Robot in 3 Days Reveal: Houdini | 9605A + 9421

Hi forum!

Teams 9605A and 9421X/V are proud to present our first Robot in 3 Days robot: Houdini.

-4m 3.25" 3:5 200rpm Drive
-1m 200rpm Side Rollers
-1m 1:7 100rpm DR4B
-1m 100rpm Cube Tube
-1m 1:15 100rpm 4-Bar

This was a very ambitious robot for 3 day, and it was a lot of fun to make. Although it does work a lot better than originally anticipated, there are some aspects of it that would need further tuning to be more competitive. Here is a brief overview of each subsystem:

This drive is fantastic. It is super fast, which we think if driven well could be very useful for this game. Sometimes speed aids in playing defense as much as torque. For example, the fast drive allows you to drive around the field and knock over all the cubes at the beginning of the match.

This Ri3D was the first time that any of its members have attempted an inverted DR4B, and as anything in engineering, V1 is never the best. All the joints had good build quality, but the tower twisted a bit due to lack of support. Diagonal bracing would have helped a lot. We chose the inverted DR4B because of how thin the 4-bar that it mounts on is.

Side Rollers
As far as we know, we are the first team to attempt 1 motor side rollers like this. Uncharted (25461Z) territory like this is never easy. The difficult part was figuring out how to transmit power from one side to the other. We decided upon having a chain about 1/8" off the ground a tray for the cube above it. The side rollers are a bit lack luster. They sometimes struggle to get the cube in the correct position in the tray. It would be better if they deployed the other way around the axis, but there were other limitations to that that we were unable to solve. We spent the majority of the time figuring our the lift and 4 bar, and 3 days is not much time for such an ambitious robot.

Cube Tube
We originally intended to do a 2 stage, deployable cube tube that would allow us to carry around 6 cubes. Unfortunately we ran out of time, and this never left the prototype phase. More information and pictures of that will come in the documentary. Personally, my favorite part of this whole robot are the passive intake hinges that grip the cube when the lift pushes down on it. These are almost 100% reliable, and I think are even good enough for a competition robot. There will be a close up on them in the documentary. For powering the cube tube, we ran out of 36t gears, so we were forced to do a standoff linkage, which was not that fantastic, but it worked.

4 Bar Lift Mover
Ah yes, the subsystem you’ve been waiting for. I think that at some point in time we’ve all thought “why not just move the whole lift?” Well, we did it. And it actually turned out pretty well. It is a pretty versatile solution to delivering your stack to the scoring zone. We didn’t show it in the reveal because we didn’t have any footage of it, but the robot’s geometries allow it to score the stack deep into the corner of the large scoring zone. It was also necessary for us to move the whole lift when scoring towers. This was the part of the robot that we thought would be the most unique, so we hope you all like it.

One of the main goals of this Robot in 3 Days was to be unique. That said, we certainly did not want to do just another tube bot, despite how simple it is. The end result was indeed an incredibly unique robot, and it actually works a lot better than any of us ever anticipated.

Have fun debating whether this is insane or a potentially clever solution to Tower Takeover :smiley:


Absolutely insane and beautiful to watch. Some tuning could make this the meta!e

As for the side rollers,



I didn’t even notice how the side rollers were geared before you mentioned it. Im surprised they work as well as they do.


Really cool, surprised by how stable the lift is on top of a 4-bar


I didn’t even think about attaching the whole arm to a four bar. I’m amazed it works. Really cool design. Question: does that make the arm a triple four bar?

1 Like

Not really. Since they aren’t mechanically linked they are treated as two separate systems. Kinda like the four-bar on top of dr4b in In The Zone.

1 Like

Unfortunately we could not mount the motor under the side roller like that design does, so we had to get a bit creative.

Great robot especially for 3 days. I have been thinking of making a robot like this, (but I can’t because my stupid school). Anyway have you seen this thread “Differential transmission - power takeoff from the drivetrain motors” it could help save your “4 Bar Lift Mover” motor so you can use it some where else.


That is an amazing robot!

It seems counterinuitive to move entire DR4B forward, instead of just the top with the cube tube, but I get your objective to have a unique design.

Will your next build use the same concept, or have you learned some limitations?

1 Like

While this isn’t my favorite design so far, several of your mechanisms are the most effective I’ve seen thus far, great job! I am particularly interested to see how your passive hinge works in the documentary

Moving just the cube tube did cross my mind while we were designing. Then I started trying imagine the support structure necessary to move it, and it is too complex to possibly be done in an ri3d, and I’m not even sure if it’s feasible for a normal robot. In ITZ the top 4 bar just had to move very light rollers, but the cube tube is far heavier. Not to mention that we were planning on doing a 6 cube capacity tube.

Also, I am VexU now, so my build will likely be very different :slight_smile:


Great job guys, I hadn’t even thought about moving the entire lift before like that.

1 Like

Transmissions are a bit hard to work into a Ri3D and it would be hard to get all of the spacing/gear ratios right. It is something that could be looked into but would probably be pretty complex.

1 Like

Yeah you are right a Ri3D is a very short deadline, but maybe it would work in a full season robot.


This was already an extremely complex Ri3D. If you compare it to some others, you will find that there are fare more moving parts and subsystems that all had to be built in 3 days.


Wow. This is eerily similar to my Plan B design, with a few key differences. Very well done.


I’m curious, the rollers almost seem like they hinder you and not help. The time it takes to suck them into place seems like a waist. Why not just ditch them and use eye coordination like most ITZ bots did to grab cones?


That would be inefficient as the cube tube would need to individually orient with a cube while roller intakes can intake a cube in any orientation.


SUPER! :robot: :+1: great robot!

1 Like

This is an impressive robot, great work!:grinning:

1 Like