The Grasshoppers 2021 Build Thread

This is going to be a weird one, but the Grasshoppers are here to share our thoughts, ideas, processes, and mistakes.

We started off this season discussing the different activities and deciding what we would like to participate in. We quickly decided to ignore the innovation challenge and game design challenge, focusing only on improvements to our 2020 robot to improve our odds of success in Infinite Recharge at Home.

What our 2020 robot looks like:

Things to improve:
Shooter - shot accuracy, adjustable range
Collector - speed and consistency
Indexer - speed, reduce capacity from 5 to 3
Wheels - optimize for maneuverability and auto pathing

Happy with:
Singulator - fastest mechanism in our power cell handling system
Drivetrain - automatic shifting and power are adequate (for now)

Climber - not needed
Sucker system - illegal, even in IR@H

We started off our CAD effort by copying our 2020 OnShape directory and deleting unused subassemblies from the main robot assembly.

CAD here.


So happy to see you guys doing a build blog this season. Always a fantastic read. What is the reason for reducing indexer capacity?


Given these rules it made sense to us to save weight by reducing our power cell capacity from 5 to 3.


Does that mean that you will be replacing the entire indexer with a lower capacity design? That seems like a pretty major undertaking to save a few pounds when what you have in place already works so well.

I’m sure there is a sound reason for taking on that challenge, but I’m having a hard time ignoring the benefit of using what you’ve got over saving a few pounds. Does the robot not drive smoothly or is it more top heavy than you’d like or something?



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I’m actually very excited to see how this develops along with other teams who choose to optimize for this new game. There are going to be quite a few teams that optimize and I suspect we will see some interesting new techniques come out of it.

Now if only a certain team hadn’t ruined a vacuum ground effect system last year…


I’m excited for that aspect too, feels almost more real world engineering to me when a group has to modify something to adapt to a new set of guidelines. It will be entertaining to watch as teams make the call between dropping proven designs or choosing to upgrade existing designs. And don’t get me wrong, we will be making some changes to optimize for the restrictions of the challenges presented, but I think we will be solidly in the upgrade camp.

I guess I was just surprised to hear that such a large component of this robot will be changed in the interest of what sounds like weight rather than performance. But in a game of tenths every bit counts!

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We had to gear down our indexer to deal with the drag of 5x cells and the long, convoluted belt run in it. By changing some aspects of the design we can speed up the indexer and shoot faster.

We may also need an accelerator stage (like 125) to improve shot consistency, which will chew up indexer space.


We decided to not do anything substantial with our drive base/chassis. Starting from scratch for IR@H we would do things quite differently, but that’s a bridge to far for us this year.


Not a ton to report yet. As usual we have a slow start due to midterms and finals for our students. Currently we are identifying specific items to improve in our revised mechanisms.

More later, when we’re really underway.

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great movie

Looking forward to this thread James, I hope someday we can see the sucker system at an event. Maybe some offseason down in Texas can help make that happen in the future. :slight_smile:


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We are currently developing a quality plan for controlling and improving our 2020 robot before we get into detailed design work. This will help us identify the key changes that we should implement in order to improve overall robot quality.

The initial results were interesting, if obvious. It showed issues with battery, radio, and powertrain were the most concerning.

We are going to convert these initial FMEA results into some form of a quality control plan.


We have established mechanism requirements:

Worked through a weighted decision matrix to choose a new collector design:

Right now some students are designing an improved collector while others are researching indexer/shooter options.

A slow season for us, but being able to spend a lot of time on these fundamental engineering tools is a good exercise.


Our 2020 robot has come out of storage and is with a programming student and coach (son and father) for development with a LimeLight, something we haven’t had before.

The indexer got pretty sad in storage, immediately munching its compliant drive wheels. It will get patched up and workable soon though.

The Quality plan is coming along too.

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First time ever for us, closed-loop vision-driven shooting. The control in this video was a single button press with <1 day of development.


Improved PID values.


3DP Limelight Bracket with adjustable angle.

strong text


Not exactly <1day. <1 day to transfer the vision aiming code from the 2019 robot to this one. I think it took a day or two to get it working on Cecilia.


Can you provide the math or empirical testing you’ve performed to back up this statement?


The video of the text bench pressing the robot didn’t make it into the post.