I’m interesed in hearing what has caused climbers to fail on the field so far, both in terms of mechanism/rope failure and failure to activate the touchpad. There have obviously been a lot of discussion about climber designs here over the past few months, and from what I’ve heard and seen, there were a lot of failures at Week 1 competitions.
What have been the reasons for failure?
Edit: forgot to add backdriving to the poll, I guess that would fall under “motor/gearbox design wasn’t sufficient” or “mechanism failure”
Leave enough time for your climb. Make sure your alliance partners leave enough time for their climbs. Remember, climbs are worth more than any rotor but the fourth.
I really saw 4 types of failures when I was in Duluth:
Rope breaking. I saw plenty of ropes with visible damage to them from being used, and at least 2 break… bring extra!
Not enough time. Sometimes it takes a relatively long time to get the rope engaged with a climbing mechanism, not leaving enough time to climb.
Not activating the touchpad. In a couple cases, the robot was up as high as it could go, but it was stuck against the steel davit and wasn’t activating the touchpad. You need to design with that steel davit in mind!
Back driving. There was at least one case of a team triggering the touchpad and then backdriving off of it before the end of the match. We also happened to find a 1/2" ratchet wrench on the field after that match. Weird.
This is a “failure” only in a way, but my team’s climber and rope were strong enough to damage the davit if our robot continued to climb past the touchpad. The officials were stern with our drive team about this, because if this happened it took a long time to remove the robot and rope from the field and then fix/replace the davit. They were almost to the point of not letting us climb.
The main solution was just to remind our operator that the touchpad lights up one second after contact, not immediately. Pulling up that extra second can cause damage to the field and to the climber.
It would be nice if the touchpad light was two-stage. “Yup, I’ve been activated” followed by “OK, now it counts”.
We have yet to try our climber in competition but in our own practices we have found the majority of failures, other than “ran out of time”, were due to forgetting to install the retaining ratchet. One time our rope coiled around a piece of robot frame instead of the drum and resulted in an alarming CRUNCH before we aborted the climb. And we’ve definitely shredded our share of plywood team-element touchpads.
Rope was dropped but we turned over the rope and it ended up wrapping around the shaft not the spool. Lesson: don’t turn over the rope.
Radio reset and we had a few CANbus errors pop up which we believe was what caused our climber to stop running halfway up the rope in Semi Final 1 where we tied. We couldn’t find a mechanical issue so our belief was the CAN errors that were on the dashboard.
Ropes being too long. This was something we saw that happened once to us and a few other teams. If your rope is too long and you are approaching it driving into the Airship instead of parallel, you’ll hit the Airship before the rope can engage prevent you from ascending.
The few falls I saw at Hub City (including both of ours) were due to straps wearing against the u-channel. This leads to the straps becoming nicked on the edge, thus reducing their breaking limit. Both of our falls were at the touch pad, and indicate that we started loading the strap to failure.
I recommend everyone sheath their ropes or straps, and check for wear after every match. Test your straps to the stall rating for your climber gear train if possible.
What we found at the Tippecanoe district was the edge of the davit may not actually have a sharp edge but it worked quite well in cutting rope under tension. A unusual amount of ropes were cut in this fashion.
5920 has been lucky to have an 100% climb success rate. Unfortunately, some have not been so lucky. Here is our untested theories of failures we’ve seen that may be a material choice issue:
“Over-driving” after the robot touches the “C” channel on the davit may be a failure cause.
“Point-loading” at the bend where the rope or strap goes from horizontal to vertical on the davit may be a failure point for some material.
Please remember tensile strength and working load specs are VERY different. You may only have 10% workload capacity of your spec’ed tensile strength. The workload burden includes over-driving on the davit, how your material is influenced by the bend, and a rope slip that can allow your robot to drop a few inches while climbing. Be careful when testing.
initially our rope would bind on the end of the of our climbing mechanism, which prevented our motor from being able to keep running.
eventually we changed our rope to a much thinner one which completely took away the binding problem and with the new rope we climbed 100%.
also in the semi finals, one of our alliance members rope was being touched and deformed by an inspector, and because of this they were not able to climb (the rope had to be shaped perfectly in some way for them to be able to climb)
i think it would be important for teams to make sure if their rope is touched by somebody that they are allowed to re-adjust it before a match starts.
Our team accidentally held the climb button too long and then ran out of rope. Then the rope snapped. Best of luck to everyone playing in a non-week one event.
Our problem was pretty simple compared to most. Our winch didn’t catch onto the rope as quickly or as easily as we wanted it to. When we did catch the rope with at least 7 seconds remaining in the match we climbed with no failures. Disappointingly that only happened twice in our 8 qualifying matches at Palmetto.
Just a standard 1" ratchet we had laying around. I suppose you would find it at a Home Depot or Lowes. Also, take a look at some of the reviews for the one you posted. Looks like people have had bad experiences with that on sharp edges as well.
As for the davit, one felt smooth, and another felt like it might be a little rough. Point is, they are not beveled and have no grommet. Prepare for it to be an unfinished bandsaw-cut edge.
Some of the main reasons for failure I saw in Palmetto were:
Binding of the rope against U-Channel
Motors not having enough torque and the robot slipping and dropping to the ground.
Ropes not having the correct load weight factor to hold the robot.
Our robot was inspected as was the rope with the knot and our rope slipped through the davit the first match. (luckily no lasting damage). Always check the rope knot to make sure it won’t slip through the field davit during practice matches.