RubyTM Installation
| Overview | |
| Required: | |
| Controller | |
| Airspeed / Magnetometer | |
| GPS | |
| Power Sensor | |
| Receiver | |
| Cabling | |
| Optional: | |
| Expander | |
| Temperature sensors | |
| Control Panel | |
(See also Configuration)
Here are general installation instructions. Before reading this document, check the [supported aircraft list] to see if specific installation instructions for your aircraft might exist.
In addition to the main controller (the red box with big "RUBY" printed on it), three small modules need to be installed in your airframe: airspeed /magnetometer, GPS, and power sensor. You may affix all of these to the main controller to form a tidy package, or you may distribute some or all of them throughout your airframe for easiest fit and best performance.
Except for a tiny airspeed pitot tube, everything can be contained within the fuselage or wing of your plane.
There are just a few hard constraints on placement:
Servos are plugged directly into Ruby's main controller. A cable and adapter run from the controller to your off-the-shelf remote control receiver.
Ruby should be powered by a "switching BEC", rather than the standard "linear regulator" found in most ESCs.
The Ruby controller unit can be mounted in any location or orientation, as long as it is orthogonally (“square”) with all the axes of the airframe, and not at an odd angle. (We plan to remove this requirement in a future update of Ruby firmware, but it is currently necessary.) Ruby can probably keep your plane up in the air even if it is misaligned 10 or 15 degrees, but it will do a much better job of maintaining solid attitude, course, and airspeed if line it up to within 5 degrees. You should draw guidelines or just “eyeball” it carefully. You can attach the unit to the floor or sidewall of the airplane cockpit / payload area, perhaps to a platform inside the airfoil near the wing root, or even to the outside of your plane. Most commonly, Velcro is used, allowing the unit to be pulled out easily so you can plug/unplug cabling or transfer it to a different aircraft. If mounting to a sloping surface such as a tapered fuselage wall, you may have to make some kind of shim out of foam or balsa to ensure that the unit is truly orthogonal to your airplane's axes.
It's best, but not critical, to mount close to the plane's center of gravity. It can be offset from center, but shouldn't be out on a wing or tail where it will experience significant acceleration due to rolling or pitching.
Although all components have good vibration tolerance, mounting on a surface less prone to vibration will yield better performance. Unlike the magnetometer/airspeed pod (see below), the controller unit can be located near magnets or wires carrying fairly strong electrical currents. Still, it is good practice to keep high power lines at least an inch or two from this unit and other electronics. If in doubt, look at recorded flight data for fluctuations in altimeter, accelerometer, or gyro readings as you give the plane full throttle.
The pressure altimeter is located in the main controller, so you should ensure that the cavity in which the controller is installed is not sealed from ambient air or pressurized by airspeed as would be the case if cockpit opened onto a forward facing air scoop.
Accurate measurements of airspeed and the earth's 3-dimensional magnetic field are currently required for the Ruby IMU to operate correctly, so proper location and orientation of this sensor is absolutely critical.
For aircraft such as pure gliders or “pusher” configurations which don't have motors or other hardware installed in the nose, it's usually easiest to mount the mag/as module near the nose, perhaps glued or velcroed to the top of the controller unit, and to run a short length of pitot tube to an 1/8'' hole at the tip of the nose. The tip of the tube can protrude or be made flush with the nose tip and held in place with a ring of hot glue.
For all other aircraft, it's usually necessary to place the pitot tube out on a wing, away from propwash with the pitot either protruding from a hole drilled into the leading edge, or run outside the bottom of the airfoil, extending past the leading edge. The tip of the pitot should extend about 1 inch past the front of the leading edge and be square with oncoming airflow at normal incidence. Hot glue can be used to build up the base and sides of the pitot to keep it from bending at higher airspeeds. (We chose flexible rather than hard tubing to reduce potential for damage and allow you to “flick” water out of the tube if necessary.)
Most commonly, to minimize the necessary length of pneumatic tubing, the mag/airspeed unit is embedded or attached to the bottom of a wing directly behind pitot tube, mounted much as you would a servo. The mag/airspeed unit can be located elsewhere if desired, however, with any length of tubing running to it from the pitot.
If you frequently move Ruby between planes, you might want to purchase additional airspeed / magnetometer indicators for more permanent installation in wings.
A conduit for the pitot tubing can be most easily made through the nose or wing of a foam plane using a thin walled 1/8'' diameter metal tube. It helps to sharpen the edges and twist as you push it in gently.
In any event, the pitot should be positioned in “clear air” unaffected by prop wash or wake from airframe. It must be “upstream” of everything else and generally cannot be placed on tail surfaces or close to fuselage. Remember that accurate airspeed measurement is a critical input needed by the IMU to calculate actual pitch and roll relative to the earth as the plane maneuvers.
Like the controller unit, the magnetometer/airspeed unit must be mounted orthogonally to plane axes. (Again, we plan to remove this requirement in future Ruby firmware, but it is a hard requirement at this time.) Large offsets from the orthogonal may cause Ruby to fly erratically or crash under aided and autopilot modes. Small offsets can cause loiter patterns distorted from perfect circles. If mounting on a wing, your mount may need to take dihedral and sweep of the wing into account. It doesn't matter whether it is located on left or right wing.
It may be necessary to flange one end of the pneumatic tube to fit on the airspeed sensor nozzle. This can be done by heating a pointed tool or large nail with a soldering iron as the tube is pressed onto it.
Most importantly, the magnetometer/airspeed module must be located away from all significant sources of magnetic field
Magnetic field sources include:
If your mag/as sensor is located out on a wing and more than 2-3 inches from a servo, it will generally be fine, and no further consideration made.
For smaller electric planes, a distance of 2 inches from servos and 4 inches from motor and motor power wires will usually suffice. For planes with larger servos or motor current, greater distance will be needed. Fields from strong magnetic latches can often extend more than 4 inches. To positively determine if a location on your airframe is suitable for magnetometer placement, watch for deviation of a handheld compass or the mag/as sensor (variables:sensor:magnetic total): as you move it towards the desired location, or mount the mag/as unit and look for fluctuations in magnetic_total as full throttle is applied. Deviations above 10% will probably yield unacceptable IMU performance.
(Note: if bench testing near ferrous structures such as “rebar” reinforced basement walls, “variables:sensor:magnetic_total_error” will often be high since the magnetic field inside your shop is different from the earth's field expected outside where the plane will fly. For the purpose of determining interference from motor / power, look not at the error value, but at the magnitude of the change in “variables:sensor:magnetic_total” as power is applied or the sensor is moved closer to servos or motor magnets.
When proximity to the ESC power cables is unavoidable, you may be able to reduce magnetic deviation by twisting the positive and negative leads together so that the fields around each wire cancel each other out. Likewise braiding the three leads of a brushless motor can help.
The GPS sensor must be mounted with the patch antenna pointed up. It should located more than a few inches away from the data modem and video transmitters (further is better). Technically, for ultimate GPS reliability, you would attach so that it is open to air or behind a minimally thin covering of plastic or balsa, but in practice we've found that the receiver is so powerful that it isn't attenuated noticeably by foam or thin wood, plastic, or fiberglass. Metal, wire, ,and carbon fiber really block the signal, however. It's generally OK to mount it inside a fuselage that isn't made of carbon fiber, as long as no wire or metal is touching or obstructing the top of the antenna. It's OK to glue velcro or foam to the top of the antenna or directly to the electronic components on the bottom of the GPS unit. You can glue or velcro the GPS sensor directly to the top of the main controller board if desired to form a more self-contained unit.
This sensor measures voltage and power flowing from the main battery to motor and all other systems. It's used for
By default, the autopilot relies critically upon the power sensor to regulate throttle and climb rate in electric powered planes. (Contact support@uthere.com to learn how to configure the autopilot to operate in a way that does not require this sensor, or to work with gas-powered planes.) This sensor can be omitted for gliders or gas powered planes if battery capacity monitoring isn't important to you.
Solder power leads from a battery connector of your choice (I.e. male Dean's plug) to the pads marked “Batt+” and “Batt-”. The pads are on opposite faces of the board. Likewise, solder the leads to your ESC +/-.
Solder the wires leading to your BEC “piggyback” style onto the ESC wires. Connecting them to ESC rather than Batt terminals will include servo and other system power rather than just motor power in the measurement and yield more accurate monitoring of battery capacity / time remaining, especially after long periods of motor inactivity. Be sure that the BEC input and output wires are not too thin, otherwise power and voltage measurements will be inaccurate and other sensor performance may be affected by voltage sag due to higher resistance.
Ruby is inserted between an ordinary off-the-shelf model airplane remote control receiver and the plane's servos and throttle. Ruby processes the signals that would normally go directly to the servos before outputting its own signals to the servos.
The receiver is connected to Ruby using an adapter connector and cable provided by uThere that is specific the brand and model of receiver and transmitter. Even if an adapter happens to fit different model transmitters that you may own, the cable might not have the correct wiring for all of them. Also, in the case of Spektrum receivers, going from a Spektrum handheld to a Spektrum module for Futaba will require a different cable.
The cable is plugged into the port marked "Handheld RX".
Note that the numbering of Ruby output channels usually does not necessarily correspond to the numbering of channels on your transmitter or receiver. The mapping is determined when you run the Ruby configuration software on your PC.
Power can be applied to the Ruby system through the "+" and "-" pins of any of the servo ports. Thus, Ruby uses the same power circuit that the servos use.
On gas, turbine, and gliders, power is typically provided by a dedicated battery pack.
On electric powered aircraft, this power is typically provided by a battery eliminator circuit ("BEC") built into the brushless motor controller ("ESC"), and it's fed into the throttle servo channel.
Alternately, a separate switching BEC can be used for more efficiency. These typically have a regular servo connector for output. You'll either connect the to an unused output channel, or
! Ruby requires between 3.9 and 6.3 volts to operate. Exceeding 6.3 volts will permanently damage Ruby and void warranty!
Ruby draws approximately 80 milliamps continuous.
For minimal weight and bulk, all Ruby modules are connected using thin ribbon cabling terminated by miniature connectors. These may be ordered or cut by the user to custom lengths. [more...]
At this time, Ruby has only been tested with cables up to length 3 feet. Longer lengths might be possible, but should be avoided if possible. Contact support@uthere.com for more information.
The cables carry high frequency digital signals. FCC testing showed that emissions were not excessive, but with sensitive radio gear and possible high power video transmitters on board, it may be good practice to use braided rather than flat ribbon cable. Contact sales@uthere.com with desired lengths or directions for creating your own.
The best way to insert a miniature connector into its socket is by using thumbnail or small screwdriver to press against the plastic just above the cable.
Removal is simply a matter of tugging on the cable, being sure to pull straight out , not at an angle.
It adds capabilities which are not necessary for Ruby's essential aided and autopilot. You'll only need it if you desire flight recording capability, extra servo channels, "control panel", or extra serial port. You will however need to connect the Expander temporarily to the Controller if you need to reconfigure the controller or load new firmware into it using the USB port.
Note that it's possible to plug the Expander into the Controller in two different orientations, but only the orientation in which they line up in a neat stack is correct. Connecting the expander in the wrong orientation may damage your Ruby. Check twice before applying power! We're sorry for not having provided some kind of keying mechanism here.
To reduce cabling bulk, the temperature sensors plug into the motor sensor, rather than directly into the controller.
The innermost sensor corresponds to “Variables:power:battery:power_battery_temperature”, but in practice is often used to measure temperature of ambient air or other components of interest such as high power video transmitter. (Well chosen batteries in good condition generally don't heat up significantly under rated loads.) The middle sensor corresponds to the flight recorder/telemetry variable “Variables:power:motor:esc_temperature” and can be tucked into the shrinkwrap of your ESC, perhaps held in place with a drop of epoxy or high temperature adhesive. The outermost sensor is “Variables:power:motor:motor_temperature”. The most effective location for it is in contact with the stationary windings of your motor, held in place with a drop of epoxy or high temperature adhesive.
[about temperature sensors...]
You can mount this indicator anywhere, even inside a transparent wing, with just about any length of cable.