Extendable Arm/Hanger Subsystem? What works best?

We’re playing around with a design for an extendable arm/hanger system for our FRC bot. It is in two pieces, uses Gates belt drive to extend/retract and a dual hook/flat piece to hang and push portcullis up. I’m thinking this is way too complicated and frankly don’t have any ideas or suggestions to make this better. What we want to be able to do is hang during the end game and manipulate the field defences during the game. Constraint: the team wants to keep the robot low to work through the low obstacle. That’s why we have a two piece arm that folds (maybe…haha) flat upon the bot and raises up into a slot and extends up mechanically.

I’m throwing this out onto the forum simply because I’m just a teacher, not an engineer. Am quite frustrated with this. We solved the hanging issue for the “Frisbee game” by making a hanger that would get us 10 points EVERY game. We wanted to get higher then but did not know how to do this. Any references, pearls of wisdom other than “google it” would be appreciated. We are at total odds on strategy; we mentors advocate an aggressive attacking strategy combined with a hang at the end. We feel this is the only way to move up from mid-table last year. The team wants to play defense only; working the obstacles, pushing boulders into the low goal and breaking down the field works. I’m at a loss to move forward. My gut tells me to back off and let the team have full steam with minimal hard decision-making on mentor’s part. My brain tells me that it’s time to press the restart button and get them to work on yet another decision matrix to get max points. It’s almost like they really don’t care what happens as long as it is easy to do. Oh well…thanks for reading my rant. I still would be grateful for any help on the extending arm that is simple, robust, and works every match.


Steve Miller
Coach-Team 3355
Purple Vipers

The climb is worth 10 points per match (margin over a challenge). It does not contribute to QP unless it’s the margin of victory for a match. We’ve decided to skip the climb and put the effort into making all of the things we will use repeatedly a bit faster instead. YMMV.

We also plan to use the ball pickup manipulator (goes over the frame perimeter) to operate the portcullis and Cheval de Frise; the adjustments needed for these are quite minor.

If you are hoping to go to big big things, such as world, I’d imagine you would want to climb. An extra 35 points at the end of a match would be absolutely mandatory. Now, I looked into a folding telescoping lift bar, it layed flat so it could get under the low bar. you would need some pistons. You COULD go the pneumatic route if you wish. But Personally I’d stick with electrically telescoping!

It’s not 35 points, in reality, when you take in to account challenging, its only worth 10 points. Scaling can definitely be ignored and still have your team make it to Champs. A great example is 2013. Challenging is like a 10 point hang then, and scaling is a 30 point climb. Unless you can do it very quickly, it’s not worth it, especially considering that in that time, you could be getting more crossing and high goal points. In 2013, you could outscore a 30 point climb by doing 2 cycles and a 10 point hang. In 2016, I expect that the only way a scaler will be playing on Einstein is if they have a last second climber like 67 in 2010, or if they can very quickly do it in less than 3 seconds.

I suspect 5/6 robots on Einstein will scale every match and do so as you said, in 3 seconds or less. You have to think that if 254 could climb the pyramid in 2013 in 6.4 seconds, a much more difficult challenge, then I have to believe that teams that plan to compete for a world championship will have sub 3 second climbs.

Further, If you’re saying the team is already on the batter ready to climb. From the time that team triggers their climb to fully scaled I think you will see around 1 second.

For those who were wondering, like me, (heres my back of an envelope calculations)

140 Lb robot = 622N
climbing ~1m in 1 sec = 622 watts.
1 CIM = 337 watts
You could climb in 1 sec with 2 CIMs, but it would be close and your extension to get the bar in the first place would have to be nearly instant.

A few things to the OP first/;
A climber is not necessary to be good this year. There will be dozens of regionals won without a single climber on the winning alliance.
2) Both an offensive strategy up front shooting boulders and a strategy that revolves around being a good breacher that scores low goals and feeds balls can be successful at a regional level.

Now if you still want to climb, there are some references to look at in 2010 and 2013. Additionally, if you skip the low bar, the challenge of climbing becomes much, much easier.

The challenge of climbing is two things:

  1. reaching the bar, and
  2. pulling your robot up

Reaching the bar can be done in a bunch of ways, including arms and elevators, some of which can be spring-loaded upwards for simplicity’s sake.

Pulling your robot up can be done in a few ways, but I think the simplest is to have a strap with a hook attached that you winch down to your robot.

Something to look up:
3467 2013 climbed the pyramid by having their arm automatically spring up with torsion springs, then winching it back down with a strap.

In the last 20 seconds you can drive around the opponent’s courtyard fully extended, regardless of whether you’re on the batter or not. So 17 second of extending while driving around still scoring, plus 3 seconds for the lift itself.

Supposing the 40A breakers can handle the over-current match-to-match attached is how it’s potentially done in under 1 second. Of course, the 80% gearbox efficiency doesn’t account for the winch and any associated pulley inefficiency. I also divide JVN’s current draw per motor by the efficiency just as a rough estimate of how much extra current is pulled due to these inefficiencies.

This particular setup would also need anti-backdrive.

Scaling Motor Calc.png

Scaling Motor Calc.png

ok…i’m having my team rtfm again. They told me they could not use springs since it was a source of stored energy. Haha…I’m a dullard aren’t I? Thanks for the info so far.

Yeah, springs are totally allowed.

Consider the possibility that whatever pulls you up doesn’t have to be whatever puts the hook(s) on the bar.

Have a look at R35. :slight_smile: