Start with 3 inch wide (1/2 inch high walls) aluminum channel, 29 inches long.
Print the seesaw al bracket and attach it to the center of the aluminum channel with machine screws.
Add the seesaw cap to one end of the channel.
Add acrylic shields to the end and right side of the channel (these are to keep Froggy from bouncing out). I screwed one piece of acrylic on and I "welded" the other by "painting" (small brush) acetone on the abs printed part--then holding the acrylic against the abs printed part.
Using the balance base a, catapult motor c and catapult motor lid (printed 3d parts), attach the servo motor to "the tower."
Attach a 1 1/2 inch diameter, 7 1/2 inch long acrylic rod to an 8 inch by 6 inch by 1/2 inch (painted plywood) base.
Find a position "midway" in the servo travel and let the motor rest there. This way, when you attach the channel in a "mid travel" position; you'll know that you have room to make it move by software where it needs to go.
Pre drill holes in the top of the acrylic rod to accept the gear bearing holder.
Mount the servo horn to the seesaw al bracket, then mount the channel to the servo motor. Fasten the servo screw in the center.