Spectrum 3847 - Build Blog 2020

Not just R10 but also bumper construction rules. Some of which are a grey area in the rules. You’re clearly not allowed to add a sheet of plastic to the outside of your bumpers to make them slippery as that would no longer meet the bumper rules, where is the line between lubrication and sheet of plastic? While you probably are allowed to clean your bumpers with mild soap/detergent where is line between cleaning your bumpers and lubricating them? When I can plausibly argue either way, that normally means it’s time for a q&a.

1 Like

I see your point, but I had not thought of this as infringing on the rule. The rule requires that the covering be fabric. Plastic sheet is not a fabric, so I guess I can see why that is not allowed. Iron on numbers are not fabric, but…

It is not clear what you can do to fabric and still have it be considered fabric (and only fabric). Clearly you can add dye to the fabric (and in fact you are required to buy fabric that has had dye added to it to make it red or blue). If you add starch, have you added something substantial that is not part of the fabric? If you melt the synthetic fiber fabric slightly with an iron, is it no longer fabric and has it turned into a sheet of plastic?

I really don’t want to derail your awesome build blog thread, so I will try to get a question posted to the Q&A. If anything comes out of that that deserves additional discussion, I will start a new topic.

1 Like

I looked at your most recent robot cad and I can’t seem to find any sort of backstop before balls enter the shooter. If you already have a ball stored at the top of the conveyor and you need to run the belts to pull a new ball in, the first ball will enter the shooter. Do you guys have any ideas on how to solve this problem yet?


Plan right now is programming, and sensors just running the balls into each other in the tower yielded less than great results, we have some ideas (multiple pneumatics to stop the balls from touching, and others) but we are not planning to implement them at this point.

We have been shopping around to find a drawer slide or a pair bolted together that will fit inside the allotted space without using a million stages. These seem to fit the bill. Do you all have the part number or source of the drawer slides in the prototype video?

Home Depot 24" Slides



Woodworking specialty stores like Rockler and maybe Woodcraft have 28" full-extension slides.

Hi Allen, I can’t seem to find your friction brake/interference latch. Would you mind pointing ou the link to it please? Thanks

It’s nothing fancy just using part of the VP ratchet system to do what we want. I don’t recommend people copy this. We basically built it during champs last season, it does work but I’m sure there are more elegant solutions.


Teams fear that if they create a build thread, other teams might copy great ideas.

Teams with build threads know that the real fear, the one that keeps you up at night, is that people will copy our bad ideas.


Oh it is definitely the scariest part of being open. So many teams have thanked us for some ideas that I really wish we had never even created in the first place.


Por ejemplo?

The 2018 - Virtual 4 Bar Intake is the one that comes to mind the quickest. It worked but the lightening bolt / zig-zag intake that we developed after that and published was so much better and easier to build and maintain.


Day 26: Intake progress and motor allocations

Intake Progress

Progress on the Protobot intake and funnel have come to their 2nd iteration.

This version fixes some geometry issues with the first and removes the belt path from the center of the funnel.

Motor Allocations

We added our motor allocations to our copy of the Spectrum Design Sheet (Designsheet.spectrum3847.org)

Motor PDP Allocations.PNG

CAN IDs were also assigned in the sheet


PCM slots were assigned as well



Are the belts purposefully loose and lacking a pulley? I assume that was just during picture taking and the pulley is going back on the outer ends of the funnel

Yeah it’s just not finished being put together yet.

1 Like

Have you tested at all using just the poly-carbonate tubing as the roller without any surgical tubing? In our testing we found they were extra grippy with each other but don’t have any tubing on hand to test it.

We haven’t done much but we aren’t sure the rubber will be needed. Almost certainly not needed on the front roller that has the flex wheels on them.

1 Like

Day 27: Tipping Point

Today marks the midway point between kickoff and our first event week 1 in Dripping Springs.

Intake and Indexer Testing

Both systems are working as expected. More videos are in our photo gallery. Our plan is to only hold 2-3 balls in the funnel and let 2-3 balls be in our tower as well. But we did want to test what happens if we human load or just don’t sequence everything properly.

Here is a cut of way of how we hope to be able to hold balls

Sheet Metal

We have sent off the CAD and drawing files to our sheet metal sponsor for our competition and practice robots as well as some parts for the elevator. Most of the other subsystems will be iterated in house until we get closer to final parts ready for sheet metal. That may not even be till after our first competition.