Locking Mechanism for Catapult?

[josmee443]

Hi Guys!

My team (Team 1758) has been working on a locking mechanism for our catapult in the past couple of weeks, but we can't seem to come up with a smoothly working design. Our most recent idea was using the locking mechanism of a doorknob. The latch of the doorknob holds down the catapult and a piston pulls back the patch to unlock the catapult. However, due to friction, this mechanism does not work all of the time (maybe 50% of the time). Do you guys have an suggestions for a good working lock mechanism for a catapult system?

Thanks! :]

[Ether]

Hi Guys!

My team (Team 1758) has been working on a locking mechanism for our catapult in the past couple of weeks, but we can't seem to come up with a smoothly working design. Our most recent idea was using the locking mechanism of a doorknob. The latch of the doorknob holds down the catapult and a piston pulls back the patch to unlock the catapult. However, due to friction, this mechanism does not work all of the time (maybe 50% of the time). Do you guys have an suggestions for a good working lock mechanism for a catapult system?

Gate latch. Ball shifter with gear removed. Pin through an eye bolt with a teflon insert. Pawl. Over-center lever. Door-lock electromagnet (are those legal this year)?

[rwkling1]

Our team is using a gate latch. It's very simple, strong, easy to use, and easy to release.

[apples000]

Doorknob.

[Ether]

Doorknob.

Any particular model? The OP said they were using a dooknob and it wasn't working for them:

...The latch of the doorknob holds down the catapult and a piston pulls back the patch to unlock the catapult. However, due to friction, this mechanism does not work all of the time (maybe 50% of the time).

[David Fort]

Pneumatically actuated hatchet that cuts the rope.
(worked back in the day just fine).

I suppose that has the disadvantage of only working once.

Our team is partial to rope clutches (from sailboat). It can take a lot of force to release, but if you are more clever than we are, it can probably be mitigated.

I like systems that are "balanced" and the force to release them does not fight against the holding force. For example, a rope wrapped around a post. It holds if the tension is perpendicular to the post, but if you rotate the post down, the rope slides off the top.

[Adam Freeman]

2008 Chevrolet Impala truck latch. Should be available at any Chevrolet dealership.

A little awkward to package/mount, but will hold a lot of load and can be easily released with a servo.

[josmee443]

Our team is using a gate latch. It's very simple, strong, easy to use, and easy to release.

Could you possibly describe how your team's gate latch works?

[josmee443]

Gate latch. Ball shifter with gear removed. Pin through an eye bolt with a teflon insert. Pawl. Over-center lever. Door-lock electromagnet (are those legal this year)?




How would those work?

[rwkling1]

Could you possibly describe how your team's gate latch works?

Sure! So our team purchased a gate latch similar to this:
http://www.menards.com/main/tools-hardware/fasteners/gate-hardware/latches/gate-latch/p-2155218-c-9694.htm
And what we have, is we attach the "peg" or whatever you want to call the piece that goes into the actual latch is mounted to our shooter. We attached a pneumatic cylinder onto the actual latch, so that when the cylinder is extended, the latch is closed, and once we retract it, it pulls back the latch, releasing the shooter. We also have a limit switch making sure that we don't winch the shooter down to much.

[DampRobot]

2008 Chevrolet Impala truck latch. Should be available at any Chevrolet dealership.

A little awkward to package/mount, but will hold a lot of load and can be easily released with a servo.

Was that what you used for your famous Einstein winning hang?

[Rynocorn]

2008 Chevrolet Impala truck latch. Should be available at any Chevrolet dealership.

A little awkward to package/mount, but will hold a lot of load and can be easily released with a servo.

Hey we tested with this exact same thing! It worked really well but we ended up going with a different shooter instead, however I would recommend it for you guys!

[billbo911]

In 2010 we used a gate latch to hold and release out kicker. You can see it in this photo before the kicker was installed in the robot.

http://billbo911.smugmug.com/Other/2010/i-MKbpT9Q/0/L/0206001500-L.jpg

It was activate with a 1 inch throw cylinder, as seen here.

http://billbo911.smugmug.com/Other/2010/i-3nLnzqH/0/L/_MG_8844-L.jpg

[Gdeaver]

I've used a pneumatic coupler and a cylinder to pull the collar back. A ball lock device.

[Storcky]

In 2008, we just used a piston to lock. You can see it up close in the beginning of this video. http://youtu.be/JKdTJSR-KuU

[J. Stofflett]

This works well for us.

http://www.mauriprosailing.com/us/1-Harken-Cam-Cleats/HAR418.html

https://drive.google.com/file/d/0B3yX55ZZS5qcOXZpajc4SklVUG8/edit?usp=sharing

[rick.oliver]

We have prototyped a latch actuated with a short stoke cylinder. The prototype used a 1/2" diameter shaft supported on bearings to simulate a CAM roller. The latch was cut from 1/8" AL flat stock such that the latch would follow the radius of the shaft and go just over top dead center. The latch is also cut away from the shaft at an angle to allow the catapult to flex down when the ball enters.

We have not completed the competition version; however, have high confidence it will work reliably. If not, thanks to the posters for alternatives.

[Ether]

We have prototyped a latch actuated with a short stoke cylinder. The prototype used a 1/2" diameter shaft supported on bearings to simulate a CAM roller. The latch was cut from 1/8" AL flat stock such that the latch would follow the radius of the shaft and go just over top dead center. The latch is also cut away from the shaft at an angle to allow the catapult to flex down when the ball enters.

Could you post a picture or two? I can't quite get a mental image from your description.

Thank you.