Hydraulic Dune Buggy Design: Is My Math Correct?

[larkinja]

Its looking really good! One question. I have a Symbols chart here, but some of the symbols don't match exactly. Do you have a chart for the exact symbols you are using? I am attempting to put together a parts list as you add things to the schematic, and this would help me.

Also, as far as the schematic goes, this design uses a variable disp pump. What would be the implications of using an actual hydrostatic pump? Are they basically the same thing only with some of the circuitry built in? I was kind of looking at this pump as a possible candidate.

https://www.surpluscenter.com/item.asp?UID=2228012107004480&item=9-6557&catname=hydraulic

Looking at this as a possible motor. Seems to mathematically fit the bill .

https://www.surpluscenter.com/item.asp?UID=2228012107004480&item=9-7490&catname=hydraulic

Let me know what you think.

Thanks

 

[drankin]

The gerotor motor looks like it will work. The RPM range is there. Working pressure is a tad lower than ideal but I'd say it's a go.

The pump in the schematic is the symbol for a hydrostat (simplified). The Sunstrand that you picked out looks like a perfect fit. Make sure the counter-clockwise input rotation will work with the engine output. See if you can find the cut-sheet and/or manual for the pump.

I'll spec out the valves for you. I plan on designing the manifolds for the valves. Most will be cartridge valves. They are inexpensive and easy to maintain. "www.sunhydraulics.com"[/URL]

Because of the lower pressures we're working with, <3000 PSI, we can use aluminum body components. Brings the weight down.

Just let me know what symbols you have questions about.

I've come up with some ideas for dynamic hydraulic braking I'll include in the next schematic.

 

[RonL]

Its looking really good! One question. I have a Symbols chart here, but some of the symbols don't match exactly. Do you have a chart for the exact symbols you are using? I am attempting to put together a parts list as you add things to the schematic, and this would help me.

Also, as far as the schematic goes, this design uses a variable disp pump. What would be the implications of using an actual hydrostatic pump? Are they basically the same thing only with some of the circuitry built in? I was kind of looking at this pump as a possible candidate.

https://www.surpluscenter.com/item.asp?UID=2228012107004480&item=9-6557&catname=hydraulic

Looking at this as a possible motor. Seems to mathematically fit the bill .

https://www.surpluscenter.com/item.asp?UID=2228012107004480&item=9-7490&catname=hydraulic

Let me know what you think.

Thanks

I have used the surpluscenter for a lot of things and have never been dissapointed.

I would also like to pass this link on to you guys, find out if they have a store near you and if not, you might contact one and order the design manuals that most apply to what you are working on.
The manuals give good rule of thumb examples for calculating use of hydraulic, air and electric power design needs.

http://www.womack-machine.com/education/textbooks.aspx

Ron

 

[larkinja]

I have used the surpluscenter for a lot of things and have never been dissapointed.

I would also like to pass this link on to you guys, find out if they have a store near you and if not, you might contact one and order the design manuals that most apply to what you are working on.
The manuals give good rule of thumb examples for calculating use of hydraulic, air and electric power design needs.

http://www.womack-machine.com/education/textbooks.aspx

Ron

Thanks for the referal on surpluscenter, definitely good to know. Thanks for the education link. I had been looking at getting some books for general knowledge on the subject.

 

[larkinja]

The gerotor motor looks like it will work. The RPM range is there. Working pressure is a tad lower than ideal but I'd say it's a go.

The pump in the schematic is the symbol for a hydrostat (simplified). The Sunstrand that you picked out looks like a perfect fit. Make sure the counter-clockwise input rotation will work with the engine output. See if you can find the cut-sheet and/or manual for the pump.

I'll spec out the valves for you. I plan on designing the manifolds for the valves. Most will be cartridge valves. They are inexpensive and easy to maintain. "www.sunhydraulics.com"[/URL]

Because of the lower pressures we're working with, <3000 PSI, we can use aluminum body components. Brings the weight down.

Just let me know what symbols you have questions about.

I've come up with some ideas for dynamic hydraulic braking I'll include in the next schematic.[/QUOTE]

Just to make sure, the motors will be ok? I am thinking about ordering 1 for now just to do some test fitting with. We are in the process of finalizing the a-arm design, and figuring out the best way to couple the motor shaft to the cv axle, so I would like to have one of the motors in hand to do that with.

Helping us with the valves would be a huge help. Thank you! We had an idea that we are not sure if would be possible/practicle. Thought I would run it by you. I might have mentioned it before, but we are contimplating using a hydraulic steering cylinder to steer the front wheels. Could a single joystick control be used to control both the motors and a steering cylinder? The control would have to be able to steer while the forward and reverse control were in any position. Similar to a computer gaming joystick. Is this possible, at least without costing a lot?

CW rotation shouldn't be a problem. We are going to gear down the engine before going to the pump, so we can reverse rotation if needed.

What exactly do you mean by designing the manifolds?

Lastly, for the valves for free wheel, and hi-speed, will those be dc solonoid type? I would assume that would necessary for timing when switching modes.

The last question of the night is about the resevoir. Am I assuming right that this is still a open circuit? So some sort of tank will be required? How small can this be? Obviously space and weight is an issue. Just trying to figure out where this may need to go. Also, is it possible to do a closed loop, or does that complicate things?

Again, thanks so much for everything you are doing for us. You have no idea how much I appreciate it. We'll have to figure out some way to repay you for your efforts.

 

[drankin]

Just to make sure, the motors will be ok? I am thinking about ordering 1 for now just to do some test fitting with. We are in the process of finalizing the a-arm design, and figuring out the best way to couple the motor shaft to the cv axle, so I would like to have one of the motors in hand to do that with.

Helping us with the valves would be a huge help. Thank you! We had an idea that we are not sure if would be possible/practicle. Thought I would run it by you. I might have mentioned it before, but we are contimplating using a hydraulic steering cylinder to steer the front wheels. Could a single joystick control be used to control both the motors and a steering cylinder? The control would have to be able to steer while the forward and reverse control were in any position. Similar to a computer gaming joystick. Is this possible, at least without costing a lot?

CW rotation shouldn't be a problem. We are going to gear down the engine before going to the pump, so we can reverse rotation if needed.

What exactly do you mean by designing the manifolds?

Lastly, for the valves for free wheel, and hi-speed, will those be dc solonoid type? I would assume that would necessary for timing when switching modes.

The last question of the night is about the resevoir. Am I assuming right that this is still a open circuit? So some sort of tank will be required? How small can this be? Obviously space and weight is an issue. Just trying to figure out where this may need to go. Also, is it possible to do a closed loop, or does that complicate things?

Again, thanks so much for everything you are doing for us. You have no idea how much I appreciate it. We'll have to figure out some way to repay you for your efforts.

The motor looks like it should work fine.

Yep, a hydraulic pilot operated joystick will work in for you. They use these on hydraulic excavators. Look into picking one up at a heavy equipment dealership (Deere, Case-Linkbelt, etc.) parts department. Might be a bit spendy new so see if you can find one used.

Because the circuit is going to require a lot of valving we're going to need a manifold to pack all the cartridge valves in. Otherwise you end up with a bunch of individual valves that you have to hook together with tees/fittings/hose/tubes. It gets really ugly really quick. A single manifold can house several hydraulic circuits into a small package. I'll send you an example later.

All solenoid valves would be DC. Preferably 24VDC but we can go 12VDC.

Never intended this to be an open circuit. I think this would work best as a closed circuit. An air/oil cooler and small reservoir would be req'd.

As far as repayment, you could start by being a contributing member of PF (top, second to left button, "Upgrade"). I think it's around $15/yr. Post some pics so the rest of us here can follow your project.

 

[larkinja]

The motor looks like it should work fine.

Yep, a hydraulic pilot operated joystick will work in for you. They use these on hydraulic excavators. Look into picking one up at a heavy equipment dealership (Deere, Case-Linkbelt, etc.) parts department. Might be a bit spendy new so see if you can find one used.

Because the circuit is going to require a lot of valving we're going to need a manifold to pack all the cartridge valves in. Otherwise you end up with a bunch of individual valves that you have to hook together with tees/fittings/hose/tubes. It gets really ugly really quick. A single manifold can house several hydraulic circuits into a small package. I'll send you an example later.

All solenoid valves would be DC. Preferably 24VDC but we can go 12VDC.

Never intended this to be an open circuit. I think this would work best as a closed circuit. An air/oil cooler and small reservoir would be req'd.

As far as repayment, you could start by being a contributing member of PF (top, second to left button, "Upgrade"). I think it's around $15/yr. Post some pics so the rest of us here can follow your project.

Great, I will start looking for one of those. I would think it would have to fall in a particular gpm range correct? What values do you think I would be safe with? Seems the pump may be pushing close to 70gpm at times. Is there a particular kind that I would need that will work with both the motor circuits AND a steering cylinder?

Is there a disadvantage to using 12v vs 24v. The engine ignition and charging system, headlights, radios, etc. will all be 12v, so it would seem to make the most sense to use 12v, but if there is a big disadvantage, we can implement a 24v system as well, just complicates things a little, and adds another battery to the vehicle.

I am officially a contributing member now. :) I will get pics up soon. I intended to take some shots when I was out there Thursday (We work on these projects every Thursday), but I had not realized the battery in my camera had died, so I will get some soon, promise.

 

[drankin]

Great, I will start looking for one of those. I would think it would have to fall in a particular gpm range correct? What values do you think I would be safe with? Seems the pump may be pushing close to 70gpm at times. Is there a particular kind that I would need that will work with both the motor circuits AND a steering cylinder?

Is there a disadvantage to using 12v vs 24v. The engine ignition and charging system, headlights, radios, etc. will all be 12v, so it would seem to make the most sense to use 12v, but if there is a big disadvantage, we can implement a 24v system as well, just complicates things a little, and adds another battery to the vehicle.

I am officially a contributing member now. :) I will get pics up soon. I intended to take some shots when I was out there Thursday (We work on these projects every Thursday), but I had not realized the battery in my camera had died, so I will get some soon, promise.

Because the pilot operated joystick is used for piloting (signalling larger components/valves), it is a low flow component. It will drive the pump swash plate with the forward and reverse operation and the steering valve (that in turn drives the steering cylinder) with the right to left operation. It is basically four variable pressure reducing valves, one at 12, 3, 6, & 9 oclock. All it does is regulate pressure, the flow capacity is very low in the area of .25-.5 GPM max in the 0-500 PSI range.

12VDC is fine. I usually work with 24VDC components when working on mobile hydraulics. It's typical with mobile hydraulic equipment. The solenoid coils are smaller, wiring is gauge can be smaller, etc.

Welcome to contributor status!

 

[larkinja]

So would this be the type of componant?

https://www.surpluscenter.com/item.asp?UID=3524012417295912&item=9-7720&catname=hydraulic

or mor like this one?

https://www.surpluscenter.com/item.asp?UID=3524012417295912&item=9-6704-JS&catname=hydraulic

Then this would control 2 different valves? One for steering and one for the motors? I don't know if any of the valves on that site will work. The pump has a 12vdc solonoid on it. What does that do? Does that operate the swashplate, or something else?

 

[drankin]

So would this be the type of componant?

https://www.surpluscenter.com/item.asp?UID=3524012417295912&item=9-7720&catname=hydraulic

or mor like this one?

https://www.surpluscenter.com/item.asp?UID=3524012417295912&item=9-6704-JS&catname=hydraulic

Then this would control 2 different valves? One for steering and one for the motors? I don't know if any of the valves on that site will work. The pump has a 12vdc solonoid on it. What does that do? Does that operate the swashplate, or something else?

The first one, https://www.surpluscenter.com/item.asp?UID=3524012417295912&item=9-7720&catname=hydraulic, is the one you want. See the 4 buttons on top? That's the four reducing valves. GOOD PRICING.

I need more info on that pump, spec sheet. Don't know what the solenoid is for. I'm pretty sure we can hydraulically actuate that swashplate. A single joystick will control the pump and steering. The two buttons at 12 & 6 oclock control the pump and the 9 & 3 oclock control the steering. We need spec sheets for all these components so we can verify everything will work together.

 

[drankin]

Here is the spec sheet for that joystick. This shows the handle and buttons as well but I just need the hydraulic performance information. If you can find spec sheets like these for the other components it would help a lot.

 

[drankin]

Found out what that solenoid is for. EDC stands for Electronic Displacement Control. So the hydraulic joystick won't work for it as is. Depending on how the pump uses EDC we may be able to disable it and go direct hydraulic. Need more info though. Because Sunstrand is no longer around you might have to try a pump repair shop for info on that pump. I couldn't find anything with Google.

 

[larkinja]

Found out what that solenoid is for. EDC stands for Electronic Displacement Control. So the hydraulic joystick won't work for it as is. Depending on how the pump uses EDC we may be able to disable it and go direct hydraulic. Need more info though. Because Sunstrand is no longer around you might have to try a pump repair shop for info on that pump. I couldn't find anything with Google.

Ya, I'm having trouble finding info on the pump too. I'l keep digging to see what I can find.

 

[larkinja]

I called about a half dozen places today with no luck. The pump has been discontinued. One guy told me that parts were not available for it. Would this mean I should stay away from it? I'm worried that if we have to replace parts, we won't be able to get any. Do you know of any pumps that might work that aren't such a mystery that would be in the same price range?

 

[RonL]

I called about a half dozen places today with no luck. The pump has been discontinued. One guy told me that parts were not available for it. Would this mean I should stay away from it? I'm worried that if we have to replace parts, we won't be able to get any. Do you know of any pumps that might work that aren't such a mystery that would be in the same price range?

That is one problem with buying from surplus dealers, too often they bid on product lines that for one reason or another have been discontinued and most of the time repairs or replacment parts can't be found.
For expirmenting or one off design work its not anything to worry with and the prices can save a bit of money.
If the plan is to build a business and sell product, you have to find and use parts and suppliers that will be around to keep your business going.

Ron

 

[larkinja]

That is one problem with buying from surplus dealers, too often they bid on product lines that for one reason or another have been discontinued and most of the time repairs or replacment parts can't be found.
For expirmenting or one off design work its not anything to worry with and the prices can save a bit of money.
If the plan is to build a business and sell product, you have to find and use parts and suppliers that will be around to keep your business going.

Ron

I'm not after selling anything, I just want to make sure I don't spend $1100 and have to toss it in the scrap pile 3 months from now. I'm curious what the reference point is though? What would a similar pump cost that is current? If I can buy three of the $1100 ones for one of the current pums, then it is worth getting the old one. If it's a smaller difference or something, then I would go with a newer one.

Maybe I should go about it this way. What would a typical life of a pump like this be. Or how soon before it needs rebuilding? Because at that point it would be time for a new one since parts aren't available.

 

[drankin]

I'm not after selling anything, I just want to make sure I don't spend $1100 and have to toss it in the scrap pile 3 months from now. I'm curious what the reference point is though? What would a similar pump cost that is current? If I can buy three of the $1100 ones for one of the current pums, then it is worth getting the old one. If it's a smaller difference or something, then I would go with a newer one.

Maybe I should go about it this way. What would a typical life of a pump like this be. Or how soon before it needs rebuilding? Because at that point it would be time for a new one since parts aren't available.

Look into a newer one. Check with some fluid power houses in your area. Berensen or Hydrapower Systems are reputable. Usually they have some competent techs to help you out with your application. A good pump will last years if the system is designed well and it's not abuse.

 

[drankin]

Updated Schematic

Haven't gotten to the controls yet.

 

[larkinja]

Look into a newer one. Check with some fluid power houses in your area. Berensen or Hydrapower Systems are reputable. Usually they have some competent techs to help you out with your application. A good pump will last years if the system is designed well and it's not abuse.

You had said that the pump we were looking at was of good size. Do you think it is to big? Someone made a comment to me yesterday that the pump was to big for what I want to use it for. They mentioned that it could produce 300 peak hp. Since the engine driving the buggy is only around 200, am I oversizing the pump to much. The math says it is about right, I'm just wondering. If I am going to be looking at a more expensive pump, there is no reason to spend more than is necessary.

Thanks for any input you may have on this.

 

[larkinja]

Updated Schematic

Haven't gotten to the controls yet.

The schematic is looking good. I think I am following it :) For the manifolds, I take it when you said you will design it, that means once everything is set to go someone will manufacture the manifold for us based on your design?

Thanks again.

 

[drankin]

You had said that the pump we were looking at was of good size. Do you think it is to big? Someone made a comment to me yesterday that the pump was to big for what I want to use it for. They mentioned that it could produce 300 peak hp. Since the engine driving the buggy is only around 200, am I oversizing the pump to much. The math says it is about right, I'm just wondering. If I am going to be looking at a more expensive pump, there is no reason to spend more than is necessary.

Thanks for any input you may have on this.

It comes down to flow and pressure (and RPM range). You want 60-80 GPM @ 2500-3000 PSI. That's a HP requirement of 87-140 HP. That pump was a little big but the price was nice.

 

[drankin]

The schematic is looking good. I think I am following it :) For the manifolds, I take it when you said you will design it, that means once everything is set to go someone will manufacture the manifold for us based on your design?

Thanks again.

Yep, I plan on designing the manifold and drawings. I would suggest "www.hpsx.com"[/URL] to manufacture it. They've made dozens of manifolds for me over the years and have a top notch machine shop.

 

[larkinja]

Yep, I plan on designing the manifold and drawings. I would suggest "www.hpsx.com"[/URL] to manufacture it. They've made dozens of manifolds for me over the years and have a top notch machine shop.[/QUOTE]

Excellent. Any ballpark idea on what it costs to have that done?

 

[larkinja]

It comes down to flow and pressure (and RPM range). You want 60-80 GPM @ 2500-3000 PSI. That's a HP requirement of 87-140 HP. That pump was a little big but the price was nice.

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?

 

[drankin]

Excellent. Any ballpark idea on what it costs to have that done?

Maybe around $1000.

 

[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.