Hydraulic Dune Buggy Design: Is My Math Correct?

[RonL]

I can't say I totally understand how the outlet pressure can be higher than the in.

I think that can happen when a cylinder has what I would call a run away load, it acts as a pump and can pull a strong suction against the flow divider.

 

[drankin]

I can't say I totally understand how the outlet pressure can be higher than the in.

Actually, the outlet can be "intensified". Take a 2 section flow divider for example. If one of the sections has no load then you now have the inlet area of two motors rotating and providing a load to the outlet area of one section. This can effectively double the pressure output of that section if that much load is present.

 

[drankin]

Update: I've talking to an associate that works with hydrostats circuits often. He is going to pass on a circuit that will give you "posi" without a flow divider that kicks in when needed. I'll redraw the schem when I get the circuit.

 

[larkinja]

OK, sounds really good. Can't wait to see it!

 

[drankin]

I just received the circuit from him. It's pretty clever. He included a comment about your engine:

"When you mentioned that this project is using a 200hp engine, does this engine have a governor? I think it is very important to use an engine governor when running hydraulic pumps with varying loads."

 

[larkinja]

I just received the circuit from him. It's pretty clever. He included a comment about your engine:

"When you mentioned that this project is using a 200hp engine, does this engine have a governor? I think it is very important to use an engine governor when running hydraulic pumps with varying loads."

Great, I am excited to see it.

The engine does have a governor on it, and we can flash the computer to set that to whatever we want. Also, we are going to drive the pump with a re-drive, so we can make any ratio we want. ie when the engine is at 4000rpm, the pump could see 2000rpm, or whatever makes the most sense. We have to do some calculating to figure that out, but the peak horsepower of the engine is around 4000, so maybe we'll govern it to 4500, and have the pump see 3000 for a ratio of 1.5:1. Something like that. This should up the torque output as well.

 

[drankin]

larkinja, this is the circuit we've been looking for. It's a load-sensing circuit using logic elements that "talk" to each other and distributes the load across all drive motors. This keeps all drives rotating at the same speed when the circuit is activated (low speed, climbing, mud, etc.). And it can be de-activated when "positraction" is not required. I'll finish drawing the schematic tonight and post it.

 

[larkinja]

larkinja, this is the circuit we've been looking for. It's a load-sensing circuit using logic elements that "talk" to each other and distributes the load across all drive motors. This keeps all drives rotating at the same speed when the circuit is activated (low speed, climbing, mud, etc.). And it can be de-activated when "positraction" is not required. I'll finish drawing the schematic tonight and post it.

Sounds good, thank you!

 

[drankin]

Do you have a local fluid power shop that you are working with?

 

[larkinja]

Yes, a few of them. We ordered the motors from Applied Industrial Tech. I have also been working with Sunsource on some stuff.

 

[drankin]

Here is the latest schematic.

 

[larkinja]

Here is the latest schematic.

Sorry, I completely missed this post. Looks interesting. How would the controls for this work. Would it just be a switch that activates it. I'm not sure I understand how it would activate when needed. What type of valves would these be?

Thanks again for this, and sorry I didn't respond right away. I have been super busy with work and got a little distracted. We should be finishing the suspension this next week, and then we will begin mounting the engine and pump. The motors should come in in a week or so. We have the spindles made and the motors are ready to be mounted as soon as they come in. We already have the wheel hubs for the motors, so we could have a rolling chassis in a couple weeks. :)

Anyway, I would like to start researching the parts needed for your drawing, so let me know what I will need.

Will this be a cartridge system with a manifold, or just simply plumbing?

Thanks again.

 

[larkinja]

Also, in case this may be of use in your schematic. We are considering using a PLC to control the pump and the steering circuit, so there is a possibility that we could control this circuit with the PLC as well, once I understand how this circuit works. One of my buddies programs PLC's for a living and is very good at it, so hopefully will be an option.

 

[drankin]

Ah, you didn't disappear!

The schematic shows normally engaged but thinking about it it should be normally disengaged. All that you would do is energize that single solenoid to have all wheels locked in.

For normal operation you would run in standard parallel. In fact, since you have everything half built you could simply run all motors in parallel without the manifold as you were going to originally and see how that works for you. You would only engage the positraction at lower speeds. So you could test out the buggy at lower speeds and see how well it runs. If you find that one of the wheels takes off without the others a lot then we can finish up the posi manifold and add it as a performance mod. The manifold would take 6-8 weeks to be built and shipped.

It would be single all cartridge valve manifold that the pump and motors would connect to.

 

[drankin]

Also, in case this may be of use in your schematic. We are considering using a PLC to control the pump and the steering circuit, so there is a possibility that we could control this circuit with the PLC as well, once I understand how this circuit works. One of my buddies programs PLC's for a living and is very good at it, so hopefully will be an option.

Steering wheel or joystick? If steering wheel then I don't seen any reason to include steering into the PLC.

 

[rmalik30]

Hi everybody!

I could see very interesting discussion going on here.
But why have you guys discontinued it ? What is the progress on buggy front ? I would really like to know that.
I am also building a hydrostatic all wheel drive agricultural tractor. Would like to incorporate your experiences into that.

I also wanted to know a little bit more about the last circuit shared by Drankin.
1.) "...This keeps all drives rotating at the same speed when the circuit is activated (low speed, climbing, mud, etc.)... "

How does that happen ?

2.) The solenoid valve has 2 orifices adjacent to it. What is the purpose of that ?
Is it to prevent complete fluid going to drain by putting high resistance!

3.) When all of the 8 valves are also connected to tank why would they function at all ?
I believe it is done to relieve the pressure when positrac is off. But this connection to tank should have been closed in positrac on mode.

I am also trying to put a diff lock feature in my HST circuit and looking for the most efficient.
Your comments on above would be helpful.

Thanks

 

[vijayaraj]

Currently i am also try to adapt hydrostatic drive for my truck. I had successfully installed and it also running other than one problem -> Jerk.


i have observed jerk during deceleration in a particular range of speed only. is there any specific reason for this type of jerk

Suggest a solution to fine tune the system

 

[shotgunner]

This free-spiining joint, is this something you have heard of, or an idea? I don't even know what you would call that. Is there an application that uses something like is? Otherwise, I do like that idea. Let me know, and I will start looking for something like that.

Jason

hey i found this thread ab about a hdyrostastic dune buggy. So i thought i would tell your that i am buildin the same. I'm using a cross motor puts out 700in./lbs. torque and at 3000 rpms. and takes 30gpm. The pump is off a case 585 forklift. Using a 11hp honda to run the pump. also using a live axle/ a 1 to 5 rear end ratio. my figues say that it'll do 62mph. I think it would very easy for you(larkinja) to pull your idea off. and if i had the same budget that's what i would use.

 

[Neilo9]

Larkinja or Drankin, any update on your hydrostatic drive project. Like you Larkinja, been playing around with a few projects and I was looking into converting an off-road yamaha r6 engined buggy to a similar hydrostatic drive system...hence I found this thread! Few pics here of what I'm working on.

 

[potatoecannon]

Larkinja or Drankin, I second the update request.
This sounds like an excellent project, and I'm curious how it is progressing.

Good luck.

 

[drankin]

Larkinja or Drankin, I second the update request.
This sounds like an excellent project, and I'm curious how it is progressing.

Good luck.

I haven't heard from him since his last post in March. I just happened to stop by here today to see if the project has been revived.

 

[amhydra]

Drankin, did you ever hear back from this guy? Would you consider using the attached in a lower flow application?

Thank you

 

[terrylutke]

Hi all. I don't know if I have posted this in the right section, but I am hoping someone might be able to lend me a hand with a project.

A friend on mine and I are always looking to build something challenging and unique. We recently finished building a truck completely from the ground up, designing all our own parts (besides engine, tranny, etc..) Anyway, inspired by our commercial lawn mower and our bobcat, we would like to build a hydraulic driven dune buggy-ish looking vehicle. Many have asked why, and the answer is simple, its something different and we would like to learn more about hydraulics in the process. I have researched power requirements, done many of the formulas, but I am having a tough time translating data into the real world. In other words, will it work)

My DATA:

Vehicle Mass - 2000lbs
Maximum Speed - 70mph
Maximum Incline - 20degrees
Wheel Radius - 13"
Axle Ratio - 2.5:1
Rolling Resistance - 0.037

With these values, I have concluded this:

Drawbar Pull - 758
Wheel Torque - 9854.524 in/lb
Motor Torque - 3941 in/lb
RPM - 2261rpm
Power Required - 141hp

If I calculate based on 3000psi system and 4 drive motors I get:

Flow Rate - 80gpm
Torque on each motor - 985 in/lb

Concluding a minimum motor size of 2 cu in/rev motor

Now for my questions. 1st, is my math correct? I did this all on paper, then created a spreadsheet that solves all the equations so I can change the variables to meet the end goal.

2nd question, am I going about this the right way. Where my confusion lies mostly is in the motors and pumps. The math does not seem to match manufacturers specs for there motors. So is a formula not accurate enough given the different types of hydraulic motors?

I am wondering if there is anyone out there with any hydraulic experience that can point us in the right direction. Maybe with component selection, and even possibly helping us coming up with the schematic.

We are just starting the research, so any suggestions would be helpful. Do don't want a traditional steering wheel. We want it to operate with two handles just like the commercial mower works. Both handles forward it goes straight. Left handle up, steers right, handles back, reverse. A gas pedal to control engine speed. Currently the thought is one motor for each wheel. Front left and rear left on the same circuit. Same with the right side. Front wheels would be on steering spindles, tied to each other, but left to free steer. Possibly use stabilizers to help with hitting bumps and ruts and returning to straight. This would just be a concept to test, don't know if it would steer well that way or not.

I am still looking for the best method for braking. On the mower, you just easy back on the handles and it stops. If you let go of the handles, it comes to a abrupt stop. Which I don't think would be very safe at higher speeds. Maybe at valve center, a bypass which allows the wheels to free spin, and then use traditional braking. I have read about using accumulators for hydraulic braking. I don't care about fuel efficiency, this isn't a car, which it what this is used for such as the UPS test truck.

Anyway, this post has gotten long enough. If anyone wants to give me a hand I would be very grateful. And just so everyone knows, this is not a design for a commercial vehicle, just boys and there toys, so let's not think in terms of production.

Thanks again,

Jason

Hi Jason..I'm new here but the topic is great.
Some years ago I built a 1/3 scale skidsteer loader with a 10hp gas engine/1 gear pump and 2 gear motors. Final drive was open chain reduction, speed range was zero to maybe 4mph. With correct tires this thing was nearly unstopable.
These days if I were to duplicate this project I would seriously consider electric drive. Just a thought

Terry

 

[Callahan]

For those who were looking for a hydrostatic differential lock valve - Bucher Hydarulics
has a package. Model number MT DV

 

[north of 60]

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.

you might want to try turbo cad with the animator plug in
its easier to use and you can simulate real world conditions before you buy/install expensive parts and peices. you can also see if there are design problems prior to the actual build. its not perfect but we use it everyday prior to building or modifiing any equipment.