Spectrum 3847 | Build Blog 2023

“What the heck?” indeed. I need to do some diagramming to make me feel confident that about the repeatability of that point in action. But still a cool discovery.

8 am physics

Looks like the cross section of the cone is a rotated ellipse. And the high point will get more compression from the wheel… creating a greater compression into the carpet on that side, making it easier for the cone to “turn” that way. We’ll be testing that today!

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I wouldn’t recommend sushi rollers; we had one of them cut one of our cubes. I still am not convinced that it is better on the launcher. We are using them right now because those are the rollers we have.

On the Cone pincher, I have a running theory that the roller has to be soft enough to compress at the tip of the cone (allowing the cone to ride up the short roller) while still being rigid enough to compress the body of the cone. Spreading the compliant wheels apart artificially decreases the total durometer of the roller.


I guess it is then how soft is too soft? I sort of can see that theory. But I needed to purchase wheels and had a hard time deciding where to spend money. I am going with softest big wheel (4" green) and smaller (2" black 60A). I would have liked to 3d print wheels, but testing the TPU wheels and stars, they both were the worst.

My basic tug-of-war was to put one wheel in each hand and try to drag with even pressure to see which wheel types gripped better, and in all cases the softer wheel won. The bigger wheels also would win by flattening in having more surface area. My 3d printed TPU wheels were 95A. If going that route you’d want a softer filament.

Where are you sourcing your belt?

This is what we are using on Alpha, bought last fall -

Black 5M Type Opened Polyurethane Timing Belt 15/20/25/30mm Width PU with Steel Wire 5mm Pitch 1-10 Meters Synchronous Belt

We have fiber reinforced stuff coming, Cloudray HTD-5M Open-ended Timing Belt – Cloudray Laser bought it last week but it hasn’t arrived yet.


Day 15 & 16

Cone Intake Testing

  • We are pretty happy with the test version of the cone intake. It’s able to pick up tipped-over cones that have their tip ahead of the flange and the flange within the width of the intake.
  • When at the right height it can pick up standing-up cones as well.
  • There are more failed attempts on in our photo gallery.

Cube Intake Testing

Basic Charge Station Test

  • We are still building part of the station but got enough built to see if Alpha could drive up
  • This is using un-modified SDS MK4i modules in the standard low 2x1 mounting configuration.


Looks great!

Would you mind sharing the distance between the two intake rollers?

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Does your charge station have the weights in it? Those affected the difficulty of ours a bit, making us have to get higher on it to tilt it to our side (building both sections has a similar affect). We are using mk4is, and we need some speed to get up. Not that bad, just something to note

The center point distance is currently ~4.25 inches in order to fit both cones and cubes.

It currently does not. We are yet to attach the second panel; additionally, we are currently sliding the side of the charge station on the carpet. We are getting some FRP today.

Sounds good. It also looked like the front angle of your ramp was too steep. We found that if it is even a bit to steep (5 degrees), then higher speed interactions result in you pushing the ramp up instead of pushing it down, making it much more difficult to traverse


Sorry but to clarify, the center to center of the 30A wheels and sushi rollers is ~4.25in? What diameter are those gray wheels?

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That’s min distance (tangent to tangent) between rollers. We use that distance as it let’s us compare different roller diameters and setusp by using the gap distance and not compensating for wheel diameter by talking about C-C distance in prototypes. It’s more important to know what space the cone and cube are fitting through than the C-C distance.

The top rollers are WCP 3" flex wheels.


After watching the other test video, my team started testing our wheeled intake prototype. We were looking to do pretty much what you show here. Good to know our ideas have a similar chance of success!

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Do you have any plans for trying VIW for this prototype? 3512 had some luck with theirs but I was curious as to if it would be possible with your larger tangent to tangent of the wheels + them being all VIW instead of a more rubbery material.

We had some earlier ones that we tried with limited success and it’s not a top priority for us. Centering the game piece is useful to an extent but we have seen plenty of teams in past pick and place games do the final adjustments by their driver. If you watch video of 3310-2017, 1619-2017(& 2018) and other teams with a wide dust pan style intake they were able to score very quickly by having their drivers adjust to holding the game piece off center.


Thanks for the response. I know in a previous reply one of your mentors talked about how your sushi rollers cut one of your cubes. How did they cut your cubes and are you looking into switching to 2" wheels for the bottom rollers?

I don’t think we have any pictures, but the cube seemed to wedge between the sushi rollers, and the rollers pinched it. One of the cubes has grill marks on it from the pinching. Our current bottom roller is just a hex shaft with silicone over it.

Adding on the edge of the sushi roller would spin on a cube and be able to splice into it.


Day 17 & 18: Week 3 Design Recap

Drive over the cable bump video

Drive up the charge station video

More can be seen on our Photo Gallery Week 2 and Week 3