ISSUE 92

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“This [issue’s] parts are used to set up R2-D2’s power supply. He is powered by SIX rechargeable batteries (which must be bought separately) that you prepare using the tester/charger and USB lead provided. In order to ensure the maximum performance, the batteries must have the correct specification, and be installed as a matched set in the battery box – which you will do when the build is completed at [Issue] 100. The information is provided here in order to give you ample time to purchase your batteries.

This is a critical issue that must be followed entirely because it relates to the extremely high-energy batteries used by our R2-D2 unit. If these batteries are handled incorrectly or even slightly damaged, they can result in an explosion or a fire that is extremely hard to extinguish. I would hate to see anyone get hurt, so take special care when handling them!

Contents


Parts

Materials: All of the non-electrical parts in this issue are plastic.

Magazine

  • Building The Galaxy – No Time to Rest
  • Droid Directory – R2-D2 Astromech Part 13
  • Understanding Robotics – Maker Culture
  • Build R2-D2: Model Instructions

Build


Buying R2-D2’s Batteries

There is a entire page in the instructions dedicated to buying the correct batteries for R2-D2. That page is included below, but here is a summary:

  • R2-D2 is designed to use six rechargeable model 18650 Lithium-Ion (Li-Ion) batteries.
  • This type of battery is readily available online, however there are unique specifications required for R2-D2:
    • The batteries MUST match (same manufacturer, model, and batch). If all bought at the same time, the batch is typically the same.
    • The batteries MUST have a nominal voltage of 3.7 V (volts).
    • The batteries MUST have a capacity of at least 2000 mAh (milliamp hours), but 2600-2800 mAh is recommended. Higher capacities will allow R2-D2 to run longer, but also take longer to recharge.
    • The batteries MUST have a ‘button-top’. They will not make contact with the battery box if they are ‘flat-top’.
    • The batteries MUST be ‘unprotected‘. Many ‘button-top’ batteries come with protection circuits hidden under the button, but R2-D2 has his own protections circuits built in.
    • Batteries described as ‘High-Drain/High-Discharge’ are acceptable as long as they have the nominal voltage of 3.7 V.

It is a characteristic of Li-Ion batteries that the worst performing battery in a pack will affect the performance of the entire pack. This is why having them all the same is important. A battery not in sync with the others can even damage other cells and/or the protection circuitry.

To prevent this, a single-cell Battery Tester/Charger is included with this issue. Using it to prepare each battery individually before placing them in R2-D2’s large Battery Box will ensure they are all in optimal condition. Once all batteries are matched and installed into R2-D2, no further special handling is required. They can all be charged by R2-D2’s internal charging system as a whole. However, keep this testing unit in case you need to ever replace the batteries, as you will need to prepare those new batteries the same way.

Preparing the Batteries

Steps 1-2

Identify the positive (+) end of your 18650 batteries with the ‘button-top’ (marked with arrows below).

I am using a set of six matched Panasonic NCR18650B 3400MAh 3.7V Unprotected Button-Tops from the 18650 Battery Store in the USA. These same batteries can be found in the UK at 18650.uk.

Step 3

Make sure the Battery Tester/Charger is not plugged in so it will operate as a voltage reader. Fit the battery into the tester matching the diagram inside battery slot:

Step 4

The digital readout on the other side will indicate the battery’s voltage. If it indicates less than 3.3V or ‘LO’, the battery is highly likely to be faulty and should not be used:

Step 5

Plug the USB Charging Lead between the port on the Battery Tester/Charger and a suitable USB power socket:

Step 6

When the USB lead is powered, the last digit of the display will flash indicating that charging has started. Charging can take many hours depending on the battery capacity.

Each of my batteries took 2-3 hours to charge fully.

Step 7

Leave the Battery Tester/Charger powered until the display reads ‘FUL’ indicating the battery is fully charged.

The charging voltage should slowly climb to 4.2V, then it will display ‘FUL’:

You can then unplug the charger and remove the battery. Repeat this testing and charging process for all six batteries.

NOTE: If the reading does not increase after 30 minutes or so on any battery, that battery is likely bad and should be discarded.

IMPORTANT: Do not fit the batteries into the Battery Box, install them in R2-D2, or charge them using R2-D2’s internal charger until after all the internal electronic are connected and ready! This will be done at the end of Issue 100.

Thoughts


Again, I cannot say enough how important it is that all R2-D2 builders out there heed these instructions!

My friend ran a vaping shop and these are the same kind of batteries used in custom e-cigarettes. He is well aware that they have a very high energy potential and, if not used correctly, can release that energy in a extremely violent way. Luckily, he has never be injured by them, but he knows people who have. They are fantastic power sources for devices like our R2-D2, but should be treated with due respect.

The Battery Box and Battery Box Cover were not used here, so keep them stored until needed in Issue 97.

Next Up


 Issue 93 – Circuit Board Base/Cover/Bracket, Battery Box Bracket

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