Our team has been using the Andy Mark Supershifter with servo shifter, but now i want to make the transition to pneumatic shifters.
Now i was wondering what are the pros and cons to going with this setup, besides the fact of being able to shift faster and the possibilty of busting the pin or screw near the dog gear
I greatly appreciate the input from the FRC/CD community
Hey Grease Monkeys…judging from the TRR results, I guess you got that chain fixed!
Moving to pneumatic shifting is a change I would encourage for you. Obviously their is a small cost in weight and complexity with a new valve, cylinders, and lines, but the improved responsiveness and reliability is worth it. Regarding the risk of breaking the dog pin/screw I would make two suggestions. If you have dogs with screws, convert them to pins by drilling out the dog and shaft, and use a mil. spec. roll pin. The threads on the screws simply provide a fracture point that will fail eventually. As for the shock induced by air shifting, minimize it by adding speed controls to the cylinders (both directions.) They can be adjusted to eliminate the harsh hammer while still giving quick responsive shifting. A regulator could be used instead to reduce the pressure of the shifting air, but this reduces the reliability of both the valve operation and the shifting. Better to soften the motion with speed control and still maintain reliable force.
Yes we did, and thank you Jspatz1, Team 1986, and 1987 for inviting us into your alliance at Ozark Moutain Brawl
would that roll pin help in preventing it from failing or would i have to replace it after a certain amount matches, i had read a post that here on chief delphi say that i should let the cylinder float on the bracket by not tightening the nut all the way and apply lock tie to keep it from coming undone, this allow the cylinder to adjust to shifter in case it not actaully center
this is uncharted territory for me especially, i appraicate all the help and advise that I can get
In my opinion yes, the roll pin will be much tougher than the screw and is the reason for dong it. Roll pins are compliant by their nature and built for shear loads. Cap scews are hardened and brittle by comparison and as mentioned the threads provide a stress concentration point for it to fracture. As long as you keep a punch and pin on hand to replace them if needed, I think the pins can be left in indefinitely. We have two that have been through two years service with no problem.
The suggestion to leave the cylinder nut loose is exactly right. The AMshifter asembly is not always perfectly alligned and any tightened misallignment will cause it to bind. We had a shifter assembly fail at champs once due to this binding. The pneumatic force on the shuttle is enough to damage itself if it binds. Rather than Loctite, we add a tapped setscrew hole to the cylinder nut, and lock it in a loose position with a setscrew.
Yes you could get them at the hardware store, but probably not mil. spec. grade which would be significantly stronger than the commodity grade you will find at the store. It would be worth ordering several from McMasterCarr you would have them in 2-3 days. I believe AM used an extra-strength grade when they were using them.
Yes a standard fractional drill will work, the pin is slightly oversize and made to flex smaller when driven into a nominal size hole.
I would think there is very little experience out there with solenoids on AM shifters since this was the first year solenod actuators were allowed. It would take a substantial solenoid to approach the force of a 1/2" air cylinder, and the size/power that is allowed is limited. To get push and pull motion you would need a push-pull solenod, or two solenods, or would have to combine it with a spring return which would increase the size needed. One would have to look at what power is allowed and see how the pull force could compare to air. You would probably need a contiuous duty type for long periods of being energized, which means less pull force for a given size. Getting to a force comparable to air would likely get pretty heavy.
If you can use a solenoid there is a substantial weight and space savings by using a solenoid to do the push/pull action you need only the solenoid itself, the relay or solenoid module to drive it. The solenoid works when a current is driven through it, a EM field pushes the actuator.
With a pneumatic system you would need the storage tank, gauges, valves, regulators etc.
We used AndyMark Supershifters with pneumatic shifters on our 2012 robot Thermite. Seeing as i’m controls captain, I come from a different perspective. The code was incredibly simple and we used the trigger of the joystick to quickly shift back and forth between gears. Seeing as we already had the compressor on board for other elements of the robot, weight was really the concern for the pneumatics element.
We used servos this year, and it was fine (once we calibrated them right).
I set it up with an Upshift and Downshift button (btns Right and Down respectively on a Logitech DualAction, yes those are face buttons), which then set the input state (high,low), which drove a state-machine through four possible servo positions (high,low,high-peak,low-peak), and that state would index a table to find the servo pwm values. It would peak and hold the servo, forcing it into gear then backing off to prevent servo burnout (we did burn out a pair of servos during the build season). I believe we were peaking for around 5 seconds.
Before doing peak and hold, we calibrated the high and low servo positions to the optimal steady-state position. The shift force immediately after requesting a shift was quite low, so I would have to jiggle the throttle stick to get both sides to shift. With the peak and hold, it usually shifted very quickly. We found that we rarely shifted, so it really didn’t matter.
During autonomous, the script engine could directly set the input state and the peak and hold state machine would run. We ran autonomous in high gear, it was fast.
All of that said, we shifted pneumatically in 2011 and 2010 with no issues. We used the AM standard piston in 2010 and shifted at 60psi, and used a similar spec pancake-stype piston in 2011, also at 60psi. We heard about the breaking screws in 2011 and replaced the screw with a roll pin at CMP. I believe our 2010 robot already had roll pins. During the 2011 season, I also worked on an automatic trans shifting algorithm, and it always assumed it could shift with little lag during shifting (including during acceleration).
All my comments are assuming a pneumatic system is already available. Comparisons to air shifting should be done at 60 psi, not 20 psi. The solenoid wattage which was allowed in 2012 would not begin to approach the force of an air cylinder for a continuous duty solenoid. Keep in mind that solenoids are one-directional, and their “rated” force exists only in a small fraction of their total stroke.
This solenoid is one-directional, push only. The spring return is only minimal to return the armature to the retracted position when de-energized. It is also intermitant duty, which means it can be energized no more than 50% of the time without overheating. A shifting actuator must maintain force in either direction at all times. This is one reason an air cylinder is well suited to the job. A continuous duty solenoid of this same wattage would have about 1/3 the force.
As I mentioned this is the first year solenoid actuators have even been permitted on a FRC robot, so there is no history of them being used for shifting that I know of. If someone successfully did this in 2012 I would be curious to hear about it.
Yes i agree with jspatz1 about this conversaion, but im also wondering about this solenoid shifter, if anyone has use this setup,please feel free to add to this conversation, i see the pros and cons about using pneumatic shifters…what are the pros and cons using solenoid shifters
Why should it be 60 PSI? Shouldn’t it be closer to the actual force required?
Our own shifters we had, we’ve always run at 20 PSI for the solenoid valves sake. I was under the assumption that it took less force than the 12 lbs to shift but I could be wrong about this as I have no experience with the super shifters.