This year most teams are making some kind of catapult out of Class 1 levers. (That’s the one with the fulcrum in the middle). I’ve been prototyping to demonstrate both Class 1 and Class 3 levers (weight, force, fulcrum). (You can post what Class you think is better and why for extra credit)
Two things I’ve been doing for awhile has been to build prototypes on the square plates. It makes it easy to build something so I can get to all 5 sides of it pretty easy. While getting to the bottom is hard with the solid squares, the ones with the cutouts will also work.
I’ve also been using my “quick frame” which is rear drive with traction wheels and free spinning front wheels with omnis on it. The frame is 6 connectors (Double 2x Wide, 2x2 Corner Connector or Double 2x Wide, 2x2 Double Corner Connector( depending on the wheels you are going to use) 6 of the 2x20 beams and a handful of 0x2 pins I can build a quick frame in about 5 mins. I’ve sized it so the plates sit in the middle and I can position them fore/aft depending on what I’m doing. Wheels can be placed in a variety of locations I just normally do the 4 corners for a simple check,
This year I’ve been sticking large connectors on the inside of the frame (2x Wide, 2x3 Corner Connector) to stick into the center space. I drop the plate with the mechanism on it and them lock it down with 0x3 pins with 1x1 beams on the end to serve as little knobs on the Bailey Pins. (You’ve heard me wax about how much I like @bkahl 's use this year in the field elements.)
So now I have a frame, I can build mechanisms that I can pop on and off the frame to build. I’ve been pretty happy with it.
Since Delaware is the founding home of Pumpkin Chunkin I thought appropriate to build a 4DOF Floating Arm Trebuchet. I had build a large, 6’ version out of wood in the late 90’s (before the air cannons became king) that was pretty decent. I thought I’d see if I could recreate it with minimal effort in VIQ parts in my test frame.
(Picture shows final position before the ball takes off.) You can see in the picture that the pivot end of the arm is pulled down by rubber bands attached at the bottom. A classic Trebuchet uses weights, the 6’ version used 2-5 gallon buckets of concrete with an eyebolt embedded in it. I tried using the VEX IQ flywheel weights, but the 4 I had on hand were not enough to move the arm quickly. The force is straight down to maximize it. It uses just 2 rubber bands in the prototype. There are pulleys on the inside and outside to guide the arm down with a pair of the black thick washers in the slide opening. There is some friction as it slides, a sheet of the flat plastic on the inside would eliminate that.
The arm moves across the center support on a triple set of 1x1 beams on an axle to make a large guide roller. I tried to make this a slot, but it turns out in testing that it just slides along the rail, so no slot needed. There are a pair of corner connectors to stop the arm motion at 45 degrees to give it the proper fire point to give the desired arch angle.
You can look at this animation of the kinematics involved. This really showcases what is going on and why this mechanism is really awesome. The wooden one got good distance and within the aerodynamics’ of a pumpkin it was pretty accurate.
You can see how the plate is mounted. With minimal effort I can move the plate fore/aft on the frame. I’ve been using the space at the back as a platform to support the loader for the arm in for the other prototypes.
I’m pretty pleased with the “hand”. The center top orange 60 degree 1x pieces are not needed, they are there in the picture to hold the ball in place (you can see the indentation in the ball) . The friction fit slows the ball some, but not enough to stop it from making the upper targets from 24 inches. I had been using Bailey Pins on the arm to adjust the length, once that was dialed in (and less than 15", I just pinned it.
In testing with the plate anchored on the table, max height was 24" and it dropped below 15" at 32". YMMV
Anyway, I thought that the three things: using the large plates to prototype on, building a test frame and the use of Bailey Pins would be interesting. The Trebuchet is for your amusement. If you are going to build one, pull the plate farther to the back, the forward arm momentum lifts the back wheels where it is now. (The original was anchored to the ground, to keep it from face planting). Brain is also in the back for weight, there is enough clearance under the arm.