Does the default position of the servos involve lifting the hexapod in to a standing position?
If so, you might be stalling the servos.
As an experiment, support the hexapod frame so that the feet are in free space and power up. Do you get the same result?
Something to think about - the SG90 is not a powerful servo. It will be VERY easy to overload the servo, asking it to maintain position with more torque that it can handle. Especially when you start walking and have multiple feet in the air - this means that there are less legs supporting the weight, increasing the torque required to maintain position.
You can do some math to see if you servos are strong enough - You just need 4 numbers:
- the 'reach' of a leg during your walking stance? By 'reach' I mean the horizontal distance between the pivot point of the hip of the leg and the foot when it is in contact with the floor.
- the weight of your hexapod
- The torque capacity of your servo (1.80 kg-cm) according to TowerPro
- the number of feet that will remain in contact with the floor while walking
Take your weight in kg, multiply it by the number of cm of reach and divide it by the number of legs on the floor during the walk. If that result is less than 1.8kg/cm, you are in the right ballpark. I would want a margin, running right at the max often results in failure as soon as some small part of the equation changes.