Hey everyone! For a project I’m doing I need a kind of motion that will wind up for a few seconds and then release full power. For this I had the thought that somehow the Vex drop off cam that is apart of the advanced mechanics and motion kit would work for this.
Does anyone know where I can figure out how to use these?
http://www.vexrobotics.com/vex/products/accessories/motion/276-2045.html
I’m not sure, but you might also want to have a look at a “choo-choo” type of wind-up/release mechanism. Just a thought.
Have a look here: (In the video, I think it shows up around 3:30-ish minutes)
https://vexforum.com/t/motor-powered-launcher/25370/1
Choo-choos are hard to work with. I built one last year. Since the main gear has to be cantilevered, you often get gear slippage. You could probably get it to work if you have the turntable kit though, because it attaches at 4 points.
That’s just the experience I had with one.
As VEX Vortex mentioned, choo choos can be difficult with the available VEX parts (it is also difficult to find sufficiently strong and flat metal), but I think it would be possible using the cam originally mentioned. I am a little skeptical of the plastic pusher’s strength, but I think you could have a lever held against the cam with elastics that would bounce out past the lever arm on each rotation. See the Robowranglers 2010 FRC robot for an example of how this could work. For vex I would probably just have the lever be some structure contacting the cam with a nylon spacer, but I don’t think that is as important.
(Note that all three cams linked to in this thread are linked to JVN) 
I would like to mention that this is jot for a robot. It’s for a school project to make Halloween decorations. And the plan is to have a wooden coffin with mechanisms inside of it that bang on it to seem like there is someone inside trying to get out.
How about a servo motor with a couple of gears, the final gear with a flexible piece of wood or hard rubber “knocker” attached. The servo turns the gears around until the free end of the knocker catches on a peg. The knocker stops advancing but the servo keeps going, placing the knocker into tension until the knocker finally snaps free from the peg, striking the coffin lid?
If you want more rapid knocks, you might consider solenoids.
Just a thought.
I think this is your best option:
https://www.youtube.com/watch?v=D6qSKVqrk5I&list=UUNEVMox4XpdLhOjHSEo-R8Q
They shaved off some teeth on the driving 36 tooth gear so it winds up until it hits the smooth part which lets the driven gear spin freely.
Here’s a video of the whole robot:
https://www.youtube.com/watch?v=-M9WZC2HTcA&list=UUNEVMox4XpdLhOjHSEo-R8Q
Wow I like both of these. I’ll definitely look into them.
One of our teams did this for a firefighting challenge (80Y but it was fire fighting). It can work. The plastic follower is not the most rigorous high strength thing in the world. So just keep that in mind.
The cam follower was attached to a mechanism that levered itself to the small airzooka puffer thing with some rubber bands to keep tension. It pulled back along the cam rotation and at the drop off, it released causing a big puff of air from the airzooka blowing out the candle.
You keep the cam spinning and get your next shot of air once you’ve rotated around again. Fairly slow speed turns to maximize torque.
An IME or quad encoder can help know when you are going to go off the edge and release the load.
Let me see if I can dig up a picture if you’re interested.
I’d love pictures. At this point I still have no idea how a cam gear works…
I don’t know if this helps you much, but here is a good example of the mechanism you are thinking of:
https://www.youtube.com/watch?v=_hTyXQUgYLE#t=108
it’s around 1:48 in case the time link doesn’t work for some reason.
Probably the search terms you want to use are “cam follower”. Maybe check out this video:
https://www.youtube.com/watch?v=ZCFKUqCFd_A
OK, it does not use the cam part since it did not fit. Sorry the pic is so big. The crank goes round, you get another firing. The cam does the same thing really but not as far of a throw.
