Building a Mini Bot

2017 was just a year for off season Mini Bots… 323’s first bot was a miniature swerve gear runner/climber running 6 775Pros in the drive (2 per wheel module)

Fun thing about swerve, small wheel bases, and high speeds - Anklebiter can roll itself over if you’re not careful.

Starstreak followed it up by being not much bigger and adding an additional 2 775Pros in the drive. https://www.youtube.com/watch?v=NSRefyWV-4w

Building small bots is fun but does require some work.

We did a 20x20 off season 6-CIM Power Up robot to play the switch and exchange, and it could flip itself over by swinging a power cube too quickly, so we ended up limiting the arm acceleration to calm it down a bit.

Anyone have suggestions for a cheap control system and motors? My roommate and I are in the process automatic our dorm room to allow us to sign in with our id’s, but have hit a bit of a wall with getting motor controllers and motors.

I plan for it to be a 100% FRC legal robot

Use your Z (or up and down) to your advantage, fitting a roborio and PDP into the same XY area can save you so much space. Also, 2 wheels is a nightmare. Remember, 3 points makes a plane.

As for cheap control systems: Cheap & Dirty Electronics for Two Motors

And for motors, i recommend browsing andymark or vex till you find what you need for the specific case (Though PG motors and BAG motors are pretty low cost).

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Do you know if they integrate with a raspberry pi? The key card scanner we are using plugs into USB which we are attaching to a pi to do the automation.

You’ll likely want something like https://www.adafruit.com/product/815 for the Pi to handle PWM stuff.

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Here are a couple of pics of a roughly 16"x16"x7" robot I made from an AM14U3 chassis about a year ago. While it has the Quick and Dirty control system and a Stinger fuse block, there’s no reason it couldn’t be built with an FRC-legal one. If going for 13x13x11, it would be easy to switch to NEOs, stand the battery up, use a shorter belt, and tighten up some of the empty width and length of the wheel well. Size eleven canvas deck shoe for scale.

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That’s really nicely packaged. I’m impressed that you had room for a battery laying flat like that.

I used the AM horizontal battery mount kit, but I did modify it a bit… I used the base plate between the inside chassis rails, and only used one of the two sides of the kit, originally to hold the bungee hook. On the other side there’s a bit of fence board 1"x2" (3/4" thick) with a clearance hole for the axle nut to keep the battery from getting poked. I later ditched the bungee and hook, and used a leftover bit of outside rail as a battery keeper on the motor side.

Whoa. I set aside a whole day off work to make this beastie in my garage, with the kit chassis delivered mid-morning. Or was this a Hitchhiker’s Guide to the Galaxy editorial lunch?

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You can also get quite a bit cheaper than that. There’s a decent up charge on the RX/TX over a similar product: https://hobbyking.com/en_us/turnigy-t6a-v2-afhds-2-4ghz-6ch-transmitter-w-receiver-v2-mode-2.html
and I’m sure dozens of teams would be happy to get rid of their old Victor 883/4/8 and SP controllers.
That’s what I’m currently building into an extremely mini bot (let’s face it, it’s an RC car with some FRC components).

Additionally, AM bundles don’t have discounts for the most part :slightly_frowning_face:

Made this during lunch. Fully functioning H-drive with a 5:1 to the 6” wheels. 20”x13”. Initially it was meant to be just a normal tank drive with omnis then I realized there may be enough room to stick an h-drive so h-drive

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You can get real small if you leave the FRC ecosystem. RX/TX units used in multirotors and combat robots get tiny.

I have a 4.5g LemonRX in my in-progress fairyweight:

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It was over the course of multiple lunches. But yes, it was made during lunch. I didn’t eat my lunch since I wanted it to work.

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We made minibots to be used as programming testbenches for testing/teaching programming and testing various things like autos or sensors etc etc.

V1 of our minibot use 2 versaplanetaries as gearboxes with 3 in colson wheels, and an overall dimension of 18"x18"

V2 of our minibot used a custom 775pro gearbox with 4in colson wheels (we sometimes swapped in omnis for driving fun), and an overall dimension of 15"x15"

V3 of our minibot used swerve modules and had a overall dimension of 17"x17"

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is this 13x13x11 mm/cm/in? You probably could considet GT2 pulleys and belts either 2mm, 3mm or 5mm depending on your size and torque requirements.

As OP is from New York USA, and as an FRC-legal battery has a couple of dimensions larger than 13 cm, I’m sure this is inches. (And OBTW, this is the size of the 2018 Power Cube.)

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Here is a simple bot we designed and built completely with hand tools. It was fairly simple to build and is great for programming practice and out reach events.
A complete easy to build FIRST robotics teaching robot. This robot is:
• The lowest possible cost.
• Great rookie member training robot to build.
• Built with all hand tools – No machining required.
• Uses all legal FRC competition components.
• Easy, fun and fast to build.
• Great outreach and programming robot.
• Small and light.
• Fast and easy and FUN to drive.


Robot in 10 hours REV1.pdf (4.1 MB)

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This is a fantastic set of plans. My only comment is that if “lowest possible cost” is your driving principle then there are a few places where you can shave some cost off of this.

Talon SRX’s are $90 USD compared to Victor SPX’s at $50 USD
CIMs are $33 compared to MiniCIMs at $30
4x1.5" Colsons are $15/ea compared to AM Stealth wheels at $4/ea
Vexpro’s hex bearings here are $40 for 8, compared to Thriftybot’s $30 for 10

All told, you can pull ~$118 ($154 CAD) out of the BOM cost. Someone thriftier than me could probably find a few more dollars.

That’s a low enough cost that I’m tempted to re-work out rookie engineering education next year to include a few of these.

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