# Hydrostatic Drive Design

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.

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

Thank you

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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
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 lets 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

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

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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.