CRNZ Antweight Core Kit Build Instructions

Please Note: These instructions are a work in progress.


Your kit should come with the following components:

  1. A Printed Chassis in your chosen color. 
    1. This will be on a “raft” (it connects the whole sheet of components together)
    2. It should include 4 parts: The main chassis, A chassis lid, A wedge module, and a Wedge plate
      Grey Chassis on Raft Example
  2. A Battery
    Battery Example
  3. 2x N20 DC Gearmotors
    N20 Motors Example
  4. A package containing 2x wheels
    Pololu Wheels Example
  5. A package containing a Power LED kit
    Power LED Example
  6. A package containing a Twist Switch kit
    (Note: This may be V1.0 or V1.1, which are quite different)
    Twist Switch 1.0 Example
  7. A package containing a Brain (the internal bot controller)
    Brain Example
  8. A package containing a Radio Receiver
    Receiver Example
  9. A package containing a pair of N20 Faceplate Mounts
    N20 Mount Example
  10. A small baggie containing a few M3 Machine Screws
    1. There should be 2x 10mm, 2x 25mm, and 4x nuts
      Fasteners Example
  11. 2 Packages of JST Power Connectors
    JST Example

Required Tools

You will require a few tools and supplies to finish the build of the kit:

  1. A small phillips screwdriver
  2. A set of small metric allen keys/hex wrenches
  3. A soldering iron
  4. Some fine solder
  5. A solder flux pen or flux paste (not absolutely required but helpful)
  6. A small pair of wire snips/cutters and/or wire strippers
  7. A small pair of tweezers, or fine tip needle nose pliers
  8. A small needle file, or nail file (not absolutely needed, but useful for cleaning/adjusting fit on parts)
  9. A Heat Gun (hot air gun), Hair Dryer, or a heat source such as a lighter, etc, for shrinking heat-shrink tubing. OR if these are not available, some electrical/sparky tape for protecting components once assembled.
  10. Safety glasses

Additional Required Parts to use the Kit

You will also need a few additional bits to be able to the kit, these items are not included with the kit:

  1. An RC Transmitter, which can communicate to an FrSky ACCST Receiver in D16 Mode.
    1. CRNZ Sells the Jumper T-Pro Transmitter, which is Multi-Protocol, and will work out of the box with these kits
  2. A Lithium Polymer Battery Charger
    1. The charger needs to have a JST Connector, and must support charging a 2Cell LiHV or LiPo battery cell. CRNZ Currently sells affordable chargers which meet this requirement
  3. A Lithium Polymer Battery Charging Box or Bag
    1. This should be a fireproof container specifically designed for charging lithium batteries, and is an important safety consideration.
    2. In a pinch, a simple steel tool box, or other non-flamable container will be sufficient for the small batteries in these kits.
    3. Never leave lithium batteries unattended while charging

Build Steps

This procedure does not need to be followed in precise order, the steps are meant as a guide, to help you complete the build, but part of the fun of building a Combat Robot is figuring out how it goes together, and trying new things, so there is plenty of room for you to do your own thing, or try assembling in different order, etc.

It is recommended you read ALL these steps completely first, before starting. 

Preparation Steps

These steps are useful to prepare parts for assembly before going into the assembly in earnest

Prep the Chassis

Preparing the chassis will allow you to verify the chassis print is cleaned up, and ready to accept the other parts. Also to dry fit the components together to get a feel for how they fit together.

Because of the nature of 3D printed parts, it’s possible that some tolerances may be slightly out, resulting in some fits that are too tight, or too loose, or holes that are partially filled, etc.

  1. You should wear safety glasses/goggles for this step, as small plastic bits may break off into the air, causing an eye injury risk.
  2. First, remove the parts from the raft.
    1. If you look closely, you will see the raft is made up of 2 layers. The very bottom layer is more coarse, almost a mesh, and the next layer is smaller (closer to the perimeter of the parts) and a bit more dense.
    2. The raft should literally “peel” away from the parts like a sticker. Do this carefully, careful to peel slowly, and not damage the parts (the raft is sacrificial, damaging it is ok)
    3. If any parts of the raft stick too strongly to the part, you can use some flat tool (a thin file, screwdriver, tweezer tip, etc) to wedge in between the part and the raft, gently pushing and twisting to work the raft apart slowly. 
    4. It can be helpful to start with the larger main chassis first, as it’s the most sturdy/stable of the parts, and the raft should come off it most easily. This can let you get a feel for how the raft separates first, before working on the more delicate parts such as the wedge, or lid.

Chassis Parts

  1. Once the parts are removed from the raft, each should be inspected for excess plastic in the holes, or openings.
    1. Look for extra strings or stray filaments which noticeably stick out, and carefully remove them
    2. Try dry-fitting the parts together, to see if things fit. If they don’t you can clean up a bit with a file, snips, or tweezers to clean up as needed until things fit well
    3. Parts should be snug without requiring too much force to assemble. They shouldn’t fall apart on their own, but also shouldn’t require excessive force to disassemble.
  2. Do a final dry-fit assembly of the entire chassis, including using the M3 Screws, and confirm you are happy with the fit
    Dry Fit Image
    1. The 2x 10mm screws are used to secure the wedge plate to the wedge module.
    2. The 2x 25mm screws are used to secure the lid to the chassis
    3. 2 nuts go into the recesses on the bottom of the chassis, these can be secured with a drop of superglue if needed, or left loose, this is up to preference
      Bottom Nuts Installation Photo
    4. 2 more nuts are recessed into the angled channels in the bottom of the wedge module to retain the plate.
    5. It can sometimes be helpful to use one of the 25mm screws as a "handle" of sorts, thread it a few turns into the nut, and use that to place the nut correctly, then unthread the screw when done. Or you can use tweezers to fit the nuts into the angled recesses first, then use the screws to tighten them into place once they are aligned properly.
      Nuts Installation in Wedge

This is what the final assembly should look like at this stage:
Dry Fit Assembly Image

Prep the drive modules

The motors get mounted to the Faceplate Mounts by soldering. It is helpful to complete this step on it’s own as it can be time consuming to get the soldering technique right.

  1. Open the package of faceplate mounts, and remove the mounts, and their fasteners.
    Motor Parts
  2. The faceplate mount attaches to the front of the motor, there is a tiny collar/lip around the shaft of the motor which should fit perfectly into the centre hole on the faceplate mount.
    Motor Mount Fitting
  3. Temporarily screw the plate onto the motor
    1. With the shaft in this hole, there should be 2 more holes which line up with screw holes on the motor. One of these holes will have gears close behind it, the other will have a larger gap. 
    2. You may have a version of the faceplate mounts with longer or shorter screws. If you have the one with several short screws, then skip this step. Otherwise, Attach 2 nuts and thread them all the way onto one of the M2 screws. These will act as a spacer
    3. Use 2 of the M2 screws to attach the plate to the motors using the one with the nuts/spacer on the side with the closer gears (if you have the one with the longer screws, as this will allow you to tighten the screws down without damaging the gears with the screws).
    4. The screws don’t need to be tight, just snug.
      Motor Mount Screws
  4. Place the mounting plate in some kind of tool to secure it in place allowing you to work, oriented so it is parallel to the ground, with the shaft of the motor pointing down and the body of the motor pointing up
  5. Locate the copper pads which align with the edges of the front brass plate of the motor gearbox. 
  6. If you have any flux available, it can help with this step, apply a bit to the motor plate around the edge (do not get any in the gears), and on the copper plate on the PCB.
  7. Set your soldering iron on high (or if it has a temperature setting, a high temp like 400C is helpful) and let it pre-heat
  8. Ensure the tip of the soldering iron is clean and tinned
  9. Heat the pcb and motor along the edge, it helps to get the soldering iron in the “valley” formed by the lip of the motor along the pcb, so it is contacting both parts with as much surface area as possible.
    1. Note: the motor can absorb a lot of heat, it will make heating this joint adequately difficult, and may take a bit of time
    2. It can help to have a bit of melted solder on the tip to increase the surface area in contact with the parts.
  10. Keep trying to apply the solder to the PCB and motor at the joint, once it is at an adequate temperature, the solder should melt, allowing you to effectively solder the joint.
  11. Repeat this for each corner of the motor, so that it is sufficiently soldered down.
  12. Be careful not to apply too much solder, you don’t want a lot of blobbing. Just enough to firmly hold the motor in place, see the photo for an example.
  13. Be careful at this point as the motor and plate will be very hot to the touch and may burn you. Do not touch it with your hands until it’s fully cooled.
    Soldering Mount onto Motor
  14. Repeat the entire process for the second motor.
  15. Let both motors cool fully
  16. Install the Wheels on the motor shafts
    1. Open the package of wheels
    2. Carefully snap the tyre onto the rim
    3. Press the wheel (with the protruding side of the wheel hub sticking towards the motor) onto the D shaft of the motor. Ensuring you leave a couple mm of clearance between the faceplate and the wheel
  17. You have now assembled your two drive modules

Prepare the wire lengths

It is helpful to prepare the lengths of wire you’ll need so you can easily assemble the circuits later in the process

For this process, the lengths will be different, depending on which type of Twist Switch you have (V1.0 or V1.1). It is important to check the package first, and confirm which one you have (It is marked on the package 1.0 or 1.1).

Note: When referring to JST connectors, the Male Connector is the one which has an outer housing and 2 pins inside, while the Female Connector is the one which plugs into the male (it has 2 holes which the pins go into, but the plug itself fits inside the male).

For Twist Switch V1.0:

  1. Prepare 2x Male JST Connectors, cutting the wires to approximately 15mm length, and stripping approximately 3mm of bare wire
  2. Prepare 1x Female JST Connector, cutting the wires approximately 25mm length, and stripping approximately 8mm of bare wire.
  3. From the cut-off wire, prepare the motor wires, by cutting 2x pairs of red/black wires to approximately 30mm length, and stripping 3mm of bare wire from both ends.
  4. Prepare the LED wires, cut a pair of red/black wires to 25mm length, and strip 3mm from one end, and 8mm from the other end.
    Wires Cut and Stripped
  5. Take out the three thin receiver wires (red, black, and white) and set them aside.
  6. Twist together one end of the LED wires, to the female JST connector wires. (Red wire to Red, and Black to Black of course). This creates a “Y” splitter for the power circuit.
    Y Splitter
  7. Tin all expose wire ends, with solder.
    Finished Wires

For Twist Switch V1.1:

(sorry photos for this section coming soon)

  1. Prepare one of the Male JST Connectors for the Battery, cutting the Black wire to approximately 15-20mm length, and the Red wire to approximately 65mm long. Strip the Black wire back to expose approx 3mm of bare wire, and the Red wire approx 8mm.
  2. Prepare the other Male JST Connector for the Brain, cutting both the Red and Black wire to 15-20mm length. Stripping both wires back approximately 3mm.
  3. Prepare 1x Female JST Connector for the Switch Output, cutting the Black wire approximately 25mm long, and the Red wire, approximately 45mm long, and stripping approximately 8mm of bare wire on both.
  4. From the cut-off wire, prepare the motor wires, by cutting 2x pairs of red/black wires to approximately 30mm length, and stripping 3mm of bare wire from both ends.
  5. Prepare the LED negative (black) wire, cut a single length of black wire to 25mm length, and strip 3mm from one end, and 8mm from the other end.
  6. Take out the three thin receiver wires (red, black, and white) and set them aside.
  7. Twist together the red wire from the Male JST for the Battery to the red wire from the female JST connector for the switch output (these ends should both be stripped to 8mm to allow twisting them together)
  8. Twist together the black LED negative wire you prepared in step 5 (the 8mm stripped end) with the black wire from the female JST for the switch output from step 3 (again these should both have 8mm stripped to be easy to twist together)
  9. Tin all expose wire ends, with solder. (note: this will effectively join the two twisted together wire pairs)

Main Assembly Steps

Assemble the Power Circuit

For this process, the steps will be somewhat different depending on which type of Twist Switch you have (V1.0 or V1.1). It is important to check the package first, and confirm which one you have (It is marked on the package 1.0 or 1.1).

For Twist Switch V1.0:

  1. First solder the single end of the “Y” cable (both red/+ and black/- wires) to the output side of the twist switch (The side with VCC labeled for the positive/red wire). The opposite side of the board is for the negative(black) wire.
    Switch Soldering Image 1Switch Soldering 2Switch Soldering 3
  2. Then solder one of the female JST connectors to the input side of the twist switch (Red to Bat+ and Black to the opposite side, same side of the PCB as the black wire on the other end)
  3. Carefully check you haven't shorted the red/black wires together. Ensuring some of the wire plastic sheath is over top of the PCB pad can help with this.
  4. Solder the spare black wire from the Y cable to the GND pad on the LED
  5. Solder the spare red wire from the Y cable to the “12” pad on the LED (Note: This image shows the red wire incorrectly installed on the "3.3" pad, doing this will make your LED VERY bright for a short while, and burn out VERY quickly).
    LED Wiring

For Twist Switch V1.1:

  1. First solder the black wire from the male JST connector you prepared for the battery (the shorter wire) in step 1 of the "preparing wire lengths" section to one end of the twist switch, on the face with the silver "nut" on it (opposite the screw head)
  2. Next, solder the twisted together black wire end from the Female JST and LED wire that you prepared in step 8 of "preparing wire lengths" section to the other end of the twist switch on the same side as the previous step.
  3. Now solder the free end of the LED negative (black) wire, to the GND pad on the LED
  4. Now solder the twisted together pair of red wires you prepared in step 7 of "preparing wire lengths" to the "12" pad of the LED
  5. Carefully check you haven't shorted the red/black wires together. Ensuring some of the wire plastic sheath is over top of the PCB pad can help with this.

Assemble the Control Circuit

  1. First solder the power input to the board:
    1. Solder the Red Wire of the remaining female JST connector to the Batt+ pad on the Brain
    2. Solder the Black wire of the remaining female JST connector to the GND pad on the Brain
      Brain Power Input
  2. Now add the Motor Wires
    1. Solder the two red motor wires you prepared earlier to the two M+ pads on the Brain (so that one wire is on M1+ and M2+ respectively)
    2. Solder the two black motor wires to the two M- pads in similar fashion
      Brain Motor Wires
  1. Finally add the Receiver to the Brain
    1. Solder one end of the 3 receiver wires to the 3 round pads marked “1, +, -” opposite the M2+/- pads on the brain.
      1. The black wire goes to -
      2. The red wire goes to +
      3. The white wire goes to 1
        Brain Receiver Wires
    2. Solder the other end of the receiver wires to the receiver, connecting them to the 3 oval shaped pads on the end of the receiver opposite the antenna, marked S, 5, G
      1. Black goes to G
      2. Red goes to 5
      3. White goes to S
        RX Wiring

Connect the Drive Modules

  1. Connect the two assembled Drive modules to the control circuit by soldering the free end of the Motor Wires onto the terminals on the motor.
    1. Red wire goes to the marked + terminal
    2. Black wire goes to the other terminal
      Drive Module Wiring

This is what the finished control assembly looks like with all it's bits attached:

Finished Control Assembly

Assemble the Components

  1. Using small tweezers, remove the antenna wire from the small coaxial connector on the receiver (unplug the small brass connector by pulling it straight off, being careful not to damage the wire or the PCB).
    Removing Antenna
  2. Place the Antenna into the bottom of the battery compartment, which is T shaped to accommodate the antenna, feeding the antenna wire through the small hole in the bottom of the chassis.
    Antenna Installation
  3. Slide the piece of heatshrink tubing which was included with the receiver over the antenna wire, so that it can easily be applied to the reveiver later.
    Antenna Heat Shrink
  4. Reconnect the antenna to the Receiver by again using the tweezers to carefully plug the connector back onto the PCB, it should snap firmly into position.
  5. Install the Power Circuit
    1. Feed the Female JST connector through the small hole that the antenna cable goes through
      Installing Power Circuit 1
    2. Install the power switch by screwing it into place with the central activation screw protruding through the hole in the bottom of the chassis, and so that the end with the female JST connector is on one far end of the battery compartment (farthest from the center).
      Note: use the plastic part with the 3 brass nuts in it to fasten it into place. The brass side of the nuts MUST be UP, with plastic against the PCB, this will prevent an accidental short should the brass wear through the PCB masking material)
      Power Circuit Installation 2
    3. Install the LED, by screwing it into place with the LED showing through the open central hole in the rear of the chassis, carefully tucking the wires for the power Circuit out of the way, leaving room for the battery in the battery compartment.
      LED Module Screws
  6. Test the power circuit
    1. If possible, test for shorts:
      1. using an ohm meter you should check that there is not a short between the +/- pins on the JST connector for the battery. 
      2. If an ohm meter is not available, simply inspect your solder joints to ensure no inadvertant connection is made between a +/i wire/pad.
    2. Ensure the twist switch central screw is partially unscrewed (the “OFF” position)
    3. Install the battery, by plugging it into the power circuit input, carefully observe for smoke or puffing of the battery for a few moments.
    4. If the battery appears ok, then proceed to turn on the power, by twisting the twist switch screw in all the way, this should engage the “ON” position.
    5. The LED should now illuminate to indicate power is on.
    6. Turn the power back off, and remove the battery
  7. Connect the control circuit
    1. Plug the JST connector on the control circuit into the output of the power circuit
  8. Install the Drive Modules
    1. Slide the Motor Mount PCBs into the slots on each side of the chassis. You should be able to push the motor all the way down until the motor shaft is nearly at the bottom of the slot (and the holes in the chassis should line up with holes in the mount)
  9. Be careful that there are no components touching metal, as they are not yet protected by heat-shrink
  10. Install the wedge module by sliding the dovetails into the slots in the front of the chassis.
  11. Final step will be to apply the provided heat-shrink tubing, or protective tape to the receiver and brain, however first you must pair the transmitter, and configure/calibrate the Brain. Then you can protect, and tuck the electronics into the compartment and close the chassis.

Protect your circuits

At this point you should apply the heat shrink to the Brain and Receiver circuits to protect them from shorts during normal operation.

Brain Heat ShrinkReceiver Heat Shrink

Pair the Transmitter

  1. Ensure there are no shorts, no metal pads/components are touching, etc…
  2. Install the battery into the bot
  3. Power on the Transmitter
  4. Place the receiver into Bind Mode
    1. There is a small “F/S” button immediately next to the antenna connector on the receiver. 
    2. Press it using a small pair of tweezers, or a small tool, being careful not to short anything on the receiver. 
    3. While holding the button, turn on the bot by twisting the screw on the twist switch. 
    4. Continue holding the button for 5-6 seconds. 
    5. The receiver should power on with both the Red and Green LEDs lit to indicate it is in Binding Mode
  5. Attempt to bind from the Transmitter
    1. If using a Jumper T-Pro from CRNZ, press the menu button on the left of the receiver briefly to enter the model menu
    2. Press the Tab button to switch to the “SETUP” Screen
    3. Use the scroll wheel to scroll down to the “Internal RF” section
    4. Ensure “Mode” is set to “MULTI”
    5. Ensure “Type” is set to “FrSkyX2”
    6. Ensure “SubType” is set to D16
    7. Ensue “Ch Range” is set to “CH1-16”
    8. Scroll down to the “Receiver” item in the menu:
      1. Scroll over to “Bnd” and press the scroll wheel to select Binding Mode
      2. Choose the “Ch1-8 Telem ON” option
    9. Bnd will blink, and the transmitter will beep to indicate binding mode.
    10. If binding is successful, the Red LED on the receiver should begin flashing.
    11. Once binding is successful, you can power off the bot, and hit the back button on the transmitter to return to the home screen.

Final Assembly & Close up the bot

Now you can safely tuck all the electronics into the electronics compartment
Assembly Nearly FinishedAll tucked in
And install the chassis lid. The lid has 2 tabs which fit into two slots on the rear of the bot, it then levers closed with the two square protrusions pressing down on the tops of the motors, holding them in place. It can be secured by installing the 2x recessed M3 nuts on the bottom of the chassis, and screwing the chassis shut with the M3x25 screws.

You can also now assemble the wheels, and install the wheels onto the motor shafts (simply press them on, with the protruding hub side facing inward towards the body of the bot. Ensuring there is a small 1mm or so gap between the bot body and the wheel hub)

Finished Bot

Configure/Calibrate the Brain

To calibrate the brain, ensure the transmitter is turned on, and armed (left switch flipped up). And then power on the bot. 

It may be helpful to perform this procedure with the lid off the bot so you can see the LED indicators on the Brain board.

Within 10 seconds of powering on, wiggle the right stick back and forth (making sure the stick goes all the way left and right each time) 10 times. If done correctly the LED on the Brain will pulse 10 times and then stay on, to indicate it’s in calibration mode.

Note: Calibration will pulse the motors to auto configure the input. This may cause the bot to fall if placed on a table etc. It should be on a reasonably large flat surface where it can’t easily fall in order to calibrate.

For completion of the calibration routine, please refer to the instructions for the Brain from CB-Tech at the following link:

These instructions may evolve over time, so that will always refer to the latest version of the instructions.

Balance the Bot

It is important that once you’ve fully assembled and calibrated the bot, and added any additions/modules/customizations, that the bot is balanced.

Since it runs on 2 wheels, you want the center of gravity to be slightly forward of the wheels. This will keep the front from lifting up (wheelie) when driving forward as you’ll want your front wedge to stay on the ground to prevent opponent bots from getting under you.

You also don’t want ALL your weight forward, as this will reduce your traction. Finding the “sweet spot” for balance will take a bit of trial and error.

The kit is designed so that there is a small compartment behind the wedge which is enclosed with the wedge installed. This area can take weights (coins, nuts, or other metal bits to add weight). So that you can balance the bot. It is suggested you secure it in place with tape, or some kind of glue (hot glue works). Then cover with the wedge once done, securing the wedge in place with the 2 10mm screws and matching nuts in the recesses behind.

Ideally your final weight is as close to 150g as possible, while still being under the limit (this will optimise your traction and pushing power).