FAQ

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Paparazzi FAQ


Is it possible to __________?

Yes, of course! That's the beauty of an open-source system - virtually any feature or function you want can be added to the hardware and/or software.

What equipment and components are suggested

Linux (Debian) compatible notebook computer, preferably with a very bright screen for outdoor use.
Most any airframe that will accommodate IR sensors and some extra circuitry - brushless motors are strongly suggested See the User's Gallery for examples.
Tiny autopilot
X-Y IR sensor board from FMA Direct P/N: CPD4SENUNIT
Z IR sensor board from FMA Direct P/N:FS8ZS
R/C Transmitter with a 3-position switch for selecting Manual/Stabilized/Auto. Some common models are listed in conf/radios
R/C Receiver with an accessible PPM signal to tap. See: Suggested R/C receivers
A pair of Modems along with any enclosures and antennas
FTDI USB-TTL cable for connecting the modem to your USB port and/or for serial flashing of bootloader code or tunnel access to the GPS receiver
A standard Mini-B USB cable and receptacle for uploading firmware to the autopilot
Lots of very durable wire, crimpers, and molex pins or pre-crimped wire.


Are internal combustion engines supported?

Yes, not relying solely on inertial measurement, the Paparazzi system is very well suited for aircraft with high vibration levels. Care must be taken to prevent oily exhaust residue buildup on the IR sensors and a simple variable must be added to properly address the special idle/kill needs of an IC engine.

Can Paparazzi fly a glider?

Sure. Paparazzi uses throttle and pitch to control climb rate but you could easily fit an airspeed sensor and modify the pitch code to maintain airspeed instead.

Will the autopilot provide enough 5V power for many/large/digital servos as well as a modem, video TX, etc.?

The Tiny includes a very high capacity and high efficiency switching voltage regulator intended to power servos, modems, video systems and other payloads. Users are strongly urged to use this regulator to power their servos rather than the linear regulator included with most motor controllers. While a linear regulator may be rated for several amps, they require a great deal of cooling and can easily overheat with only a few hundred milliamps of continuous current without cooling. By comparison, the switching regulator included on the Tiny can work continuously at 2A with little or no cooling. It is very important to realize that the servos in any stabilized aircraft will operate continuously and therefore a linear regulator that powers the servos reliably in manual flight may easily overheat in autonomous flight.

Do I need a separate battery or regulator to isolate the autopilot, servos, video, modem, etc. from one another?

The autopilot processor and sensors are powered by a 3.3V regulator and therefore are rather isolated from voltage fluctuations on the battery or 5V bus.

Can I use a Sirf, Trimble, etc. instead of the u-Blox GPS receiver?

Yes, but it would require a tremendous amount of work as some of the navigation code is dependent on some of the UBX messages. NMEA does not provide messages in the desired form and substantial calculation would be required for conversion. Any of the other proprietary protocols would work but you would need to write your own protocol handler. u-Blox is one of the most expensive receivers on the market but offers great performance, size, and speed as well as the ability to easily configure the internal Kalman filter parameters to expect significant acceleration in 3-D space - a very important feature. If you find a more capable receiver, let the group know about it, but this is not the place to save $40.

Does Paparazzi use DGPS, WAAS, EGNOS, or MSAS?

Most modern GPS receivers have the ability to process serial data sent from an external DGPS receiver, but the advent of WAAS/EGNOS has made the early ground-based DGPS transmitters nearly obsolete. The u-Blox GPS receiver supports all common SBAS systems (WAAS, EGNOS, and MSAS), as well as any standard form of external DGPS. It's important to understand that DGPS merely improves the accuracy of the position estimate by subtracting any static error. The only way to improve the precision of the GPS is by improving the antenna or the GPS module itself. See Wikipedia:Accuracy and Precsion for a detailed explanation of these terms.

How does the R/C receiver interface with the autopilot?

Standard hobby R/C transmitters multiplex up to 9 channels of PWM servo data into a single PPM signal which is encoded onto an FM wave for transmission, this signal is then decoded by the RF section of the R/C receiver back into the original PPM signal containing 9 servo position PWM values. This signal is normally then sent to a demultiplexer (i.e. 4017) where it is separated into 9 individual servo signals on 9 individual pins. The Paparazzi autopilot intercepts the signal between the RF section and the demultiplexer and does its own demultiplexing, filtering, and processing before multiplexing the manual or autonomous servo commands back into a single signal and passing them to the 4017 to be distributed to the servos.

Why does Paparazzi tap directly into the R/C receiver instead of using individual servo signals?

By connecting directly to the RF section of the R/C receiver we are able to obtain up to 9 channels of R/C servo data from a small, lightweight inexpensive 4 channel receiver with only 3 wires needed to connect the components. Furthermore, the autopilot then has direct access to the raw R/C signal where it can be filtered, evaluated, and assessed for quality. The autopilot can then alert the user of any loss of R/C signal as well as perform any pre-configured autonomous commands in response to a loss of signal.

Are PCM or 2.4GHz R/C systems compatible with Paparazzi?

Not that we know of. Even if these systems use the same type of multiplexed signal at some point in the data path, it is highly likely that this signal is handled entirely within the confines of a single IC and is not externally accessible. A general rule of thumb is that if you see any type of demultiplexer on your R/C receiver, you can look up the data sheet for it and likely tap into the input pin with success. Some information on compatible R/C receivers and how to find the PPM signal of your own receiver is given in the RC receiver section.

What R/C transmitters are compatible?

No mixing or programming is done in the transmitter so even the simplest models will suffice but one important requirement is a 3-position switch to select among the three autopilot modes: manual, stabilized, and auto. Those handy with electronics can replace a dial with a switch and resistor if needed. The transmitter's PPM values need to be recorded and the channel used to control the autopilot mode must be stated. Some commonly used transmitter configuration files are provided in the conf/radios folder and the syntax of these files is easy to follow for those using other brands or models.

Can a gamepad/joystick be used to control the aircraft through the modem?

Yes, the code to do this was written some time ago though it was not tested in flight due to latency concerns with the primitive Modems#Coronis_WaveCard Coronis modems used at the time. Any of the modems currently recommended should work well in this manner but the theoretical reliability is still questionable due to the fact that no interrupt or prioritization structure exists for the telemetry data so any manual control inputs would be lumped in with the rest of the data to be lost or delayed as needed.

What Motor Controllers (ESC) are compatible?

Any controller can be used, the exact PWM value that is sent to the controller for 0-100% throttle is completely configurable in the airframe file so all controllers are compatible and any controller will arm properly with or without the use of an R/C transmitter. Upon each boot, the autopilot immediately sends whatever you have defined as 0% throttle (typically around 1200ms) and maintains that signal until a manual or autonomous command is given. Most modern controllers are "auto calibrating" which is an undesirable feature for R/C pilots and even more so for autonomous systems but can be dealt with. The calibration is done by defining the PWM value at boot to be 0% power and then defining some initial arbitrary mid-range value such as 1500ms to be 100% until a higher value is seen. The net result of this behavior is that the motor is given full power at any command above 50% throttle until 100% throttle has actually been commanded at least once. This is not an issue for planes that routinely take off at 100% throttle but can disrupt the throttle tuning and altitude control on any flights where 100% throttle has never been commanded. Castle Creations controllers can be configured for "fixed endpoints" which permanently sets the range to 1250-1850ms providing a consistent and predictable throttle response.

Can traditional throttle stick programming be done on the ESC once connected to the autopilot?

Yes. If the transmitter is on with the throttle at full or whatever is required for your ESC when the autopilot is first booted, the autopilot will immediately see the manual control signal and the throttle position and pass that along to the ESC as the first value, triggering the programming mode.

Does Paparazzi support digital servos?

Of course. Digital servos use exactly the same electrical interface as their analog counterparts, the only difference being in the way they control the motor. Analog servos use a Proportional feedback loop, meaning the voltage sent to the motor is proportional to the difference between the measured and intended position of the arm. Digital servos use a Proportional + Derivative (PD) feedback loop. The derivative term considers the current speed and direction of the servo as well as the speed and direction of the pilot's stick command. The derivative term will increase power to the motor if the servo is moving the wrong direction (providing faster direction changes) and will reduce/reverse power if the servo is near it's desired position but moving too fast (reducing overshoot). The net effect of this is that a digital servo can use a much stronger P term without risk of oscillation and overshoot because the D term is there to intelligently dampen it as needed and boost it whenever it can.
How does the inclusion of a D term make an analog servo become digital? Analog servos use a simple opamp to linearly relate the motor voltage to the difference between the potentiometer reading and PWM signal, whereas digital servos use a microprocessor to analyze the potentiometer position and velocity as well as the current and recent PWM signals to calculate the optimum voltage to send to the motor.
Important: Please be aware that autonomous flight involves continuous movement of all servos. Make sure your power supply is capable of handling this and that your servos are capable of continuous operation without overheating - especially if you use digital servos.

Can I solder wires directly to the autopilot instead of using the molex connectors?

Yes. All of the molex headers are thru-hole and you can easily solder small gauge wire directly to the pins that protrude from these headers on the back of the board. It's important to note that standard servo wire cannot be soldered reliably in this fashion - you must use only high-grade wire intended for soldering (no vinyl insulation!). See the Wiring section for suggested wire types and sources.