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June 18, 2011 

Quick-start instructions for the ServoChron™.

The ServoChron™ is a low cost time delayed single/dual servo controller designed for use as a parachute deployment or staging mechanism for Water Rockets. There are other potential applications for the ServoChron™ as well.

If you are looking at the ServoChron, you may be interested in building the successor project, the LaunchPad AlTImeter. The Model Rocket Altimeter that you build yourself. Just go to the link AlTImeter/manual.htm to find out more about this new project!

The core of the ServoChron™ is the Texas Instruments MSP430 LaunchPad. This $4.30US board is an inexpensive microcontroller hobbyist experimenting platform that you load our FREE application firmware into with a USB cable. The FREE ServoChron™ Firmware file created by U.S. Water Rockets turns the MSP430 LaunchPad into a user programmable dual servo deployment system timer/controller.

The custom firmware acts as a timer and servomotor driver which monitors a trigger switch and individually actuates two separate servo motors when a preconfigured delay time for each has elapsed following the trigger condition. You can use any switch you prefer as a trigger, or use a simple 'break wire' method. If you are interested in saving weight, you can utilize the custom launch detect switch described in [Launch detect switch tutorial].

The trigger switch detects the launch of the Water Rocket and the timer delay is set to the predicted time to reach apogee. One servomotor usually is used to deploy a small drogue parachute at apogee, and the second servo motor is used to deploy a larger main parachute some time later. This arrangement allows the rocket to quickly but controllably descend on the drogue parachute closer to the ground, where the larger parachute takes over and slows the final portion of descent to a rate which minimizes the chance of damage to the rocket upon landing. This arrangement is designed to prevent the rocket from drifting far from the launch area due to winds by reducing the time spend descending, but still providing a gentle landing. Another application commonly requiring dual servos is to deploy two independent parachute systems at apogee for redundancy. There are limitless applications to explore.

[Click to enlarge] The ServoChron™ is a low cost servo timer and controller for Water Rocket Parachute Deployment..

[Gallery] Click the image above to view more images.

ServoChron™ 2 Features:

• Total Dual Servo Deploy System cost under $13.00US
• Dual servo control
• Built on ultra-affordable MSP430 LaunchPad Platform ($4.30)
• Operates on 3.7V-6.0V DC. You may use various power sources notably a single lightweight Lithium Polymer rechargeable cell.
• User defined servo positions for each servo
• User programmable delay for each servo from 0.000 to 30.000 seconds in 1 millisecond increments
• USB Firmware update (with included cable! No special programming hardware to buy!)
• Edge sensitive trigger input with automatic polarity detect
• Trigger input capable of sensing contact open or close events shorter than 10 nanoseconds
• Innovative 2-button operator interface with easy to remember setup
• 3 Status LED's
• UART (Serial) diagnostics mode
• Dimensions: 2.0 x 2.6 inches (50.80 x 66.04 mm)
• Weight : 0.635 oz (18 grams)
• Includes testing and arming operational modes
• Fully RoHS compliant. Contains legal levels of lead and hazardous materials

Purchasing information:

The ServoChron™ firmware costs NOTHING. You will need to purchase your own MSP430 LaunchPad board, servos, and battery. See the assembly section of the
ServoChron™ Manual
for full parts list and prices. The total Bill of Materials for a complete dual deploy system, assembled, and ready to fly will be approximately $12.90US.

The following steps are the quick-start instructions for the ServoChron™. Please Download the
ServoChron™ Manual
for the complete documentation and assembly instructions.

Step 1: Get the parts:

Purchase the components for your deploy system. The
ServoChron™ Manual
has links to suppliers for these components.

1 MSP-EXP430G2 MSP430 LaunchPad Value Line Development kit
1 T1601S-30 Turnigy 160mAh 1S 130C Lithium Polymer Cell
1 HK9727 Mini Plug Extension for Micro Battery
2 HK9710 JR Type Servo Extension 10CM Servo Lead
2 HXT1500 9g / 1.6kg / .12sec Micro Servo

We were able to purchase the necessary parts for under $13.00 for this tutorial

[Photo Gallery]

Step 2: Get the FREE software and manual:

Download the FREE software packages used in this tutorial. The ServoChron™ User Manual has links to the software you will download.

Elprotronics FET-Pro430 Lite (from

ServoChron™ project Firmware file (from

User Manual File (from
ServoChron™ Manual

[Photo Gallery]

Step 3: Solder the Battery connector:

Solder a battery extension lead to the test points near the USB connector on the MSP430 LaunchPad. This is where the battery will connect when the USB cable is unplugged. Caution: Do not connect a battery and USB power source at the same time. This could damage the battery, or your computer.

[Photo Gallery]

Step 4: Solder the servos:

Solder the servo extension leads to the test points on the MSP430 LaunchPad. Each lead has 3 wires. A control wire which is typically white or orange, a power lead which is usually red, and a ground lead which is usually black or brown. The power leads of the two servos and ground leads of the two servos will connect to the same test points as the power and ground leads of the battery. The control leads of the servos go to the test points marked 'P1.4' for Servo 'A' and 'P1.5' for Servo 'B'.

[Photo Gallery]

Step 5: Connect a Launch Detect System:

Solder a wire to the test point marked 'GND', and another wire to the test point marked 'P1.7'. These wires will connect to a switch that will open or close when the rocket launches, or a simple breakaway wire that will disconnect when the rocket launches.

[Photo Gallery]

Step 6: Build a deploy system for your servos:

There are a vast number of schemes for deploying a parachute with a servo available on the internet. You can either use an existing design, or think of a new design you can call your own. Be creative.

[Photo Gallery]

Step 7: Configure the ServoChron™ 2:

The user manual contains detailed instructions for loading the firmware into the ServoChron™ 2. The manual also explains how to set up the servo timers and positions as well as troubleshooting/error codes. Please read the directions in the manual to configure the settings.

[Photo Gallery]

Step 8: Finishing:

Your ServoChron™ 2 is complete and ready to launch! We hope you enjoy this low cost timer and experience many safe landings.

[Photo Gallery]

Creative Commons License ServoChron™ Tutorial by U.S. Water Rockets is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.
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