User manual

Table Of Contents
kit. Two terminal programs, Crosscut and Crosscut for Win, are also provided. Crosscut is DOS-
based and Crosscut for Win is a Windows program. Instructions for installing and operating
these emulators are provided in Appendix A, “Operating Crosscut for Windows and Crosscut”.
Drive Motor
The drive motor control interface is composed of three DIO lines. One of the lines can be
programmed to output a pulse train with a variable duty cycle. A dedicated analog channel
measures motor current during deployments and diagnostic testing. Current is steered through the
DC brush motor with a standard HEXFET H-bridge. A logic network controlled by the DIO lines
drives the switch. Unregulated battery voltage is applied directly to the motor through the H-
switch to minimize losses that would reduce the endurance of the system.
One of the DIO lines sets the motor direction for upward or downward profiling. The
second line enables or disables the motor and applies a dynamic brake. The dynamic brake can
support several pounds of positive or negative buoyancy and is set electronically by grounding
both terminals of the motor through the lower legs of the H-bridge. The third DIO line is
programmable to enable the motor to free wheel or send the motor in a specified direction during
a profile. In free wheel mode, the motor is not driven by the battery and offers no resistance
(other than friction) to external torque. The motor is automatically set to free wheel during
launch to reduce slip related wear of the drive wheel.
IMPORTANT
Do not attempt to accelerate the MMP too rapidly. Any sudden transition in the voltage applied
across the motor can spike motor current and torque causing the drive wheel to slip against the
cable. To gradually increase MMP speed from 0 cm/s to the full profiling speed (nominally
25 cm/s) slowly increase the applied voltage from 0 V to the full battery voltage.
Based on testing at McLane, the applied motor voltage is ramped up linearly over a
30 second period to start each profile. Pulse width modulation (PWM) is used to accomplish this
without sacrificing efficiency in the drive train. The programmable DIO pin is set to produce a
20 KHz pulse train and the drive voltage is varied by changing the duty cycle from 0 % at the
beginning of the ramp to 100 % at its end. It is the reactance of the motor inductance and a
parallel capacitor that filter the pulse train and produce a smooth average drive voltage from the
pulse train. Once the duty cycle reaches 100 %, the pulse train is turned off to reduce processor
overhead and the DIO pin is simply set to the run state.
Appendix B-7