a loss of traction and control.

A gear flow divider is the best way to go in my opinion.

Ok, just a thought.