GalacTech 4926 - Build Blog 2022

Team 4926 is opening the books! We are thrilled to throw our hat in the ring as official Open Alliance member. We’ll post here as frequently as we can including the following:

  1. Game Analysis - Statistical Analysis via Monte Carlo type simulation
  2. Prototyping successes and failures!
  3. Engineering analysis
  4. Dad Jokes
  5. Links to CAD - - So that will be our “Main Latest”
  6. Pleas for help?

GalacTech loves the idea of sharing in FIRST, so we are stepping into the open! Bring on Rapid React and 2022! Let’s Go!


You can probably make the robot viewable through if you want to go that route.

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Very interested in seeing how this goes. I am interested in trying something like this on the game this year.

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We’ve done this for years now and have a pretty thorough process. We’ll probably have a draft up by Monday with more details by the end of the week! We’ll post the whole thing!


January 9th Update:

Today was mostly a day to read the manual and do some sketching to realize how hard the high level climb is. We’ll post some more of our sketches this week.

Our big deal today was tuning up our Ballistics model for the Rapid React CARGO. We developed this tool a few years ago based on Ether’s Math. (Come back Ether!) The big deal here is measuring the terminal velocity. I have described the technique previously here.

This year we dropped the CARGO from a 5 story parking garage and measured the time it took to travel the last 48in. We calculated 66.7 ft/s with two different slo-mo videos. This agrees well with published data for the terminal velocities of basketballs, 45mph is a typical reported number. That feels fast, but I’m posting this file with that number. It would be nice if someone else did that experiment from an even taller structure.

This model is crudely tuned to a UPPER HUB shot 8ft away with a 2500 rpm motor turning a 6" wheel direct drive. We’ll prototype with this setup tomorrow night! Happy hunting!

Rapid React Ballistics with Drag.xlsx (778.4 KB)
MOD: replaced file, as requested

--------------------- Science Update -------------------
Boundary Conditions for Ball Drop Test:

  1. Ambient temperature ~ 0C
  2. Air Density 1.2 Kg/m3
  3. Air Dynamic Viscosity = 1.7e-5 kg/m-s
  4. Measured Terminal Velocity = 66.7 ft/s
  5. Experimental Reynolds Number = 3.55 e5
  6. Experimental computed Cd = 0.23 (ish - is possible for a rough sphere in this Re range)

Statistical Game Analysis Initial Version - Enjoy
This is a work in progress, we have made some changes and comments need to be updated, but there are scoring distribution predictions for alliance play.
Rapid React Team 4926 Game Analysis rev2.xlsx (39.9 MB)

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First version is posted if you are interested.

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Day 3 - January 10th - Analysis and Prototyping!

Completed an Intake prototype
This version used 3” compliant wheels but we tried 2” Thrifty Squishy wheels and Thrifty VIW too. All see to work pretty well.


90% complete with a launcher prototype - 2 NEO Direct drive, 2 sided 6” wheels

Practice chassis wiring - read to roll!
Competition chassis assembly in process
Reviewed our Ballistics analysis as a team - see previous post
Reviewed our Statistical Game Analysis as a team - see previous post

20 Students in the shop tonight. Whew!


Lunch time Ballistics Update. Added some notes and the ability to move the opening of the UPPER HUB in the graph through a Distance to Target spec.

Rapid React Ballistics with Drag.xlsx (778.4 KB)


Day 4 January 11th - Prototyping

Based upon our ballistics model the students created a ‘2-sided’ 6” Hi-Grip wheeled launcher. We were attempting minimum spin. We just got it running tonight and had a couple of attempts. See the picture and video link below. Our ballistics model suggested a 2200rpm 6” wheel would launch the CARGO 20 ft high over a span of about 4-5ft. That is pretty much what this prototype does; check out the video!


We also got our practice chassis rolling as a flat bot tonight, so we’ve got that going for us. Our competition chassis is right behind it!
Practice Chassis Video


Any chance you’d be able to link some resources for working these numbers out for the people at home? My back of napkin math brings me to a surface speed of 57.6fps on your 6" wheels. However using 57fps as my exit velocity on the couple of projectile calculators I have, results in some pretty large distances for the ball trajectory… Obviously there will be some losses between the object being shot and the surface speed of the wheels (grip on the ball, time in contact with the wheels, and I’m sure other things too), but those would be some massive losses (50% +) in this case.

Yes, that setup has more capability than anyone ever needs, but I like to start with some more capable and then lower the capability to our needs rather than the other way around. Plus our roof is 20 ft tall and provides a nice calibration data point!

As far as the math is concerned, please check my post above with my lunch time edited Ballistics model. Earlier versions had a math error in the exit speed, but that model has everything in there except the math to calculate terminal velocity from a ball drop experiment. I plan to take some ‘calibration’ videos to show how well we correlate to the math in that model. Keep checking in on us and have a look at that model. If you have questions ask away!

Wow, now I just feel stupid that I missed the post LITERALLY ABOVE the one I responded to… Thanks for pointing that out… :sweat_smile:

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As promised, but a little late, here is the 2022 Rules Test for 4926.


I hope I’m not overstepping my bounds here, but below I’ve linked a GoogleForm based off your rules test. I took out the short answer prompts that couldn’t be tweaked into a multiple guess format; I also took out the Indiana & District-specific questions to make it more universal.
Feel free to make a copy of it and change your personal copy as you wish. The link I’ve shared has full edit rights, so please only edit the copy you make (unless you see spelling errors or the like).

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Nope I love it! I just posted it as we gave it, but this is a nice and more broadly useful variation.

Day 8 - January 15 2022

It has been a few days since we posted. In this update we’ll discuss the following topics.

  1. Robot and Game Play Technical Profile
  2. Intake prototype #3
  3. Calibrating our Ballistics Model - Measured exit velocity

Robot and Game Play Technical Profile - LINK TO PROFILE
This will be a document in evolution for a week or 2, but this is what is looks like today. Here are the top 10 must do:

  1. Must Taxi in Autonomous
  2. Minimum 1 Shot in Autonomous
  3. Target Autonomous script
    -Pickup (Different autons for different CARGO pickup positions)
  4. Need a Human Player with better than 25% capability
  5. High Hub capability
  6. Must make from the Fender
  7. Make a shot from Launch Pad
  8. Floor CARGO Pickup
  9. Hold 2 CARGO
  10. Climb to MID HANGER

Intake Prototype #3 - VIDEO
This video shows a fast moving intake over a 5" bumper with 1" of ground clearance.
NEO - 2000 rpm
48/65 gear reduction on first shaft
Belt reduction 18/24 pulley reduction for 2nd shaft

We’ve tried, Thrifty 2" squishy wheels, 4" Andy Blue Intake wheels, 2" VIW, and we think this setup works pretty well with the 3" AM green wheels and minimal compression ~0.25" It is time to take it to CAD and hook it up to some motors to deploy and stow it!

Launcher Calibration -
This was hard but fun. Our setup is shown in this image. 6" Hi-Grip Wheels on both sides.

We adjusted CARGO compression in this setup at 0.25", 0.75", 1.25", 1.75"
We got nothing at 0.25" - the ball just spun on the wheels!! :slight_smile: :slight_smile:
0.75" - 1.25" - 1.75" all gave us VERY SIMILAR EXITS speeds measured looking up as the ball leaves with THIS radar gun.

We had never used a radar gun and you need to measure in line with trajectory, so we measured from below the ball, but above the wheels so the gun did not see the wheels. We set the wheel speed to give a theoretical exit speed of 26.5mph, and we measured 17, 18, and 17mph through multiple trials at 0.75", 1.25", and 1.75" respectively. Basically that launcher is 65% efficient at converting wheel speed to launched speed. So, here is a plot of the Theoretical Trajectory and the Empirical Trajectory calculated by reducing the exit speed to the measured value.

Side view of a 1480rpm shot - ~11ft peak height. It matches our calibrated model nearly perfectly! I was very happy with that, but not with a launcher that only gives 65% of the wheel speed! There must be better versions that convert more speed to CARGO. Maybe we’ll add some primer wheels to get the ball moving faster prior to the main launcher wheels. People seem to use those a lot and now we see why! Good Luck everyone!


Day 12 - January 19, 2022

We’ve made some progress to share on robot requirements and topology.

  1. Weight Budget - We have done quite a bit of work to establish a parts library in Fusion with accurate weights. Using a weight budget this early should guid us on the design and prevent more trouble later. Team 4926 had major weight issues in 2015, 2019, and 2020. Not this year! Maybe. :slight_smile:
  • Drivetrain = 40 lb (frame, wheels, transmissions/motors)
  • Climber = 10lb (2 stage, telescoping with motors/trans, and frame mount)
  • Intake = 20 lb
  • Launcher = 25 lb
  • Electronics/wiring = 15 lb
  1. Topology - We have discussed layout of the design with the 3 major elements of intake, launcher, and climber. Since we are designing for single mid-climb we have to determine which side we are launching from and which side we are intaking from. After debating the various merits, we’ll have the intake and launcher on one side of the climber, but we’ll intake from the rear our launch over the climber out the front. Balancing the weight for a clean climb may still be a challenge, but that is where we are headed. (See CAD section next)

  2. Our Main-latest CAD link is updated! Not huge progress, but some!


Day 14 - January 22, 2022

Short update from a long day.

  1. We now have 2 Kit Chassis flat bots running, both of the long and narrow configuration. One is 6WD and the other 8WD. The 8WD is very much preferred from a driving control perspective and with the AM nut holders, the wheels will be easy to replace! Win Win! We’ll convert the 6WD to 8WD next week.

  2. We advanced CAD quite a bit with implementing the CARGO tunnel under the Thrifty Climber. The final CAD may replace all this lighter construction, but this represents the functionality. We’re still working the handoff from the conveyor to the launcher, and we need to determine a final height for the launcher.

4926 has been hard at work prototyping and CADing our entry this year. We’ll have more exciting stuff to share soon, but we wanted to show ‘Clean CAD’ approach to design our top level assembly. We are using the AM Kit Chassis this year and our Robot consists of that plus 4 major subsystems. Our top level assembly consists of the Kit Chassis and those 4 subsystems attached with a single constraint. This vastly simplifies the Top Level Assembly view.

A virtual build looks like this. This was done with just turning off visibility of the subsystems with 4 clicks and screen captures. I need to make a gif…and no it isn’t done yet!!!