My 6DOF pneumatic stewart platform

[misterfarmer]

Hello,

At first, my excuse for my bad English.

A couple of weeks ago i found some old pneumatic cylinders. For years I had the plan to build an motion simulator, so now the right time has become.

I started with building some universal point connections for the cilynder.



After that i made two excactly the same triangles. The sides of the triangles where the same length of an cylinder (in).
I couldn't find information about sizes for stewart platform so i was guessing this is the right idea. (I do not know yet)



The idea for the potmeters was found on the internet. I saw a guy who was making it with some tape measures.

The picture shows concept one. There was a litte problem, i bought some potentiometers but the can turn around 300 degrees. This is 11cm with the cylinder, but the cylinder can reach 25cm. So i had to remake it with a bigger wheel and a rope. This is only for testing, if everything is okay i will buy some 10 turn potentiometers but the are to expensive for testing .


Because i use pressed air i needed something to split the air. First i thought i can use one air hose and use an three way splitter at each cylinder. but this was not working because the first cylinder gots more air.
I made a small splitter out of steel.





The used solenoids (wich i found too) are 24v. I wanted to use an arduino, so i figured out how to switch 24v with an arduino. I'm not very good with electronic but i solder something I thought it will work.. You see some different parts, that's because i ordered not enough online, so i bought the other parts at the local store.



For programming the arduino i used the code in this post. But i rewrite it to 6 cylinders and made some other modifications because i do not use the motorcontroller (i don't know if this is okay)
http://x-sim.de/forum/viewtopic.php?t=943

Now i'm testing with the whole thing, there is only one problem. In and out is not a big problem but when i give the command to stay in the middle it is shaking up and down and can't find the right position. So i'm testing with some things like pressure.



[YouTube]https://www.youtube.com/watch?v=oBdAX3x9LOw[/YouTube]

[tronicgr]

Nice try! Did you try to load it yet so see if it compresses the air in the cylinders? I would live to see a video of this.

Back in 2005 I was planing to use pneumatics until I was told the prices for servovalves...



Thanks
Thanos

[misterfarmer]

Hello Thanos,

at first thanx for your reaction.

At the end of the post i posted an link to a youtube movie: https://www.youtube.com/watch?v=oBdAX3x9LOw

You can see how it is searching for the middle point but cannot find it. I think the problem are the potentiometers.

at the end i was sending the command to go in, that give no problems. also max out is no problem.

More testing was not possible because a 24vdc wire hits the arduino so i had to order a new arduino.
next time i will make another movie. i guess monday. someone is making new wheels for me for the potentiometers because i made them with a saw and he has an cnc.

[Riton]

I think your problem for the middle point is the reaction time and accuracy of stop.
you have proportional valves?

[misterfarmer]

In the code i use, there is a tollerance build in. and a brake distance. So i used that for my rewritten code also. When i setup a breaking distance about 300 it happens too. But next week i will also make another movie with the different things i tried.

EDIT: i read your message in the morning so i was not awake. the valves are switching on and off, so i don't think they are proportional i cannot change the value of airflow with my arduino.. a potentiometer is measuring the distance of the cilinder. so i thought when the script compares the distance of the cilinder and the distance it has to be, i can stop opening a valve. When it has to move the valve will open for in or out.

[Riton]

yes that's right in theory, but what happens?
there is compression of the air, reaction time, your operation is on / off.

if you can not stop quickly and very precisely your cylinder, it exceeds the set, then tests to come back .....

it is very difficult or impossible to solve.

it is as if we had a motor on / off.
you must slow down to stop!

tests to check to reduce the pressure, the speed of the cylinder to the minimum possible.
Then see if you improve the situation.

[misterfarmer]

Thanks, i will test some more with the pressure. I did this before and the platform was moving very slowly and searching for the point to stop. yesterday i received an new arduino so I can test further next week.

The words "difficult to solve the problem" are very hopefully.

[misterfarmer]

I think i've found the problem. i use 5/2 valve's. the problem is there is no stop. so when i close the valve it will give air untill the other valve will open. So i have to find 5/3 valves.

[misterfarmer]

well, i have to wait for the new valves so i spend some time on making a seat for the simulator.

so i started to draw something in sketchup after that i made it out of aluminium. This is not strong enough for my body so i have to make an frame out of steal or aluminium, i think im going to use steel because i cannot weld alu.

here ar some pictures

[misterfarmer]

Hi there,

Another update,

I am still waiting for new valves so I had some sime to make a frame for the steering wheel and the seat.

I will upload some pictures so you can see the progress. There was not enough metal so i had to stop and wait untill monday.