Here’s a (horrible quality) test fire video. Launcher is at 35 degrees, firing at the low power setting - http://www.youtube.com/watch?v=FYzdV9iDF7M
I’ll try to share better quality video later, preferably after we mount the thing right side up to the robot.
That’s impressive. What are you doing in terms of spring force? What’s the weight of the ram? What’s the starting gap between the ram and the ball (if any)?
It reminds me of a MK19 grenade launcher…
http://imagizer.imageshack.us/v2/640x480q90/547/sy7r.jpg](http://imageshack.com/a/img547/8959/sy7r.jpg)
Currently, there are two www.centuryspring.com #81153 springs on there, providing about 50 lb. of force each in the low power setting, and 80 lb. of force each in the high power setting.
The high power shot is selected by extending the 2 3" stroke cylinders, which adds 3" of pre-load onto the springs.
The motor/gearbox pulls the springs back to firing position (roughly 6" of pullback). When the launcher fires, the majority of the stroke takes place with the ball in contact with the ram.
The ram is 1" round igus aluminum rod with a McMaster 3/8" wide, 20 DP, 14.5 PA rack gear affixed. The rod slides through two open-top igus linear bearing pillow blocks. I actually don’t know how much the ram weighs. The overall claw/launcher combo projects to weigh around 35 lbs.
I was kinda thinking a .30 or .50 cal machine gun, but I think I like yours better. 
Holy Perspective! It looks like its 4 feet tall 
That is terrifyingly awesome. Great job as always!
The main structural element is 4" x 4" x 1/8" wall aluminum, if that helps.
Our linear launcher (not actually a puncher, but similar) uses aluminum extrusion with those same dimensions as its main structure, and our winch gear system is integrated, so our aluminum box structure serves both as a gearbox and launcher track all in one piece. Since our launcher stores a ridiculous amount of energy, we now understand that these types of ball shooting mechanisms may just need that much structure!
Wow, that’s surprisingly little force for such a great launch. We’re hitting 220 pounds at full pullback in our shooter, and we’re still not getting much distance as we want.
Any reason for the tiny little pusher plate? Or are you going to replace this with something else?
We’re pretty happy with the efficiency. I cannot imagine it is the only reason, but our rack and pinion cocking system completely disengages the cocking pinion from the rack on the plunger rod - the pinion has missing teeth by design - so there is no drag on the plunger rod from a winch when it fires forward.
The igus linear bearings and aluminum shaft are also (literally) quite slick.
Any reason for the tiny little pusher plate? Or are you going to replace this with something else?
Honestly, the shape/size was kinda arbitrary - we just wanted something larger than the diameter of the 1" plunger rod to start. The end of the rod is threaded so we can put in larger-diameter endcaps if we want and examine the effect on distance (and more likely, shot consistency).
Hi Travis
How far are you hitting the ball?
This looks like a really long shot but I’m assuming that the camera perspective affects it a bit. What is the maximum effective range of this launcher?
Our low power shot was hitting from about 16’ tonight.
Is that shots from 16’ into the goal, 16’ to hit the ground, or something else?
I know nothing is going to happen but i sure would like to see a steel cable thru the center of that spring. I just don’t see a way to hook one up in this picture. Maybe once it is mounted. I worked on garage doors for 30 years. Please be careful.
I can almost wrap my head around how it works, but not quite… How are you selecting the high or low shots? I think I understand, but am not positive…
The high power shot is selected by extending the 2 3" stroke cylinders, which adds 3" of pre-load onto the springs.
The motor/gearbox pulls the springs back to firing position (roughly 6" of pullback).
So… for the low power shot you pull back the spring 3" (using only the pneumatic cylinders) and for the high power shot you use the motor to pull the spring? Or both? Can you switch between powers on the fly (i.e transition from low to high or high to low without firing in-between)?
I can’t believe how compact it is. I thought it was huge until I recognized that it was in a vice, and then everything else started coming into perspective. It’s definitely one of the coolest things I’ve seen so far
That would be 16’ to the bottom of the goal as indicated on the white FRP target in our shop. We’ll have access to a real practice goal once we gain access to the auxiliary gym, where we have the room to set it up.
We planned on running some “anti-explosion” means through the springs at some point. I can suggest sooner rather than later. They really appear to be contained well by our delrin spacers, but if the springs fail due to internal defect in unexpected fashion (we do not stretch them beyond their recommended max deflection), we’ll want something to prevent them from being launched into orbit.
I hope the catapult folks (and safety inspectors) are equally as concerned with the high velocity tips of catapult arms weakening, breaking, and launching into space at some point. 
Thanks - we were aiming for a compact design. Here’s another video of our shot with an appended closeup look of the launcher firing - http://youtu.be/v_7ZfDrzMA0.
The cylinders only affect the setting for the shot power. They are fully independent from the motor/gearbox-driven rack/pinion mechanism that cocks and fires the ram.
There are two shot power settings:
Low power setting - cylinders are retracted. Motorized rack and pinion stretches the springs about 6" total from a barely-stretched starting point.
Higher power setting - cylinders are extended to 3" stroke, Pre-stretching the springs 3". Motorized rack and pinion stretches the springs 6 additional inches for a total deflection of 9".
A carriage rides on round bearings inside the 4" x 4" shell. This carriage is driven by the two shot power cylinders - it moves the steel shoulder bolts to which the front spring loops are attached - these shoulder bolts travel inside slots milled into the sides of the 4" x 4" (this is the part that looks like a cocking lever on a machine gun). The rear spring loops are attached to a steel crossbar running through the back of the 1" aluminum ram. The shot select system can be actuated independently from the motor/gearbox cocking mechanism. I will try to get closeup video of this actuation tomorrow.
The motor/gearbox drives a 20 DP 56T steel pinion gear with about 6 linear inches of teeth on it - the rest of the teeth are cut off, creating a “flat” on the gear. The pinion teeth engage with the steel rack gear attached to the 1" aluminum ram, stretching the springs and cocking the launcher back. To fire, we simply run the pinion into the “flat” zone, permitting the springs to release their energy and the ram to fire forward. We run the pinion from the flat zone to the mesh zone to re-$@#$@#$@#$@# <-- HAHAHAHA re-“male chicken”] the launcher and repeat the process. We only run the motor/gearbox in one direction - there is a ratchet integrated into the gearbox for anti backdrive.
What type of sensors are you using to determine the status of the pinion gear? An encoder on the gearbox?
I assume the “default” state of the launcher is in a cocked position. How many teeth are engaged with the rack in the cocked position? Are you concerned or have you done any analysis on the potential of breaking teeth when only one (or two) are engaged right before you release?
While it would be nice to have an angle sensor on the pinion shaft (it would be a Cherry AN8 360 degree model), I do not believe it absolutely necessary. What is necessary is to have two endpoint sensors on the rack. We expect to mount one at the launcher extended point - probably an inductive prox switch from automationdirect.com to pick up the rack or some other steel target. The other sensor will pick up another suitable target with the launcher retracted and about 1/2" - 1" of linear travel left before the trip point.
We performed an Inventor FEA analysis on a single tooth of the rack gear - the results indicated the system could handle a 200 lb load with a 2:1 safety factor. The springs on the robot currently top out at a combined 160 lb. launcher load. As I stated above, we expect our cocked position to be in a spot 1/2" - 1" short of the pinion trip point, with multiple gear teeth in mesh.
