pic: Team 256 presents our offseason robot: Stockade

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[Feroz1325]

Looks very nice, just a few questions...What is the point of the rectangular rear superstructure? Is there some sort of linear extension on the climber hooks, or are they just connected to the end of the piston rod?

[MichaelBick]

Looks very nice. The only thing I'm concerned about is the hanger. We broke one of our pistons by getting only half of the hanger on the bar before we pulled up, bending one of the piston rods. What I would reccommend doing is a 254 like ball bearing setup so that the piston rods to not take any side load. While the current set up will work, you might find that your pistons get slower/stop working after a lot of matches.

[Cash4587]

Originally Posted by Feroz1325

Looks very nice, just a few questions...What is the point of the rectangular rear superstructure? Is there some sort of linear extension on the climber hooks, or are they just connected to the end of the piston rod?

What it looks like to me with all of those holes is that the are able to move the hooks back and forth to get the COG right for hanging.

[DampRobot]

Originally Posted by MICHAELABICK

Looks very nice. The only thing I'm concerned about is the hanger. We broke one of our pistons by getting only half of the hanger on the bar before we pulled up, bending one of the piston rods. What I would reccommend doing is a 254 like ball bearing setup so that the piston rods to not take any side load. While the current set up will work, you might find that your pistons get slower/stop working after a lot of matches.

When this happens to us, we just bend the piston back... with our bare hands. For our offseason robot, though, we are considering some sort of pivot setup.

Andrew, looks sweet. Very judicious use of right angles. I'll be interested to see how your multi-disc auto works out.

[Andrew Schreiber]

Originally Posted by DampRobot

When this happens to us, we just bend the piston back... with our bare hands.

Which, interestingly, makes your pistons illegal since they have now been modified.

[AdamHeard]

the issue with the hanger is actually the hooks being off center. If the hooks had a tweak in them so that when hanging the bar is inline with the cylinder, that'd be much better.

EDIT: Like this



The significance is now the cylinder is loaded purely in tension (aside from the force of you ramming into the pyramid) when you hang. Otherwise you'd have a constant bending moment trying to bend your cylinder shaft.

It also looks like you're using two 1-1/16" bore cylinders. Unless you're storing energy in springs when they raise (or you're very light) this isn't enough force. Even then it's marginal.

[MrTechCenter]

Looks great, Andrew! Can't wait to see it at CalGames and Madtown!

[RKIyer]

Nice robot. Just wondering, is your frisbee storage open behind?

[T^2]

Originally Posted by AdamHeard

the issue with the hanger is actually the hooks being off center. If the hooks had a tweak in them so that when hanging the bar is inline with the cylinder, that'd be much better.

EDIT: Like this

[snip]

The significance is now the cylinder is loaded purely in tension (aside from the force of you ramming into the pyramid) when you hang. Otherwise you'd have a constant bending moment trying to bend your cylinder shaft.

It also looks like you're using two 1-1/16" bore cylinders. Unless you're storing energy in springs when they raise (or you're very light) this isn't enough force. Even then it's marginal.

This isn't the only time the cylinders are loaded, though. If your driver doesn't approach very carefully (and therefore slowly), you'll probably ram into the side of the pyramid with the hooks, and bend the pistons. We did just that at the Sacramento Regional. We fixed this issue by Champs by attaching the hooks to long, thin steel rods, which were silver-soldered into a fitting that screwed onto the piston. This allowed our driver to drive at the pyramid as quickly as he wanted, and only the rods would flex. (They were thin enough to still be out of their plastic range at that point.)

[Cash4587]

After looking at it y'alls shooter is exactly set up like ours. We used the Canadian urethane wheels (1114 and 2056 wheels) in a 3:1 and 4:1 versa as well. The wheels and gearbox combo was VERY reliable and is a great set up. The only thing different with y'alls shooter is we used a vex motor to push the disks into the wheels. we didn't use pneumatics at all on our bot.

[KrazyCarl92]

http://www.team20.com/wp-content/upl...2013-robot.jpg

This photo of our robot is from the last few days of build season. The climber hooks are made two pieces of 1/8" sheet aluminum, waterjet cut into a shape like what Adam suggested, then with stand-offs between them and flat-head bolts holding it all together. This mitigates any bending load on the piston when lifting. We then have C-channel that goes around the hooks. The front edge of the C-channel is what would contact the lowest bar of the pyramid when our driver slammed into it. We did end up adding another diagonal brace to the C-channel at our 2nd regional to add stiffness. This design worked well - we have not bent a lifter piston all year.

I prefer to design robots in a way that the driver doesn't have to think twice about driving hard. If we have to tell our driver "don't drive to the best of your ability in a way that gives us the best chance of winning a match because this could break," then we're doing it wrong.

The draw back of this approach is that our robot cannot go under the pyramid. This ability was already sacrificed by other aspects of our design, so it didn't really matter for us. We prioritized a simple, linear design, holding 4 discs, scoring upside down discs (before the rule update; only satisfactory prototype was a large rotary shooter), and floor pickup over driving under the pyramid. Maybe if we had used a compact linear shooter or used a bucket hopper and come up with the idea of spring-loaded hooks like we saw on other bots, we could have gone under the pyramid.

Looks solid, Andrew. Does that floor pickup have a pinch bar or roller bar above the lexan plate?

Originally Posted by Feroz1325

Looks very nice, just a few questions...What is the point of the rectangular rear superstructure? Is there some sort of linear extension on the climber hooks, or are they just connected to the end of the piston rod?

As mentioned earlier in the thread, the back end is so that we can move the pistons back for CoG adjustment.

Originally Posted by RKIyer

Nice robot. Just wondering, is your frisbee storage open behind?

In the model the back of the feeder currently is open. We use zipties as a "back" since we don't need too much contact area on a frisbee for it to slide into the bucket. Worked wonders for us during the main season.

Originally Posted by KrazyCarl92

Does that floor pickup have a pinch bar or roller bar above the lexan plate?

There is a 1x1 aluminum pinch bar that holds the frisbees in while the arm rises, and it's in such a position that in the vertical position the frisbees can freely slide out.

Thanks for the advice on the climber, Adam and Carl. I'll be sure to look into the centered hook design and reinforcements.

[KrazyCarl92]

Another thing to consider for the climber:

Unless you have really solid weight estimates everywhere in your CAD model, it's going to be difficult to know your COG. However, if you want the robot to lift level, you will need to know the forward/aft position of your COG. To achieve this, we left room for the hooks anywhere along the length of the robot within about a 1 foot span. To locate our COG we stood the robot up on its frame with a wheel on each side between the table and the frame and rolled it forward and back until the bot remained level without us supporting it. The location of the COG is directly above the line segment between the contact points of the 2 wheels on the robot frame. This allowed us to locate the hooks such that the robot would lift level.

It looks like you have some play with where you can mount the hooks, so perhaps this will help make your robot lift without much swing.

Originally Posted by KrazyCarl92

Another thing to consider for the climber:

Unless you have really solid weight estimates everywhere in your CAD model, it's going to be difficult to know your COG. However, if you want the robot to lift level, you will need to know the forward/aft position of your COG. To achieve this, we left room for the hooks anywhere along the length of the robot within about a 1 foot span. To locate our COG we stood the robot up on its frame with a wheel on each side between the table and the frame and rolled it forward and back until the bot remained level without us supporting it. The location of the COG is directly above the line segment between the contact points of the 2 wheels on the robot frame. This allowed us to locate the hooks such that the robot would lift level.

It looks like you have some play with where you can mount the hooks, so perhaps this will help make your robot lift without much swing.

Yeah, I designed it knowing I'd have to make the climber position adjustable, so I made sure we could change it easily with the multiple holes in the 1x1 it sits on.