Pnuematics and changing positions of it

Hey guys first time on here asking the question but we have a pair of cylinders that are what is shown below but the team had some concerns on if the rod would bend or not if we angled the cylinders in such a way that when either side of our robot lifts up it would bend? We have an idea that we will probably need to have the cylinders straight up and down when it is lifted but will need to be angled in the robot’s level or parallel to ground position so that our front wheels can grab the HAB Climb level

The rods shouldn’t be subjected to side loads.
They are a soft steel and can be bent.

Try to provide some side load support, for instance, we usually have the rod push down a pad with an attached pvc pipe support that extends with it, then the pvc passes through a metal support like a pair of closely sized holes in a belly plate. When the pvc is pressed sideways it transfers the force to the belly plate rather than the cylinder rod.

There are other methods, too.


Thank you, could u get a picture of this for more clarification?

In the example Mark offered, the PVC pipe is a guide tube that prevents the cylinder’s piston rod from experiencing any (big) side forces. I doubt he has a photo, it’s just an idea.

Bottom line is, those rods bend more easily than you think, figure out a work-around.

OK, so those look like about 1.25" diameter cylinders? At 60 PSI, each one can lift only about 60 pounds. Keep that in mind. The formula is (area of cylinder piston (sq. in.) * air pressure (lbs per sq. in)) = Lbs of force.

pneumatic cylinders should only ever be subjected to loads parallel with the axis of actuation of the air cylinder i.e., no side-loading. Pictured below are some high end commercial options, but the idea for your frc robot is the same, if the loads for application will subject the cylinder to force in 2 or more axes, then supporting load bearing slides or supports must be put in line with the cylinder that are designed to take this loading, below the cylinder is the middle rod, the other two are linear bearings, and in the other the slide is on the side of the cylinder, and the rod of the cylinder is the thing sticking out in the middle. Another option is always to relocate the cylinder so it is not subjected to these loads.

this can be accomplished in frc in many ways, bearings on versa frame, or the method some others have posed in this thread for example

Going at the “other methods” - We used pneumatic cylinders to raise/lower the intake of our 2014 robot, pictured here.

You can see the cylinder mounted to the arm, a bit above and to the right of the FIRST logo on the ball, and to the chassis at the top of the near “tower”. Because this system was on both sides, there was not a chance for much side-to-side motion, but it was definitely necessary to allow the ends to pivot like a hinge at both ends. We did these with the built-in rear pivot mount of the cylinder and a clevis on the rod end. You can get a good idea of this by configuring and rendering it at Bimba:
It’s been a few years, but I think this is what we ordered: (things I skipped don’t matter; leave them alone)
Bore Size: 1 1/16" [09]
Stroke: 12"
Acting: Double [D]
Mounting Style: Rear Pivot [P]
Pivot Style: Standard Pivot Style

(Not included with cylinder)
Pivot Brackets: D-167
Piston Rod Clevis: D-1661 Front
Mounting Nut: Without Mounting Nut

Configured Part Number

As you can see there is a pin at either end for the cylinder to rotate about, and a bracket at the rear end. Bimba (and many others) sell specific hardware for thee front end, or you can make your own from angle brackets.

Taking this to the next level, open up the hatch back of a nearby vehicle and see how the air springs are mounted, on ball joints at both ends. This keeps the air spring from bending in any direction.

Edit: Looking at yours with the rear port, you would need a front block trunion to do this style of mounting; you can just reconfigure the Bimba above to have this as “Mounting Style”.

I’ve attached a sketch that I think represents Mark’s idea. Others can let me know if this captures the idea correctly.

Thank you, the formula will really help, is there a way since we plan on only lifting one end of the robot to be able to catch the level 2 climb to prevent major bending? If we lift up one end of the robot with it perpendicular to the drivetrain (our 1st option) I understand it will bend but will it have less of a chance of bending if we have the cylinders perpendicular to the floor but resulting in having a cylinder that is not perpendicular to the robot (our 2nd option) or possibly the centermost angle between the two options?

Have you done the force calculations on those cylinders, obviously I don’t know how much your robot weighs, but they look pretty tiny for lifting even just the front end of a robot

The greatest amount of force will be when the robot is completely parallel to the floor, so you should mount your cylinders perpendicular to the drive train, but then I would put a cup mounted ball bearing on the Tip of the cylinder, so it can roll forward as the cylinder extends and the robot becomes more inclined, it is still not ideal without support, but should yield the minimum amount of damage, also those rods are toothpicks, even with this system, they would fail pretty fast, if you can I would get some larger cylinders.

Yes, with two cylinders the 60psi cylinders should be able to lift the robot which will be 60-70lbs since it’s almost done correct me if I’m wrong. We have been making an idea similar to the roller bearing which was a basic handmade caster shown below and we plan on putting a thick, threaded plate on that is 1/4” thick so that the robot has less resistance by attaching the caster to the end of the rod. Will this work the same way that you mentioned?I honestly don’t know if we have the money to get a heavier duty cylinder or the time to get one.

The cylinders are small compared to what anyone else would use but they are very similar to what GeeTee used only a 5.5 inch stroke hopefully these show better.

What is the bore of those cylinders?

The bore should be a 3/4”

Also, with regards to the wheels, it’s a similar idea, but there is a high chance you will still run into issues, because a ball bearing system can freely move in all directions, while your wheel can only move forward and back, the fact of only moving forward and back is fine if you were just extending and retracting the cylinders, but you are not, you are driving. How this complicates things is that I can practically garuntee that you will not line up perfectly with the platform and even if you do, you still have to drive on which will cause you to turn a little bit throughout the process . When you turn it will generate a side load on the wheel known as “scrub” as the wheel has to overcome friction to slide sideways to continue on the straight path, when this happens you will generate large sideloads on the cylinder, leading to the same issue you where trying to solve in the firstplace with the wheels, but now the friction will be greater because the wheel has more contact area and a higher Cof, when this happens you will trash the rod, and be back where you started before the wheel.

A 3/4 bore cylinder will generate 26.51 lbs of force not the 60 you are talking about

A 3/4" cylinder at 60 psi exerts a force of ~26.5 lb. Given a combined stroke length of 11", that’s a total of ~24.3 ft-lb of work, meaning it will lift a 100 lb robot an average of a bit under 3" (perhaps 6" at one end and none at the other) if it’s perfectly placed and works vertically the whole way.

Alright, what if we tried to run a brace in between both casters to stabilize the side to side force of the cylinders and reduce that? Also since we need to lift a 60 lb robot this will be far beyond supported with the two cylinders if this is correct GeeTee?

Does your 60lbs include battery and bumpers? If not add another 20lbs on. Also gee two’s calculations assume a best case scenario in all circumstances with no safety factor, while it is possible that with factoring in your situation the cylinder may* be able to lift your robot, I would have to know a lot more about mounting, robot shape, and weight distribution to make that determination, I would not count on it to work 100 percent of the time as there a whole lot more factors that go into a system this on the edge of working. With regards to your idea to tie the cylinders together, this would help a little bit, but the loads would be in the same direction in both cylinders, creating a sort of parallelogram, so it still would not bode well for a quick turn of a reasonable size, or if you were to bump into something :grimacing:

It does not include battery or bumpers so yes it would hit around 80lbs so we will need to be more cautious when doing this lift process even with tying the two cylinders together right?