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Gobble Squabble: Selecting Batteries

Gobble Squabble: Selecting Batteries

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Key factors to consider when selecting the battery and vendor for your Antweight combat robot:

  • We recommend using LIPO batteries in Antweight combat robots, due to their ability to deliver maximum power at low battery weight.
  • We recommend 3S LIPO batteries with a capacity of around 480 mAH if you use a spinning weapon; you can use a smaller (lower mAH rating) battery otherwise, if desired.
  • 3S LIPO batteries actually output 12.6 V and therefore enable you to use 12 volt motors and parts. Note that a BEC circuit must be provided in the robot to power the receiver and any servos when a 3S battery is used. You can assume 1 – 2 volts of drop before the control power gets to your robot motors.
  • 2S LIPO batteries actually output 8.4 V and are a good match to 6 volt motors. 2S LIPO batteries can power servos directly in many cases.
  • 1S LIPO batteries: some advanced roboticists make their own power stack using multiple 1S batteries. For example, 2 1S batteries in series to power the control system and servos (if any), and add a 3rd 1S in series for the high-power drive motors. (But, as noted below, NEVER cut or modify the actual battery leads — do all your stacking and inter-connection on the custom-circuit side of the battery connections.)
  • Only purchase LIPO batteries with a JST main power connector — it can deliver all the power needed for this size of robot, and is much smaller and lighter than other connector types.
  • You will also need a battery charger rated for LIPO batteries. You should purchase 2 batteries, just in case, and have a way to replace the battery in your robot in less than 5 minutes.
  • WARNING: NEVER cut or modify any of the leads to a LIPO battery; they should always be used in factory-original condition. DO NOT plug the LIPO battery into your robot wiring until all of the wiring is 100% complete with no bare metal exposed anywhere.
  • CAUTION: until you do more research and get more experience, don’t recharge your LIPO batteries using more than 1.0 A current. A common cause of LIPO battery failure is recharging batteries too fast or too hot. The inexpensive chargers listed below don’t allow you to change the charge current, but use a value below 1.0 A.
  • Leave the charging connector (it has 3 or more conductors) attached to your battery.
  • If you don’t want to manage these risks or want a lower cost solution, you can use 9V alkaline batteries with 6 volt motors, but your robot won’t have the speed or endurance of a LIPO-powered one.
  • Shipping considerations: all shipping companies put special handling restrictions on packages containing LIPO batteries. This has the most impact when you’re buying from vendors located outside the US, causing longer shipping delays (which is why no eBay sources are listed here, but it also impacts Fingertech). But if you purchase US-based batteries from Amazon or Hobby King (be sure to specify a US warehouse when shopping at Hobby King), shipment times can be quite low — especially for Amazon.
  • Summary of LIPO battery ratings:
    • S: the number of charge cells in the battery. The working battery output voltage = S x 4.2 volts.
    • C: the designed maximum peak output current of the battery, in amperes. Antweight robots rarely need more than 10 amps, peak — and that’s only if a brushless-motor-driven weapon is used. C ratings of 25 to 35 are fine for these robots.
    • mAH (milli-amp hours): the total current the battery can deliver over time. A combat match is 3 minutes long, or 1/20th or 0.05 of an hour. If a robot needs 10 A of current over the full 3 minutes (this is very unlikely), the battery capacity must be at least 10 x 0.05 = 0.5 AH = 500 mAH to supply that current.
    • Connector size: a JST connector is big enough for 10 A current loads, and even more. Due to its small size and weight, we recommend using batteries with JST connectors over other options.
Overview of LIPO battery options for combat robots

Available Sources for LIPO Batteries

Available Sources for LIPO Battery Chargers

If you use LIPO batteries (recommended for maximum robot power), you’ll also need a charger.

This information is original work by Techno Chaos and is published under the terms of Creative Common license mode Attribution-NonCommercial-ShareAlike (CC BY-NC-SA).