Improved Calibration Routine

[BarbourSmith]

I've been talking to Keith Selbo (our resident mathematician) about how to make the calibration of the machine as easy as possible and he made some EXCELLENT suggestions that I wanted to get written down.

The problem we are solving is that the machine needs to be calibrated in-order to work accurately. Because of the non-linear way in which the machine relates rotational motion of the motors to movement it is important that the machine know the distance between the motors and amount of chain paid out. These values are stored in nonvolatile memory so even if power is lost the machine won't loose it's calibration.

Measuring these dimensions with a tape measure is going to result in user error and confusion. Keith suggested that the machine has a built in measuring system which would be more accurate than a tape measure. Basically we can use the motors, encoders and chain to establish the machine's dimensions.

Here's my slightly modified version of how this could work.

To measure the distance between the motors accurately:

1. Set both motors to have one gear tooth pointing straight up
2. Attach last link on left chain to the top tooth on the left motor
3. Pay out chain until it reaches the right motor, hook chain onto top tooth
4. Reverse left motor direction to tension chain removing droop. The tension can set automatically because the motor voltage and speed of rotation are known. If we need to we can take into account chain droop but I don't think it will be significant
5. The value of the left motor encoder will now reflect the distance between the motors

To measure the length of chains

1. Set both motors to have one gear tooth pointed straight up
2. Use the motors/encoders to pay out the correct length of chain. This will have to be done one chain at a time because until there is some tension on the chain the sprockets are not self tailing and can catch the chain.

[BarbourSmith]

Added