Spectrum 3847 | Build Blog 2023

Day 6: Alpha CAD started

We have decided to follow the 1678 model of building an alpha robot. We quickly realized while testing intake prototypes that we will likely need to bolt them onto an elevator and slider to be able to fully tune them to the needed configuration and if we are going to do that we should just bolt it all to a chassis.

Alpha will be built on top of the swerve chassis from our 2022 practice robot. It will give us a chance to figure out many of the potential problems in our design and start programming and driver practice.

Five Mechanical Systems with current specs

  1. Drive Train, Controls, Bumpers: MK4i 24.5” x 27.5”
  2. Elevator: TheThriftyBot blocks for Alpha, likely continuous with a timing belt, Falcon+MAXplanetary
  3. Slider: Basically a sideways elevator, Falcon+MAXplanetary
  4. Intake: Pinch Rollers and over bumper ball intake: Falcon+Belts
  5. Launcher: Top spin or no spin launcher (still testing): Falcon+Belts

Day 7: 4-Bar

Switching to 4-bar from Slider

We are switching system 3 from a linear slider to a 4-bar linkage. This allows us to use our full elevator extension for raising the intake and use the 4 bar to lower the intake to the ground for pinching cones and picking up cubes over the bumper. This system configuration won’t allow us to crash the intake into the robot like the elevator+slider setup would. This should give us more reach and extension than our previous configuration.

In this sketch, the circles represent three of the intake’s positions. The lowest setting is for intaking cones from the floor, the middle for intaking cubes, and the highest for its stowed position. The orange lines are the bars in the fully extended position.

Continuous Timing Belt Elevator

We worked on one of the possible ways we will power our elevator- by using a continuous timing belt to drive up and down the elevator. This has some advantages. We only have to tension one thing instead of the two a cascade setup would require. When we are scoring low and mid, we will only raise our carriage, which should keep the CG slightly lower.

Robot Inspiration


How much compression were you running with this setup?

We don’t know. We were using this prototype largely as a proof of concept and did not take measurements for it.

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Day 8: Elevator and Controls

Elevator go brrr (doesn’t go brrr yet).

Today we made a lot of progress on manufacturing alpha. We made an elevator using 2x1 REV MAXTube and the Thrifty Bot bearing blocks. Unfortunately, the pattern doesn’t match up to the MAXTube, so we had to match drill into it. Our Final version might use the West Coast Elevator bearing blocks because they match up to the MAXTube. Here is a picture of our progress:


Our Apriltags came in today, and we got them on the acrylic backing. Gamma Ray 2021 was upgraded to 2023 Code and Firmware to help start getting our code base for X-Ray 2023.


Day 9: Alpha Elevator Assembly

Today we focused on mounting the Elevator onto the Alpha Chasis. A couple of unique things about it are the way we mount the crossbar and A-frame. Here is the concept pioneered by the EngiNERDs in 2022. The tube extends thru the plate providing more strength and keeping the end of the tube open so it’s easy to bolt/nut into and you can remove debris.

We also built and rigged the elevator.

The ratcheting wrench allows for the elevator to be easily tensioned. Using a wrench to provide ratcheting tension has been used by many teams including 125 in 2018.

FIRST Choice Round 2 Priority Lists Lock Monday, Jan 16th

Make sure your team has completed their FIRST Choice Priority lists for round 2. Multiple items were added to the site and all teams were given more credits to use.

Robot Inspiration

1678-2022: 4-bar linkage, bushing, chain mounts, etc


Has the Bambu X1 changed the way you design and/or prototype so far? I’ve been wondering for a what this newer generation of faster, input-shaping 3D printers (e.g: Vorons, Bambu, Creality w/ Sonic Pad, etc.) could do for FRC iteration (e.g: Printing new designs and testing in the same build meetings instead of needing to wait overnight).

The Bambu has had some issues today. But usually, we are printing parts more than twice as fast as we can on our Prusa minis. The most significant benefit I’ve seen is making high temp pulleys extremely quickly and pretty high quality.


It’s definitely nice for it to be fast but we also already had our Prusa Minis(12 of them). So often we were able to print a lot of small parts in an hour or two anyway.

The X1C does let us get parts off about 50% faster than the minis so it is very nice when you just need one pulley or something like that.

This weekend the Bambu was giving us several errors and had some failed parts for the first time in a while. We updated the firmware and cleaned some things and it seems to be running well again.


I understand the motivation for using a continuous elevator - but any reason for the timing belt over just dyneema? Are you worried at all about tooth skipping?

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We have considered it and it’s one of the reasons we are testing this on the alpha robot. It’s possible this will change to a chain-driven cascade elevator at some point which would be pretty easy.

Continuous timing belt elevators have been done successfully by multiple teams 125 and 2910 in 2018 are two examples that quickly come to mind.


FYI, this finally got an answer:

We cannot rule absolutely on hypothetical ROBOT designs, and the final decision as to legality of a particular ROBOT lies with the Lead ROBOT Inspector (LRI) at each event. However, having a COMPONENT that passively moves is not a change to the ROBOT configuration.


Day 10 & 11: Design Recap

Every Tuesday we hold our design recaps

Elevator Test Video


Day 12: Alpha Elevator Explained

Our Alpha elevator uses a timing belt and idler pulleys as its motion system. It’s designed around the 0.5” hole spacing on the REV Maxtube and uses the REV Max tube plugs to allow us to bolt the idlers into the rail.

The main drive pulley is a 32 HTD 5mm hex pulley with a TheThrifityBot 3D print ½” hex insert in it.

The belt for the elevator has to be designed so that each of the vertical run is perfectly vertical, any angle in those runs will cause the belt path to change total distance as the elevator moves up and down thru its motion.

To allow these to be vertical paths we are 3D printing our own idler pulleys that are based on the width of the 5mm timing belt and the ½” hole spacing.

The 3D printed idlers are explained here

Tube Spacer Link: McMaster-Carr We sanded these and then cut them to length on our lathe.
These spacers may also work for this purpose but we haven’t tried them yet - McMaster-Carr

STLs and STEP files for the pulleys can be found here: Printables

3D printed Idler pulleys for 5mm belts with ½” hole spacing.

For Alpha, we are using 3D printed tube plugs with the ½” OD tube spacer and 3” long 10-32 bolts so they are supported through more of the tube and can’t bend as easily. We haven’t been able to test the shoulder bolt solution with the aluminum tube plugs yet as we are still waiting on that order to arrive. We will decide if we want to use the long bolts with tube spacers or the shoulder bolts in the coming weeks.

The belt is tensioned by mounting one end of the belt to a hex shaft that is spinning in a ½” ratcheting wrench (you can also do this with a ⅜” wrench and ⅜” hex shaft). So if we need to add tension you just turn the shaft a few clicks tighter.

The other end of the belt is secured to the elevator using a laser-cut polycarb bracket and zip ties.

We are currently using TheThrifityBot Constant Force spring and mount from the TTB Elevator Kit but we will likely move to a custom design for our competition robot.

The side bearing blocks on the Alpha Robot are the TTB Bearing Block Kit and for our competition robot, we are planning to use WCP Inline Clamping blocks since their hole patterns line up with the REV tube and tube plugs.


Day 13 & 14: It’s Always a Launching Game

A pretty short one today


Today we experimented a bit with launching cubes and made some progress. There is still a significant amount of work to be done, and we are still changing all the spacing to see how the cube reacts.

)](Week 2 - Spectrum 3847)

Cone Intake:

We found that softer rollers seem to grip onto the cones better. We can intake cones at really aggressive angles. More refinement is still needed.

)](Week 2 - Spectrum 3847)


It looks as though in a majority of your recent tests and set ups, you’ve opted for more of a block of wheels, whether it be 2” compliant or sushi rollers. Have you found a difference between using wheels in a denser fashion vs more spread out?

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“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?