Need help building r/c car circuit

[jclaudii]

I am building a device that will allow me to start my r/c car using a conventional 12v battery. I have two batterys, one is a sealed battery out of an old cellular bag phone, the other is my real car battery.

I need the little hobby motor to turn with about 8 volts instead of 12 so it will last longer. There is also a glow plug that needs 1.5 volts applied to it.

Now if I follow ohms law, How much current do I apply to the forumula. because my car battery is like 800 cranking amps. I want to tone the current down also to help improve little hobby motor engine life. Also, for the 12v to 1.5 volt drop in voltage I believe I have figured on either a 2.1ohm @ 5A or a 5.25 Ohm @ 2 amps. Not exactly sure how much current is needed to light a glow plug.

Any help or schemetic would be greatly appreciated. I always seem to fall short when dealing with voltage drops and wattage this and that.

Thank you guys alot,

 

[checkmate]

Since your power source is 12V, and since the motor drops 8V, the remaining 4V will be wasted somewhere. What you should do instead is to run a 12V motor, but drive it with PWM signals to reduce current consumption.

 

[jclaudii]

what are pwm signals....do they make a 12v hobby motor?