Stiffness of brushes

Hey all,

I dont have access to any of the brushes used to hold the hatches- can anyone answer how stiff the bristles are on the brushes and confirm if “average grip” velcro can securely hold a hatch when ripping it out?

Thanks
Matt

I’m not sure I can give a great description of the brushes, but I would say they are medium rigidity. Honestly, medium grip velcro might work, but I probably wouldn’t bank on it. It’s kind of like a door sweep…

Wait, it is a door sweep!

If you are near a home depot, they can be found there really easily (pending team density of course). I stopped by on my way to the workshop from work and picked up all we need for our field.

@messer5740 It is hard to describe the density and stiffness of the bristles on the brush. The local Home Depot in Cranberry, Pa to team 5740 is showing 14 brushes in stock, I would suggest to go and handle or buy one to get a good idea of the brush structure. The item is sold as Frost King C35PH.

I purchased one of the door sweeps yesterday. Not surprisingly, it seems that the force that will be required to pull a cargo hatch out will be highly dependent on the separation between the brush bases. My original calculations from the field drawings showed the two parallel lengths as being 17.15" apart, between the inside of the plastic portions, and the (unofficial) hatch panel I ordered from AndyMark is 17-1/16", which is about 17.06". At that point, I was skeptical as to whether anyone would be able to get the hatch panel. I re-ran the numbers, and got 17.67" apart, which seems much more reasonable. My plan is to mount two of these segments 17 2/3" apart in a horizontal plane and measure the weight required to pull the hatch panel I have through. This will need to be increased by 50% to account for the third brush, but this will be a “top end” requirement, as I have a slightly oversized hatch cover, and the brushes will certainly become more compliant as they are used.

Something that bothers me a bit: The “brush” piece has plastic bristles apparently fused together inside a somewhat crimped apparently aluminum channel. The plastic mounting piece is definitely a separate part once you open the package. I cut mine into 6" pieces separately, and when I reinserted the brushes into the brackets, they don’t want to sit still. I’m not sure if FIRST is planning to keep the brush pieces from moving through some sort of crimp process, or through adhesives, or what, but something will be required or we will have brushes way out of position at times.

We noticed this issue as well. We have several concerns with this layout.

  1. We are planning to grab a hatch panel and come straight out of the load station, but looking at the drawings and layout for this station it looks like the outer diameter of the plate could catch on the brush. If it doesn’t catch it will be incredibly close not to.
  2. The bottom of the load station is cutout to allow the bumpers to go underneath it, but it’s so deep that the bumpers will likely not hit a wall to slow down the robot, so we expect many “hard hits” on the load station as robots pull into get pickup plates. With that said the brushes are very much in the line of fire and will likely get hit by incoming robots. This situation could impact #1 and prevent the hatches from being removed by pulling horizontally straight out.

I mounted two of the brushes facing each other with the inside faces of the white plastic 19 5/8" apart. My hatch panel is an AM copy, but it IS the correct outside diameter (19"); my initial measurement was taken with a rather cheap tape measure. I then oriented this horizontally so that the pull out force was vertical. I was able to balance the panel on the two brushes with difficulty; if I slid the panel off center less than a millimeter it would fall out. Given that the panel weighs approx 2.5 lb (per Vex), a 4 lb (18N) grip should pull the panel out pretty consistently.

After seeing some fairly well secured gears knocked out in STEAMworks, I recommend having another order of magnitude of pulling/holding force available.