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Thread: Hydraulic / Pneumatic help please

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Old 08-03-2004, 12:33 AM   #1
Quarry Creeper
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Default Hydraulic / Pneumatic help please

I am going to be a junior in high school this year and hope to start my Junior/Senior SciTech project. I want to build a 1/5+ scale R/C of the Dodge Raminator monster truck (the one in my avatar). I was thinking weadeater engine and hydraulic steering. I have never worked with hydraulics but have experience with pneumatics. I designed and built the pneumatic system for my schools First Robotic robot, it was a simple system though: 2x single action cylinders, one dual action cylinder, two air tanks/reservoirs, each cylinder had a flow control, ECT.

Sorry for the long read but my actual question is can you use a pneumatic cylinder in a hydraulic setup? Am I correct in believing that hydraulic cylinders are rated for a higher PSI? If so is that the only difference? I was looking at Bimbaís ĺĒ Standard Air Cylinder #043-DP. So to recap me question is can I use a pneumatic cylinder as a hydraulic cylinder safely? By safely I mean if I build everything correctly it wonít or should not explode or shoot the rod out.

If my project gets the go and is successful I plan on transforming the core components into a crawler. The monster truck seems easier and more fun to start the project as.
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Old 08-03-2004, 01:14 AM   #2
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Default Re: Hydraulic / Pneumatic help please

You could technically use air for steering. You are correct hydraulics are a much higher pressure ~1200 psi in our buggy.

Using air the steering wouldn't be as strong. It would be prone to "bumpsteer" Air is compressable, hydraulics, and most liquids are not.
So if you were driving straight and a rock hit the outside of the left tire it would turn the wheel to the right just because it can compress the air that is in the cylinder. If you had hydraulic fluid in the cyclinder that would not happen.
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Old 08-03-2004, 11:07 AM   #3
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Default Re: Hydraulic / Pneumatic help please

I also don't think you can safely run hydrolics in a pneumatic cylinder. Pressures are different, and I do believe that the seals and such for air would not hold up to fluid.
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Old 08-03-2004, 01:41 PM   #4
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Default Re: Hydraulic / Pneumatic help please

Thats a tough project you're thinking of there, but it would be pretty cool.

For the steering i would go with hydraulics for a few reasons;

- its much easier and you don't need a compressor or anything to get enough pressure into the system

- hydraulics are more reliable in general (provided the seals and everything are good)

- hydraulics are less prone to bump steer (as mentioned before)

- and lastly its more realistic

as for a gasoline engine i'd say anything over 20cc will get the thing going pretty fast
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Old 08-06-2004, 04:54 AM   #5
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Default Re: Hydraulic / Pneumatic help please

Thanks for all the help and suggestions. I agree that it will most likely be hard. But the only way I will find out is if: school approves of the project, I can get non helical ring and pinion gears made for a extremely reasonable price, and I can find a suitable engine and properly sized hydraulics or pneumatics. As for the steering I think in all practicality I would go with pneumatics. I can use quick connect joints which I donít think you can use on hydraulics and mom + hydraulic fluid * indoors = not good. The only downsides I can see would be that pneumatics are less realistic like, I would need an onboard compressor, and I donít know if pneumatics can be set up to extend proportionality not just open or close. I need to research full hydro steering more but canít find any monster truck specific information so I am going to go reread Pirates hydro steering bible. I will post more questions later.

As for the engine I plan on weadeater like I said before or possibly a kart engine. If anyone has a broken or worn small engine that they wouldnít mind giving away please contact me. If you are in Colorado it would work out the best since shipping is not worth the price in my opinion.
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