Hello,
What i meant by saying the i2c is done manually is that the i2c communication, in the code we are using, does not use any additional library other than wire.h
The library we use for sabertooth is the one provided by the official site of the product. You can find it in the following link: http://www.dimensionengineering.com/info/arduino
The IMU we are using is the breakout board GY-521 which already includes 2k2 pull-up resistors and an onboard regulator for 3.3v as i have checked. The schematic can be found here: Arduino Playground - HomePage
I have tried powering the board with 5v instead of 3.3v i was previously using in case it was a problem owing to the onboard regulator but i am still not getting any different results. I also tried powering on the MPU6050 board with an optocoupler after a short delay but i was unable to get any readings afterwards.