Monday, March 20, 2017

Nerf - or knocking over water bottles with foam...

So I got into nerf blasters recently. For me that means not only getting a blaster and darts but looking at ways to increase potential. How can I make it fire darts faster and more accurately.

It's a nice way to unwind, and leave any workstress behind. I'm sure some view an actual firing range as perfect for this - but for me, knocking over empty Poland Springs water bottles in the comfort of my living room is perfect 😁. That's really all I'm doing - knocking over a row of water bottles.

There's various types of mechanisms for launching darts. Spring based blasters force a piston down a tube compressing air quickly forcing a dart from a barrel. Flywheel based blasters use two spinning flywheels to project a dart. Air blasters build up air in a chamber, usually by pumping - and then eject the air all at once.

I started with buying a few spring based blasters. There's no spinup time like electric blasters, and while compressed air blasters are the most powerful, I haven't seen that many. They're there, but really require modding to bring out their full potential.

One of the first blasters I went for was the above hammershot. Painted it, changed the spring, added a spacer for tension, sealed the plunger tube spaces better. A little tape for a tighter o-ring fit, and alternate 7 shot brass barrel from ebay. For comfort, I added the tennis racket handle wrap. Nice one handed blaster - but not quite powerful to really aim accurately.

Here's how The spacer was created - A roll of paper and 3d pen. A 3d pen is like the end tip of a 3d printer - but controlled by your hand.

The spacer keep the spring under more tension, meaning more force and faster compression in the plunger tube. The roll of paper keeps the spacer hollow for the orange guide rod to pass.

While I was very pleased with the handling and look of the hammershot,I wasn't content with the performance. I also think that with a stronger spring than I was already using I'd break it. I picked up a cycloneshock next. The cycloneshock is another revolver but uses larger darts. By using a barrel mod, It fires the regular sized darts much much harder than other blasters. an extra spring at the back from another blaster and you're getting.

From searching forums, one of the weakpoints of the cycloneshock is the plunger rod where the springs push against. 3D pen to the rescue. Some grinding later and it fits perfectly while keeping the rod from bending.

After modding these of course I had to try building my own.

Turns out pneumatics are really interesting. Compressed air can do so much. Here's the gist. Using a pump - like a bike pump, to send air through one type of valve - a Quick Exhaust Valve, the air gets stored in a "tank". When ready to fire, lowering the pressure on the side of the QEV where it's getting pumped causes all the air to rush out from the tank. It's more efficient than using a regular switch, since as the switch is opening, the rate of exhaust starts slow. With the QEV, the air flow hits maximum almost immediately.

The basics of the QEV can be seen below.

Since the pump and release valve are at the same port on the QEV, a tee fitting works fine there. At the start, the release valve is closed. As you pump, the QEV directs air to the tank. The system pressure builds. the air between the pump, through the tee, through the QEV and in the tank is all the same pressure. When firing, the release valve opens and air rushes from the tee. As air starts flowing from the tank to the tee, it trips the QEV exhaust valve, and instead rushes out to the barrel.

Putting this into practice isn't quite as hard as you may think. I definitely overbuilt my first blaster, with too large a tank, too high a pressure potential, and too much space between the release valve and QEV. The release valve does "waste" a little air to create the low pressure for the QEV - but it's miniscule in proportion to the air in the tank - it's the air between the pump and QEV that will rush out. In  my build I redirect it to the back of the barrel - bit pointless since it's not going to add any extra performance really.

How hard can this overbuilt steampunkish blaster hit?

Really. Freaking. Hard.

Next up - make a spring based blaster and another air powered one that's more comfortable and practical. Perhaps design a barrel that can take a standard nerf magazine for reloading...

Monday, September 26, 2016

Odroid XU4 - My new NAS

Few thoughts on ARM:

ARM has been kicking ass and taking names for several years now. It's no surprise that other companies would want to acquire it - Japanese company SoftBank finished it's acquisition of ARM a couple days ago, at an astonishing $32 Billion.

ARM doesn't make anything physically - but they do create CPU designs and license them. ARM based processors are found everywhere today - in cameras, routers, smart TV, cellphones, game consoles, laptops, even servers.

For ARM based servers, the goal is energy efficiency where raw performance is secondary. Rarely would one look at arm over the standard x86 and consider it for a performance advantage. Even newer Atom processors (though the line is effectively dead *supposedly?*) is generally more powerful.

There are many use cases where processing power isn't quite necessary though. When I/O is the bottleneck, or where we need reliability, or need to keep a server running with little power, the importance of fast processors is far less. In multiprocessing environments, where a few heavy CPU bound processes can stymie a fast processor with low core count, a slower processor with high core count can still stay operational, letting a user do whatever else they may need to do.

On the Odroid-xu4:

A good use case would be a webserver, file storage or network cache system (memcached, cachewho [my own thing...]), home automation server. For my own purchase of an Odroid-xu4, I am using it as a NAS, with minor web/development jobs.

Here's the specs on the little bugger:

CPU     : Samsung Exynos 5422 (2GHz Cortex A15 x4 + 1.3GHz Cortex A7 x4)
RAM     : 2GB LPDDR3, 933MHz (16bit interface, 14.9 GBps bandwidth)
GPU     : Mali-T628
Video   : HDMI (standard type-A), 1080p capable
Audio   : HDMI, i2s (no audio jack)
USB3.0  : 2 ports
USB2.0  : 1 port
Storage : EMMC, Micro-SD
Network : RJ-45, Gigabit Ethernet
GPIO    : 30pin + 12pin section (i2s, i2c, spi, ADC etc.)

Possible uses:
HTPC - video out via HDMI means this is a compact way to create an HTPC system. various operating systems are supported - several Linux distributions, and even Android.
NAS - Standard Linux isn't too hard to turn into a NAS, but there's also dedicated storage distros like Open Media Vault.
Web Server - Python, Ruby, Apache, Nginx, PHP, Node - loads of ways to get a web app running here.
Media Streaming - Plex can turn this into a media streaming server.
Home Automation - Much in the same manner as a Raspberry PI can be used. This is probably a little less optimal, since the extra power over a Raspberry PI isn't really needed.
Robotics - GPIO pins can communicate with servo boards and arduinos and other devices giving control over mechanical parts, input for sensors, and the device of course packs a lot of processing capability.

The advantages of this over an x86 device:

Cost - $80 + SD card ($10?). x86 devices are quite cheap if you go with Atom, though not quite at this level. If you do find one, it's usually not a complete system, or lacks USB 3.0/gigabit ethernet.
Noise - very quiet fan, optional no noise case. Not really much of an advantage over Atom which doesn't need a fan in many cases either.
Size - while there ARE Intel Stick PC devices, they are lacking some connectivity - often USB3.0 and/or Gigabit Ethernet. The combination of these is necessary for a decent NAS, or any server where you want fast transfers. Looking at devices that offer USB3.0/Gigabit Ethernet means lots more money.

NB: recent SolidRun board can give this a run for its money, though it's more expensive, with some options at several times the price.

Why Odroid-xu4? Why not a Raspberry PI which has more community support?

I'm making a huge deal about Gigabit Ethernet and USB3.0 over the usual USB2.0 and 10/100Mbps Ethernet, because it's quite relevant to current media types.

A Raspberry Pi 3 is a powerful device for it's size and cost being the same credit-card size as the XU4 with a retail value of $40. It has a solid quad core CPU, but USB2.0 and 100Mbps Ethernet. It's certainly usable for a storage server, but reading from a disk would be limited to the slowest speed in the chain - 12.5MBps. That's mind numbingly slow when you're syncing a terabyte or six. 

For perspective, lets consider how different bandwidths handle 1 TB of data:

│    Interface    │       Bandwidth      Time/TB  
│"Fast" Ethernet  │  12.5MB per second 0.97 days
USB2.0           │  60MB   per second  4hr 51.3m │
Gigabit Ethernet │ 125MB   per second  2hr 20m   │
USB3.0           │ 625MB   per second  28m       │

While you won't always need to sync terabytes of information, you will be concerned with hundreds of gigabytes. Easily happens when you're getting back from holiday and took a lot of RAW images and uncompressed video. Of course you cannot expect these speeds - the harddrive itself has a limit. Of course when you're syncing from one external drive to another external drive (as is my plan) you're looking at half the bandwidth in the best case - the same bus handles reading from one drive and writing to the other. So that seemingly acceptable 12.5MBps drops to just over 6MBps - and we're assuming maximum theoretical speeds. With the USB3.0 speeds, I can comfortably sync one drive to another and not take much of a hit - I'd most likely bottleneck near the maximum write speed of my drive.

To NTFS or not to NTFS....

Assuming I use the Odroid-xu4 for a LAN, what filesystem to use? NTFS is relatively limited compared to EXT4. The primary concern was the extra CPU utilization that NTFS would take over EXT4, however NTFS will be compatible with my other computers/laptop. My initial sync was over USB anyway directly connected to the windows machine that currently holds my library - so NTFS, purely for compatibility sake.


I got the OpenMediaVault image from here.

Win32diskimager can put the ISO on an SD card.

From there that's it. Put the card in the mini server and boot up. No need for a directly connected mouse and keyboard, just ssh into it, or use the web interface. For most things NAS related, the web interface will suffice.

So you can make users, shared on connected drives, mount/unmount the drives, make users, cronjobs etc. 

I also came across this blog here

which was invaluable in configuring the NTFS drives for better performance:

Use on demand CPU governor -

in: /etc/default/openmediavault
 omv-mkconf cpufrequtils
 update-rc.d cpufrequtils defaults

CPU governor tuning:

 apt-get install sysfsutils

in: /etc/sysfs.conf

 # cpu0 sets cpu[0-3], cpu4 sets cpu[4-7]
 devices/system/cpu/cpu0/cpufreq/ondemand/io_is_busy = 1
 devices/system/cpu/cpu4/cpufreq/ondemand/io_is_busy = 1 
 devices/system/cpu/cpu0/cpufreq/ondemand/sampling_down_factor = 10
 devices/system/cpu/cpu4/cpufreq/ondemand/sampling_down_factor = 10
 devices/system/cpu/cpu0/cpufreq/ondemand/up_threshold = 80
 devices/system/cpu/cpu4/cpufreq/ondemand/up_threshold = 80


 cpufreq-set -g ondemand -c 0
 cpufreq-set -g ondemand -c 4
 service sysfsutils start

NTFS mount options:

in: /etc/default/openmediavault

I strongly suggest you read the original link at Obihörnchen's blog to understand what each command does.

Drive performance:

root@odroid:~/major# dd if=/dev/zero of=./testfile bs=1000M count=1 oflag=direct

1+0 records in
1+0 records out
1048576000 bytes (1.0 GB) copied, 12.7106 s, 82.5 MB/s
root@odroid:~/major# dd if=/dev/zero of=./testfile bs=1000M count=1 oflag=direct
1+0 records in
1+0 records out
1048576000 bytes (1.0 GB) copied, 12.6035 s, 83.2 MB/s

Getting over 80MBps write - that's much better than I was expecting.

root@odroid:~/major# dd if=./testfile of=/dev/null bs=1000M count=1
1+0 records in
1+0 records out
1048576000 bytes (1.0 GB) copied, 11.272 s, 93.0 MB/s
root@odroid:~/major# dd if=./testfile of=/dev/null bs=1000M count=1
1+0 records in
1+0 records out
1048576000 bytes (1.0 GB) copied, 11.313 s, 92.7 MB/s

Getting over 90MBps read - again a really decent result for a single disk.

My understanding is the drive I'm using (Western Digital RED 6TB should handle double that - 175MB/s read/write - and it's possible I might achieve that with EXT4 on this same platform. More testing is needed when I purchase another drive. For now, I'll enjoy the speeds that are near the maximum of the interface, and easily faster than my AC Wifi provides.

The drive I'm currently using will be accompanied by a few more later. This is achieved by using an external 4-bay harddrive enclosure.
Next to the Odroid, this stack of drive bays looks huge. It isn't :D
This is a Vantec HX4R.

Bays lock in place with a clip. The enclosure supports SATA and USB3.0, and from the sticker you can also see RAID settings - 0, 1, 0+1, 5 JBOD - and in the way I use it, just as a hub for all drives. That top drive is a drive I removed all drive parts and interfaces from. It's just a shell - holding some screws for the other bays but makes for a good hidden storage unit.


These benchmarks were taken using the on demand CPU governor configuration described. I've compared it against my laptop, and desktop.

Desktop: Core i5 2400 (Sandy Bridge), 16GB RAM

Laptop: Celeron N2940 (BayTrail-m), 8GB RAM
Odroid-XU4: Exynos 5422, 2GB RAM

It's interesting noting the specifications of these:


█    CPU        █  Power?             █ Cores  Frequency intro 
 Core i5 2400  █  95W TDP            █ 4      3.1-3.4   █ 2011  
Celeron N2940 █ 7.5W/4.5W TDP/SDP   █ 4      1.83-2.252014  
Exynos 5422   █ 10W/14W max CPU/GPU █ 8      2.0/1.3   █ 2015  

While it may seem that the Exynos 5422 is a higher watt CPU, this was achieved from tests from the odroid forum. Typically the entire system hovers at a wattage my laptop's processor will only dream of. There's further tweaks that lower power too - such as down clocking the GPU to reduce power as a server even more. It should also be noted, the Thermal Design Power (TDP) and Scenario Design Power (SDP). The Intel-AMD war brought in marketing departments that spread BS over these numbers. TDP was the rating the silicone was designed to handle. SDP was a typical workload. Nothing really was equal in comparing AMD and Intel CPUs that stated these. 

The power supply for the odroid system is 5 Volts, 4 Amps. That's 20 Watts. Consider that in several cases here, the GPU is also adding to power consumption:

Either way you compare the Baytrail Celeron against the Exynos 5422, the Core i5 is sorely out of place. The question is is the performance also that far out there, or do the lower powered processors give it a disadvantage in efficiency?

I ran each test a several times to get 3 close results, and kept the middle.

|               | Odroid-Xu4 | Baytrail Laptop | i5 Desktop |
| Mencoder      |    3148    |     2478        |    795     |
| p7zip (text)  |    7.342   |     6.708       |    2.675   |
| p7zip (video) |    174     |     143         |    32      |
ImageMagick   |            |                 |            |
Apache bench  |            |                 |            |

It's apparent that the i5 desktop is several times faster - but maybe it's not fast enough. This CPU power can jump over 70Watts when under heavy load. That puts it at least 10 times the power of the other CPUs. It's really interesting the see the large difference in 7zip on data that can't be compressed well (video) compared to data that compresses a lot (text). My laptop's CPU is never that far ahead of the Xu4 either. Expect laptops with ARM to gain in popularity (there's already Chromebooks and Android). Especially with the Atom line no longer available for that purpose.

Friday, September 9, 2016

Arduino is fun - great for custom Radio Control signal handling

I've been having some fun with arduino. They're quite cheap boards, with arduino nano coming in at ~$3 per board. That's $3 - THREE. That's pretty awesome for a small amount of custom processing power. Unlike a board like the Raspberry PI which has to run a full Linux kernel, this just runs whatever script you write. As such, the timings are very consistent - it's excellent for handling servo PWN signals where you need to measure pulses from ~1000-2000 microseconds accurately. From my experience the resolution was 4μs.

This makes it excellent for managing radiocontrol PWM signals in complex RC vehicles. 

That wrapped up red component in my latest RC vehicle (another hobby, I build RC cars...) is an arduino that reads in steering and another channel and processes it to output a new signal that lets me choose if I want the truck to have 4 wheel steering, or crabwalk (both wheels point the same way making it go mostly sideways).

Definitely one of the more interesting vehicles I've built, and a decent summer project (though I did start last year wrecking the transmission pushing myself in a chair). 

This actually started out with me receiving a non-working unit for handling quadsteer that I had purchased on amazon. When using the unit, the servos lacked power, wouldn't center, and were slow. I used an oscilloscope to diagnose the signal and saw the pulses were 40 milliseconds apart. For Radio control PWM signals, the leading edge should be 20 milliseconds apart. What was essentially happening was the server would get a signal and act on it for 20 milliseconds, and then not do anything for the next 20 milliseconds.

So I turned to arduino nano in the hopes to making my own. Below I've setup that arduino nano on the breadboard to mix signals as I'd like. Each square on the oscilloscope is 10 ms, so my working prototype is showing the proper waveform. This is what was wrapped up in electrical tape in the first picture.

Below is the code I wrote to handle this. The idea is to read two channels - the steering and a spare channel to know if to invert the steering between front and rear. Since I'm reading the time of the pulse, I need a little math to normalize 1000-2000μs to -1 to 1 and back again. This lets me multiply the channels so I can then smoothly transition between crabwalk/quadsteer. 

Should be noted we're using interrupts to gather input channel data. This is a non-blocking method for gathering the input. I just requires us to determine the time of the pulse by subtracting the time the clock had at the signal's leading edge.

#include <Servo.h> 

volatile unsigned long leadingedge1;
volatile unsigned long leadingedge2;
volatile int pulsetime1; 
volatile int pulsetime2;

//declare servo pins
int servoin1  = 2; // pin 2 - steering
int servoin2  = 3; // pin 3 - inversion channel
int servoout1 = 9; // output read servo is pin 9, front is pin 2
Servo rearservo;

int ch1_1=1500; //last 3 values are stored
int ch1_2=1500;
int ch1_3=1500;

int ch2_1=1500;
int ch2_2=1500;
int ch2_3=1500;

int execute=0;

void setup()
  pinMode(servoin1, INPUT);      // sets the digital pin 1 as input
  pinMode(servoin2, INPUT);      // sets the digital pin 1 as input
  pinMode(servoout1, OUTPUT);    // sets the digital pin 9 as output
  pinMode(servoout2, OUTPUT);    // sets the digital pin 9 as output
  leadingedge1 = 0;
  leadingedge2 = 0;
  pulsetime1 = 1500;
  pulsetime2 = 1500;
  attachInterrupt(0, chan1in1, CHANGE);
  attachInterrupt(1, chan1in2, CHANGE);
 // Serial.begin(115200);        // for debugging

int mmode(int a,int b,int c){ //extremely basic meant to rid spikes from interference.
  int d=(a+b+c)/3;            //either return mode, or average of last 3 values
  if (a == b){
  } else {
    if (a == c){
    } else {
      if (b == c){
  return d;

void dostuff(){
  long product = 1500+((((long)pulsetime1-1500)*((long)pulsetime2-1500))/450);
  // dividing by 500 would be more exact, but this gives a little extra turn
if (product > 2200) { product=2200; } else { if (product < 800) { product=800; } } /* Serial.print("P1.");   Serial.print(pulsetime1);   Serial.print("--P2.");   Serial.print(pulsetime2);   Serial.print("--x.");   Serial.print(product);   Serial.println("--T."); */ rearservo.writeMicroseconds(product); } void chan1in1() { if(digitalRead(servoin1) == HIGH) { leadingedge1 = micros(); } else { if(leadingedge1 > 0) {
      pulsetime1 = ((volatile int)micros() - leadingedge1)-24;
      //24 us added from other operations? center needed normalizing to 1500
if ((pulsetime1>800)&(pulsetime1<2200)){ leadingedge1 = 0; ch1_3=ch1_2; ch1_2=ch1_1; ch1_1=pulsetime1; } pulsetime1=mmode(ch1_1,ch1_2,ch1_3); execute=1; } } } void chan1in2() { if(digitalRead(servoin2) == HIGH) { leadingedge2 = micros(); } else { if(leadingedge2 > 0) { pulsetime2 = ((volatile int)micros() - leadingedge2)-24; if ((pulsetime2>800)&(pulsetime2<2200)){ leadingedge2 = 0; ch2_3=ch2_2; ch2_2=ch2_1; ch2_1=pulsetime2; } pulsetime2=mmode(ch2_1,ch2_2,ch2_3); } } } void loop() { delay(3); //delay is non blocking if (execute==1) { delay(3); noInterrupts();
    dostuff();  //do stuff after the receiver has sent all pulses
    //technically we're using the receiver clock to time when we process data.
interrupts(); } }