Building a Compact, Portable Test Box

Finished Test Box

Fabrication files

NCR Test Box PartsDownload

The above .zip file contains the .dxf’s for the flange, side plate, polycarb holddown polycarb panel (if you want to route it out or similar) and the .step file for the polycarb pull handle. The steel for this build was all laser cut by SendCutSend.

While it’s certainly possible to build a bot, show up to an event, and run it without taking the time to test it’s not the best idea. Similarly, if you’ve got a weapon capable of damaging your opponent, you’ve got a weapon capable of doing real, lasting damage to a person. If you want to test it, you need somewhere safe to do it, and a test box is a great way to protect yourself, protect the other people around you, and test your bot.

With that in mind, I wanted to replace my old bulky test box with something that hit a nice balance of usable space and portability.

The core goals of this design are:

  • Small enough to easily go through a door
  • Able to be mounted to a wheeled platform
  • Big enough for almost any 3lb robot to be tested safely
  • Easy to build
  • Easy to repair
CAD Model of Test Box

Goal 1: Small enough to go through a door.
The main structure of the test box is a 26.5″ square frame that can be built to effectively any height. It’s rare to see a door narrower than 30″ so this should fit with room to spare.

Goal 2: Able to be mounted to a wheeled platform.
The hole patterns on the exterior of the flanges will allow the test box to be securely bolted to a frame using a simple hole pattern and #10 hardware.

Goal 3: Big enough for almost any 3lb robot to be tested safely.
With 1/2″ plywood walls the internal usable floorspace is just over 23″ square. Only the largest of the large in the 3lb class can’t fit that footprint.

Goal 4: Easy to build.
The main frame design uses two main parts, a flange and a side plate at qty. 8 each, made from laser cut mild steel. These components key together to aid in fixturing for welding and provide easy attachment points for wall and floor panels. Additionally, the top polycarbonate panel is retained by bolt on flanges and a pin lock to allow a simple rectangle of polycarb to used without any drilling required. The dimensions also allow for 2′ square 15/32″ thick plywood project panels from any local hardware store to be used for the walls and floor with little to no modification required. Similarly, the polycarbonate retainer height can be easily adjusted via 5/16″ OD spacers sized for #10 bolts. For mine I added adhesive backed felt pads to help with sliding the panel in and out. With sufficiently stiff polycarb panels you likely can slide the panel straight back with no issue. If you notice sagging then a small bonded tab that lifts the edge of the panel as it slides in will make closing the test box easy.

Goal 5: Easy to repair
The mild steel frame, easy to swap hardware, and use of commercially available plywood panels means that there’s typically a quick, easy repair option for almost any kind of damage.

  • Fresh cut parts slotted together
  • Clamped for welding
  • Off the shelf walls and floor
  • Welded and ground
  • Welded and ground

For my build I opted to paint much of the plywood, while it’s not necessary it does add a nice finishing touch to the whole thing.

  • Floor fitting
  • Checking alignment
  • Walls going in
  • Mostly assembled
  • Polycarb retainers and felt installed

So, what’s left to do? At this point the test box is fully usable. Most of the box is held together using some fairly short #10 wood screws and the pin to lock the polycarb panel in place is McMaster #98320A125 if you want to track down the same part.

RadioMaster MT12 Joystick Mod

For a long time, I’ve wanted a ground style transmitter with a third channel that wasn’t a basic switch or slow scroll through an input range. Not long ago RadioMaster released the MT12 which is a ground style radio running EdgeTX.

Before I get too deep into what I did, here’s the finished mod:

  • Finished mod being bonded to the removable base plate
    Finished mod being bonded to the removable base plate
  • Finished mod being bonded to the removable base plate
    Finished mod being bonded to the removable base plate

Here are the STL’s you’ll need to print your own:

Joystick Housing Body

Joystick Back Cover

With that out of the way, here’s how this was made:

After the MT12 was delivered and RadioMaster told me there wasn’t a CAD file available I looked into free 3D scanning apps, eventually settling on Polycam. I took the MT12, set it on a flat metal plate, scanned it, then exported the scan, used a converter to get it into STL format, imported it into Solidworks, then made the first version of the main housing.

  • 3D scan of the MT12 done with Polycam
    3D scan of the MT12 done with Polycam
  • Raw STL imported to Solidworks
    Raw STL imported to Solidworks
  • Raw STL being used to mock up first draft of the joystick mod
    Raw STL being used to mock up first draft of the joystick mod
  • First draft mod being used to validate scan geometry
    First draft mod being used to validate scan geometry

Overall, it was ok, but a bit bulky. It also meant that I couldn’t grip the transmitter the way I wanted to. Enter the realm of near impossible to machine parts that are effectively trivial thanks to 3D printing. The second version of the housing dramatically changed the shape and added mounting features. It also made it clear that I’d need at least a short cable extension. V3 quickly followed with fine tuned mounting and a cover for the back of the joystick.

  • V3 geometry to determine fits/location and cable length
    V3 geometry to determine fits/location and cable length
  • V3 geometry with rear cover installed
    V3 geometry with rear cover installed
  • V3 with a test for a removable mounting strap
    V3 with a test for a removable mounting strap

I didn’t happen to have the right connectors on hand, so a quick Amazon order later and I was ready to build an extension cable. For this step the big thing is making sure you don’t swap around the order of the wires from cable to cable since that could cause input issues or damage a board.

Extension cable installed
Extension cable installed

With the mod tested and the housing painted it was time for the final step, bonding the housing to the removable base plate with one of my favorite adhesives, Shoe Goo.

  • Finished mod being bonded to the removable base plate
    Finished mod being bonded to the removable base plate
  • Finished mod being bonded to the removable base plate
    Finished mod being bonded to the removable base plate

The paint’s a bit glossy, so I may give it a matte clearcoat at some point, but beyond that I’m very happy with the final outcome.

High Steaks Deep Dive

Have you ever thought of a terrible pun? Has that terrible pun resulted in dozens of hours of work to transform it into a tangible object?

Big wheeled bots aren’t new. Bots like Huge, Gabriel, Starchild, and plenty of others have been out there fighting for years and are inspiring new designs all the time. While thinking about the pros and cons of this style of bot the thought came up: What would happen if Team Food Fight built a big wheel style bot? While I can’t say what the bot would look like, a name immediately came to mind.

With that pun, the CAD effort began and Hotkoin was contacted for the logo you see above.

So, what are the goals of High Steaks?

  • Re-use the hubmotor and electronics from M-80
  • Test viability of PLA+ for semi-protected structural elements in a 3lb bot
  • Test segmented cleats as a means of increasing grip and adding structural stability to UHMW wheels
  • Lean hard into the theme

With those goals the parts list and profile started taking shape. High Steaks would recycle the drive and weapon esc’s from M-80 along with the hubmotor. Some left over FingerTech Mega Sparks would be the drive solution with an extra 2:1 reduction to the wheels.

Cleated UHMW Wheels
Welded 4130 Chassis Being Tempered
12lber For Scale

If you’re gonna go all in on a steak theme, you can’t be generic on your weapon disk. This lead to the question of just how steak-like a disk can be made to look. After some digging around I settled on two base colors and the Montana Cans white marble effect paint.

This Was a Very Clean Process
Raw and Ruined

With the electronics pulled mostly from an existing bot the wiring process was fast with the main challenge being routing wires between the two halves of the chassis. The rear channel was snug, but it wasn’t too difficult to pull the wires through with the assistance of some forceps and a bit of patience.

  • Electronics Overview
  • Power Switch with TPU Mounting Spacer

Thanks go out to SendCutSend for making the weapon disks, steel chassis components, and spring steel cleats. The UHMW wheels and carbon fiber armor panels were made by CNCMadness.

  • Top View
  • Bottom View
  • I Swear It’s Not On Fire
  • Weapon Lock On Theme

With all the pre-event goals met that leaves the final question: How did it do?

Overall I’m very happy with the performance. The one serious design issue that popped up didn’t really impact the results, but with the width of the tips on the side forks it would require the axle to be removed to replace a wheel, which isn’t ideal if there’s a time crunch. Because of that some new side forks have been designed that keep the aesthetic while allowing the hex bore on the wheels to slip over them for easy replacement. Beyond that, some extra UHMW wheels and cleats have been made to ensure enough spares are on hand and that there’s a heavier duty wheel option for bots where wheel damage is particularly likely.

Outlier Deep Dive

Outlier prior to competing at Robot Battles 71

Outlier is the teams newest 1lb bot and is the end result of trying out a bunch of new stuff and new ideas.

Going into the design the core goals were:
1. Build a 1lb electric lifter that’s competitive
2. All brushless (this goal came in after initial concepts used some brushed parts)
3. Run 4s lipo effectively
4. Test viability of TPU lifter arms
5. Try new wheel construction methods

  • Early concept with a brushled lifter motor
  • Layout is starting to take shape
  • Design as built for Robot Battles 71

CAD from the early concept stages through the design that was made

Over the course of a few design revisions and a few product releases the bot went from a semi-direct brushless drive, brushed lifter with all of the components integrated into a single chassis to an all brushless lifter with replaceable weapon modules and indirect brushless drive.

Key components in Outlier:
Drive/Lifter: Repeat Robotics Repeat Mini Mk3’s (prototype HR gearbox for the lifter)
ESCs: Repeat Brushless Drive ESC for drive, Repeat AM32 Drive ESC for the lifter
Battery: 2x 2s 250mAh lipos from Palm Beach Bots
Power Switch: FingerTech Mini Power Switch
Weapon Module Structure: Custom Printed by Team Malice
BEC: iFLIGHT 3S to 6S Micro 5V 3A BEC

In addition to the above, the chassis, forks, and plow on outlier were made from 0.050″ laser cut 4130 steel from SendCutSend, the baseplate was 1mm carbon fiber from CNCMadness, and there were a lot of PLA+ and TPU parts printed in house.

  • Weapon module test fit
  • Weapon module test fit
  • Lifter gear and wheel hub
  • Chassis test fit
  • Plow test fit
  • Silicone to TPU bonding test
  • Completed wheels

Assorted photos from the build including test fits and some adhesive testing

  • Rolling chassis
  • Weapon module test fit

Test install of the drive wheels & weapon module

With that done and the event rapidly approaching a lot of things happened off camera with the end result being a working 1lb robot.

First drive and arm wiggles

A bit of lifter testing

Outlier is a pretty dense little bot and was probably one of the more challenging wiring jobs I’ve done.

Outlier (left) along side Firecracker (middle) and Quark, (right) two of our 150g bots.
Ready to fight

So, how’d the event go?

Can’t really complain.

The good:
The drive power was insane, even with the fairly grippy silicone it was easy to spin the tires.
The chassis and drive mounting held up great, even with some major hits repairs were easy.
The TPU lifter arms took crazy hits without any trouble.
The PLA+ – TPU – Silicone wheel combo held together well even when taking some nasty hits

The bad:
The D shaft I was using had a very small flat, so between the Delrin gear and printed TPU adapter it was struggling to transfer torque, so the lifter often struggled to lift.
Changing configurations took longer than I’d like which meant I ran a config that wasn’t well suited to my opponent and took some massive damage to the weapon module & plow during the fight
After a few fights in close succession the printed PLA+ motor guards deformed, jamming the drive motors in the final, luckily late enough that it didn’t cost Outlier the match.

  • Damaged but still usable wheel
  • Post event teardown showing deformed PLA+ motor guards

So, what’s next?
1. New homemade titanium D shaft for the lifter module
2. Modified, lighter, 1095 steel plow design that will allow weight for wheel guards so changeover time is reduced between configs
3. Explore additional wheel configurations
4. Connectorized weapon motor to allow easy swapping of entire weapon module

Introducing Outlier

What’s the current meta in the Antweight class? Compact verts? Probably. Big horizontals? Fair chance. Wedges? Certainly a contender. Whatever it is, it certainly isn’t… Outlier.

Some brief specs:
Drive motors, weapon motors, and esc’s from Repeat Robotics.
2x 250mah 2s LiPo from Palm Beach Bots wired in series.
Welded 4130 chassis with a printed weapon module and carbon fiber baseplate.

Robot Combat Best Practices

Introduction

There are a lot of guides out there that will talk about specific parts that are good to use, materials you should build from, and where to get parts. Those are all important things to know and are a critical part of gaining the understanding you need to build a combat robot. This guide isn’t about that. This guide is on ways to approach whatever bot you’re building that can set you up for the best experience possible.

What are “Best Practices”

Best practices, in this context, are the tools and techniques you use in the design, build, and battling of your robot that set you up for success. Success doesn’t necessarily mean wins, as that may not be the goal of the bot. Success means delivering on the idea you had for the bot.

Core Best Practices

Design for Your Manufacturing

The best design in the world isn’t worth anything if you can’t actually make it. What fabrication options do you have available? Do you have the time, tools and skills to do it yourself? Do you have the budget to outsource? Is this even something that can be made? These are all things you need to think about when designing.

Design for Availability

The perfect part may exist, but you need to actually be able to get it for it to be useful. Everything from screws to speed controllers can run into the problem of it being the “perfect” solution that you can’t order. You also don’t want to find yourself in the spot where you can’t buy spares of your preferred weapon motor because it was discontinued 4 years ago and the ebay seller you’ve been buying from finally ran out of stock.

Design for Safety

No matter the size of your bot, thinking about safety features early can be a massive help. How will your weapon lock actually work? Where are the sharp corners/edges? How easy is it to access your power switch? Not spending the time on this early can result in having to modify your design after the bot’s been built to accommodate a mandatory safety feature. Beyond that, having an easy to install/remove weapon lock and easy to operate power switch will make your load in and load out go smoother which means you’ll be ready to fight or repair faster.

Design for Assembly

When designing your bot take time to think about how each part goes into the bot. It’s very easy to design yourself into a corner where all of the parts are physically capable of occupying the space as designed, but due to how the bot is constructed or the order in which things go together you can find yourself unable to install a part or without access to a critical fastener.

Design for Repair

This is robot combat. Stuff will break. Unless you’ve got a spare robot for every fight, which while technically an option is a massive expense and likely a significant waste of resources you’re going to have to make repairs. When you look at a design you need to consider the parts that are most likely to take damage and look at the process to repair or replace them. If you’ve got 20 minutes to repair between fights and it takes you 15 minutes to get a busted gearbox out you’re likely not making your next match with a working robot.

Design for Failure

Classes in robot combat are defined by a weight limit. This means that for any given class you don’t have infinite weight to make parts stronger. If a bot gets hit hard enough something will fail. Ideally, this something is not catastrophic to your ability to finish the match, is easy to replace, and isn’t the most expensive part of the robot. Designing mechanical fuses so you can influence the failure points can create a situation where you’ve got inexpensive, easy to address repairs between fights instead of having to toss out more expensive parts because none of the cheap stuff broke.

Design for Maintenance

Similar to repairs, inevitably there’s stuff you’ll need to do to your robot between fights. Maybe it’s replacing worn out wheels, sharpening the leading edge of a wedge, or adjusting belt tension. It almost certainly will also be charging or changing your batteries. Think about how these tasks will be performed and try to minimize the time this will take. You’ll thank yourself later when you have repairs that need to be done on a tight timeline and all of the regular maintenance isn’t occupying most of that time.

Advanced Best Practices

This section covers topics that are much more involved and time intensive than the core best practices section. Treat these topics as “worthwhile if time allows” as you can get by without them when necessary, but integrating them into your process will be well worth the effort.

Driving Practice

The more time you can spend driving your bot the more comfortable you’ll be running it at an event. To the degree practical, matching the type of floor and floor coating will only help. With non-spinners and bots that aren’t likely to throw parts/debris you can get a lot of practice in by using a floor and a small protective barrier to keep the bot contained. On bots with spinning weapons or other systems that can send chunks flying you’ll need to think more on containment which may limit your practice surface options. Ideally you’ll be at the point where you’re comfortable enough with your bot that the bot is doing what you want without you actively thinking about how to manipulate the controller to cause that action.

Design for Aesthetics

There’s nothing wrong with keeping things simple, but taking the time to add some color, shape, or style to your bot can result in a bot that is memorable in and out of the box.

Minimize Tools and Hardware Variation

To the degree you can, you want to minimize the number of different wrenches, nuts, bolts, drivers, and other equipment needed. This will save both your back and time in the long run. If you’re working on a bot and you’ve got some 10-32 bolts in there in 7/16”, ½” and 9/16” lengths you should probably take a step back and see if there’s a good option to reduce that to one length, similarly if you’re designing the bot and have an entire catalog of thread sizes it’s worth the effort to look at areas where you can change the bolt size used and cut an entire bolt size out of the spares pile for an event.