finally i can´t get this current because the waves are so distorsionated about the motor,and it is impossible to check the different of voltage
R1 simply needs to allow around 85mA across about 3V, so 310 ohms should be fine.
i think that to calculate R1 we have to do 3(Vcc)-0.2(Vce1)-0.7(Vbe2)=2.1V
and the current is Ic2/gain2=2/25=0.08A
*so R1 is=2.1/0.08=26 ohm(then if this is the max value to get saturation,i try 24ohm)
so the current will be finally 2.1/24=0.0875mA
and for R it is correct, at the output of CRIO i have 5V,so the voltage across R is 5(output)-0.7(Vbe1)-0.7(Vbe2)=3.6V,
the current at the base is 0.0875/40=2.1mA
* and R must be maximum 3.6/0.0021=1.8K
and ok,it will give me a current at the base of 2.1 mA,but it is the limit,but the gain will be higher than i guessed,so this current really will be lower and it won´t be a problem,yes??and i think to that the current that we guessed of 2A will be lower too,so it will help too
then finally with this values of R and R1 that i calculate *,i have with 50%duty cyle a average voltage across the motor of 2.3V(so much i think),with duty cyle of 20% i have 1.5V,and with duty of aprx100% i will have aprox 3V
why is that happen?i hope to have: average voltage across the motor of 1.5V with 50% dudy cycle,and about 2.2 with 75%