My team is looking at the possibility of making a t-shirt cannon robot over the summer and just for fun we thought of putting the cannon on a pan/tilt module.
We’ve never done anything like a pan/tilt assembly before. The tilting part is pretty easy for us to figure out from what a few of us figure though the panning part is tripping us up a bit. In 2006, we (or rather last year’s graduating class) made a swerve drive using some sprockets mounted onto some wheel 80/20 assemblies. I did some searching on the forums and it appears the same idea/method is plausible. What I wasn’t sure of was the alternate methods that could be used.
In other words, what could be used to provide smooth panning-like motion to a t-shirt cannon assembly (probably with some weight to it) with support for an encoder?
We waterjetted a giant aluminum sprocket (LOTS of teeth! :ahh: ) to bolt onto ours in 2009. Drove with a globe & small sprocket. Worked great, but not for the faint of heart in terms of machining :yikes: .
Our team also used McMaster Part #: 18635A52 for our turreted shooter last year. This bearing worked very well… it was very smooth and seemed like it could support far heavier loads than our 20 pound, centrally-mounted shooter!
To control it, we simply used a single rivet to attach a timing belt, and ran the timing belt with a globe motor - we had a push-button limit switch at each extent of the turret’s travel, and an encoder on the output shaft of the globe motor. I can’t recall the specs on the encoder, and I’m only 80% sure that the encoder was mounted on the output shaft.
Altogether, this set up worked very well for us - it allowed us to autonomously score a couple moon rocks, too!
Our team did the same thing as the others last year for our rotateable turret. The turn-table comes with a screw on the side of the turntable, we just cut slits in a timing belt and used that screw to attach the timing belt. Then a globe to rotate with a small gear on it to turn the timing belt.
In 2009 we built a turret for our robot. It was made from a PVC ring and four V-Channel bearings. It worked flawlessly and still works perfectly today. We will also be modifying it to be our T-Shirt cannon robot. Here are some pictures to help out.
The ring of screws created a sprocket out of the PVC ring so the gates belt could rotate it.
Look closely at the top of this one and you can just see the final product. In this picture the turret is pointed to the right and the motor is visible behind the “C” in “Force”.
I’ll see if I can get some more detailed picture of the drive mechanism. BTW, we included a pot for position feedback. That allowed us to actually follow another robot and fill 'em up in Autonomous.
We used a lazy susan for our 2009 shooter as well – we rounded a very large ring out of a piece of plywood and then Gorilla glued a timing belt to the outside to turn it into a giant sprocket, then drove it with a timing belt sprocket attached to a globe motor.
It worked great, with about 340 degrees of movement before we ran into the edges of the belt – but that’s where we had our limit switches anyway!
An encoder was mounted to the assembly, but we didn’t end up using it.
1319 did this in 2006 with our pan and tilt turret used for shooting poof balls. The only difference was we used an aluminum ring instead of a PVC one as well as 8 (2 on each corner) V-channel bearings. It certainly does work flawlessly. If you have a copy of the behind the design book our robot is featured in it and I believe has a close up shot. PM me if you want more info or pics.
The TechnoKats t-shirt cannon was mounted on the team’s Rack & Roll practice drivebase for a while. Tilt control was a simple chain and sprocket on the arm’s “shoulder” joint. There was no need for a pan mechanism, as the robot itself can turn to face whatever direction is desired.
If we hadn’t donated the 2008 Overdrive robot drivebase to our sponsor for target practice, it would have made a fantastic t-shirt cannon platform. Maybe we can mount the remaining superstructure to a simple mecanum drivebase and drive it around that way.
We were fortunate to have the water jetting done for us. If you have more questions I will see if I can get someone to either get me some more pictures of it or let me back into the shop so I can snap some of it for you.
The sensor was indeed mounted on the output shaft of the motor and it was a US Robotics magnetic position sensor. The bearing worked great for us - it even has pre-tapped mounting holes in it.
