Team 2840, Blue Tide: Prototype ALL the Things!

[Joe Schornak]

As we move out of our prototyping phase into final fabrication, the time has come to share some videos of the past week-ish's work. The current plan calls for a long barrier-traversing, bridge-balancing mecanum drive with front and rear ball intakes and a two-wheel CIMulator-driven shooter. Since these videos were created we have made many improvements and modifications.

Behold the drive system! The sets of raised kit wheels protect the mecanums from smashing into the barrier head-on while giving them a more advantageous angle of attack to lift the robot.
http://www.youtube.com/watch?v=lQLnh...yer_detailpage
We felt that plywood wasn't representative of the actual barrier surface, so we screwed on some Lunacy regolith. Interestingly, it still works, despite the bridge lowerer being in the way:
http://www.youtube.com/watch?feature...&v=wfWem0AkPfU

Behold the bridge ram! It swings down to lock into place and uses the weight of the robot to push down the bridge:
http://www.youtube.com/watch?feature...&v=OjCgx9XPV6E
Again, since plywood isn't representative of the actual bridge surface, we attempted a simulation by attaching some polycarb panels. We were initially worried by the traction of the mecanum wheels on a plastic surface, but they seem to work alright, even better. The bridge ram in this video was an older version that didn't work quite as well as the current one:
http://www.youtube.com/watch?v=tUhNt...yer_detailpage
(While not shown, we can also push the bridge down from the side, which could be useful in helping allies onto the bridge)

Behold the shooter! The final version will have flywheels, since our tests have shown that they reduce the shot spread. We will be optimized to score from the key, but the power of four 550s in CIMulators will let us throw balls across the whole field. CIMs are used here for convenience:
http://www.youtube.com/watch?feature...&v=d41pDyWn6fk

Not shown in our videos (yet!) is our turret and loader design, which will insure consistent feed speed and thus more accurate shots. We're also refining vision tracking and PID on our summer-project test robot (suspiciously similar to 1726's 2009 bot), which will be incorporated into the final design. I'll be happy to answer any questions about our designs so far.

[SuperBK]

Aren't only 4 sims are allowed? Don't you have one for each wheel and two for the shooter?

[Taylor]

Originally Posted by SuperBK

Aren't only 4 sims are allowed? Don't you have one for each wheel and two for the shooter?

..

Originally Posted by Joe Schornak

We will be optimized to score from the key, but the power of four 550s in CIMulators will let us throw balls across the whole field. CIMs are used here for convenience.

[DavisC]

Great work, really like the videos!

Yea to back up your idea of Banbot 550s, I have 2 of them hooked up to 4 wheels total (same kind you are using) and we are shooting brand new balls 60+ feet with 4:1 gear ratios. We plan to switch it to 16:1. Good Luck!

[Donut]

I like the bridge ram testing, we've decided upon a similar design (dubbed "the wedge") that works quite well at bridge tipping. This design requires no extra effort on the driver's part beyond driving straight at the bridge. Are you still able to unlock and retract the ram if needed?

I'll be curious to see the feed mechanism, a lot of teams are using the wheeled shooter design but I think a good feed is what will really set the accurate and consistent shooting teams apart. I know 2840 was a force at AZ last year, look forward to the webcast of your robot.

[eedoga]

We had a similar idea for crossing the bump, but we were concerned about balls getting stuck under the robot causing penalties. How are you planning to deal with that if the floor gets littered with balls?

[Joe Schornak]

Thanks, all!

Originally Posted by Donut

I like the bridge ram testing, we've decided upon a similar design (dubbed "the wedge") that works quite well at bridge tipping. This design requires no extra effort on the driver's part beyond driving straight at the bridge. Are you still able to unlock and retract the ram if needed?

We plan on only deploying the ram immediately before pushing down the bridge, so it will be stowed and protected for most of the match. The locking plate is servo-actuated, so the arm can be retracted, which will be useful when trying to cram robots onto the bridge.

Originally Posted by Donut

I'll be curious to see the feed mechanism, a lot of teams are using the wheeled shooter design but I think a good feed is what will really set the accurate and consistent shooting teams apart.

I can't show the loader quite yet, mostly because the current system uses about a dozen clamps and two feet of duct tape. Our tests showed that the variable with the greatest impact on shot accuracy was feed speed, so the challenge was to design an automated system that could load balls at a constant and precise rate. We're shooting within a 9-inch diameter circle with our current system at a distance of 20 feet, so the trick will probably be making an accurate targeting program to match.

Originally Posted by eedoga

We had a similar idea for crossing the bump, but we were concerned about balls getting stuck under the robot causing penalties. How are you planning to deal with that if the floor gets littered with balls?

We'll have a belly pan to keep things out of the robot and guards around all the places balls aren't meant to go, while the bumpers will be mounted at the absolute minimum height needed to cross the bump. While there will certainly be balls scattered around the field, we won't be seeing balls absolutely everywhere like in Lunacy. It should be reasonably easy to find a crossing point that doesn't have balls in the way.

[gingersalad]

Why are the kit wheels horizontally offset, instead of in line with the mecanums?

[Joe Schornak]

Originally Posted by gingersalad

Why are the kit wheels horizontally offset, instead of in line with the mecanums?

Each of the wheels has its own chain, run off double sprockets on the Toughboxes. The offset is there to get the sprockets to line up with the one on the gearbox. However, it seems to work just as well to have one somewhat longer chain going around all three sprockets to power each wheel pair, with the wheels in line. Barring anything particularly drastic, we'll probably switch to this setup for the final bot.

[DavisC]

Well let me give you an update, follow the advice if you want.

Today I tested the 16:1 Banebots on the shooter and, starting at ground level the ball would land about 13' away (fully charged battery).
So I then switched back to the 4:1 and I just suggest coding down the speed for closer shots.

[Joe Schornak]

Originally Posted by DavisC

Well let me give you an update, follow the advice if you want.

Today I tested the 16:1 Banebots on the shooter and, starting at ground level the ball would land about 13' away (fully charged battery).
So I then switched back to the 4:1 and I just suggest coding down the speed for closer shots.

I believe that we're using 4:1 Banebots in our shooter. While more torque will make the shooter wheels reach their target speed faster, a higher RPM is more important to a long-range shooter. Flywheels will allow the shooter to put more energy into each shot. We'll probably run our shooter constantly throughout the match to eliminate the spool-up time of a low-geared, high-speed motor.

[Tuba4]

Make sure that your bridge ram is fully inside the frame perimeter at the start of the match. If it is not, it would be in violation of G21. Check the Q & A as well.

[s_forbes]

Neat stuff! You guys are taking a very similar approach as us to a lot of the game challenges. Clever use of mechanum wheels in the drivetrain to cross the bump as well! I'll be sure to check out the finished product up close in person at the AZ regional.