After seeing so many teams having robots that backdrive after a climb, and having witnessed a couple of matches where robots lost their climb because they backdrove and let go of the touch pad, it makes me wonder, why don’t people use a ratchet system. I understand that most can make a custom ratchet system to stop the climber, but there are many easy solutions.
For example, all my team did was use a socket wrench with a 1/2in socket and put it on the end of our climber hex shaft. Then we literally just ziptied the other end of the socket wrench to the metal support bar holding the climber mech… This method and the ziptie mounting solution has yet to fail.
Is there a reason the teams that let their robots backdrive don’t use methods such as these to prevent backdriving?
Our drivers wanted the flexibility to spin the motor either direction depending on how we caught the rope. Then our robot dropped. Then we backdrove after the socket wrench fell off. Now we have 1/2 socket wrench attached in such a way it will never come off. Ever.
We have a ratcheting box end wrench with a flex head on the climber shaft. the open end of the wrench is trapped by a long stud and a wingnut. Spin the wingnut off a few inches and the wrench can be folded back along the hex shaft. This lets us backdrive to get the robot off the rope.
The first method that comes to mind are bolts on either side of the handle.
Another very simple method is switching to a half inch ratchet wrench with an open crescent wrench on the other end. The ratchet end can easily be placed on the climber shaft, and another piece of threaded thunderhex shaft screwed on the bot so that it is spaced perfectly for the crescent wrench side to sit around.
A piece of angle aluminum attached to the frame that is faced in the direction where the leg of of the aluminum acts as a stop is a very simple and light method.
We did a bolt on either side, but had problems of the ratchet folding outwards. We were thinking of using reusable zipties to hold it down, which the driver would be able to disengage post-match.
I really don’t like zip ties here. Especially after hearing about the incident with a zip tie failing during the release of the robot from the airship for 1868.
Dont get me wrong, zip ties are great… Just not in high load situations like this
Containing the wrench in a piece of 1x1 tube is also an option.
Some teams use a zip ties on the non-loaded side, so that the wrench forces itself down onto aluminum on one side but it held close to the aluminum via zip tie.
On 5677 we had the same exact setup and it worked perfectly fine during CVR. We put two bolts on both sides of the wrench and also sent a bolt with a washer through the crescent side of the wrench and screwed it down to an aluminum upright. It was basically impossible to move the wrench. The thing that sucked about this was our rope had a lot of tension and our velcro was hard to unravel so we had to unscrew the wrench every time we had to come off the field.
We now have a bolt through the hole at the bottom of the handle (there’s either a regular box wrench or a second ratcheting wrench on the other end) but until we figure out a safe way to unwind the robot with the ratchet on, our backup plan is to just keep driving the robot up until the match ends then letting it unwind after.
(It turns out it’s really hard to release the ratchet while there’s load applied, and when you’re at the top of the rope you always lift it to release the load.)
Basically, I’d check to be very, very sure that something can’t easily snap and the ratchet swing around and hit someone. There’s a lot of force behind it. We didn’t think anything would break, until it did.
Correct me if I am wrong, but the reason the zipties will not work is because the ratchet is holding 120 lbs of torsional force. The ziptie would be holding 120 lbs times the length at which the zipties is away from the shaft. The knee jerk untrained in statics and dynamics response to climbing would be that the robot weight is purely held up by whatever framework is holding the shaft, but I don’t think that is true.
Im not the greatest at statics, so perhaps someone can clarify this a little more.