We have a couple of waypoints to hit this week, and a detailed to-do punch list helps me figure out what has to happen when. This description might help you figure out how best to deploy our human resources to meet our near-term goals of CATAPULT prototyping & testing Wednesday, and BALL-PICKER-UPPER by Saturday.
Tuesday
I will cut the dovetails on bumper set #2. Tomorrow students can cut swim noodles and attach them temporarily to the plywood frames with masking tape. (Be sure they have reread the bumper rules before doing this.) After bumpers mounts are designed and T-nuts drilled into the plywood, the naked but assembled bumpers will be delivered to the seamstress.
Kicker / catapult mock-up:
Chris and I had a decisive kicker/catapult mock up session with David Tues before dinner and all parties agreed that the overhand motion beats the underhand swing. We might need to fabricate a new four-bend catapult arm to fit outside the 16″ width of the inner chassis rails, but the existing six-bend pipe could find its way onto the first prototype.
I want to fabricate a strong (steel?) subframe to which the arm is splinted. (I’m thinking that adjustability and field repairs/mods will be easier with separate pieces.) The steel piece will also comprise the pivot, spring attachment points and the anchor point for the moving end of the winch strap. Lots of force on this part! I will crunch some numbers tonight or tomorrow to figure out what distances are in the ballpark for ball:pivot, winch:pivot and spring:pivot.
Ball-picker:
I’m waiting for the keyway tool to arrive on Thursday before the business end of El Toro can be finished. In the mean time, both motors are nicely mounted on a subframe, pivoting in pincer fashion. Elastic cord (or a suitable metal spring) needs to be added to supply inward force on the pincers, so an appropriate mounting point for this elastic needs to be added.
To pass or catch a ball, the picker subframe needs to be able to be retracted quickly to the upright position. This lifting part still needs to be designed. Perhaps a 92 rpm window motor rotates quickly enough to provide this function? The mech can simply cycle like windshield wipers, but it should probably have a limit switch so it can figure out where “up”, “down” (and “park”?) are.
Integration:
The ball picker has two motions and three distinct functions which need to be tested with the ball, the bumper and the catapult in place. This integration is not trivial and will require some patient tweaking before it can fulfill its load, unload and catch functions satisfactorily.
Let’s do some sketches to see what range of motion is needed, and whether we can go “up” to grip the ball for passing, yet “park” the device where it will not interfere with shooting nor hang so far overboard as to get wrecked in a sideswipe collision. My current idea is to power it up & down with a window motor and a limit switch on a spring, but there may be a more elegant way to actuate it passively. Such as…
What if a small wheel was installed on each CIM at base of their shafts? The wheel would bear on a strip of material inboard of both CIMs (functioning essentially like an inside sector gear, if you know what that is). When the CIMs begin to rotate in “ball getter” mode, the small wheels would drive the contraption to lean overboard to contact the ball. When driven in the opposite direction, they would climb back aboard and grab the ball to be passed. Because the ball forces the spinning rods apart, contact with the small wheels and their bearing surface would be lost when handling the ball, and its climbing tendency would be negate when it would be counterproductive.