Fall 2015 MicroBiPed Battery
BATTERY TRADE-OFF
By Michael Balagtas (Manufacturing Engineer)
Approved by Paul Oo (Project Manager)
Approved by Railly Mateo (Systems Engineer)
Picking a battery with our level one requirements (Toy, compact, cheap) brings many conflicts to our final decision, so a trade-off study will be done between a generic 9V battery, two 3.7 LiPo batteries, and a Powerex Imedion AA batteries.
Our overall mission is very simple: climb up a short incline and come back down in a figure eight. At worst, the mission will take no longer than 10 minutes, and that is assuming that the robot will shuffle due to lack of traction. However, we still need to compensate for our large current requirements. The eight servos to be used have a current draw of about 150mAh each and the Arduino Micro has about 100mAh, putting our overall current budget to about 1.4Ah. Considering the mission duration, we can take some liberties with this amount and set our goal to about 300-400mAh. The characteristic curves of the batteries will be ignored to simplify this process.
| Manufacturer | Material | Voltage | Quantity | Current Rating | Dimensions | Volume | Price |
| Energizer | Alkaline | 9V | 2 | 230mAh | 46.4mm x 24.5mm x 15.5mm | 17620mm3 | $12.00 |
| Syma | Li-Po | 3.7V | 3 | 500mAh | 42mm x 25mm x 9mm |
9450mm3 | $8.95 |
| Imedion | Ni-MH | 1.2V | 4 | 2400mAh | N/A | N/A | $10.95 |
The table above compares 3 possible batteries to use for the µBiPed project. The table compares material, supplied voltage, quantity, current rating, dimension, volume, and price. After comparing the 3 batteries, we realized that the project needed to pushed further into manufacturing before we could decide which battery to choose.
Considering that the device is marketed as a toy, safety and choking hazards are a priority, therefore Lithium Ion is out of the picture, leaving us with the above options. At first glance, it looks as if the Imedion would be a landslide decision because of its current rating, but that’s too much for our mission parameters. To narrow down our decision, we will conduct a few studies: size, operational time, and price.
As a toy, cheap power sources is a requirement for easy access to power off the shelf. By and large, the Syma Li-Po wins over every other choice
We want the biped to be as small and as light as possible, so the smallest and lightest battery is the most desirable. However, the number of batteries is also taken into account. The Energizer only requires one battery to operate properly, whereas the Li-Po requires two and the Imedion requires four. The Syma Li-po would be comparable to that of a 9V battery once stacked together but they’re also light; the Imedion is tempting but there was no data for the batteries. As for right now, this study is a stalemate.
The last and most controversial of the above parameters is the current rating, because the current rating can change based on the current draw. Therefore, to streamline the process, it is assumed that these are ideal. The Imedion easily overpowers everyone else in this department because of its 2400mAh rating, but that is due to its unloaded nature. Nevertheless, we will assume that it takes the edge here
Conclusion: Either the Syam Li-Po or the Imedion will be utilized. The decision is heavily leaning towards the Syam because of the mass and given data.