This past weekend, I attended W0W (Week 0 Warmup) put by Team 2338 in Aurora, Il - great event.
They had the various field elements setup including the hangar. There wasn’t a lot of climbing but Team 111, Wildstang, did a couple of manual climbs and traversals with their latest robot. They may have only done a single traversal as they felt things were still a little risky (don’t blame them for a second - seeing it done was once was great, but scary).
Watching that, something that occured to me was the fact that a big part of the actions of a traverse (which our team is aiming for) were essentially blind. It would be nice to “know” that your hooks have engaged the appropriate bars and be able to confirm or abort a traverse attempt either automatically or even manually through a set of dashboard indications. Much like Frank Constanza inventing Festivus, I thought there might be a better way.
So I started messing around with the “Smart Hook”. It’s a 3D printed hook insert designed to be sandwiched by a pair of aluminum plates to carry a microswitch at the top center of the hook opening thereby providing a sensor to indicate hook to bar contact. Now you could indirectly count on an increase in lift motor current to tell that a mechanism was starting to take robot weight, but depending on the lifting mechanicals, that might not indicate multiple hooks are engaged whereas an actual physical hook to bar feedback signal might be a confidence booster for both automated and manual climbing efforts; especially when using multiple hooks like the typical paired setups.
The CAD can be found at Onshape
Some details on the design:
The CAD file as-is is intended to clamp onto a 1" square extrusion with the hook “insert” extending into the extrusion it is mounted to. There are a number of variables which control key aspects like widths, thicknesses, hook wrap angle, etc. There is also support for the locating the microswitch - the microswitch fits into a cavity in the 3D printer center insert which locates it in the center of the insert and there is a matching “plug” which fills the remaining space capturing the switch in the insert. The plug has about a 3 degree draft to it for easy insertion and the insert includes a hole centered on the inside side of the microswitch to allow the switch to be pushed out if needed. There is an opening on the back of the insert to provide wiring access to the microswitch sufficient to allowing wiring after the hook is fully assembled. The switch is located to ensure that when activated, it is reliably triggered but not pushed to the end of it’s travel so it should last essentially forever as it’s not being abused by taking any of the robot’s weight.
The entire hook “sandwich” is secured using 5 1/4" fasteners with 2 more fasteners securing the outer aluminum parts of the hook to the lifting extrusion. With the aluminum outer parts, the hook should be plenty strong enough for what we are doing. The 1/4 bolts are probably overkill and could be replaced with 10 or similar-sized hardware for weight savings.
The design can be parametrically scaled but I’m not adept enough with Onshape to handle the relocation of the microswitch in an automated manner (though I’ve got some ideas I might mess with); that means after you get the general hook geometry the way you like it, you’ll need to address the microswitch location but it’s not too bad. You’ll likely need to touch up the switch recess after doing that.
The basic hook geometry puts the center of the hook eye vertically in line with the center of the lifting extrusion for to keep the forces straight through the assembly vertical when in that orientation.
Here are a few pics to prove it happened:
For the last photo, I wired up the LED to the NO side of the switch to activate it when engaged - you’d probably want to connect it to the NC side of the switch so you could have a supervised circuit and detect a failure before grabbing a bar. I printed a short stand-in for 1 1/4" pipe to activate the switch.
Use it as you may or ignore it as you might - if you use the idea and someone digs it, tell 'em your using “Zog’s Smart Hook”.
– Chris Herzog, Lockport Porterbots #4292