LANDTASTIC
The Ultimate R/C Model Retract
Controller
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This
low cost project is used to slow down retractable landing gear. It also adds
remote activated Landing Lights and a Lost Model Finder
feature.
Wish
to see it in action? Just click the photo on the left to see the short demo
video.
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A big parkflyer crowd
pleaser has got to be retractable landing gear. The spectator "Wows" you
hear when the gear goes up is a big reward. But it just doesn't look right
to see the wheels fling closed at lightning speed instead of slowly
retracting.
The solution is to
use a "servo-slow," which is an add-on device that {like its name implies}
can slow down a R/C servo. But instead of using a commercially made solution,
we rolled up our sleeves and designed our own. The result is much more than
a retract controller and you will soon see that it is simply fantastic. Or
in this case, it is Landtastic!
Landtastic is a little
microcontroller based device that allows you to slow any proportional R/C
servo. With it installed between your R/C receiver and servo, your landing
gear will move at realistic scale speeds. Servo transit times can range from
one to ten seconds.
In addition to the
servo-slow feature, it can optionally add remotely activated landing lights
and anti-collision strobe lights. This project is ideal for scale model aircraft
since attention to these little details will usually earn additional contest
points. And more crowd pleasing "Wows".
Please note: It
can also be used to slow down a camera panning servo. This will allow you
to obtain smooth camera movement from a switch or stick controlled R/C
servo.
And for those that
need extra protection, Landtastic even includes a Lost Model Alert feature.
By installing a miniature (but loud) piezo buzzer, your model will emit a
high pitched alarm noise whenever the Tx is turned off. This is perfect for
locating models lost in the brush.
Your R/C equipment
is not modified in any way. Landtastic connects between your servo and the
receiver's Gear or Aux channel. For proper operation, your R/C transmitter
should use a toggle switch control; spring-centered sticks are not
supported.
Landtastic Feature
Summary:
-
World's first fully
featured, user programmable, R/C parkflyer landing system controller.
-
Slows down any proportional
R/C servo, allowing up to ten seconds of retract time. Servo torque is not
affected.
-
End-of-travel inertia
brake gently parks the retract system.
-
Sophisticated navigation
lighting; Remote activated Landing Lights and anti-collision Tail
Strobe.
-
Lost Model Finder alarm
for those unexpected landings in the brush.
-
Compatible with AM/FM/PCM
systems. Note: The Lost Model Alarm is not available when used with failsafe
(PCM or DSP) receivers.
-
Works with stock
proportional servos, analog or digital.
-
No modification required
to the R/C system. Plug-in installation.
What's Tiny, Black, and Has
Eight Legs?
The project is based
on a tiny black 8-legged chip (no, its not a spider). Our 8-legged host is
a
MicroChip
Technologies PIC12F629/675 MCU. Also known as a PIC microcontroller.
It requires software (called firmware in this situation) that is available
in the file download section.
The PIC decodes the
R/C servo signal and adds a time integration factor to the servo pulse in
order to slow down the servo. It also handles the landing light's on/off
control and blinks the strobe light. Furthermore, it carefully checks the
servo pulse for suspicious signals and will discard any that are corrupt.
If the R/C signal is missing it will sound a very loud alarm (hey, just turn
off the R/C Transmitter to find your lost model).
Even though a
microcontroller is used, cost is minimal. You can build the basic system
for under $10. Total parts count is very low (two parts!) and the assembled
prototype weighs under 5 grams. It can be as small as you care to make it
(typically about 3/4" square).
The
eight pins on the PIC chip exist as one of three kinds of signals: Power,
Digital Input, or Digital Output. The digital inputs are level sensitive
and are said to be logic high when the voltage is greater than 2.0VDC
and logic low when they are less than 0.5V. Output voltages are similarly
defined. Logic high output voltage is equal to VCC and a logic low output
is 0VDC.
If you are ready, let's
take a quick tour of the various signals on the PIC chip:
PIN |
FUNCTION |
DESCRIPTION |
1 |
VCC
(Power) |
Allowed voltage
is 3.9 VDC to 5.5 VDC @ 2mA current draw. Landtastic works well on a four
cell R/C pack (4.8V) or the 5VDC BEC output of most electronic speed controls
(ESC). Do not
exceed the maximum voltage. |
2 |
RC-OUT
(Output) |
R/C servo pulse
Output. This output connects to your proportional servo. Can directly drive
up to five servos. |
3 |
LMA
(Output) |
Lost Model Alert.
This optional output connects to a piezo buzzer. Logic high active, must
be buffered by a transistor. |
4 |
RC-IN
(Input) |
R/C servo pulse
Input. This input connects to R/C receiver. |
5 |
STROBE
(Output) |
Anti-collision
Strobe light. This optional output connects to the Strobe light. Logic high
active, must be buffered by a transistor. |
6 |
LANDING
(Output) |
Landing Lights.
This optional output connects to the Landing Lights. Logic high active, must
be buffered by a transistor. |
7 |
CONFIG
(Input) |
Configuration mode
enable. This pin is used to configure the Landtastic for operation with your
R/C system. Logic low active (e.g., connect to ground). |
8 |
GND
(Power
return) |
0 VDC. Ground. |
Your exact PIC choices
have some flexibility. You can use a PIC12F629 or PIC12F675 (your choice).
The PIC is a "Flash" part, so it can be re-programmed hundreds of times.
This allows for cheap software upgrades since the same part can be used.
Be sure to properly
select the PIC's configuration fuses before chip flashing. They should be
automatically set by the hex file, but it is always a good idea to verify
them. These fuses are managed by special settings within your chip programmer's
menus.
For example, the screen
shot on the right (click for larger view) shows how they may appear in your
hobby grade flash tool. The required fuse settings are summarized below:
|
Oscillator
(OSC): |
IntOSC GP4 |
|
Watch Dog (WDT):
|
Disabled |
|
Power Timer
(PWRT): |
Enabled |
|
MCLR (Master
Clear): |
Disabled |
|
Brown Out (BODEN):
|
Enabled |
|
Code Protect
(CP): |
Disabled |
|
Code Protect
Data (CPD): |
Disabled |
Warning:
If your chip programmer asks if you wish to use the OSC CAL value from the
hex file, then be sure to click the response that leaves the value alone.
If you use the data from the file it will over-write the factory stored CAL
data and the PIC will be rendered useless! You should also read this:
OSC cal data corruption work-around.
The required firmware
(hex file) that is needed to flash-program the PIC is provided at no charge
for personal/hobby use. This means that a R/C hobbyist can install
the firmware into their PIC, license-free. You are not allowed to do this
for others and you cannot sell the project. In other words, anyone
that wishes to offer a pre-programmed part (or a finished product), must
first contact the RC-CAM site for written
permission.
Sorry, but the text
based source code is NOT available.
Construction: It's Tool
Time!
There are two sets
of schematics for you to choose from. One shows the basic Landtastic design
that offers just the servo-slow feature. Only two components are needed;
the PIC and a capacitor. The second schematic shows the deluxe version, which
includes the optional Navigation Lighting and Lost Model Alert. This version
requires very few additional parts and is highly recommended. By the way,
you can pick and choose your options as you see fit -- you do not need to
install them all. The board's components are from
www.digikey.com and
the navigation lighting LED's are from
www.superbrightleds.com.
The circuitry can be built using nearly any technique you wish. Ours
was built on phenolic perfboard and point-to-point wired using 30 gauge insulated
Kynar wire (Radio Shack #278-502 white or #278-503 blue). I recommend a
temperature controlled 40 watt or less soldering iron (700° tip).
On the left you can
see the basic Landtastic circuit (no options). The cable connects to the
R/C receiver and the 3-pin header under it connects to the servo. The 2-pin
header on the right is used for configuring the Landtastic. Not shown is
a little jumper block that temporarily plugs into it to make feature setup
an easy task.
Perfboard layout is
not critical except that the C1 cap should be close to the PIC, which is
seen as the little yellow blob at the top end of the IC. If possible, use
a socket for the PIC chip (machine pine type is recommended).
If size and weight
are issues, you can skip the perfboard altogether. Instead, just solder the
parts directly to the IC socket. If weight is really an issue, skip the socket
too.
If you wish to use
any of the optional features, then perfboard or a custom PCB will be needed.
For example, the board on the right has the Tail Strobe and Landing Light
options on it. It only took two transistors and three resistors to complete
the job. The two SIP sockets at the lower right are used to connect the
navigational lights (high-lumen LED's), but you can hardwire yours if you
wish.
Adding the Lost Model
Alert requires just one more transistor and a tiny piezo buzzer. By the way,
the buzzer serves double duty. During system configuration, it will beep
special codes to indicate the setup/config status. This is very convenient
and highly recommended, but adding the buzzer is not mandatory.
The R1, R2, and R3 LED current limiting resistors show values for
the LED lamps that are specified. However, you may wish to use alternate
colors or intensities, so be prepared to optimize the resistors for your
chosen LED's. We created a handy online resistor calculator to make this
a painless effort. Please visit the RC-CAM
LED Calculator web page and follow the instructions. Valuable LED information
can be found there too.
The LED's are connected
to the board using appropriate lengths of small gauge wire. I highly recommend
using 30AWG Kynar (wrapping wire). Do not worry about the wire's small size
-- it will carry enough current for any LED that you may use.
Be careful how you
run the tail strobe LED wiring near your receiver's antenna. Some R/C
installations have antennas that run down the length of the fuselage or inside
the wings. This might be the same path that your LED wires need to travel.
The two will not get along unless you separate them by at least a couple
of inches. And to further reduce the chance of R/C receiver interference,
each LED's wire pair must be twisted along their entire length, about three
twists per inch. The schematic shows this as criss-crossed lines, so use
that as a reminder.
In
the rare case where servo glitching occurs at the strobe's blink interval,
you should try installing the optional C2 cap. Also helpful is a tiny ferrite
toroid core installed on the tail strobe's LED cable. The core must be installed
within one inch of Landtastic's circuitry. At least five wraps (more is better)
tightly threaded around the toroid core is all that is needed. Two likely
candidates are the the
(Electronic Goldmine
#G4357, 0.31" OD x 0.15" ID x 0.14"H) or the
Digi-Key
#P11364. The photo on the right shows an example of the Goldmine core
with five wrapped wires. It was not needed on our model.
For more information
on Navigational Lighting projects you might want to read the
RC-CAM Nav-Lights page. Perhaps
you'll pick up a tip or two from that project.
Let's Test Basic
Operation:
It's time to check
out your newly built board. Let's assume you built the deluxe version with
all the options. If your circuit is not using the extra features (Lighting
and/or Alert) then just skip the text that mentions them.
Please double check
your work, especially the wiring to the J1/P1 connectors and U1 pins 1 and
8. Simple mistakes can destroy electronic parts, servos, and may generally
ruin your day. If
any step fails, immediately remove power and check you work.
-
Plug J1 into your
receiver's gear channel and connect the servo to P1. Verify that the jumper
at P2 is NOT installed. If possible, remove the pushrod from the servo if
it is connected to your retract mechanics.
-
With the R/C Tx
(transmitter) turned off, turn on the Rx (receiver). After a short
delay, you should see the tail strobe slowing blink (20 to 30 beats/min)
and the piezo alert should beep at the same rate. This demonstrates the Lost
Model Alert feature.
Note: The Lost Model Alarm is not available when used with PCM
Rx's or those that have failsafe-like features (as seen on some of the new
"DSP" designs).
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Turn on the R/C
transmitter. After a moment, the beep should stop and the tail strobe should
go out. The servo may slightly jump, at full speed, as it initializes to
its home position.
-
Flip the Tx gear switch
to the other position. The servo should move, but at a speed that is much
slower than usual. If you watch closely you may notice that the servo's speed
slows even more at the end of the travel; the final little stepping is the
inertia brake. If the strobe light is not winking (double blink at about
50 beats/min), then flip the gear switch again. The landing lights should
turn on and off, depending on the switch position. Do not worry if the servo
direction or light control is reversed. We will take care of that in a
moment.
But First, a Word About Our
Sponsor:
With Landtastic, your
R/C transmitter's mix features are unaffected. Only the servo speed is changed.
So it is often more convenient to set up the retract mechanic's travel before
you install Landtastic. Once installed, you will need to configure it for
your desired travel speed, servo direction, and Tx switch's gear-down position.
We will fully explain how to do that in the next section.
The nice thing about
Landtastic is that it includes a servo reversing feature. This is handy to
have if your Tx does not include that on its Gear/Aux channel.
When you use the optional
landing lights and tail strobe options, a special Arming Feature is employed.
The lights will not be enabled until the Gear/Aux channel is put through
a simple initialization sequence (similar to motor ESC arming).
So, when you first
turn on the system ALL the lights will be off. This helps conserve battery
power while working in the pits.
Here is the proper
way to use the system when the lights are used (you can ignore this section
if they are not installed):
-
Set your Gear/Aux switch
to the "Gear Down" position. Turn on the R/C Tx, then turn on the R/C
Rx.
-
When you are nearly
ready to launch the model, hold the model off the ground (to protect the
retracts) and cycle the Gear/Aux switch at least one time.
-
The strobe light and
landing lights will now be operational.
-
Once airborne, flip
the retract switch to the "Gear Up" position. The landing lights will go
out as the landing gear retract. The anti-collision strobe will remain
on.
System Configuration: Have
it Your Way
At this point your
newly assembled board is ready to use. If you like the default five-second
retract time then no further action is required -- just install it and head
on out to the flying field. However, if you want to personalize the system
for your special needs, then we've got you covered!
The various operating
parameters are user-configureable. All it takes is your R/C transmitter and
a little jumper that is installed on Landtastic's P2 connector.
The configuration is
stored in the PIC's EEPROM memory. It is retained even if the battery is
disconnected. A one time setup is all that is necessary, but you can change
it as often as you would like.
You will need a servo
channel controlled by a variable stick or knob in order to enter the
configuration data. Sorry, but the simple on/off toggle switched channels
cannot be used for this. I suggest you borrow the elevator channel for the
task. Let's assume that is what you will use.
Before you get started,
you need to identify the native stick direction for both the Gear/Aux and
Elevator channels. With the Landtastic board removed, connect the retract
servo to the Rx. Set the Gear/Aux switch to the "Gear Down" position. Make
a mental note of the servo's position.
Now connect the same
servo to the Rx's elevator channel. Move the stick around to determine which
stick direction moves the servo {in the same direction} that represents the
Gear Down position. During the programming steps, when asked to move the
stick to the Gear Down (or Gear Up) positions, please use what was observed
here. To configure Landtastic, please follow these simple steps:
-
Connect Landtastic
to your R/C Rx's elevator channel and to the servo. Verify that the Tx's
elevator trim lever is centered and that dual rates, if present, are
disabled. If your Tx has adjustable travel volumes (EPA, T-ADJ, ATV) then
ensure they are at least at 100% (125% is best).
-
Install the jumper
on P2. With the Rx off, turn on the Tx and hold the stick in the extreme
"Gear Down" position.
-
With the Tx stick held
in position, turn on the Rx. If the piezo buzzer option is installed, you
will hear one or two beeps, depending on the stick's position (one beep for
normal stick direction, two beeps for inverted stick direction).
-
You have just told
Landtastic the Gear Down stick position. So far, so good.
-
You will now notice
that the servo is slowly moving back and forth. It is waiting for you to
enter in the servo travel speed. Just move the stick until you see the retract
speed that you like best. There are ten available speeds, from about one
second to a little over ten seconds.
-
Once the best speed
is found, hold the stick steady while you remove the jumper. A long beep
will be heard to indicate that the configuration data has been stored. You
can now move the stick around to watch the servo cheerfully use its new speed.
If you ever wish to change the speed and/or stick direction, then go back
to step 1.
When fast servo speeds
are used (under five seconds of travel time) an end-of-travel braking feature
is available. When enabled, it will slowly step the servo whenever it is
close to stopping. If you wish to change this (enable or disable it), then
follow these steps:
-
Continue with the setup
described above in step 1.
-
Turn off the Rx. Re-install
the jumper on P2.
-
Turn on the Tx. Hold
the Tx stick exactly at center position (a spring loaded stick's hands-off
position).
-
Turn on the Rx. You
will hear three or four beeps. Three beeps indicates that you are requesting
to turn the inertia brake on, four beeps means you want to turn the inertia
brake off.
-
If a piezo buzzer is
used, and an undesirable beep count is heard, then turn off the Rx's power
NOW and go to step 12 (this conveniently aborts the brake mode change).
Otherwise, continue with the update by leaving Rx power on.
-
Remove the jumper --
the brake programming is complete. Please note that this configuration feature
is a toggle function. Each time you fully complete steps 7-12 you will toggle
the inertia brake on and off. Please keep this in mind if you do not have
the piezo beeper installed.
Once you have re-installed
Landtastic on your Rx's Gear/Aux channel and connected the servo to the retract
mechanics, you need to verify proper servo direction. If you discover that
the servo direction is reversed, do NOT fix it by using the reversing function
found on your R/C Tx. Instead, you must configure the servo direction from
Landtastic. Please follow these steps:
-
Ensure the jumper is
removed from P2. Turn on the Tx and Rx.
-
Re-install the jumper
on P2. This will toggle the servo direction. You will hear five beeps or
six beeps, followed by silence. The servo will not move.
-
To enter the new servo
direction please go to step 16. To abort the change just turn off Rx power
and continue to the next step.
-
Remove the jumper and
confirm servo direction is correct.
File
Downloads: It's All in the Details
The technical details
are available as file downloads. There is no charge for the information when
used in a personal (hobby) project. Commercial users must obtain written
approval before use.
Please be aware that
the information is copyright protected, so you are not authorized to republish
it, distribute it, or sell it, in any form. If you wish to share it, please
do so only by providing a link to the RC-CAM site. You are granted permission
to post links to the web site's main page
(http://www.rc-cam.com/).
Please respect this simple request.
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Schematic
Files: CAD files for the circuitry. PDF Format.
Revision: A. Released
Jan-19-2004.
Jan-24-2004 Update:
Added drawing of 2N7000 pinout. |
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PIC Object
Code: Firmware (HEX file) for flash-programming the PIC chip. You should
occasionally check for updates.
Revision: V1.1. Released June-01-2005. |
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Instructions:
PDF file of the configuration instructions.
Released
Jan-19-2004. |
The Small Print:
If you need a part
then please consult the sources shown in the project (see schematics download).
I do not work for, nor represent, ANY supplier of the parts used in this
project. Any reference to a vendor is for your convenience and I do not endorse
or profit from any purchase that you make. You are free to use any parts
source that you wish. |
All information is
provided as-is. I do not offer any warranty on its suitability. That means
that if you build and use this device, you will do so at your own risk. If
you find software bugs then please report them to me. I can only make corrections
if I can replicate the bugs, so please give me enough details to allow me
to witness the trouble. |