Model Rocket Launcher WiFi ESP8266 Part 7

 Introduction 
This blog continues from Part 6 of the ‘Wi-Fi-controlled rocket launcher’ with a summary of board changes to suit an off-the-shelf enclosure and the addition to the circuit of a starter continuity check.

Updated Launcher PCB

Hardware Change
A hardware change was made to the output circuit to detect when an unfired starter is connected to the launcher output. One of the output drivers has a built-in diagnostic feature which sends the voltage at the device's output pin to a sense pin when the driver is switched OFF. By adding resistive pull-ups to the output driver, the starter's electrical continuity can be determined in most circumstances.

Output Resistive Pull-up Addition

Shorts across the output, failures in wiring or components on the circuit board are not taken into account.

Driver MSENSE Output

To test the proposed starter continuity solution on the current board, the ESP module was not fitted. The SENSE input on the VN7040 was connected to the onboard 3.3 V supply. This configures the driver in the desired mode.

An external 27 k pull-up resistor was added between the output and the 3.3 V supply. The low-driver input for the starter was then connected to the 3.3 V supply.

Testing Starter Continuity Solution

To validate the MSENSE output voltage, a test wire was connected to the MSENSE output and to a multimeter.

With no Estes starter fitted and the low driver switch ON, the voltage at the MSENSE output was 3.9 V. With a new Estes starter fitted, the voltage at the MSENSE output is close to 0 V. Using the onboard regulator, the voltage range will be suitable for the ESP Huzzah digital levels. Without the onboard 3.3 V regulator, the Huzzah's onboard regulator could be used.
The continuity measurement will be integrated into the code as a continuity check before a launch. It is acknowledged that a starter or shorted output results in the same measurement by the ESP.

For reference, a larger-value pull-up resistor on the output, such as 100 k, does not bias the output driver. No MSENSE output voltage is produced in this instance.
Note on Aerotech Starters
The Aerotech starters were tested on the bench with a power supply.

Aerotech Copperhead Igniter (Starter)

Using a power supply set to 8 V at 2 A, the starters will fire reliably. Applying that requirement to the launcher, two 4.2 V cells could be used in series on the launcher to fire the Aerotech starter. This was not confirmed through testing.

Circuit Board Update
As mentioned in the previous launcher post, an off-the-shelf enclosure will replace the 3D printed case. The Hammond Manufacturing part RP1135C or the Ritec RP1135 were two compatible enclosures. Choosing a wider enclosure provided more circuit board space and new layout options. Most of the surface-mount components were consolidated on one side of the circuit board.

Updated Launcher Design

Switch and External Cable
As two actions (a switch and the website launch button) must be realised for a launch to occur, the existing toggle switch arrangement will remain unchanged. For those desiring safety, a missile-style switch or a suitably rated keyswitch could be used instead. For the external cable interface, a gland will be used to maintain basic ingress protection.

In the next post, the new circuit board build and testing will be covered.

Model Rocket Launcher WiFi ESP8266 Part 6

Introduction 
This blog continues from Part 5 of the ‘Wi-Fi-controlled rocket launcher’, providing a summary of code changes, battery voltage measurements and an alternative idea for the launcher housing.

Launcher Screenshot (Firefox mobile)

Code Change
With 18650 batteries used in the updated launcher design, it was decided to add a basic battery voltage measurement on the served webpage. Voltage measurements are updated only when the user refreshes or presses a button on the mobile device. The WiFi code uses a PUSH/GET method or a request-reply action. The code could be updated to automatically refresh the page or implement a WebSocket solution, which would provide near-instantaneous battery voltage updates.

Battery Voltage
The refresh rate for the ESP ADC battery voltage input was set to 250 ms. To provide a reasonably accurate voltage measurement, the resistor divider and the forward voltage of the reverse polarity diode were included in the scaling factor. It should be noted that the accuracy of the ESP battery voltage will be impacted by differences in the diode forward voltage. During bench measurements, the error was less than 0.1 V for the voltage range 3.5 V to 5 V.

Battery Measurement with Engine Starters
To validate the battery voltage measurements, resistive dummy loads and several Estes starters were used.

Resistor as Load

Starter as Load

Standard Estes Starter

Tests will also be conducted with Aerotech starters in a future post.

The two graphs below show the battery voltage when the starters were initially operated in free air and then fitted to an Estes engine. A single, fully charged 18650 3200 mAh from Naccon was used for the duration of the testing.

The green trace in the plots below represents the actual time that the ESP provides power to the starter.

Battery Voltage with Starters (Free Air)

Battery Voltage with Starters (Installed in engine)

Launcher Case Update
When the original rocket launcher post was first published, model rocketry was still popular in my region, and model rocket engines were not restricted from sale. Due to changes in model rocket supply and to improve design accessibility for the wider community, it was decided in the next circuit board revision to change the launcher housing. An off-the-shelf ABS case will be used. Although this is a return to the original design, it should give more hobbyists access to the design.

Model Rocket Launcher WiFi ESP8266 Part 5

Introduction 
This short blog update continues from Part 4 of the ‘Wi-Fi-controlled rocket launcher’. A prototype design featuring 18650 batteries with the ESP modules was tested.

Rocket Launcher 3D Model

Design Change
As suggested in Part 3 of the blog, the design was updated to integrate two 18650 batteries onto the rocket launcher circuit board (PCB). The battery configuration can be set on the PCB to be either series or parallel using jumper resistors.

Dual Battery Series or Parallel Option

The linear regulator on the Adafruit ESP32 Huzzah board can accept up to an input of 6 V DC, meaning that an additional regulator was not required, depending on the battery configuration.

A fully charged 18650 battery is rated at 4.2 V, so the series battery resistor jumper option should be used with the optional DC-DC regulator. Using the DC-DC regulator should also allow very close to the full capacity of the battery to be utilised.

On the ESP32 Huzzah, the input to the linear is protected by a series diode. This series diode reduces the effective operating voltage of the battery by approximately 0.28 V. Depending on the battery manufacturer and the load current, the cell voltage could be around 3.4 V when the State of Charge (SoC) is between 0% to 10%. The dropout voltage of the ESP32 board may prevent full use of the cell capacity.

A pre-wired Multicomp part MCR13-36A2-11 was selected to replace the previous power switch.

Replacement Switch

Testing
The board was populated with the two output drivers, ESP mounting headers and the dual battery holder.

Bottom Side of Launcher PCB

The jumper resistors were configured for parallel operation. The optional 3.3 V DC-DC converter was not fitted. Since there were only small design changes, the board was powered first with a 3.3 V supply, then with a charged 1650 battery.

Top Side of Launcher PCB

It was noted that during testing with a fully charged battery, the ESP32 did not boot correctly. This issue was caused by GPIO 15. The Status LED is connected to GPIO 15, which is connected to the 3.3 V supply through a current-limiting resistor. A pull-up on GPIO 15 changes the ESP behaviour. To resolve the issue, the LED will be driven to 0 V on the revised design. A pulldown resistor already exists on the ESP board.

Other Changes
To measure the 18650 voltage, the onboard voltage divider values were adjusted to meet the ESP's maximum 1 V limit. The resistor footprint was standardised to 0603. This feature will be tested with the igniter in the next post.

Model Rocket Engine Test Stands

 Introduction 
This blog provides ideas and an example for 3D-printed metal rocket test stands designed to accommodate the popular Estes-sized model rocket engines.

Rocket Engine Holders

Why an Engine Test Stand?
To conduct rocket engine tests and measurements, a model rocket engine test stand was required. The stand was designed to serve as a motor anchor and mount on the horizontal axis. Since pricing from 3D metal printing companies has become more cost-effective, two stand designs were tried. Cost-reducing changes were implemented in the first revision test stands with a focus on reducing the printed weight.

Development and Manufacture
Autodesk’s tool, Fusion 360, was used in the development of the rocket engine holders. JLC3DP performed the 3D printing in stainless steel (BJ-316L). 

What Changes?
Since 3D printing can be charged by weight (or volume), and because the thrust axis of the rocket engine is well established, the side walls of the rocket engine stand were partially excluded. The exclusion (cutout) in the stand body, as depicted in the images below, reduced the weight by approximately half. Additional changes could be made to reduce the weight if the focus were on cost-effectiveness, and with that in mind, the CAD files are provided at the end of this post for download.

3D Printed Test Stand
The first test stand was a simple prototype for Estes A-C engines. Some engines did not fit entirely into the 3D-printed metal holder, while others were easily inserted. This was because there are variations in the diameter of rocket engines, and older engines may have expanded with age.

Model of Model Rocket D Engine Holder

Model of Model Rocket C Engine Holder

Some videos below show how the motor was mounted. As a side note, the exhaust temperature was measured at almost 600 C, 100 mm from the engine nozzle.

 

 

 

Downloads
Files are exported from Fusion 360.

Fusion 360 C Engine Holder Model

C Engine STL File

The D engine holder model below has a 0.5 mm larger bore than the model in the above videos.

Fusion 360 D Engine Holder Model

D Engine STL File

 

Model Rocket Launcher WiFi ESP8266 Part 4

Introduction 
This blog is a brief update following on from Part 3 of the ‘Wi-Fi-controlled rocket launcher’. A design to replace the lead-acid battery in the launcher was assembled. 

Some field shots of the updated launcher are provided at the end of the post.

18650 Replacement for Lead Acid Battery
A printed circuit board (PCB) with two 18650 batteries was designed to replace the 12 V lead-acid battery used by the launcher.

The operating voltage of the launchers' ESP32 controller and the output drivers is around 3.3 V, meaning the parts were suitable for operation with the 18650 voltage. However, the main DC-DC converter (LMR50410YFQDBV) would need to be changed or bypassed, as its operating voltage is 4 – 36 V. The standard operating voltage of a single 18650 cell drops below the 4 V threshold of the DC-DC converter.

The Keystone Electronics 18650 battery holder, part #1043, was chosen for the PCB design. When selecting parts in the initial PCB layout, two 1043 battery holders were more cost-effective than a double 1850 holder, Keystone part #1049. The Keystone double battery holder had become the cheaper option at the time of writing.

Dual 18650 on PCB

The dimensions of the PCB were made to fit into the existing 3D printed launcher case.

Dual 18650 PCB in 3D

After the PCB was manufactured, a single Keystone battery holder was fitted. For connection compatibility with the spade tabs on the lead acid battery, spade connections were fitted on the PCB using TE Connectivity part #60465-2. As can be seen in the image below, the spade connections were secured to the PCB with M3 mounting hardware.

Partially Populated 18650 Board

Out of curiosity, the DC-DC converter on the launcher was run from a single 18650. First, the previous voltage divider created by the resistor pack RP1 was removed. The shutdown input on the DC-DC converter (LMR50410YFQDBV) was then connected to the supply (VIN) with a 10 R resistor.

Existing DC-DC Converter Shutdown Circuit

 

Modified DC-DC Converter Shutdown Connection

Using a fully charged 18650, the launcher powers ON briefly. When the 18650 voltage drops below 4 V, the DC-DC converter fails to turn ON and the output voltage becomes unstable. Having the PCB with different 18650 connection options may be part of the next board review.

Field Tested Unit
The two launches below are taken from a recent rocket day.

PCB Artwork - Model Rocket

Introduction 
In this blog the circuit board tool, Altium Designer, was used to create circuit board artwork in the form of a model rocket keyring. The recent prototype of the Wi-Fi rocket launcher post inspired this blog.

Model Rocket Keyring

PCB Artwork
To start the project, a black-and-white image of the rocket keyring was downloaded from a suitable website. An image called SpaceShipOne was downloaded from CleanPNG (all credits).

Scaled Rocket Image (Courtesy CleanPNG)

The original image was scaled by 25% before importing into Altium. Shown below is the result of the import. As can be seen by the imported image, the image did not produce solid lines which was required for the keyring.

Imported Rocket Image

Rather than manipulating the PNG file for an improved import result within Altium, the outline of the imported PNG was drawn over with circuit board tracks (traces). For simple shapes such as the rocket, using Altium is relatively easy however many other packages could be used to achieve the same drawing.

Drafting Rocket Primitives

The image below shows the imported image and the hand-drawn image side by side. Minor changes can be noticed on the rocket fins compared to the original image.

Comparison of Hand Drawn and Imported Rocket Designs

One item not included in the circuit board file was the board outline. This is commonly added on a mechanical layer but this was not added to the design. It has been noted that many other free software tools are being used to create circuit board artwork. Therefore, with the alternative software in mind, the board manufacturer was asked to add a circuit board outline.

Manufacturing
For the circuit board manufacturing, the company JLCPCB was used. JLC included a board outline 0.1 mm from the circuit board trace. The final product is shown below.

Model Rocket Keyring

Download
For anyone interested in producing a keyring, the Gerber file pack is available below. A board outline should be spaced at least 0.1 mm from the outermost circuit board traces.

Rocket Keyring Gerbers

Model Rocket Launcher WiFi ESP8266 Part 3

Introduction 
This blog continues from Part 2 of the ‘Wi-Fi-controlled rocket launcher’. In this blog, the software changes to suit the ESP8266 are mentioned. Additionally, a mechanical 'proof of concept' for the rocket launcher is shown using a 3D-printed case.

Bench Test of Rocket Launcher

Code Change Summary
In the earlier version of the model rocket launcher design, a PSoC microcontroller with Bluetooth was selected for communications. When moving to the ESP8266, the Bluetooth communications interface was changed to a Wi-Fi interface. Using a Wi-Fi interface simplified the design when compared to developing in Android Studio.

To support a broader audience using the ESP8266, it was decided to perform software development using the Arduino platform.

/** *****************************************************************************
* @file   main.c
* @version 1.0b
* @date 10/02/2024
* @brief 
* 01/03/2023  Moved code from original PSoC version into Arduino
* 13/01/2024  Changed code operation, updated launch state machine
* 24/01/2024  Client connection issues noted during testing
* 10/02/2024  Code cleanup. Changed deprecated server.available() to server.accept()
****************************************************************************** */

#if !defined(ESP8266)
  #error For ESP8266. Check
      Tools->Board setting
#endif

/*_TIMERINTERRUPT_LOGLEVEL_ from 0 to 4 */
#define TIMER_INTERRUPT_DEBUG         1
#define _TIMERINTERRUPT_LOGLEVEL_     1
#define ENABLE_DEBUG_PRINTS           true
	

Most parts of the original code from the PSoC, including the launcher state machine, were either updated or rewritten. Code changes were needed for the ESP and targeted toward proper encapsulation.

ITimer.attachInterruptInterval(TIMER_INTERVAL_MS * 1000,TimerHandler);  /* 10 ms system timer */
      

Snippets and libraries from the Arduino community were included in the new launcher code. Specifically, credit goes to Khoi Hoang for Timer Interrupt examples and Martyn Currey for ESP Wi-Fi implementation.

How Software Was Developed
The code was developed using the Arduino IDE. Initial testing for the ESP code was performed using a Windows laptop for the Wi-Fi connection primarily to test the webpage interface. Testing subsequently progress to  an Android phone.

Shown in the image below is the first rocket launcher web page. Additional information such as battery voltage and launch state may be included on the web page in later updates.

Rocket Launcher Webpage

 

Launcher Case
After reviewing the previous enclosure and cost, it was decided to design a 3D-printable enclosure to house a small lead acid battery and a control board. The lead acid battery is only temporary and will be changed to an 18650-cell(s) capable of a high-discharge current.

For the 3D-printed case, two mechanical parts were drafted in Fusion 360. These parts comprised of a base and a lid as pictured below.

Rocket Launcher Case (Fusion 360)

 

Launcher Hardware Assembly
With the ESP code allowing the desired launch operation, the circuit board, wiring and battery were assembled and added to the 3D-printed case.

Rocket Launcher Test Assembly

During the assembly, it was noted that the pluggable circuit board headers, although simple to install and use, were expensive and consumed space. On the subsequent revision of the board, as displayed below, the pluggable headers were replaced with through-hole solder pads that suit a larger gauge wire.

Updated Launcher Board

Additionally, the toggle switch used for controlling the power was salvaged from another project. There are no manufacturer markings on the switch to generate a Bill of Materials. More clearance was added around the toggle switch body to suit other types of toggle switches such as the model shown below.

Standard Toggle Switch

Complete Test Assembly
For a bench test, a lamp was used as the igniter as pictured below. A short video of the operational launcher is exampled in the video.

The next post will feature the updated launcher circuit board and field testing.

Model Rocket Launcher WiFi ESP8266 Part 2

Introduction 
This blog continues from Part 1 of the WiFi-controlled rocket launcher. In this short post, load testing was performed on the igniter's power supply and the output drivers.

WiFi Rocket Launcher Blank PCB

Power Supply
The DC-DC converter, Texas Instruments part LMR50410, was tested for switch ON voltage threshold and response. Since the converter powers an ESP module and output drivers for the igniter, the load current test was set for 300 mA.

Power Supply Portion of Rocket Launcher

An external power supply was connected to the launcher board. The voltage was increased in increments of 100 mV until the converter activated. For this board, the threshold was 4.1 V. The output switch ON waveform is shown below.

Rocket Launcher Power Supply Supply Turn ON

A resistive load resulting in 330 mA was connected to the 3.3 V supply for testing. The output voltage dropped from 3.3 V to 3.28 V when the load was connected.

Rocket Launcher Power Supply Supply Transient Response

The transient response for the power supply was measured for a 50 % load change. Captured in the image above is the response showing a recovery time of less than 200 ns for the supply voltage to settle back to 50 mV.

Output Drivers
The output driver circuit design had been established from the previous version of the launcher circuit board, which meant the operation was already known.

Rocket Launcher Output Driver Load Testing

To test the output drivers on this board, a 5 Ω resistive load was used. The two output drivers were powered with 12 V to simulate the primary power source. Using the 3.3 V from the converter, the two drivers were activated.
V(supply) = 11.92 at drivers no load, V(supply) reduced 11.79 V with approximately 2.3 A load current because of cable losses.

Measurements were taken with 2.3 A of load current
V(load) = 11.19 V
V(diode) = 401 mV
V(high side driver) = 102 mV
V(low end driver) = 124 mV

In part 3, the code for the rocket launcher will be started in Arduino IDE.

Model Rocket Launcher WiFi ESP8266

Introduction
This blog follows the redesign and development of a model rocket launcher controller that features WiFi communications to control the launch process. This design uses an ESP-based microcontroller module. The Arduino platform was chosen for code development.

Rocket Launcher 3D Model

Redesign
To control the launch in the previous model rocket launcher design, Bluetooth communications were used between a PSoC microcontroller and an Android phone. The interface was changed to WiFi to remove the need for developing a phone application. Controlling a rocket launch through WiFi would be independent of a phone or computer operating system.

WiFi Module
For the launcher redesign, an off-the-shelf ESP module capable of WiFi was chosen from Adafruit. The ESP module was chosen for a few reasons. Firstly, the module’s price was relatively low (USD 10). The module was readily available compared to other dedicated microcontrollers. Lastly, using an ESP module meant that the rocket launcher design could be migrated more easily to other ESP devices.

Adafruit Huzzah ID 2471 (Courtesy Adafruit)

Reused Design
The same section of circuit responsible for driving the rocket engine igniter was taken from the previous design. This section consisted of high (VN7040) and low-side (VNL5030) switching drivers (ST Microelectronics).

Rocket Launcher Igniter Drive Circuit

Circuit Updates
To begin the schematic update process, the ESP module was created in the schematic libraries. The new part replaced the previous PSoC microcontroller and associated circuitry.

The Altium PCB model was downloaded from the website SnapEDA.

Capture of Adafruit Huzzah PCB Footprint from SnapEDA

Schematic Updates
On the ESP module schematic page, the power supply connections and ST driver control signals were mapped to the ESP.

Rocket Launcher - Huzzah Circuit Connections

Audible notification of an impending launch was retained using the buzzer. Connections were mapped to the ESP.

Rocket Launcher - Buzzer

The display (LCD) was infrequently used in the previous design so it was removed and replaced with an LED.

The launch button input to the ESP module was retained for testing purposes.

Rocket Launcher - Optional Launch Button

Connections were made to ESP module pins that had no special functions.
 
Output Drivers
Schematic changes were made to the ST output driver’s power supply. This was required to match the ESP module’s DC 3.3 V supply voltage. The feedback monitoring from the ST drivers was removed from the design because of the reliable performance of the ST drivers.

Power Supply
A DC-DC step-down converter was retained for the power supply. Texas Instruments part LMR50410 featuring an integrated diode was selected to replace the previous DC-DC converter.

Another benefit of the DC-DC converter is its operating voltage which is wider than the ESP modules linear regulator (LDO). The LDO has a maximum rated input voltage of DC 6 V. This voltage does not suit all battery chemistry types.

Rocket Launcher - Power Supply

Battery voltage monitoring using the ADC on the ESP through a resistor divider was kept for experimentation and possible future use.

Circuit Board
There were no caveats defined for the shape of the circuit board (PCB). The placement of components drove the PCB shape. Minimal design constraints for the PCB meant that the PCB was set up for components on both sides.

The capture below shows the PCB top layer with the ESP module, power supply underneath the ESP module, buzzer and optional screw terminals. To fit the power supply beneath the ESP module, pluggable headers were utilised to space the ESP module off the board.

Rocket Launcher PCB - Top Layer

The next capture below shows the PCB bottom layer containing the output switching drivers and related components.

Rocket Launcher PCB - Bottom Layer

Four PCB layers were used for the launcher board stack-up. Captures of the two internal power planes have not been shown.

After component placement and routing, the board size reached a comfortable size of 62 x 44 mm. On the longest PCB axis, a set of 3 mm strips were added to suit mounting in an enclosure. Pictured below is a 3D side and rear view of the board.

Rocket Launcher - 3D Side View

Rocket Launcher - 3D Rear View

In part 2 of the launcher blog, the PCB construction and initial testing will be performed.