The lower portion of Quad Pod II is made of PVC pipe. The upper portion contains the motor mount and the electronics. The legs are made from 1/2" PVC pipe, and are about 30 inches long. There are four cross pieces that are about 17 inches long. They are attached to each other by small angle brackets and screws. The support structure is attached to the legs with electrical tape. The support structure adds firmness, and moves the center of mass downward. The legs are attached to the motor mount platform by small angle brackets and screws.

Quad Pod II is designed so that the center of mass is below the motor. This simplifies the control of the motor position versus having the center of mass above the motor. As long as the motor is maintained in a vertical orientation the rocket will tend to swing back to vertical alignment. The center of mass is indicated by the black stripes on the legs, which are about 9 inches below the motor mount platform. Quad Pod II weighs about 2.4 pounds with an E9 motor installed.

A test video demonstrates how the Quad Pod II maintains the motor mount in a vertical position as the rocket is moved at different angles. When power is applied the controller moves the motor mount to various positions to test the servos. It then moves the motor mount to the vertical position, and accumulates the average X and Y values for 2.5 seconds. After the calibration period, the controller drives the motor mount to a vertical position based on the output of the gyro chip.

The motor mount is postioned by two Futaba S3114 micro servos. They have a torque of about 1.3 pound-inches, and weigh about one-quarter ounce. The control arm is about 5/8" long, so the resulting force can be as much as two pounds. The servo can rotate 60 degrees in 0.1 seconds.

The control electronics uses a Parallax SX18 controller chip with a 2D rate gyro chip. The rate gyro was purchased from SparkFun Electronics. It consist of a small PC board containing a surface mount IDG-300 dual rate gyro chip plus some resistors and capacitors.

A LTC1298 12-bit analog to digital converter is used to feed the X and Y rotational velocities into the SX. Software in the SX integrates the rotational velocities to determine the absolute angles from vertical. The angles are used to control the servos to maintain a vertical orientation on the motor mount. The program also combines the instantaneous rotational velocity to damp out oscillations.

A four pin header is included in the circuit to allow for in-circuit programming of the SX chip. The cicuit was constructed on a prototyping board available from Radio Shack.

Launch 1. Quad Pod II performed well in the first flight. The mass of the rocket was 1.11 Kg (2.44 pounds). It rose to an altitude of about 8 feet and remained vertical during the flight. The plume from the rocket motor could be seen angling back and forth to maintain the rocket in a vertical orientation. The wind was about 5 mph, and the rocket landed a few feet from the pad after motor burnout. The Quad Pod sustained some damage to the angle brackets holding the legs to the platform. This caused the rocket to be bent slightly.

Launch 2. It was difficult to level the rocket for the second flight because of the bent brackets. The platform was leveled, which caused the legs to be at an angle. This caused the center of mass to be to the side a few inches. The rocket rose to an altitude of about 10 feet, and oscillated back and forth a few times during the launch. It was about 8 feet high at motor burnout, and it fell on its side when it hit the ground. This bent the angle brackets even more, and they will need to be replaced. The launch video shows how the rocket oscillated back and forth. The movement is more apparent is the slow motion video.

8/9/2008, Alamo Rocketeers Launch

Launch 3. The Quad Pod II was launched on an Apogee F10-4 motor. The Quad Pod II was weighted with four 2.5" long 1/2" bolts. This added 295 grams, which made the total mass 1,453 grams. It rose about one foot off the ground, and then sat upright on the ground for the last 6 seconds of the motor burn.

Launch 4. I removed the four bolts, which made the total mass 1,158 grams. The rocket reached a height of about 30 feet, and then settled to the ground. During the flight it travel to the left about 40 feet. The rocket landed at an angle on two feet, and fell on its side. However, the Quad Pod did come to rest on all four feet by the end of the motor burn. The launch video shows that the rocket began moving to the left immediately after it left the ground.

I looked at the Quad Pod after the launch and discovered that the center of mass was not directly below the rocket motor. The center of mass was a few inches in front of the motor, and slightly to the left. This may be the reason that the Quad Pod did not seem to drift with the wind, which was around 8 MPH and blowing toward the Quad Pod from the position of the video camera. 8 MPH is about 12 feet per second. During the 6 seconds of the flight the Quad Pod should have drifted about 96 feet. The drift to the left was at a slower rate, but the speed appears to increase throughout the flight.

8/29/2008, LDRS Launch, Argonia, Kansas pictures

5. Apogee F10-4. The night before I left for LDRS I added a feature to detect the launch event. This would be needed because the rocket would sit on the pad for several minutes before launching. I use a magnetic proximity switch, identical to the switches that are used in doors and windows for home security systems. I attached the magnet to the service arm that is used to hold the igniter clips. The magnetic switch closes after the Quad Pod has travelled about a half inch from the pad. I was hoping to launch the Quad Pod on one of the near pads, but the RSO told me to setup on one of the far pads. He was unsure on how safe the Quad Pod was. My brother-in-law, Chuck Pawloski, helped me set up the Quad Pod. This took several minutes, and then we had to wait several minutes before the LCO launched it. A photographer from Rockets magazine was at the far pad, and he took several pictures of us during setup around 12:46 pm. The Quad Pod was finally launch at 1:17 on pad 78.

The Rockets Magazine photographer took still pictures of the entire flight at about 5 frames per second. The rocket only went about 16 feet high, and the flight lasted about 5 seconds. It did touch ground with all four feet, but it was travelling about 10 MPH horizontally due to the wind. This caused it to roll over on touchdown. It did not suffer any major damage. The photographer also recorded a video of the launch, and recorded an interview with me. He said that this will probably end up in the LDRS 27 DVD set.

9/20/2008, Amateur Rocketeers of Texas Launch, Meek Ranch, Fredericksburg, Texas pictures video

6. Apogee F10-4. The Quad Pod flew well once again. It achieved an altitude of about 20 feet, which was similar to the LDRS flight. There was very little oscillation during the flight. I captured a video clip of the flight. It touched down on all four legs, but fell over as before. It landed about 12 feet from the pad. The gears in one of the servos are stripped,so this servo will need to be replaced. I have used up all of the Apogee F10 motors that I bought, and this is probably the last flight for the Quad Pod II.

My current plan is to build a finless rocket that uses the Quad Pod II motor mount plaform. I believe I can reshape the platform so that it will fill within a 5.5" body tube. I may be able to reduce the size even further to fit in a 4" tube. Other possible changes will be to upgrade the gyro to a full 6-degree IMU. This will allow the rocket to determine its spatial position, and maintain a fixed position.