The VEX ratchet system was not used. However, to keep the catapult held downwards, a custom ratchet made out of a pinion with rubber bands was created. By using a rubber band to hold the gear down, it provides the ability to turn in one direction as the rubber band stretches. However, in the other direction, the gear is forced against a metal piece, stopping the catapult.
Robot is partially dismantled but… here’s a picture of the system in case there’s some confusion!
http://i67.tinypic.com/rs8rqv.jpg
Think… they are more confused than ever now… lol…
Very nice robots. How do you think motor distribution will change with V5? Especially with regard to the drive train and the advantages(?) of having as many V5 motors on it as possible.
The team did a fair bit of prototyping in the past few months. In fact, we just had a discussion this morning. We kind of know what we want to build for singopen and also a rough idea for worlds.
But sorry that we don’t want to reveal too much at the moment… coz we will be facing off China teams in singopen, need to retain whatever small amount of advantages we might have.
But we are actually looking forward to v5. 8 motors are more than enough for our current design. 1 motor for either catapult or flywheel and 1 motor for intake. There are still 6 motors left to play with.
So, when it turns the other direction, the 12T gear get stopped by the metal? Am I understanding?
You are right , the immobilisation of this pinion stops the entire catapult from moving . It’s also visible in the picture. It was built in a hurry so it does sound sketchy and might not be the best implementation but it worked well enough during the competition:)
What gear ratio did you guys use for your catapult? and what gear in the ratio did you implement the pinion? I can’t quite tell from the picture.
The gear ratio is listed right at the beginning of this thread 
Oh. Oops
I am still super confused about the double catapult’s ratcheting system, could someone explain?
I specifically don’t understand how does the catapult stay back when down, but still has the ability to shoot forward ( doesn’t a ratchet prohibit movement in one direction).
The ratchet is on the slipgear so the slipgear can only rotate in one direction, thus holding down the catapult until its release point. Thus the catapult can shoot.
I’m also trying to build a ratchet but can’t seem to figure out how the rubber band let’s it spin one way but not the other. I was thinking of using one of those gravity ones, if y’all know what I mean
As you can see in this picture, the ratchet gear is different from a regular gear. The tooth on the top right corner will have a rubber band on its tooth on the right, pulling down, so that it forces the the lever towards the gear. Thus, when the gear turns clockwise, the lever skips the teeth on the gear but comes back every time because of the rubber tension. however, if the gear tries to spin anti-clockwise, it cant do it because the lever locks and it stops the tooth on the gear that it is currently contacting. So, the lever would be attached to the tower or something and the slipgear would be on the same axle as the ratchet gear so that it can only spin in the direction that will cause the lever to skip, and when unpowered, it would hold its position and not snap the catapult back so you can make it stop for loading.
well… guess we shouldn’t underestimate the torque from the motor 
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OOF
Yep, unfortunately we have been afflicted by this scenario as the copyright claimant has chosen to block the video rather than monetise it. We’re working very hard at the moment to resolve the issue but if it doesn’t turn out right we might have to go with a soundless video or find another song :((
Hi, I’m new to the forum but have a few important questions. My team and I have almost figured out the two ball catapult, except for the ratchet. We have to change the motors to high strengths and build the rachet. If you could list the parts or maybe post some pics of the gear train at a different angle it would be greatly appreciated. Best of luck!
They’ve already taken apart the robot and are hiding their current one because they plan to compete in China I think and don’t want to lose the element of surprise
this is the ratchet they used in the video (@meng any announcement on when that’ll be put back up?) it’s just a few responses up tho
Totally unrelated but as I’m scrolling down I keep seeing
and it’s super gratifying. Thank you so much everybody!
Also @meng why did your kids use 2 low strength gears instead of a high strength gear? Thanks!