FRC 4481 Team Rembrandts 2020 Build Thread

I don’t know the exact dimensions of the prototype, in CAD it’s looking like it will be around 25.5" in diameter and probably the height of ~ two powercells on top of each other. Hopefully the CAD is done tomorrow and we can upload a couple more pictures with dimensions


Thanks. Do you think it could be any smaller? Because a 25.5in diameter takes up a massive chunk of the robot’s drivebase. My team’s prototype looks like it’ll be around 24.5-25in, but that still seems really big.

Difficult to say at this point. I think we can squeeze it into 24".
There are other hopper designs that consume way less volume but feed consistency is tricky.

We would love a 5 powercell 1 second dump from the sectorline in the inner goal. (5/5) To achieve it a rapid consistent feed is required. (as long as we don’t have to make too much consensus on other sub system performance and packaging)

1 Like

This has been a fantastic resource so far. I’m happy to see all the teams that are doing this. Still slightly disappointed by this part though:


Love this thread. A wealth of information for new teams and people interested in systems.

Week 2 - Update 1

Our media & branding team is on fire this season! They just finished their week 1 recap video:

We started the week with a general meeting with an update on every subsystem. Walking through the concepts that were build as prototypes and make general decisions on the way we want to head.

Storage Update
We’re liking the spinning hopper and started on the CAD. Trying to narrowing it down to 24-25" OD and looked into how to power the wheels and spinning rotation.

Since we’re aware of the packaging issues that might arise we’ve been working on a different style hopper. Inspired on the Week 6 Insanity Ri3D robot. (See below) Basically a wheel/omni spinning flimsy within an arch and some balls. No good video of it yet!

Shooter Update

Concept 1 - Two wheel shooter

We first build a two wheel shooter prototype.

As a little expected see a lot of other videos: the ball curves a lot. Although feed consistency is bad in this video, the variation in wheel speed, ball compression and guidance etc. will make it difficult to get consistent shots up and running.

Concept 2 - Hooded Flywheel

We modified the two wheel shooter to a hooded shooter.
Running with 1 NEO on 1:1 chain driven.
Double 4"x2" fairlane wheels with double x 4"x2" colsons as mass.
NEO runs at 100% power and no control loop. Software team is working on the smart velocity control loop on the NEO/Spark Max. Hopefully we test more of that tomorrow.

Sideview video:

Slowmo video through inner port:

The powercell needed to be pushed against a NEO (design fault :slight_smile:), hence the first and last shot being a little off.
Trying to refine the shooter tomorrow night >
Add 1 more NEO + Smart velocity.
Target: 5 powercells within 1 second > 5/5 inner port!

Other Subsystems
All other subsystems brainstormed about their plan for this week.


Looking at a combination of the #125 - 2017 intake and Everybot 2020. Designs were started to have something build by the end of the week.

Control Panel

Working on the color sensor and probably a wheel to spin it. Will be decided whenever general packaging of the robot is clear.


Refined their first prototype to make it able to drive on an angled switch at 14.5 degrees. Besides that looked at the packaging and implementation of a linear stage arm.


Possibly dumb, possibly brilliant idea…if you go with the spinning hopper, could you use that to turn the Control Panel Wheel?


Looking really good! What was the compression for the hooded version?

IIRC: 2” was what we ran. I’ll double check tomorrow


What was the material that was wrapped around the wheel used in the climber? Everything is looking really good though!!

It was rubber glued on a 3D printed wheel. I forgot to take a close up picture tonight, I will tomorrow! :+1:

1 Like

I just had a mini heart attack until I saw this…

Week 2 - Update 2

We had some troubles on Wednesday with the Spark Max controllers and Neos hence we why we didn’t post any shooter videos yet.

The software team has worked hard to fix it and we were able to shoot with our wooden prototype.

Shooter Update

2" Compression
2 Neo’s, geared up 1:1.38
2x 2" Wide 4" OD fairlane wheels
Closed loop control
No extra flywheel mass

For this weekend we’ve designed a flexible shooter testing setup:

We can adjust the compression, change between 4" and 6" wheel, add extra mass, change backing plate etc.
Hopefully we’ll have it shooting by tomorrow.

Currently we have a pully running of a 1:1 VP stage from the Neo. Tomorrow we’re going to add a new pulley:

It’s a 12 teeth gear, press fitted in the pulley which makes it mountable to the Neo which saves space in the overall design later on.

It’s printed in CPE. Hopefully it holds up :wink:

Storage Update - Wheel of Doom(WoD)

Wheel of Doom!
We send out our sheetmetal order on Wednesday night and our partner: De Cromvoirtse produced it on Thursday and we could pick it up on Friday.
Top View of the Wheel of Doom on our DT:

Side view:

It’s still pretty tall; getting balls up there is still going to be a challenge.

We’ll be mounting it on the DT tomorrow and power it through the software, we did a manual check on battery power to see if it worked.

Full storage, ejecting @ ~ 120 RPM:

Slowmo storage, ejecting @ ~ 120 RPM:

We know, we know… “BUT HOW WILL YOU GET THE POWERCELLS IN THE WHEEL OF DOOM?” We’re working on it, once it’s mounted to the DT then we can add the surrounding lexan and control it through a software cycle to serialize the balls.
We test by hand the following sequence:
Shake shake
Quick spin
Shake shake
Quick spin
And that actually worked pretty well. We’ll definitely get a video for you tomorrow :wink:

We’re not doubting that the consistency of rapid feeding into the shooter in this concept can be insane. We’ll probably be able to over-power-the shooter enough to be able to hit a 5/5 outer circle shot in 1 second dump. We’re hoping for a 5/5 inner port from the sector line in 0.5 second this this hopper.

Although getting the powercells in the wheel of death, getting them high enough to drop in and the entire packaging is going to be a difficult assignment.

As a back up we’ve been working on a couple other concepts.

Storage Concept - #6135 & #3847

We needed another concept to make sure we have a good back up plan for the WoD. Current progress looks good. The concept allows human feeding easily, you can easy configure the ball layout for AUTO for a fast rapid fire rate, we could speed up the first wheel more than the others. Through using 2 different belts and 3 different pulleys we can spin each wheel a different speed > allow the power cell closest to the omni to be sucked in the fastest/quickest.

See a couple of videos below:

We’re thinking of CADing this up in the weekend and have a prototype of this by next week including with matching intakes.


Clever! I’ll remember that trick.


Your Wheel of Doom is looking fantastic! how is the wheel rotating?

We lasercutted a Sprocket and mounted the whole WoD on a lazy Susan bearing. Turned out really well!


And it’s mounted to a 775 pro on a VersaPlanetary run by #25 chain.

The motor has a overal reduction so it spins 120 rpm on the WoD. (Vp + Sprockets)


Week 2 - Update 3
This week has been productive and made some good progression!

This post will be mostly devoted to the Wheel of Doom concept. The software team and shooter team ran in plenty of Neo + Spark Max problems. Eventually with some help of #125 we think it boils down to some bad wiring quality on our end. Hopefully we can rewire the shooter tomorrow and see if we can fix the problems and can actually start testing our shooter.

Control Panel

Depending on the eventual positioning of the control panel mechanism it might need to be able to fold in/flop out. Current idea is using the REV color sensor, a wheel on the side to spin it and using a pneumatic cylinder for folding actuation.

See video below:

Intake - #254 2017 style

To accommodate the other storage concept we’re working on.

The intake for this concept is slightly different since the balls don’t have to travel so far up vertically to drop them in the wheel of doom.

Intake on the video below is based on the 254 one from 2017, it’s easily made by drawing a sketch/outline in SolidWorks. Then we printed the bearing layout on a A4 paper, print it out, cut it out, tape it on wood, drill and cut from there. I’ll try to make some pictures from these steps in the next update. It allows for a little more precision prototyping instead of just slamming some stuff together.

See video below of the intake.

Wheel of Doom

We’ve shot dozens of videos this weekend of testing and cardboard upgrades on the wheel of doom. Sadly my Adobe Creative Cloud license was expired and I need a team member to re-activate it. I wanted to edit a compilation test video of the iterative process we’ve went through this weekend. (In premiere pro but I couldn’t sadly.)

So for today’s update I’ve picked out a couple video’s to show the current performance and list the lessons learned so far.

Letting powercells by gravity before spinning

Dump 5 powercells at once > getting stuck

Spinning too fast > powercells can’t fall in their pocket

Slower speed runs pretty good

Intake + WoD #1

Intake + WoD #2

Intake + WoD #3

Intake + WoD + Eject = Full Cycle

So yeah… some videos look quite promising. Remember we’ve shot A LOT of footage:

So there are a lot of videos where balls get stuck, inconsistency, all balls fall in but the speed is too slow, feed rate of the balls too fast/too slow etc. Our general take-aways are:

  • Ejecting speed can be extremely high but getting the powercells quickly in the pockets is a different story. Spinning the Wheel of Doom faster is no solution, gravity needs time to do it’s work.

  • The balls need to stay within their pocket while spinning to prevent them from getting stuck on pinch points. But they will still need to be able to be pulled out by the omni. We added some cleaning sponges which worked pretty good. In the revision we’ll work the sponges and another lexan idea.

  • We covered the sheetmetal brackets with wood triangle covers. Compare the piciture above and below this point see what I mean. It seemed to increase performance/settling time for the first 3-4 powercells since they don’t get to lay on top of the bracket.

  • We have tested with 2 different idle omni wheels. The first test we ran the blue and white omni’s but we noticed that the blue plastic part of the hub would contact the ball and give too much friction. Luckily we had other 4" omni’s laying around with a metal housing but more importantly: the rollers were the only material touching the balls, no plastic hub. The switch helped quite a lot.

Blue Hubs & White Omni Rollers
Black Omnis

  • The first 3-4 powercells are very consistent and quick, usually getting the last powercell in it’s pocket is what takes pretty long. We feel that software can come into play here. Knowing which pocket and how many pockets are empty let’s us directing the powercell into the pocket quicker. For the new revision adding distance sensors to the pockets will be interesting.

  • We wrote a new version of the current code on which we can read the motor controller current. Knowing when it draws more current allows is to spin it counter-clockwise to prevent balls from getting stuck. Sadly no footage of it yet, waiting on some members to send it to me :smiley: Or they’ll upload it in the thread tomorrow.

  • Currently in the footage the idle omnis were “rolling above a pocket”. Basically taking up effective space the powercells need to settle in the pocket. We moved the omnis more towards the shooter tower and that worked out pretty good. Whenever I receive footage of the last two upgrades I’ll upload them as soon as possible!


What angle relative to the ground is the ‘ramp’ for your backup index design?

Have you tried with the whole revolver tilted on an angle forward toward the intake? That might help the balls settle into their slots quicker. Also might make it get jammed more often :stuck_out_tongue: