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Welcome to the technical reference wiki for Duke Combat Robotics. If you want general information about the team, see our website.

Semester ant-weight build schedule

Students work in groups of 1-4 to build an ant-weight (1lb) combat robot, with an internal competition being held at the end of each semester. Students are strongly encouraged to keep to the following schedule to ensure they end up with a robot they can be proud of!

Week	Fall dates	Spring dates	What to work on
	late August - early September	mid January	(Pre-season: first ~3 weeks of classes)
1-2	mid September	late January - early February	Wiring harness, "scrap bot"
3-5	late September - mid October	mid-late February	Research and design of prototype bot. Figure out overall shape, how to attach motors, etc. SendCutSend* order #1 happens at end of week 5
6-9	late October - early November	March	Fabricate and assemble full robot in detail, test it in the box, see what's bad, fix it, etc. SendCutSend* order #2 happens at end of week 9
10-12	mid-late November	early-mid April	Do test skirmishes with your robot, refine as needed.
13	early December	late April	Competition! Typically the first Saturday or Sunday of undergrad reading period.

* SendCutSend is a commercial service that offers precision cutting of many materials. We especially use them to order laser cut AR500, an armor plating steel suitable for combat robot weapons. See technical tutorials below for details.

Making your first combat robot

2S LiPo battery

N20 brushed DC motor

Brushed dual motor controller

"Tyler wheels" - two part 3D printed wheels for N20 motors

A2212 Brushless DC (BLDC) motor with motor controller

Microzone MC6C transmitter and receiver

Automotive rocker switch with LED

Our internal competition is for antweight robots, meaning a weight limit of 1 lb (454 g). We follow the SPARC rules, which you should read (they're not long).

This tutorial assumes you're making the most common type of antweight design: two drive wheels and one weapon motor with a spinning kinetic weapon. You don't have to make a bot like that, but it's a good place to start.

Components and general layout

The basic combat robot doesn't have any code or autonomy -- it's plain remote control, like an RC car. We use the following components:

1. Lithium Polymer (LiPo) batteries, typically of the "2S" (7.4V) variety. These connect with a yellow XT30 plug, but also have a white connector used only for charging. Example.
   • NOTE: LiPo batteries can be dangerous! Don't over-drain them, puncture them, or short them out. If you do, they may swell, become hot, and even shoot fire. Dangerous-looking batteries go in the "oh crap" metal box in the Foundry, or in the team's sand bag.
2. Brushed DC motors. Used to drive the wheels. We typically use "N20" model motors, which have a little integrated gearbox. Example.
3. Wheels. We mostly use "Tyler wheels", a two-part 3D printed design that Tyler Bletsch came up with. Some groups order commercial wheels or do something else instead. If you give a desired diameter in #3d-printing on Discord, Tyler will print some for you. CAD.
4. Brushed Electronic Speed Controller (ESC). An electronic component that listens to the radio receiver and governs brushed DC motor speed and direction accordingly. We use a model that controls two motors from one unit: example.
5. Brushless DC (BLDC) motors. Used for spinning kinetic weapons. These have 3 wires instead of 2, and need a different kind of controller. They get to crazy fast speeds. We most commonly use A2212, but some groups use RS2205, which is more fragile but has an easy to use screw shaft.
6. Brushless Electronic Speed Controllers (ESC). Listens to the radio receiver and governs the brushless DC motor speed. Example.
7. Electrical connectors. We use various wire and electrical connectors, including:
   1. XT30: Yellow, two conductor, can only be plugged one way. We use these for all high power connections (battery, brushless ESC)
   2. JST: Red, two conductor, can only be plugged one way. Lower current than XT30, these are what come on the brushed ESCs, and what we solder onto the brushed motors.
8. Switch and LED. You gotta have a power switch that is externally accessible. The cheap and easy option are automotive rocker switches (example), but more ambitious groups can use screw switches to prevent accidental deactivation of your robot.
9. Radio transmitter/receiver. We use standard RC transmitters and receivers. Example.

The electrical layout of the above typically looks like this:

We'll cover how you achieve this below.

Battery management

LiPo batteries are dangerous and must be treated with respect!

The general rules:

• Don’t over-discharge: Run down to 3.2V per cell (6.4V for 2S). If unsure, switch batteries!
  • This means you should NOT just leave the same battery in your robot the whole semester!!
• Don’t stab or mangle the batteries
• Don’t short out the battery (connect + to – directly)
• If battery exposed in a robot test, end the test immediately
  • If a battery is exposed in competition, you lose immediately
• Banish suspect batteries: We have a sand bag for potentially bad batteries. Send a battery here if:
  • Puffy: It been abused and thus released gas and inflated.
  • Over-discharged: Voltage is below 3.0V per cell (6.0V for 2S)
  • Hot: If it’s so hot you can’t hold it (60 C)
  • Pierced (but stable): If it got poked in the past and isn’t doing anything else

If a battery is smoking, burning, or is recently pierced:

• GET IT OUT or GET IT DOWN:
  • If it is safe to do so without being near it (e.g. inside a container, held by the wire by long handle pliers, etc), put it into the metal hazard box OR take it to the loading dock out back
  • If it cannot be moved, use a tool to get it onto the floor and away from people and flammable objects
• Advise Bletsch and/or Foundry staff
  • If risk of spreading fire, excessive fumes indoors, or other major risk to people or property, call public safety (911)
• Use fire extinguisher if actual flames are present; be patient, flames may repeat
• Let it burn out

Charging:

• LiPos get their white JST-XH port plugged into a balance charger. All lights green = done.
  • If a light NEVER turns green, battery is cursed, must be banished (see above)
  • Charged? Move to “charged” bag.
  • Needs charge but all chargers busy? Leave in charger bag.

Wiring harness

Your first task will be to solder a bunch of wires together to run power to everywhere you need it; this is called a wiring harness. Here's the schematic:

Wiring harness schematic

Use the 18AWG red and black wire we have. To solder XT30s, you can follow this video. I recommend these steps:

1. Gender: Determine which XT30 gender you need. Note: connector genders are based on the shape of the METAL, not the plastic -- the XT30 male is the two protruding prongs inside the recessed plastic housing.
2. Polarity: Look at the embossed + and - on the connector. I recommend marking - with a black sharpie (or + with red) on the connector you intend to use
3. Plug a spare of the opposite gender into the one you intend to solder. This will prevent warping during soldering.
4. Cut/strip wire so only about 4mm is exposed (see video)
5. Remember heatshrink tube! Put about 1cm of tube loosely on each wire.
6. Don't forget the heatshrink tube! Once you solder, you can't put the tube on, and you'll have to desolder.
7. Actually don't forget the heatshrink tube! It's easy to forget, so I put it three times here.
8. Tin the back of the XT30 with generous solder on both + and -. Also tin the exposed wire. ("Tin" just means to melt solder into it)
9. Melt each wire into the solder on the connector
10. Shrink the heatshrink tube with a heat gun. You did remember heatshrink tube, right? By the way, don't use the soldering iron to shrink it, use an actual heat gun.

Soldering to the switch is quite similar. Again, don't forget heatshrink tube!

Scrap bot

With that done, you can slap all the components together onto a piece of scrap garbage and drive it around! Just plug stuff up as shown in this diagram:

Notes:

• The channel numbers on the receiver correspond to axes on the transmitter. Channel 1-4 are the left/right X/Y axes, but it's basically random which is which. Channel 5+ are the knobs/switches at the top of your transmitter. Use trial and error to see what's what, and I recommend labeling your transmitter's axes with gaffer tape once you figure it out.
• The three-conductor wires are either black/red/white or brown/red/yellow. Either way, this corresponds to ground/power/signal. Signal (white/yellow) goes toward the numbers on the receiver!
• The vertical axes of the radio that has no spring to it ("throttle") is a good candidate for your brushless motor weapon.
• The dual brushed ESC has two inputs: black/red/white and a single yellow. These two signals, by default, do "differential" drive, meaning that one signal wire is "forward/backward" and the other is "steering". Which one is which is arbitrary based on how you built things. You can force it to be "axis1 = motor1, axis2 = motor2" by flipping the little switch on the brushed ESC.
• The two axes on the other stick are good candidates for "forward/back" (Y) and "steer" (X) for the dual brushed ESC.
• This is all trial and error, so hook it all up, and see what controls what.
• If everything is basically right except for an axis being inverted, enable the reverse setting for that axis. Most of our transmitters have a simple toggle switch for this.
• The brushless ESC came from flying drones, so it has a safety mechanism to it. The throttle for the brushless must be set to zero for a few seconds before it will enable. When disabled, the motor will make a periodic regular beep. When enabling, the motor will play a little affirmative bip-bip-bip-beeeep tone, then you're clear to throttle up. Sometimes you need to "calibrate" the ESC by sweeping throttle all the way up and down its movement, then leaving it to zero for few seconds to enable.

Using the above tips and some trial and error, get your transmitter doing what you want to the motors, stick everything onto some junk and drive your junk bot! Once you're driving a junk bot, you're ready to design your real robot.

Common robot designs

I need to add more content here, but here's a placeholder to get started. Research these categories and figure out what you wanna do. For your first robot, kinetic weapons are strongly recommended.

Fabrication tips

Tyler Wheels

(TBA)

Weapon fabrication with SendCutSend

One of the easiest way to get really strong, resilient weapons is have them commercially laser cut out of AR500 armor plating steel. Info:

• We do this with a service called SendCutSend. The club will do two SendCutSend during the semester, so mind those deadlines.
• Figure out how your weapon will mate with your motor, gear, pulley, or whatever.
• Ideally, 3D print a prototype out of PLA or TPU and prove it works before ordering in AR500 steel.
• Look up the thickness on the SendCutSend site, and post the material, thickness, quantity, and the DXF file(s) to #sendcutsend on Discord.

Weapon hubs

(I need to expand on this) A hub affixed to the BLDC motor is the most common way of coupling a weapon to it. The common cheap and reliable solution is an A2212 motor with a TPU hub that hugs the entire body of it retained by a 1/8" shaft collor on the output shaft. The weapon is then mated to this hub via friction or fasteners.

Tip: if your weapon can slip with respect to the motor, that will help to protect the motor from shock loads during hits.

Meta-information: About this Duke MediaWiki

Access: This wiki uses the same underlying software as Wikipedia, mediawiki. To edit, you need to login (upper right of the page) and to have been granted edit access. To request edit access, ask Tyler Bletsch to add you. All club members are eligible to get wiki access; just ask. Note to Tyler: You can edit who has wiki access at your policy group at this link. Details here here.

Editing: The various edit buttons bring up different editors, but all do the same thing. Use your favorite.

Making pages: Link to a page with a new name, then go to that empty page and edit it to add stuff there.