Yup.... but you gotta let yourself in some deeper water....
To do an exact 90 degree spin you need encoders...
encoders are like switches that measure a certain amount of "clicks" per revolution of one wheel...
Google about encoders and servos.... NOTE that RC servos are NOT real servos... They are a hybrid...
A real servo let's you know the position of the motor or it's speed... RC servos get a pulse and you assume
it will run at the speed requested....
So do a little goggle and we will help you out more if we can!!!
Cheers!!!