Robot in 3 Days: BNS Edition

A few of the members of Team BNS decided to join in on the fun and try our hand at building a Nothing but Net robot in three days.

We present to you, Mangonel.

https://vexforum.com/attachment.php?attachmentid=9465&d=1435015756

Mangonel is designed to quickly gather and score balls on the field from close to medium range, supplementing another robot which would be capable of full field shooting.

Drive:
6 motors with internal turbo gearing direct driving 3.25" wheels.

Launcher:
2 high speed motors pull back surgical tubing to power the catapult. A piston locks the arm in its ready position, and releases to let the balls fly.

Intake roller:
1 motor with turbo gearing pulls balls into the firing tray.

(That makes 9 motors total, in case you were wondering. More could easily be added).

The inspiration for the launcher came from the VEX robot built for FRC Rebound Rumble.

Enjoy!

Edit: Here’s the link again in case you missed it https://www.youtube.com/watch?v=tmmjL8r8-E4
Mangonel.jpg

Looks mighty fine. Any chance we’ll be treated to a video of it in action?

(there is a link of a video in the original post :slight_smile: )

I love it! I’m especially impressed by the way it adjusts its tension. Not to mention how it can devastate a potted plant from across the room. :slight_smile:

Very nice work. :slight_smile:
Good to see an alternative design that works well and is not too complicated to build. A long throwing catapult is difficult given the non-expansion requirement for this game limiting arm length and rotation. Did you manage to stay within 15" cubed with this robot? If not, do you think a 15" catapult robot is feasible?

Ah you caught us, length wise we’re about an inch oversize :wink: Width and height wise it’s fairly easy to keep within 15" at all times, however we found it difficult when the catapult released to keep the tail of it under 15". I don’t expect this to be terribly difficult to figure out, but it will require more planning to keep everything in size.

Any ideas on what you will build for your 24" robot?

https://vexforum.com/attachment.php?attachmentid=9465&d=1435015756

Mangonel is designed to quickly gather and score balls on the field from close to medium range, supplementing another robot which would be capable of full field shooting.

Drive:
6 motors with internal turbo gearing direct driving 3.25" wheels.

Launcher:
2 high speed motors pull back surgical tubing to power the catapult. A piston locks the arm in its ready position, and releases to let the balls fly.

Intake roller:
1 motor with turbo gearing pulls balls into the firing tray.

(That makes 9 motors total, in case you were wondering. More could easily be added).

The inspiration for the launcher came from the VEX robot built for FRC Rebound Rumble.

Enjoy!

Edit: Here’s the link again in case you missed it https://www.youtube.com/watch?v=tmmjL8r8-E4

This is easily the most secretive robot that BNS has ever created. Most of us didn’t even know they were building it. :slight_smile:
First time I heard of it was when youtube told me the video finished uploading. I have to say I am pretty dang impressed with the robot. The 2 balls fly together so well making a double shot actually feasible.

Well done Owen, Justin and Rob.

Does the lack of a nestled home for the balls make variability in the double shoot? Would some tank tread feelers as guides assist in accuracy? Or is it pretty consistent in target hits?

(That poor plant is getting a beat down)

As a parent that has destroyed more than a few vacuum cleaners, I’m always impressed when I see $1.2 million in parts laying around on the carpet and seeing that some of them are loose nuts and bolts.

Nice design, like the adjustable tension option. This robot reminds me of my favorites from clean sweep that tossed balls 12’.

(Strike fear in the heart of your local cleaner salesperson. Hand full of 1x 2x 3x Lego and a few VEX nuts, bolts and the 45 degree angle, drop them on the carpet.)

Yes that is one source for inaccuracy that could be fixed. We originally had another version of the launcher that used pneumatics with metal guides that would allow the balls to “nestle” and this was surprisingly accurate. With our current robot, we setup a medium sized bin and could get both balls in more times then not at varying distances. Generally speaking, there is side to side variation for the reason you described, and distance variation since we don’t have a system yet to ensure they were pulled down the same amount every shot. There is no reason that we used a plate vs guides on this final version apart from we never got around to adding the guides.

I realize this is a fairly subjective answer, but it’s tough to give anything quantitative until we get a real net.

Can’t forget the famous “GIVE THAT TEAM AN AWARD RIGHT NOW”!

Very Nice work guys! And Owen, I’d love to see this design go far, just don’t continue the trend of “very first 15 goes to worlds” :stuck_out_tongue:

Thanks Greg, but also why not? :frowning: That’s the fun thing to do. But nah don’t worry, I think you can expect some changes on this little cutie pie of a robot.

Seeing that already 2 teams are using elastics as their launching systems, do you guys prefer using elastics as compared to flywheels? A lot of teams I know don’t like to use elastics because they wear out over time…

Another question if I may?

Once the rack and pinion is in the lowered position (elastics tensioned), do you apply a trim to the motors so that they hold position until the shot is fired? I am trying to gauge how hard these motors may be working in this stalled state and therefore if overheating could become an issue?

I guess that leaving the elastics slack until the robot is ready in a shooting position is one way to minimise this.

Thanks :slight_smile:

There are certainly tradeoffs for a flywheel vs elastics. For flywheels, they tend to be really large and bulky and requires a lot of energy to be wasted even when the robot isn’t shooting. Elastics allow the motors to work only when needed but can be dependent on how well it’s tuned and as you mentioned, how much the elastics change. I think designs using elastics have more potential (heh heh) in the long run, but it’s June and my perspective could change tomorrow :slight_smile:

Also, the surgical tubing we used to my knowledge doesn’t wear down much, if not at all, over time. Cam from his thread also mentioned he found found rubber bands that stayed consistent over a large amount of shots.

This was one thing we were originally worried about but were surprised to see a holding power of 15/127 was enough to keep it in a locked position. We haven’t run into any issues from the motors burning out or becoming weaker in any way, even when we keep it holding for minutes at a time.