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Teamoutburst, this is a great idea that I have been experimenting with as well.
Let's just get a few things straightend out first.
The car will increase in weight, BUT this will be less than adding another battery. The centre of gravity won't be affected as much as an internal daul cell bit, therefore keeping the car's handling in check. (Dual cell's with the batt piggybacked on the rear of the car is a waste of time, internal dual is the only way to go.)
The current WILL increase, not decrease. Ohms law will back this up.
The problem is one of supply current. I've done some tests and on a normal 1.2V battery the car pulls the following currents.
1) Fwd or Rev = approx 90mA
2) Fwd/Rev + Steering = approx 160mA
3) Car is idle = 7mA
I've designed a few converters that take 1.2V in and spit out 3.3V but none of them can supply the much needed output current for this motor and steering circuitry. The TPS61015 is only rated to 250mA for a input voltage greater than 1.8V. For a 1.2V input it would be approx 150mA. Again this is not enough. Keep in mind that increasing the voltage you increase the current. So the measurements above will probably double/triple for a 3.3V source.
I've been researching this pretty heavily and still on the lookout for a suitable DC-DC converter. Team, you can email me on ph2t@prahranpianos.com if you have any specific questions or just want to techo chat, lol! If you want I can post all the converters I've checked out to help you if you'd like. Most of them are available as free samples from all the major semiconductor component makers....
One possible application is to remove the 1.2V -> 3V converter on the RX PCB (This is used to drive the RX chip and AM receiver ONLY) and replace it with a 1.2V -> 5V step up converter. You should get a great increase in range with this mod, hmmm might go and try that tonight............
Best of luck.
ph2t.
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