Platform for Simulated Helicopter Motion
3DOF (Pitch, Roll, & Yaw)
3DOF main support frame with universal joint/roller bearing hub assembly.
The universal joint allows movement for "pitch and roll" axis positions.
On top is the rotating hub which allows for the "yaw" axis (tail rotor control) movement.
Heavy truck universal joint with the hub's spindle welded in the top center of the universal joint flange.
The universal joint came from a vehicle wrecking yard, the heavy duty hub and spindle from a farm implement supply.
Pitch and roll control arms (3" steel channel) welded to top universal joint flange.
The simulator sits on this welded steel frame,
which bolts to the rotating hub, which defines the yaw axis pivot point.
This linear actuator will be tested as a possible drive system for the pitch, roll, and yaw axis control motion.
The 12 volt linear actuator has a 10:1 gear ratio, ball bearing screw, 12" stroke, and can move 500 lbs.
Yaw Axis
(Left Photo) An offset mounting bracket for the linear actuator was fabricated and bolted to the extended pitch control arm.
(Right Photo) The shaft of the linear actuator is attached to the pivoting yaw frame with a small universal joint.
Photos show linear actuator yaw positions to right and left.
Pitch Axis
In order to mount the actuators inside the frame, ball bearing equipped jackshafts were installed, to accommodate the length of the linear actuators and redirect the output direction from horizontal to vertical. This jackshaft connects the pitch axis control arm to the linear actuator.
Roll Axis
This jackshaft connects the roll axis control arm to the linear actuator.
This board contains the DC motor controllers and relays for controlling the pitch, roll, and yaw motors. The motor controller circuit boards are connected to the flight computer with two USB cables. Here the linear actuator is being tested with a 12V battery, but future testing will be done with an 18V DC power source.
Position Sensors
These are the position sensing potentiometers that keep track of where the pitch and roll axes are at any given time.
The potentiometers are driven with a ball bearing supported plastic timing pulley. A short length of timing belt, which has one end attached to the axis control arm, drives the pulley. A tensioning spring on the other end of the belt keeps it tight. This system helps prevent any "backlash" that might occur with other types of gearing, or lever type attachment points to the potentiometers.
All three linear actuators have been installed to the motion base frame,
and the motion platform is now installed under the cockpit for final balancing and testing.
Balancing is critical to this type of design, to help allow the motors to handle the extreme platform positions.
For a single occupant (pilot only) weights are placed under the passenger seat to help with balancing.
These helper springs serve two functions. They prevent any "slack or flop" in the drive train when the platform passes over the center position and they help take the load off the motors when the platform reaches the extreme positions.
