Compromises often have to be made. So here is compromise number 1 of the project – the batteries. I had three choices for batteries:

 

 

1. Lithium polymer cells. Big ones, and a bunch of them. This turned out to be way too expensive for now, and is a future upgrade path for this thing if it works and my finances dictate it.
2. A series of 4/3AF cells. They could fill the space between the wheels most efficiently, had the capacity, but were nameless and unproven. It would have provided 36 volts, 4.2AH, and upwards of 50 amps.
3. A bunch of Sanyo N3000CR full-C NiCads, old school style. I have about 40 of these cells, which are proven in the world of big combat robots. They are potentially good to 100+ amps burst discharge, but are only 3 amp hours in capacity.

 

Due to time and wiser economics, I decided to forego the nameless cells for now and use the N3000CRs. I won’t have much run time with this, especially at full power, but the amp rating means I’ll run less of a risk of exploding batteries. Life would be perfect if they had made the ElectricX2 one inch longer, but in the end, I can only fit 28 cells in the middle channel between the wheels. Maybe I can hide another two somewhere! 33.6 volts is reasonable enough for now.

 

Batteries are often the limiting performance factor in any electric vehicle. I didn’t feel like lugging giant 12 volt lead-acid batteries around, even though they would have been the simplest solution. The batteries as they stand are completely hidden under the frame, which makes for a very clean outside appearance.

 

Here’s some pics of the battery pack work. It’s not complete yet, as I haven’t determined the location of the rest of the electronics. The project page has been updated to reflect this change. Read more “The electrical system”