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Old 06-15-2003, 05:43 PM
Hooters Driver Hooters Driver is offline
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Join Date: May 2003
Posts: 59
I think the batteries should all be on one side but which side depends on the layout of your track.

I have done a lot of research on charging lithium batteries. The two major concerns with lithium batteries are that you don't charge them above 4.2 volts per cell and that you don't exceed a charge rate greater than 1 time their MAH rating (e.g. don't charge a 1020 MAH lithium battery faster than 1020 MA). Because of those two factors they are a little more tricky to charge but if you use a good quality charger specifically designed for lithium batteries you shouldn't have any problems.

If you use lithium-poly they come in a soft case which will vent in the event of overcharging instead of blowing up. That is the same way that NIMHs are designed, therefore the li-polys should be almost as safe as the nimhs.

With a li-poly you can get two 1020 MAH batteries for about $20. The pair will produce 7.2 volts and only weigh approximately 41 grams.

Two more important things to consider when choosing batteries: increasing voltage will increase the power output of the motor, increasing the MAH rating will increase the run time of the car.

Here is a comparison chart between nimh, li-ion, and li-poly batteries:


Battery  # of Cells  Voltage    Weight  MAH Rating
nimh       &nbs p;   4    &nbsp ;    4.8   &nbs p;     50 gms       &nbsp ;750
nimh       &nbs p;   6    &nbsp ;    7.2   &nbs p;     75 gms       &nbsp ;750
li-ion       &nbsp ;   2          7.2   &nbsp ;     52 gms      1020
li-poly       &nbs p; 2      &nbsp ;  7.2     &nbs p;   27 gms       &nbsp ;660
li-poly       &nbs p; 2      &nbsp ;  7.2     &nbs p;   41 gms      1020




Now on to the motor problems. I have never driven either of the cars you mention but I have driven a futaba 1/20 scale indy car (it also has a longitudally mounted engine) and it suffered from the same problem as the mini-x. If you look back through the mini-x archives you will find a past discussion of the loose/tight condition I have described.

You can correct this problem with chassis tuning but it is difficult to get equal left and right hand cornering when you are fighting the motor (handling will change significantly depending on whether or you are on or off the gas). It makes much more sense performance wise to use the torque of the motor to increase rather than decrease traction.

I realize it is difficult and would require more fabrication to fit the motor on the chassis when lined up that way (probably impossible with a 180 motor) but a perpendicular motor placement should allow for a better handling car.



Re: Added info

1.0 mm will probably be thick enough if you reinforce it with a top plate. I am currently using .030" (.762 mm) cf for a mini-z/mini-x hybrid project I am working on. It is very thin and flexes a great deal but this car has a solid rear axle so I am using the chassis flex as my rear suspension. On a past project I used .060" cf (1.52 mm) and it had absolutely no flex in it.

Last edited by Hooters Driver; 06-15-2003 at 06:27 PM.
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