[caver01]

The short description is this:
Bit config= Honda s2000, green gearset, stock soft wheels, 3.8 motor, and 150mAh NiMh batt.

ZZ= Stock Yellow Mustang, orange gearing, stock motor (2.2?) stock tires, and 2 150 mAh NiMh batts!

Here's the deal. I bought a bunch of NiMh batteries from TinyRC. Put one in the Bit. Easy enough. Also dropped in the 3.8 motor. Bit top speed beats the ZZ, but if there are ANY turns involved, the ZZ kicks but every time!

So, the ZZ has dual NiMh batteries. I will post pics, but the technique involved NO soldering to the batteries at all. I did the following:

First, I replaced the existing battery with a new 150mAh. Then I prepared 2 wires with soldered copper contact strips. The strips are about 3/8" long and about 1/4" wide, hole in one end. The length of these leads are about 3". So, if you follow, I now have 2 wires, 3 inches long, with copper tabs on each end.

Next, I took another 150mAh battery and simply taped the tabs of the wires to the contact points on each end, then wrapped black electrical tape around the barrel of the battery to secure the end tape. The result is a spare battery now with two 3" leads extending from the end.

Finally, all I needed to do was to insert the loose copper tabs between the existing battery and one of the contacts, sheilding the tabs from each other with a peice of cut plastic from some packaging material to insulate the tabs. It looks like so:

--------Car battery contact
_
( ) Existing battery
--
------------Tab 1
--------plastic insulating strip
------------Tab 2
-------- Car battery contact

So, this is a friction-fit second battery in series. If you want the batt in paralle, well, just fit the tabs AROUND the existing battery. Now, all I have to do is put the circuit board down, and let the spare battery sit above it all, and snap on the body!

That's it! A dual battery mod that has no actual chage to the body, chassis, no solder on the car, etc. The second bat is simply INSERTED into the existing battery contacts as noted above. I did not have to deal with moving battery tabs, or some of the other problems with solder on batteries that I have read about.

Now, I did leave the old circuit board cover off so I can fit the battery above it and still put the body on, but if I really wanted to spend the time, I might try to arrange the second battery into the belly of the car. This works fine for me though as is, and it is easy to just pull it out if I want to do that.

In addition to the car, I had to modify the controller to deliver power direct to the car when charging. This involved bypassing the circuit board in the controller to power the charge station directly off the batteries. This has been outlined elsewhere, but it was pretty simple. Second, I had to up the voltage in the controller to provide higher charge power to the dual batts in series. I now run with 3 batteries in series in the controller. I simply made a wooden slug for one of the built-in batteries and wired the slug to a Radio Shack 2-AA snap on connector battery holder. This was not an elegant solution, but I did it that way to prove it works.

Man does it work! My brother controlled the ZZ and I had the Bit. He charged the ZZ for 2 minutes. For the next half hour, I charged my bit 3-4 times and he only recharged once! Accelleration was great! The ZZ now runs circles around by bit. We dragged once, and the room was not big enough for me to overtake the ZZ, but it would have happened. My top speed was better than the dual ZZ, but even a single turn would put me behind. Geared differently, we might be more evenly matched, and perhaps my 3.0 in the Bit would work better too, but for now, the ZZ is my car of choice. Great range, better speed, more run time, more torque, and a true body scale that is simply more realistic. For me, this dual battery mod is EXACTLY what the zz needs!

Note, I did not do any permanent mod to the zipzap such as clipping off resistors, no PCB mods to boost power to motor--nothing. Just added the battery and charged it!

Further testing needs to be done to see if my batteries burn out, if I am over charging them etc. Anyone care to comment? I am charigng two 150mah NiMh batts with 3 alkalines (4.5 volts) for 2 minutes.