4-Rotor Flying Robot

The OU 4-rotor flying robot is based on the Silverlit XUFO. We have added an Atmel Mega8 microcontroller equipped with a Devantech compass. This microcontroller overrides the RF receiver of the XUFO and provides its own pulse-width-modulated control signal. Because we insert this signal immediately after the RF stage, the functionality of the XUFO gyroscope is left intact.

Physical Interface

From the Power Supply

We are using RadioShack 13V ~10A power supplies. These are sitting on the tables next to the helis (as many as two helis will be connected to a given power supply). For each heli, there are two connections:
  1. Power to the craft itself
  2. +5V regulated power for your off-board control circuit. Note that the regulators that we are using can become quite hot to the touch (but not hot enough to burn).
In both cases, ground is black and power is red.

To/From Heli

The heli has a pair of 3m length cables attached to it. The first cable provides power to the craft (as described above).

The second cable provides the bidirectional serial interface as a 2-pin connector. The pin assignments are as follows:

Note: this serial interface uses +5 and 0V to encode the serial data. If you are directly connecting the heli to a device that uses the same encoding (such as another Atmel mega8 microcontroller), then the connection can be made directly. However, if you are connecting to a standard RS232 interface (e.g., a DB9 serial port on a desktop/laptop computer), then you will need a level shifting circuit (see an example circuit).

Serial Protocol

Querying the Compass State

The host transmits:

The heli responds with:

Where DDDD is a 4 digit decimal number that gives the orientation of the craft in tenths of a degree. Note that "\n" is the character '\n', not the characters '\' and 'n'.

Commanding the Heli

Roll. The host transmits:

Where DDD is a 1-3 digit decimal number that determines the current roll command. Values outside of the range 1-255 are ignored. A value of 128 corresponds to "no roll"; higher values correspond to positive roll (rotation about X in the figure).

Pitch. The host transmits:

Where numbers larger than 128 correspond to positive pitch (rotation about Y) .

Yaw. The host transmits:

Where numbers larger than 128 correspond to negative yaw (rotation about Z).

Throttle. The host transmits:

Where the rotors will begin to spin around values of 80. Values in the vicinity of 140 are sufficient to hover.

Emergency. The host transmits:

This command immediately sets roll, pitch, and yaw to neutral, and throttle to low.

Debugging Commands

These commands are most useful when you have attached the serial interface to a terminal or a computer executing a terminal program (e.g., kermit or hyperterm).

The host transmits:

The heli responds with a list of the actual signals being presented to the heli (in units of 1/2 usec). For roll, pitch, and yaw, 2000 is neutral.

The host transmits:

The heli responds with a list of the current calibration potentiometer states (in units of 1/2 usec).

Powering On

Step 1: Main Power

Step 2: Craft Power

Step 3: Tuning the Neutral Position (Optional)

Once the gyro has been spun up, you have the option of turning the neutral position for the pitch, roll, and yaw dimensions. By "neutral position", we mean zero pitch and roll (and hence, no tendency to translate) and zero yaw (no acceleration about the yaw dimension).

The procedure is as follows:

  1. Send neutral commands via the serial interface for each of pitch, roll, and yaw (128 in all cases).
  2. Holding onto the craft from its base, bring throttle to a level that produces a significant amount of thrust (~120 will work).
  3. Using a small screw driver, you can then adjust the pitch, roll, and yaw potentiometers until all three are truly neutral.


Safety for the Human

Although the rotor blades are moving at a high rate of rotation, they have very little momentum. As a result, placing one's finger in the path will hurt, but not damage the finger. (Besides huring) since this can damage the craft, however, this is not suggested.

For those who will be holding onto the craft during testing (while the rotors are spinning), safety goggles will be provided.

Safety for the Heli

Although the crafts are rather robust to abuse, it is important to take steps to protect them. In general, it is bad to run the crafts against the ground or the ceiling.

fagg [[at]] ou.edu

Last modified: Tue Mar 24 00:13:28 2009