Tuesday, April 18, 2017

Raspberry Pi Plant Watering System

Here's what I've been working on at Infusion lately: documenting the Raspberry Pi based plant watering system that measures the moisture content of the soil and triggers a relay-driven valve to water the plant:

Control software was built using node-red, with a FRED endpoint to talk to the cloud-hosted node-red instance that allows a public dashboard to be displayed (public dashboard available here).

One of the awesome things about node-red is that you can easily view the dashboard from a browser, and with FRED you can access it anywhere:

Detailed hardware and software write-ups on the PiShield site.

Saturday, April 08, 2017

Cheapest Brushed Tricopter Ever? [Detailed Part 1]

What started off as a mental exercise turned into an actual implementation of not the first, but perhaps cheapest possible brushed tricopter in existence that I'm aware of. An overview of the list of parts and some sample flights are available in this previous post.

Quick Intro

Before starting, there are some existing work including this one which basically describes the entire idea, but requires a very well made yet somewhat $$ Multiflite Pico flight controller. Since this was purely a casual exercise and I've already spent a hefty budget on larger brushless builds, I wanted to keep it as cheap as possible.

Main Challenges of a brushed Tricopter

The concept of a tricopter is relatively simple: instead of pairs matching counter-rotating in a quad (2 pairs laid out on the same plane), a Y-copter (2 side by side and 2 overlapping at the tail), hex (3 pairs, single plane), Y3 (3 pairs overlapping), Octo (4 pairs), etc... Instead, a tricopter has an odd number of rotors, which means that the yaw cannot be controlled via rotation of the driving propellers alone. In order for yaw compensation, a tail servo allows the third motor to tilt, providing the counter-rotating forces necessary to keep the craft pointing the same direction while having independent control of the overall throttle.

Both BetaFlight and CleanFlight have tricopter modes, and in these modes, the first two channels become servo controls while the remaining channels (3-6) become motor driving outputs. However, with brushless boards, normally only brushed motors are expected as outputs and so the PWM outputs are usually attached to the gate of a driving mosfet through a resistor, which then switches the motor pads between V+ and GND. This means that one would not be able to, out of the box, add any servo to these boards.

There are two main issues here:

First, I would need to bypass the MOSFET motor output of the servo channel for the tail. This would involve finding a spot on the PCB to solder an extra wire to.

Second, I would need to move the motors to channels 3, 4, 5. Here's where another issues arises: most brushed FC's that physically support only 4 motors are hardwired to channels 1-4, which means there are only mosfet drivers and motor pin pads for those channels. The reassignment in tricopter configuration would result in channels 3, 4, 5 being used, and channel 5 would not have any driving circuitry. While it would be possible to hack the FC code (BF or CF) to move the servo assignment to, say, ch 5 or 6 and retain the motor driving hardware, there is a further issue since on the PCBs, the latter channels are completely unused (not soldered to anything), and would require direct soldering of a fine wire to the tiny pins on the QFP microcontroller package itself- not a feat for the faint of heart!

*edit*: a helpful redditor mentioned that in BetaFlight the resource mapping function could potentially solve some of these issues without recompiling the FC code. It doesn't quite solve the problem of potentially having to solder directly onto the microcontroller package, but its a start! May be worth trying out as there are a number of cheap F3 brushed controllers out there that only have 4 motor drivers...

The Multiflite Pico is the only brushed FC I'm aware of that explicitly exposes servo output on a pad, which makes building a tri possible. However, it is also out of budget for this project. (And if you've ever flown a brushless mini-quad of *any* size, you probably don't want to invest any significant amount of cash into any brushed build these days... but I digress.)

The Solution

As luck would have it, the Eachine Naze32 brushed board (many clones under "HappyModel" and "Realacc" exist from various other retailers, and in fact the "Eachine" branded one actually came with Realacc markings on the bottom... ;) is a hex-capable brushed flight controller that I also had an extra of on hand from the popsicle quad build. This means that there are additional mosfet channels available, so even after the servo assignment to CH1 and 2, it would still be possible to use motor channels 3-5. The next step is to find exactly where the CH1 motor output is. For that, I dug up the naze32 schematic along with the datasheet of the STM32F microcontroller. Following (red rectangles in the image below) show the pin we're interested in:

What you see on the actual board is one pin of a SMD resistor that connects between the microcontroller's PA8 pin (29 on package), and the gate of the MOSFET for motor 1. After checking with a multimeter and confirming those two are indeed the same point, I proceeded to solder a wire onto that pad which should in theory provide the PWM servo output. (It might not look that difference in size, but its MUCH easier to solder onto that SMD pad than the leg of the microcontroller itself - not only is it considerably larger, but perhaps more importantly, there are no other pins nearby!). It was also a good time to test out the fine tip of my new super cheap (but working well so far) iron. Here's what it looks like:

The white cable is the signal, while brown (5V) and black (GND) make up the rest of the servo connections. Since the micro-servos I plan on using is super low power, using the 5V regulator of the board is OK. However, looking back it would have probably been better to use VBatt directly (unless I plan to use this board in 2-cell mode with more powerful motors... more on that later). Since the white cable is just connected to the resistor pad, adding a dab of super glue under the white cable prevents it from ripping off.

Next up is to test that it works:

And it does!!!

Second part of the build log TBA...

Tuesday, March 28, 2017

Cheapest Brushed Tricopter Ever? [overview]

Here's adding to the family of brushed, popsicle-frame based micro-copters: a tricopter!

The first part of a detailed build is available here. This post is mostly an overview of the parts used as well as some sample flights.

Part list:

- Eachine Naze32 Brushed FC ($7): note that newer ones like the F3 will not work. (Or at least not as easy)
- DasMikro FlySky Receiver ($10): version B, for PPM output on CH8.
- Eachine 8520 Motors ($12): I'm really interested to try the RacerStar or Chao-Li ones to see if I can get a bit more oomph out of them, as currently its a bit anemic even with ladybird props. Maybe 2s?? :P
- Ladybird 55mm props ($8): works great now for the quadcopter. Have some 65mm King Kongs on way which hopefully provides more power and are considerably cheaper at $5 for 10 pairs intead of $8. There are less clearance issues on the tri compared to the quad.
- 3.7g servo ($2.50): could have gone lighter, but was the cheapest I could find on AliExpress at $2.50. The Emax 2.5g should work too (and may be better quality) but is a whopping $5!
- 1x rubber grommet ($1.50) for ghetto-mounting the tail motor to servo horn
- 3x "craft grade" popsicle sticks from the dollar store
- Prop guards ($2.30)
- Elastic bands

AUW is about 50 grams before camera.

Total was a bit over $40 without FPV stuff, with a lot of spare props and grommets, plus an extra motor (Since the tail servo handles all the yaw and the number of motors are odd anyway, the third motor can be any direction). Not super cheap compared to RTF quads available on the market these days, but I'm not aware of a tri in this price range, and it was a pretty fun build process! I would love to hear how one might go cheaper on this if anyone has any ideas! :) I expect 720 motors could work, but the cost savings would be negligible. Oh and I forgot to include the price of the battery, which was from my V222 quad...

Using FlySky i6 receiver with 10-ch mod. (swich off AFHDS 2A to bind).

Indoor flight:

Outdoor flight:

While not as anemic as the initial popsicle quad with the weak triblades, its definitely could do with some more power. Hopefully the 65mm props in the mail would help. I should also consider removing the prop guards as they add a tiny bit of weight, and also see if getting different batteries would help. (These are from a unbranded multi-pack I got for my V222, and there's no discharge rating on them. Have some 600mAh 25C's coming, so will see if the battery may be the limiting factor here...)

*update* the 65mm props have arrived, and there's a lot more thrust now! Check it out:

And some flight footage:

*update2*: Yet another outdoor video with the 65mm props:

This time I had a larger area to play in and was able to fly a bit harder. It flew well generally, but I'm finding that the props are a bit loose and pop out relatively easily (this could have been after an incident where I crashed it indoors while tuning perhaps)... by the end of the second pack, I had lost the tail prop in flight and crashed it such that one of the main popsicle sticks have unglued... luckily all electronics appear to be intact. back to the workbench!

Bonus pic the happy DIY multicoper family (so far):

Thursday, March 02, 2017

Popsicle Quad, V2

So after the first version, made with HaagenDaz sticks flew a bit, I wanted to make some upgrades. Specifically, I wanted a.)more power and b.) a bit more clearance to mount an AIO FPV (all-in-one first-person-view) camera, such as the TX02 that I had on hand. To do so, alas, would require a slightly larger frame. So I picked up a bunch of "craft grade" popsicle sticks (there's only so much sugar we can handle) from the dollar store, and got to designing a new frame.

I wanted to keep on using the rubber grommets as before, which were quite good at holding the motors. The final design I came up with the following: (series of relatively self-explanatory photos)

The end result, with the old Eachine triblades:

The new props, based on the suggestion of a redditor, are the 55mm ladybird props. I also tried some hubsan x4 props which were also an improvement, but only had a set and broke them quickly testing indoors ;) I see some newer KingKong 55mm and 65mm props, which might also be good to try out. They are also a bit cheaper at $5usd for 10 pairs instead of ~$8 for 8!! The main thing is to use props with 1mm shaft holes, and to ensure there's enough clearance of course!

Looks like the props are about half a gram heavier each. The extra thrust however, was totally worth it. It's actually a bit hard to fly indoors without a prop guard, so I waited a while before good weather and opportunity arose. Here's a flight in a park taken with a run cam 2 (sorry for slanted camera placement... it's a bit hard to tell sometimes ;)

Unfortunately, I haven't had time to do any FPV flights with it, and my ghetto FPV system (to be described at some point) is quite clunky. The camera adds 10 lbs 5 grams, which is about 10% the total weight of the quad. Being 200mW it also draws about 400mW, which is not negligible for such small flight batteries. A 25mW (such as the TX01 or the switchable power TX03) transmitter would be more appropriate for this build.

Saturday, February 25, 2017

HäagenQuad Micro: a tiny quadcopter based on an ice cream stick frame

Since the weather is pretty unforgiving here in the wintertime, I wanted to build a small indoor micro-sized quadcopter but still keep the control systems that are present in the larger racing/acro machines.

Originally wanting to use a 3D printed frame for this build, but after having calibration and belt wear on the Y axis, I ended up with something a bit different while the replacement parts for the printer are yet to be installed. This attempt to use popsicle sticks for a quad frame is by no means the first, but unlike that example I'm using separate "DIY" quadcopter components (typically found on Eachine QX-series for those who want to just get a complete kit with all the parts). The advantage is you get a fully configurable flight controller that can run Beta/FleanFlight, but the tradeoff is you need an actual transmitter which increases the cost. I'm using the FlySky i6.

Everything is available from Banggood. For Canada I've found that using the registered + insured option gets the shipment faster, and may help alleviate issues as experienced by many. (For other Chinese retailers, the ePacket option is great as well)

Here's a complete list of parts along with their product links. (Prices may fluctuate due to sales etc). Note they are affiliate links which mean while its the same price as if you went on the site normally, purchases generate a very small commission for me. First time trying this feature out...

Motors/props ($11.25 USD): Eachine 820 Motor (4x) + Props kit (2 sets)

I'm guessing they're similar to the ChaoLi motors. They come in CW (red+ blue-) and CCW (white+ black+) wiring. While they might spin when polarity is reversed, from what I understand the brushes may wear out much more quickly so its best to make sure they're hooked up correctly!

If I was to order again, I might try the RacerStar ones, which may be better (or simply better looking with the nice red paint scheme... red means faster, right?? ;))

Flight Controller  ($7.05 USD): Eachine Naze32 Brushed Controller

In the racing multicopter community the Naze32 is starting to show its age, and F3/F4/F?? controllers with faster processors are starting to become the standard. While the latter are available for brushed builds, it's not really necessary for a small project like this. However, I've noticed that at least F3 based ones are only a few bucks more, so if I was to make another one, I'd probably go with those. One other option would be to go with a built in receiver, such as this one for FlySky, which would make the wiring and mounting a lot cleaner! The tradeoff of course is you won't be able to use the receiver by itself for another project... Similar options exist for DSM and FrSky

Receiver ($10 USD): DasMikro Ultra Mini

Select "Type B", which has the PPM out and makes wiring super easy. Also supports 8CH with a modded Flysky i6, so you can add extra switches and knobs if you like to additional AUX channels!

Rubber Grommets for motor mounting ($1.60 USD): 20 pack 

Make sure you select the 8mm version. Outer diameter is about 10mm, not counting the lips that stick out a bit further. 10mm an important dimension as that should be the size of the hole on the arms.

JST/losi Connectors:

Instead of the losi battery connector that came with the FC, I went with the 2.54 JST since I had a bunch of those lying around.


- 2x Häagen-Dazs ice cream sticks (other popsicle sticks may work, if the ends are wider than 10mm)

- Elastic Bands

- Bits of paper etc to stick under the FC to make it level with the frame, if needed

Build Process

The trickiest part of the build, for someone not familiar with woodworking is getting the right sized hole on the arms. At first I was ambitious and wanted to drill an enclosed hole, but quickly found out that it is very difficult to do so with a regular power drill. It turns out for delicate wood like this the best way to cut through is either with a small knife, or a really high RPM grinding tool (e.g. Dremel, etc) with the right attachment. Also in the end I found out that it's OK for the outside to be open as the grommet will still sit snugly in the opening, as follows:

The first thing I wired up was the FC to the radio. Since we're using PPM, we only need a single signal wire, as follows:

Then, we just have to connect up the motors to each channel. I soldered directly onto the FC, and the only thing you have to make sure is the right motor direction. For CleanFlight, the directions are:

So motors 1 and 4 are CW, while 2 and 3 are CCW. The Red+/Blue- wired motors are CW, while the White+/Black- are CCW, respectively. So we just have to solder each motor to the correct pins on the FC:

I skipped a few photos along the way, but here's what it looks like all hooked up:

The battery get strapped in underneath, using the same elastic that holds the FC in place. Not the most secure mount, but it works!

Here's the AUW of everything:

At almost 50 grams, it is interesting to see that there are many brushless builds these days that are around similar weight. Exciting times we live in! Anyway... how does it fly?

Turns out, not very well! After some discussion online, people have recommended me to move away from the triblade props that come with the eachine motors. While they are super quiet, there isn't a lot of power. I have some ladybird props on the way which should make a difference. Stay tuned!

Here's an updated outdoor video using the new ladybirds. As you can see it actually manages to get off the ground (and clips a tree at one point and still recovers...)

Other Potential Changes

I haven't decided if I should switch everything to losi since they're much easier to plug/unplug compared to JST. On the other hand I have 5 batteries with JST already and it would take quite a bit of soldering to change them...

Finally, a family pic with a WlToys V222 (showing its age compared to modern toy quad options, but still a great intro to quadcopters), and the perpetually in-progress QAV250:

Bonus Peek:

Here's the next version, with larger and more powerful props (hubsan x4 shown, but also have ladyprops which feel even better), as well as an AIO video tx:

Tuesday, January 24, 2017

Harmochord restoration with a 3D printer (mostly Dad's work!)

In the summer of 2016, we stumbled across an interesting find at a pawn shop in Verdun:

It's basically an accordion with an electric pump instead of the manual bellows, designed as a table-top instrument! Single bank of reeds for the keyboard, and a relatively small array of bass notes compared to the full size accordions

After trying it out in the store and verifying that at least every key makes a sound, we decided it was worth the $20 and the effort to lug it back home on the bus (it probably weighs around $15kg or so...)

The things that were apparent immediately:

- It was "Made in West Germany", which makes it probably the most interesting instrument I have owned thus far...
- pump appears to work fine
- 3 black keys are missing
- a few of the bass notes would stick when pressed

Things we found out afterwards:

- The "briefcase" actually was supposed to contain 3 legs, which allows the instrument to be self standing. Those were missing as well. (oh well...)
- slight leakage in some of the bass notes, causing either weaker sounds or other tones when some notes were pressed

As a keyboard player, the first thing I wanted to do was to get replacements for the black keys. Never got around to it with busy school and family schedule, but when my dad stayed with us for a bit, he took on the project.

This is mostly a documentation of the result of his efforts!

Here's a close-up of the missing keys:

A 3D printed model was made in SketchUp:

It was a basic 2D profile that was pulled upwards, and then a small rectangular extrusion was added (top left of picture).

Here's the key being printed and the finished product:

Here are keys in their final location. Note that the key bed (not 100% sure if that's the right term here) isn't in the best of shape, so things aren't super aligned and some of the existing keys also aren't completely straight either.

Finally, a short demo of how it sounds:

There are a few more things that need to be fixed. My dad managed to get rid of the sticky behaviour of the bass notes, but the leakiness of some of the notes are still there. Here are some shots of the mechanism when it was open, for curiosity's sake:

So at some point, I might tackle that... (but there's also a good chance it won't happen until the next time Dad visits! ;)

Tuesday, October 25, 2016

Raspberry Pi Robot with PiShield, Part 3: Fast video streaming

I fiddled for a good part of the day trying to find a low-latency local network video streaming solution to implement a "FPV"-like control for the robot using a RPi camera module. It turns out a bunch of existing solutions (like VLC streaming etc) have really high latencies. This is OK for things like a security camera, but not so much for realtime control.

Finally, this rather hacky solution using netcat appeared to work best:

1. On the client (viewer/controller, running on a Mac) side, run:

 nc -l 5000 | mplayer -fps 30 -cache 1024 - -x 640 -y 360

 2. On the RPi side, run:

 raspivid -n -t 999999 -fps 12 -rot 180 -o - | nc IP_OF_VIEWER 5000

 netcat is used to listen and send; raspivid grabs the video and pipes it to netcat, and on the other side netcat pipes the received data and spits it into mplayer.

 This was the only way I could get less than 1s of latency on the video feed, although it still wasn't great. Having a good USB wifi dongle also helped a bit. Finally, changing the dimensions of the video using raspivid actually made it much slower, probably due to software resizing of each frame on the fly compared to just sending out the raw feed from the camera.

 Next steps: get some more interesting sensor info from the PiShield, and get a separate power source since there seem to be random system freezes when the motor and Pi are both running off the same power bank.

UPDATE Oct 26:

with the advice of a very helpful redditor who suggested gstreamer, I gave it a shot this evening.

On Raspbian, gstreamer1.0 is currently already in the official repos, so no need to add custom sources as these earlier instructions.

For OSX, I just downloaded and installed the latest compiled version from the official source. It also handily tells you that by default the path for the commands are at


From here, we can either have a tcpserver on the Pi that a client can connect to, in which case:


raspivid -t 0 -h 720 -w 1080 -fps 25 -hf -b 2000000 -o - | gst-launch-1.0 -v fdsrc ! h264parse !  rtph264pay config-interval=1 pt=96 ! gdppay ! tcpserversink host=minibian.local port=5000

Mac (note explict path to gst-launch-1.0 command, since I haven't added it to path):

/Library/Frameworks/GStreamer.framework/Commands/gst-launch-1.0 -v tcpclientsrc host=IP_OF_RPi port=5000  ! gdpdepay !  rtph264depay ! avdec_h264 ! videoconvert ! osxvideosink sync=false

Now UDP would be faster, and in this case it would be similar to the netcat example where the RPi would define the UDP "sink" using the IP address and PORT of the viewer (on the Mac), which would yield the following:

RPi (note destination should be explicitly defined by the source this time):

raspivid -t 0 -h 720 -w 1080 -fps 25 -hf -b 2000000 -o - | gst-launch-1.0 -v fdsrc ! h264parse !  rtph264pay config-interval=1 pt=96 ! gdppay ! udpsink host=IP_OF_VIEWER port=5000


/Library/Frameworks/GStreamer.framework/Commands/gst-launch-1.0 -v udpsrc port=5000  ! gdpdepay !  rtph264depay ! avdec_h264 ! videoconvert ! osxvideosink sync=false

Eye-balling the two versions, I feel like the UDP version is slightly snappier, but considering that my network is not very congested, I have a feeling the difference wouldn't be as much as if I had a lot of traffic running. Regardless, this is a HUGE improvement over the existing solution! Should try to do some timing tests to see if I could get a better measure of the actual latency - perhaps using a photo of a stopwatch like this guy did (which was one of many sources I originally consulted for the netcat solution above as well)!

finally, here's a test on the actual video latency of the setup above: looks like its somewhere between 150 and 200 ms.


Yet another option, is to use RPiCamWebInterface. In the end I didn't get around to do the latency measurement, but it feels *almost* as fast as the previous solution. The other bonus is the client user interface is far nicer!

Here's a sample video showing the stream in action: