Please Help: Mechanical Stop For Cascading Climb System?

[Joaomc15]

We are using a 2-stage cascading elevator system with chains for climb, however, a mechanical stop for the climb was not incorporated so it slides down after power is no longer provided to the motors driving the system. I realize that this is a design flaw, but is there any way to apply a mechanical stop that would prevent the robot from falling back down, or at least slow down the rate at which it falls so that it would still be off the floor 5 seconds after the end of teleop.

A ROBOT is considered HANGING if, five (5) seconds after the ARENA timer displays zero (0) following TELEOP, it is fully supported (either directly or transitively) by its GENERATOR SWITCH.

The main hindrance are the sliders that move up and down the stationary beam because it limits the mountable space on the stationary beam to less than an inch on the top and bottom.

We were looking at springs to slow the fall but any suggestions are welcome.

[JohnD]

These work great https://www.vexrobotics.com/217-6048.html

[Joaomc15]

Thanks for the reply. Is there anyway to disengage this ratchet during match because our system would need to go up to hook onto the generator switch, then pull down to lift the robot off the ground so we would need motion in two directions at first.

[JohnD]

Not this one. We have to manually release it at the end of the March.

[thomasart]

If you can use air cylinders, Spectrum 3847 has a brake that uses a pancake cylinder to lock the shaft in place

Spectrum 3847 - Build Blog 2020

Day 20 Largely we have been getting more of our subsystem designs CADed. Shooter Design [Shooter Cad.PNG] We are experimenting with adding a rear kicker wheel to the shooter setup. The idea being to have more linear acceleration into the shooter wheel and less spin. It would be powered off the front accelerator wheel using polycord in a figure 8. We have learned to use Solidworks surfaces to allow us to CAD a curved shooter hood and then unwrap it so we can easily laser cut it from a flat pie…

Also, FIRST Capital did something similar on their Robot in 3 Days:

[garyk]

I’ve seen a couple techniques to do this:

A bicycle disc brake, actuated pneumatically. Not a good solution if you aren’t already using pneumatics.

A ratchet wrench - not a ratcheting socket wrench, but like an open-end wrench but with a ratchet, that’s reversible.

It’ll let your motor shaft turn only one way, and to retract the elevator somebody lifts the ‘bot to unweight the ratchet, then flip the reverse lever.

Don’t use a crappy wrench, and secure its handle with a strong, metal bracket.

A couple of years ago a ‘bot had this setup but its handle was secured with plastic zip ties. The zip ties let loose in the pits, and the student facing it lost a tooth.

[garyk]

OK, I didn’t realize you have to turn first one direction, then the other. I’m back to the disc brake idea. The advantage is that you need to actuate it only once per match. If you don’t already have pneumatics, maybe you could use a spring to get the brake to clamp. Somehow latch the spring compressed/stretched to hold the brake open, then pop the latch with a servo after you’ve climbed?

Or use a servo to stick an obstruction in the chain or sprocket after you’ve climbed? I admit this is, as my students say, janky.

[Joaomc15]

Couldn’t I use a servo to reverse the ratcheting wrench after the climb arms are at their highest position, while not bearing any of the weight of the robot, then pull down lifting the robot, but then the wrench would lock it in place?

[ForeShadow00]

We first used hooks connected to a servo arm that would hook a bolt on the lift as it started to descend when it lost power. Just used a ratchet strap hook. We moved away from that because brake mode in the spark maxs with the neos are working great.

[aldaeron]

I am not sure what the space looks like around your elevator. I agree with others that the easier solutions would use a pneumatic cylinder to get linear motion to lock everything in place. But if you don’t already have a pneumatic system on the bot - here is an idea that only uses motors. I would be careful about servos - the ones allowed can be pretty powerful, but my experience with flipping ratchet wrench switches is that if there is any load on them, it is nearly impossible to flip them.

Constant force springs can get pretty beefy (40 lb version). These can get heavy! They have a LOT of power - use gloves and extreme caution around them (they give very unpleasant bruises)! Have them pull the elevator down and use your motors to overcome their pull. You might want 2-3 of them depending on how much they dip. I have seen quite a few bots that are up at T=0 but only by a few inches and slide down to touch.

Good luck!

-matto-

[Praj]

Yep. We did this last year for our suction climb which had to go both directions. We would leave it disengaged than run our lift up to drop our suction pad. Once we had our suction on the platform we would engage the ratchet and push the lift down.

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[Attention]

I’m just going to point you to this. You’ll notice that the arm is able to go up and down once even with the ratchet engaged.

[pfreivald]

We used a Versaplanetary ratchet during Power Up, with a pneumatic pin that we pulled to activate it once we were in position. A hex wrench on your winch gearbox is another option. A third is a dog gear brake.

[garyk]

Using a servo to flip the ratchet’s reversing lever is a great idea! Since you need to flip it only once/match, maybe you could put a weight on the servo’s shaft so it’d build up some angular momentum and “knock” the lever, and/or preload the lever with a spring. You’ll have to do a bunch of testing, esp. with the amount of load on the wrench.

Somebody mentioned speed controller’s coast/brake setting - to be honest I’d forgotten about this - make sure it’s in the brake setting.

[anonymous_7476]

Have you tried putting your motors in brake mode? It works with us and we have a pretty much identical design as you do. While it is suggested to have a brake, if you have a gear reduction you should be able to stay up long enough with this software change.