Vorpal The Hexapod Battery Recommendations

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There are several battery types that will successfully power your VH12 Hexapod. The batteries you choose will affect how long the robot will run, recharge time, etc.

This article explains your options.

Battery Safety Tips

Rechargeable batteries are by far the most cost effective and environmentally friendly kind of batteries, but some simple safety rules are recommended:

• Never, ever put non-recharegable batteries in a battery charger!
• Do not mix different types of battery, do not mix old and new batteries.
• If you are using rechargeable batteries, make sure you are using the right kind of charger for the batteries you are using. Follow all manufacturer recommendations.
• Never leave batteries charging unattended. Never charge batteries "overnight". It is safest to charge batteries in a place that will not be damaged by heat, just in case the rare instance of a damaged battery overheating during charging occurs.
• Investing in a "smart" charger is well worth the extra cost, as they will generally keep your batteries in much better shape than "dumb" chargers. You can buy a dumb charger for under $10, but if it damages your batteries so they can't hold a full charge, did you really save any money? A good smart charger may be a few dollars more, but will keep your batteries running for many hundreds of charges. Don't be penny wise and pound foolish!
• If you are charging batteries, it is normal for them to get warm, but if they feel hot, if smoke is coming off them, if you smell a "burning plastic" type odor, if you see sparks, or if they appear to be swelling or discoloring, disconnect the charger immediately from the wall socket and wait for things to cool down before touching. Exercise caution, remove smoking batteries to the outdoors or a ventilated area.
• If there is any visible damage to a battery or if it appears to be swelling, stop using it immediately and do not attempt to recharge it.
• Some kinds of rechargeable battery cannot be disposed in the trash but must be recycled, follow all instructions and markings on the battery and follow your local community recycling practices.

Gamepad: Any kind of 9v Transistor Battery

The gamepad has minimal power requirements and can be powered by either non-rechargeable or rechargeable 9v transistor batteries. (These are the common rectangular batteries often used in smoke detectors, small radios, clocks, etc.) Alkaline, NIMH, NICAD, or LION batteries in the 9v rectangular format will all work fine for the gamepad. The gamepad was designed to fit a standard 9v battery in its battery compartment. You can expect several hours of usage. Do be sure to turn the gamepad off when not in use.

Technical info: The gamepad typically draws about 50 to 100 mA, which is mostly consumed by the Bluetooth module. Thus a 500 mAh alkaline 9v battery will last about 5 to 10 hours, while a 250 mAh NIMH rechargeable battery will last about 2.5 to 5 hours.

Hexapod: Only Use Rechargeable Batteries

Non-rechargeable batteries, such as alkaline batteries, cannot produce enough current (amperes) to drive the robot reliably.

The major types of rechargeable battery used today are Nickle Metal Hydride (NIMH), Nickle Cadmium (NICAD), and Lithium Ion (LI-ON).

The hexapod kit comes with a six-cell AAA battery holder that uses a female JST connector (red connector). However, you can find 6xAA battery holders and easily add a JST connector if longer battery life is desired.

Below we discuss the different options for the robot.

NOTE: Our kit comes with the 18650 batteries discussed first below. The other options are for Makers who are building using their own parts or who wish to experiment with different battery options.

Two 18650 Size LI-ON Batteries

These batteries can be found on Amazon.com and camping stores. While a little less common than AA or AAA, these are actually ideal batteries for this robot, giving you long run times at a reasonable weight. You can also find them for about the same cost as the more common batteries (two 18650 cost about the same as six AAA but provide several times as much run time! The chargers are also about the same price as AA or AAA chargers.)

The "18650" battery is commonly used in flashlights and many of these are made to output high currents which easily are high enough to power the hexapod. Two in series will provide 7.4 volts nominal (which is enough for the hexapod's needs). These batteries can provide very long battery life for the robot. For example using two 3000 mAh 18650 cells you can expect about one full hour of continuous motion. (However note: it is best to let the servos "rest" after several minutes of vigorous activity, you shouldn't run the robot full out for an hour!)

Generally speaking, you should choose an 1865 with at least 2500 mAh capacity to ensure you are not overtaxing the batteries. Often manufacturers will publish the number of "Amps" the battery can safely output. The robot only needs at most about 3 Amps during short surges but it typically draws about 2.5 Amps.

Note that these batteries require special chargers. You can find 2 x 18650 battery holders, but you will need to solder on a female JST connector.

The battery compartment inside the robot is large enough to accommodate a typical 2x18650 battery holder.

We have done tests on EBL brand 3000 mAh 18650 batteries and found 60 to 70 minutes of run time in "demo" mode (which is almost constant motion). As of this writing they are about $3 each and a smart charger from EBL is about $12. We use these for all our demonstrations!

6xAAA Rechargeable NIMH or NICAD Batteries

You can use a 6xAAA battery holder to power the robot using NIMH or NICAD batteries. Typical battery life for continuous use after a full charge would be 15 to 20 minutes of continuous motion using batteries with 1000 mAh capacity. Of course, if the hexapod is moving sometimes and motionless other times, your actual time may be far longer.

6xAA Rechargeable NIMH or NICAD Batteries

You can use a 6xAA battery holder with a female JST connector to power the robot using NIMH or NICAD batteries. If the batteries are rated 2000 mAh (typical for this size) you can expect 30 minutes of continuous motion. However, because AA batteries are about twice as heavy as AAA batteries, they do put a little more stress on the servo motors.

Other Options for Advanced Users

If you know about batteries and wish to design your own system for the robot, here are some factors to bear in mind:

• The robot requires 2 amps during typical use but may spike up to 2.5 to 3 amps for short periods.
• The voltage regulator requires 6.5 volts input to keep the servos powered at 5.0 volts nominal, so do not design a battery system with less than about 6.5 volts output at 2 amps. Running the servos with too low voltage may shorter their life.
• The maximum recommended battery voltage is 12.0 volts, beyond that the 5v regulator used for the servos might be damaged and the Arduino Nano onboard regulator (which is fed directly off the battery, not the 5v regulator used for the servos) might overheat.

Example 1: the robot will run quite well on two AA LIFEPO4 batteries (which have 3.2v nominal cell voltage and when charged will meet the 6.5 volt minimum, and can output easily 3 amps). You would probably need to get a 2xAA battery holder and solder on a female JST connector.

Changing the Battery Connector

This is a build-it-yourself robot kit, so if you wish to use other styles of battery connectors such as Tamiya, PowerPole, or XT60, go right ahead and make the change. A few minutes with a soldering iron is all it takes.