jgraber
Due to Game day venue scheduling, and field sharing scheduling,
Dallas BEST hub has a late kickoff and a late week 5 demo day, today.
Here are some general notes:
- Several teams plan to pickup the copper cart by surrounding it from the narrow end.
- Few teams can get the Aluminum under the overhang.
- At least 3 robots had omni wheels of some kind.
- Several teams are using lazy susan as a turntable, to allow arm to reach to the side to do the pipe repair.
- Several teams asked if the cardboard box we provided to hold the consumable kit was legal cardboard;
Since we provide corrugated cardboard < 1/4" thick boxes, yes it is.   24"x100" or any other shape adding up to 2400 sq inches cardboard is allowed.
- One team used a door spring from last year kit, which is not in the kit this year.  They considered winding their own spring from piano wire, but ended up using 25x #32 rubberbands instead, in the usual 4bar configuration, and said it works even better than the tail-end door spring.

Common Rookie team errors:
- 4 wheel or 6!wheel robots, which are unable to turn due to wheel scrub,
     I encouraged them to use a PVC slider, or a skate wheel caster instead.
- Try to lift an arm with servo, or two, or with direct motor drive.
     I encouraged them to put the arm on then large pulley driven by loop belt from the small drive pulley on a motor.
- Using duct tape or masking tape or electrical tape on the cortex, wires, motors, servos.  
    I encouraged them to replace it with blue tape instead, so they would be able to pass complliance inspection.
- Notebooks were due at 2pm.  Several teams had trouble printing them at the last minute, and will have to make other special arrangements to drop off their notebooks on Monday.
- Some teams had not yet gotten programming to work.
- Some teams were still building wheel hubs or caster wheel brackets today.
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Katniss
What were most teams using to pick up commodities? A grabber of some sort?
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jgraber
Not so much.
- Several robots have a two-finger gripper on an arm on a turntable, with the intent of doing repairs on the pipe and/or air-filter and/or retrieving a core sample, but the arms are only powered by servos, so I don't think they can lift very much.
- There was one well-built double 4-bar arm with a double pinch gripper that looks like it can do the repair pipe easily, (if the copper cart is not in the way.)  This team converted from illegal door-spring to legal rubber bands for lift-assistance.
- All the best looking robots were built to pickup the copper cart from the narrow end with a fork lift.
- Most of these used large motors for wheels, and wheels 8-10" in diameter.

The aluminum is the only commodity on the floor that needs to be picked up.
The rest falls from the sky and you can catch it on the way down.  
So a grabber seems only useful for the pipe, filter, core-sample.

Commodities are never worthless,
but I suspect iron, copper and coal will be worth less (than they were before) in the 2nd and 3rd phases.
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cxluckey
could you explain what the 4 bar configuration is for the rubber bands.  We may use rubber bands and I'm interested as to whether it will solve our breakage problem.

Thanks

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jgraber
See almost any Vex competition, such as RoundUp game from 2010 where I found this picture.
A common Vex arm is double (left,right side) 4-bar parallelogram.
There is a side post near the top of the upper arm (near the shoulder)
There is a side post near the bottom of the lower arm (near the hand)
These posts get closer together as arm rises, and farther apart as arm lowers.
Rubber bands go between these two posts,
 and trades off the gravitational potential energy of the mass of the arm: E=mgh
with the spring potential energy in the rubber bands: E=0.5kxx
Spring constant k is increased by adding more rubber bands (up to 25 count #32 rubber bands for BEST)

Rubber_band_4bar.jpg 
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dmgauntt
What do you mean by "Omni wheel"?  Last year my team put the skate wheel on a pivot (like a shopping cart caster), and that worked wonderfully.
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jgraber
3rd supports in BEST are typically PVC/plastic sliders, or swivel wheel casters.
On a flat field, I like non-swivel mounted golf ball casters also work well:
   slide forward, rotate during turning, but they don't handle thresholds as well.
An increasing (from 1 to 2-3) teams are going to Omniwheels:
  google search Omniwheel shows many examples.
In other robotics competitions, commercial omniwheels are used as drive wheels for holonomic movement.
I've only seen them used in BEST as caster wheels.   
They have a different volume and mounting profile than casters.
One local team uses wood disks on Igus shaft axles.
I found this picture from Texas BEST 2011 more easily,
showing majority plastic construction, with piano wire axles.
 Omniwheel_cmp.jpg
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