Pneumatic Lift Help

[Tinnittin]

This year we decided to lift our robot with pneumatic pistons with wheels on the end. We have two pistons in the front (one each corner) and one in the back. Here is a picture of the robot with a set of smaller pistons that we got to work:

We used adjustable flow rate valves to balance them. The main problem occurs when we switch them out for larger ones. These larger ones have a 20 in. stroke and can raise us up to Level 3. The problem is getting them to go up evenly. We can’t find a consistent balance between the front going up and the back going up (at 120 psi). Does anyone have any recommendations for tuning flow rate valves? Should we start with them closed, find a balance, and then increase speed, or go in the reverse of that? Thanks.

[zucker42]

Pneumatic cylinders in unison

We are using two of the exact same air cylinders. When we activate the solenoids, they do not extend at the same speed. We have adjusted the valves many times and can not get any type of consistency or pattern. One time one will be faster and the next time the other will be faster. Is there any possibility of getting them to extend at the same speed? We have even tried plumbing them to receive air from different air tanks.

There are more threads from this season if you search.

[Timebomb]

I don’t think it should matter much which direction you tune from, just try to do it with known increments (write down how many turns you do).
That said none of your cylinders should be at 120 PSI, the max working pressure is 60 PSI and if you are using 120 psi into anything that’s illegal and you won’t pass inspection.

[Tinnittin]

The storage tanks are at 120 psi due to the large size of our pistons, they eat through all of our 60 psi in the working pressure. The pistons also need to be near 60 psi themselves to lift the weight of the bot. But we have enough air on board so this isn’t a problem.

[Tinnittin]

I wasn’t able to find any with this same problem. Maybe my Google-Fu (or delphi-fu) isn’t what I thought it was. Do you mind pointing me in the right direction?

[anon31892661]

We are in same boat so far mechanical assist seems a promising path

[zucker42]

Sorry if my post came across as condescending. I was on mobile and couldn’t post fully. I linked one of the threads I was referring to in the original post.

Particularly pay attention to hrench’s posts in that thread.

Here’s another thread.

Balance Pneumatic Hab Level 3 Mechanism

Another option is to use a 5 port, 3 way solenoid with a closed option to accomplish something similar, I believe. Whichever way you do it, make sure you follow R93A. In particular, make sure when you open the pressure vent plug, the pneumatic system is completely depressurized. Relevant thread and post: I also particularly liked the mechanical solution from hrench in that thread.

Basically two approaches that I’ve heard teams try are to use closed center solenoids and controls, or to use some type of lift governor as explained by hrench.

Also, maybe I’m just misremembering, but it is significantly harder to find threads with the new Discourse search compare to the vBulletin search.

[zucker42]

Another idea I think I got from CD was to mechanically connect front and back with some latching mechanism, possibly using a gate latch actuated by a servo.

[RABBIT76]

Are you guys using any flow controls on cylinders.

[Tinnittin]

We have adjustable flow rate valves for each cylinder, which are placed between the solenoid valve and the cylinder’s valve to extend.

[chapman1]

Could you use gyro feedback to control two solenoids, with one solenoid feeding the rear pistons and one feeding the front pistons? Lift the front until +5 degrees. Lift back until -5 degrees. Lift the front again until +5 degrees. Lift back again until -5 degrees. And so on…

[chapman1]

I suppose solenoid control might also be accomplished in analog fashion… A rocker switch (or a couple of limit switches) with gravity and a pendulum-type extension providing level reference.