Yeah, I wish that we would’ve been paired up at the end, but I’m soo glad y’all won!
It didn’t feel right when we first started cutting them, but then it was…ok, how many more can we cut off to speed this thing up.
how well did the faster gear box work did it go just as far
There was no difference in the distance between the faster and slower gearboxes. The biggest challenge is getting the intake to keep up with the shooter.
How did you calculate the number of teeth to remove from the gear for the ‘slippage’ and the distance between ‘slips’.
^ super technical terms here!
We knew how far the hammer had to be pulled back with the testing that we did before we attached any gears. After we attached the gear, we simply counted how many teeth we needed to achieve that distance. We then divided that up on a 60 tooth gear.
How long is your hammer? Sorry about all the questions
11.75" inches
Great work guys!!! My team is working on a similar catapult design, but instead of using a slip gear we are using a nautilus gear. I see that your team is using the impact of the hammer to propel the balls. Have you tried using the same slip mechanism to launch the balls ''the traditional way" (leaving the ball at the end of the bar)?
In asking because my team has been struggling with the traditional method ,we have to use a large number of rubber bands in order to achieve the range. Does using the instant impact reduce the number of rubber bands that you have to use?
How long is the arm of your catapult? The longer the arm, the fewer the rubber bands. Where are you placing your rubber bands? The higher up that you place them on the arm, closest to the cup of the catapult, will give more power to each rubber band; this is assuming that you are attaching the rubber band holder at the top of your catapult stop. When the catapult has fired and the catapult is at its peak, are the rubber bands level with each other? The more level the rubber bands are at the top, before the catapult is pulled back, the more power each rubber band will give you. We only use 2 rubber bands in our current design, but we were able to get the distance we needed with only 1 rubber band using the same launching mechanism positioned differently.
As a long range shooter when a catapult launches a ball the base must absorb the energy of the catapult; when the hammer launches a ball, the majority of the energy is transferred to the ball. So, the base of the catapult will need to be much heavier than the base of the hammer; especially if you are going to be firing more than 1 ball per second accurately. The biggest advantage to the catapult, in our opinion, is the fact that they are not affected by the differences in the balls; the hammer must be weighted perfectly to compensate for this.
Because we do not have to compensate for the weight of the ball or the pan, we are able to use fewer rubber bands, but thats not the only reason. While the “hammer” and the “catapult” have the same motion, they are different; its the difference between throwing the ball and kicking, pitching the ball and batting. Using the catapult with the slip gear vs the cam/nautilus gear will not change the amount of rubber bands that you need to get distance. The launch angle and the weight/length of your catapult will determine the distance.
Im currently in a VEX U team, building the 15 inch robot, and my catapult lenght is maxed out. The angle of departure is about 20 deg and we using +4 rubber bands in order to have the range. The rubber bands are attached from the begining of the cup to the end of a 15 inch CChannel tower. As you said earlier we are having problems with stability and are adding weight in order to maintain the bot at the same place when launching. Also our parts were suffering the strain of the catapult, we managed this by reenforcing each part of the design. For example, joining 2 cchannels in order to avoid defflection in the bar of the catapult. Reducing the number of rubber bands would fix many of our problems.
Another aspect is that we have a relativetly small pullback (aprox. 2.5 inches lineartly).
I will follow your recomedation and try to find some room to increase the angle. I really appreciate your input.
I would bet that you could take the exact launching mechanism that we are using and fit it into a 15" robot. The entire mechanism is less than 14" long, less than 5" wide, and less than 13" tall when the hammer is at its tallest point. When you watch the how to video on the slip gear, you can see the angled piece that we built to achieve our long shot ball height. You can achieve the same thing by moving the ball further back, so that the hammer arm makes contact with the ball at about a 35 degree angle. Our current bot was put together the night before our first competition, and our intake dictated a lot about what we could and couldn’t do. In our new design we are going to be making several changes to our intake to maximize our shooter.
Sorry, how did your team create the actual slip gear?
I can’t speak for 9541, but I know you can take the teeth off a gear with a bandsaw and then use a coarse file and sandpaper to smooth out the gear where you cut it. If you don’t have a bandsaw, you could probably use something like a small fret saw or even a hacksaw blade removed from the handle/holder to carefully, patiently cut away the teeth.
If you have a Dremel, you can put on the sander bit and use that, too. With a Dremel, I would NOT use a grinder or mill bit. The mill bits have a tendency to grab the plastic and dig in. The grinders just gum up with plastic. You might be able to use a Dremel cutting wheel if it’s meant for plastic, but I would be very cautious about doing so - it’s easy to slip with those, and sometimes the plastic melts in weird ways. Only use a Dremel with adult supervision, of course. And safety glasses.
We used a dremel with a cutting wheel. First, cut the two farthest teeth on low. After that you can turn the dremel up and cut the teeth in between the first and last. Once you get to the point that you really can’t see the teeth anymore, stop using the dremel and pull out the file. After you’ve run the file across it a few times, run a fine grain sand paper, like 2000 grit, over it a couple times for good measure. I’ve seen a couple teams copy our mechanism but totally butcher the slip gear and it worked fine. I’m just of the mind set that the better that it looks, the better it will perform. 
I may have totally miss understood your question. I was up late at night hitting my arm against the wall, wondering what mechanism would make this fluid motion. I thought of a hammer on a revolver pistol and immediately thought of using a slip gear. I know that a revolver doesn’t use a “slip gear”, but I was thinking about the different firing mechanisms on weapons and the hammer slipping on a seer, combined with the motion of my arm, just made me think of giving it a try.
Did the first iteration shoot full court? If so, how many teeth did you cut out from the 60 tooth gear?
We are a rookie ream, can you shoot me an email? corbin[dot]werner[at]stu[dot]barren[dot]kyschools[dot]com. Thanks!
Yes.
We cut out 8 left 12, cut out 8 left 12, and then cut out 8 more. This gave us 3 shots per rotation.
We’ve since built a couple other launchers and we only needed 10 teeth to achieve a full court shot. We only use 2 rubber bands. I’m sure that you could get a full court shot with only four or five teeth, but you will need more than just 2 rubber bands.
The how to video is at the top of this thread. We will be posting another video later in the week as well.