okay i have the ardumoto shield (SparkFun Ardumoto Shield Kit - KIT-14180 - SparkFun Electronics) sitting on top of my ardruino uno.
i supply power through the arduino power jack from a 12 volt battery i have taken from a elektrik drill.
i can measure 12.66 volt on the VIN + and - pin on the ardumoto shield but when i give it full gas (write 255 out on the pwma pin (pin 3)) but i can only measure 8.41 volt on the output pin (pin 1 and 2) on the ardumoto shield.
why is it i cant measure 12 volt on the output pins when i give it full gas?
my motor is a 12 volt 1.6 amp dc motor that i have taken from the same drill as i took the battery.
i am totaly new to this so sry if i have missed somthing...
1.6A is too much to draw from the Vin output. That current has to go through a blocking diode on the Uno which is likely not rated for that kind of current. It doesn't completely explain the 4.25V difference (unless you're REALLY stressing the diode and operating it in the breakdown region). In any case, it's a bad idea to try to source more than ~500mA out of the Vin pin.
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The DIN Rail Mount kit for Arduino: quickly attach your Arduino to standard DIN rail
If I remember correctly, the L298 has a ~2v voltage drop through its internal transistors - that, along with the diode drop, would explain the remainder of the 4.25v difference.
The Ardumoto shield has a separate Vin trace - use it.
And there will be some voltage droop due to battery's internal resistance...
This 'issue' with the L298 keeps coming up - it has Darlington output stages so its not much use at low voltages like 6V - not sure why its designed like that since it causes a lot of heat to be dumped in the output stages.
so first i need to supply the power the the motor from the battery via the vin + and - pin on the ardumoto bord
and then correct if i am wrong but to be able to give the motor 12 volt when i give it full gas i will need to supply the ardumoto bord whit more then 12 volt like lets say 14 or 15 volt?
Yes, that's right. Although, please use 'full power' or '100% duty cycle' instead of 'full gas' - your Arduino is using electrical power, not combustible fuel =).
okay thx so far so good.
by giving power to the ardumoto bord directly insted of through the arduino's power jack i now have a motor out of 9.41 volt so a littel better. (thx to RuggedCircuits for that)
i am still missing 2.6 volt so i was wondering if there was some kind of reverse resistens? a componet that will increase the volt out of the battery so i get the 14.6 volt i need?
You're looking for a boost regulator circuit - be aware that you'll need to get one rated for your current requirements, which are relatively high (most boost converters are made to run low-power chips off of lower voltages, and are limited to only a few hundred milliamps).
Boost regulators are not over-unity devices - the power coming out will be less than the power in (power = current x voltage).