Page 117 - Build Your Own Combat Robot

Build Your Own Combat Robot
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Following are some advantages of NiMH:
The NiMH energy density is the best of all the usable battery types
currently available.
With proper care and storage, NiMHs will last through more than
300 charge cycles.

Because NiMH packs are small, it is easy to keep them in the refrigerator
for long-term storage.
The voltage output remains constant until almost fully discharged.
This provides full power to your robot for the duration of the match.
They can be stored without a charge without damaging effects.
They have no memory effects when used for this application.
They have no cadmium, so they don’t have the related health problems.

The emerging NiMH battery technology will see improvements. In time, expect
a lower cost, a higher number of charge cycles, lower internal resistance resulting
in a higher maximum current rating, and lower self-discharge rates.
Following are some disadvantages of NiMH:

It is the most expensive rechargeable battery technology.
It has the lowest life of the rechargeable battery technologies. After
300 charge/discharge cycles, the battery capacity measurably degrades
while the internal resistance increases.
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When stored at 25 C, the NiMH battery can lose up to 5 percent of its
charge per day. When fully charged, the NiMH can self-discharge to an
80-percent charge within five days!

Occasional cycling to 80-percent voltage is required to keep the internal
resistance of the battery low. If the robot is noticeably slower, you know
the battery has reached this level. It is best to do this every 20 charge
cycles or so.
NiMH are high-maintenance batteries, requiring careful monitoring,
charging, cycling, and low-temperature storage to yield long life.

Alkaline
The alkaline battery is the most common primary battery in America. It is used to
power most products from radios to flashlights. Small robot kits often will use
them as the power source. Alkaline batteries cannot handle a high rate discharge,
so they don’t work well for combat robots.