94999E - Yokai VEX Change Up Mid-Season Reveal

Team 94999E - Yokai Mid-Season Reveal

VEX 94999E | Yokai Change Up Mid-Season Reveal - YouTube

We are proud to present our mid-season robot for Change Up! This bot has been used at two tournaments so far, throwing one and winning the other. We have leared a lot when building and competing with this robot, as we hope to convey below.

About the Bot

The most notable subsystem on our robot is our intakes. When designing, we wanted something space efficient when folded up, as well as something that would provide even compression on the ball. In the end, we decided to attach the intake using a 4-bar linkage.

As the 4-bar allows for outward movement of the intake at any point, we have even compression on the ball, allowing us to more easily tune the intakes. In addition, we were able to use the movement of the 4-bar linkage for a compact deploy, as shown.

(Old picture from when we still had an ejector)

The main downside of these intakes is increased slop in the joints. Due to the compact nature of the 4-bar, we were unable to use proper screw joints for the 4-bar joints. Because there is nothing bracing the screws in one place, they have a tendency to loosen and become sloppy. While this does not impact the performance of the intakes, it is something we hope to fix in future iterations.

Most other parts of the robot are pretty standard. The backboard is not the cleanest, so we plan on replacing it in the near future. We added a wedge onto the back in hopes of performing better defense, and it does work, my driving just doesn’t utilize it to the fullest extent. We will be removing the wedge as Live Remote Tournaments become more prevalent.

As for why we removed the ejector on the back, we simply did not use it. We figured we would be better off attaching the motor to the indexer, allowing us to run the high speeds we show in the reveal. The rubber band ramp for the balls will likely be replaced by a more efficient surface, plastic, later in the season.

One issue we noticed in the design this afternoon is the indexer jamming. If the robot gets too close to the goal, the ball will sometimes not go into the indexer, but rather jam it against it and the plastic of the goal. It’s fairly hard to explain, but it is visible in our match videos. We believe this can be fixed by increasing the distance the hard stop is from the robot, so it should not take long to fix.

We have competed at a tournament today (2/27 as of posting), and here is some match footage from the event.

Match Footage

Qual 18: VEX Change Up 94999E - Unofficial Whitewater Tournament Qual 18 - YouTube
Quarterfinals: VEX Change Up 94999E - Unofficial Whitewater Tournament Quarterfinals - YouTube
Grand Finals: VEX Change Up 94999E - Unofficial Whitewater Tournament Grand Finals - YouTube

These were just updated as I’m typing this, so the resolution may not be up to 1080p just yet. I will remove this part when it is.

Thank you for watching our reveal, and good luck in the rest of the season! If you have any questions, feel free to ask.


This is, without doubt, one of the robots I’ve seen this year.


i disagree i havent pressed the vidro yet

1 Like

Wow! That’s a great robot! Could you post a gif of your intakes flipping out? Thanks!

that 4 bar flipout is actually kinda brained. Way easier to tune compression compared to a normal back flipout

i’ll suggest having a faster intake though (around 600rpm) since it seems like balls jam on the bottom while cycling since its significantly slower than the rollers


They just need a full rebuild of intakes. Is you noticed they didn’t descore from middle and might now have descored at all.

:+1: ezgif-2-b3392fbe99a9

Definitely! That is one of the main changes we will be making in our coming rebuild.

Yes, the robot does have difficulties actively cycling center at the moment. This is not, however, caused by the intakes, but rather by a piece of metal that stops against the goal too early. We have had higher priorities than fixing this, but do plan to soon.


Thank you that’s perfect!


Nice! What caused the change to an x-drive? If I remember right, it was a tank before. Also, why did you get rid of the pooper? And what did you use to cut the flex wheels? Thanks!
Edit: are those 2.75 omnis on the x-drive? That may be kind of slow.

The main reason we changed to an x-drive is that we are more comfortable driving it, as we used an x drive all through Tower Takeover.

Our original x-drive was geared 5:3, hence the 2.75 inch wheels. At the time, the bot was, and still is, way too heavy to support that gear ratio, so we scrapped and and decided to power the wheels directly. Increasing drive speed, and reducing weight, is the main reason we will be rebuilding in the near future.

We never used it, so we decided to put the motor on the indexer to reduce burnouts at high speeds, and make the shots more consistent (in terms of launch speed) and powerful.

We used scissors and a hacksaw. I would not recommend doing it this way, as our cuts are not the cleanest, but it worked.


Did you ever tune your backboard. It seemed sometimes the balls didn’t go into the goal smoothly and rolled around. For example in the last piece of footage. I was also wondering if you ever looked into making any sort of wedge for the goals for smoother intaking.

We plan on redoing the backboard when we make other major changes, so fairly soon. You are correct in that it could be much smoother, but it is functional for now.

We have a prototype made! We’ve had competitions these past few weekends, so our energy has mainly been focused on autonomous, rather than build. After this weekend, another comp, large improvements will be made!


Loved the 4 bar for extending the intakes so much that I had to play with the idea. Maybe you have already considered this, but just to offer a suggestion for when you do rebuild…

As constructed, the 4 bars are a bit flexible when fully extended. This happens (at least on my model) because the 2 standoffs that are two of the bars almost share the same axis when the intakes are extended. This allows them to rotate axially about the joint made my the standoffs, the stand off connectors, and the shaft collar. It introduce some slop that makes your intakes bounce around.

4 bar - single connector

I payed with using 2 standoffs per 4-bar linkage to give the model more rigidity. It’s a tiny bit bulkier, but it very stable. In the gif below, its wouldn’t rotate and is moving only because I couldn’t hold it stable enough.

4 bar - double connector

Anyway, just a quick suggestion to help improve a great idea.


Are you suggesting something to push the goals open? If so, would you say they are worth it? I’ve been considering adding little wedges to the tops of my intakes like the 9181 teams have.

I have had them for most of the season and are pretty helpful. I came up with it (not saying I was the first one but it was original) mainly due to my team and I having the goals too tight and thinking that’s how they were supposed to be. At first I wanted the wedge to come of the indexer but due to weird constraints we decided to have it on the intakes. Overall it just helps with intaking a lot and would recommend it.


Yeah I think it would be easiest to add on the intakes.

In general, is there much friction trying to push into the goal with those sliders attached? Curious if I would need to remove them for programming skills or not. I’m too lazy to add odom to my robot so obviously it matters if it moves around a bit unaccounted for.

We used to have a pooper to but it was really slow and impractical

Here I will pm you. I don’t want to clutter this

I came up with it



I didn’t mean it in that way.