New Thrust Stand

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edwardw

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Hey All,

After this weekends static testing we found one thing we needed to change about our data aquisition. Our current thrust measuring device was a 4 ton Harbor Freight hydraulic jack that was modified. We found one problem - the area of the cylinder was greater than 1 in^2. Why is this a problem? The reason is Pressure = Force/Area. When I press down with 10 lbs on the stand, the pressure was less than 10 PSI. That means that for every pound we didn't generate 1 PSI for our pressure transducer to pick up. Our resolution wasn't that great :( While this was okay for our trial run, I decided something needed to be done.

What I came up with was a system that had an area of less than 1 in^2, and I only had to machine one piece. I decided to use a 6" long, 3/4" brass nipple. This has an inside diameter of .817" This would mean that my approximate area would be .52 in^2. This mean for each 1 LB placed on the stand - I would generate almost 2 PSI for the pressure transducer to pick up. This is much better. I also needed a way to measure the pressure - and dissapate the force of the motor into something. The solution there was a 3/4 brass tee - the kind that is machined from a solid piece of brass. This is flat on one side, making it perfect for sitting upright and standing by itself on level ground. And, since it was a tee - I could plug one side and use the other to hook up to my pressure transducer - two birds with one stone. The whole assembly is filled with nice thick automotive grease.

The only piece I had to machine was the 'piston', the part that would be putting the force on the fluid. It wasn't too hard - I bought some 1" solid stock. Then I turned it down to 10 thousands less than the inside of the pipe - to .807". I then put two grooves for o-rings at the bottom and then one near the top so that there would be no 'slop' when pressing down. I also left a shoulder at the top so that if a pipe burst - the piston would stop on the brass pipe and not go all the way down.

Below is a picture of the device, unassembled. There are 8 parts (not shown is the flare nut on the left side), and three o-rings. I think that it is pretty simple and straight forward. Some preliminary testing is yielding good results. I'm happy!

The total cost of everything was $25. I have a pressure transducer - so that isn't included. I didn't think that is too bad for this. Also, the reason we went with a pressure transducer instead of load cell is that when you cato - there is a big spike - most of the time this breaks the load cell. With a pressure transducer there is a fluid to absorb some of the explosion.

I was thinking of making these for other EX people on the forum - I would buy the brass pipe - machine the piston to fit - and send that too you. That way you could buy all the rest of the parts to fit your load cell. Good idea?

Edward
 

jetra2

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People,

Not only is Edward very, very good at making parachutes, he's also a master at sugar motors. I have absolutely no doubt that this device will be excellent for whatever kind of EX you're doing, be it sugar, BP, or APCP. I highly recommend his work for whatever you need!

Jason
 
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