BrushedSparky v0.2

you can purchase Sparky2 here

BrushedSparky version 0.2 arrived a few days ago. 

Improvements

There are a number of improvements over the previous revision.

• A bigger motor mount hole allows for stronger mounts.
• Using a 1.2 mm PCB shaves a bit of weight off. 
• Changed the 5V step up regulator for a new one that is more efficient (and doesn't hum).
• Using a more available VTX module so I can build more :)
• Shuffled some components around for a slightly slimmed profile (also got a stencil to make it faster to populate).
• Current monitoring (enables mAh consumed calculation)
• Switch to disable VTX for flying LOS
• VTX channel selection via the FC
• LEDs on the arms for following via FPV
• Two additional PicoBlade connectors for clipping arms to it and making a hex. Also two more buffered outputs on the back such as for LEDs.

I'm still controlling it via Tau Link Module, which gives me voltage, current, mAh remaining (as well as logging) on my phone relayed using the module in the transmitter. See the previous writeup for more information. Quite convenient since it gives me audio alerts. The new revision of Tau Link Module also has SPort support so hopefully I get this information on the Taranis soon.

Assembly

The bare board assembled (without VTX on bottom) is only 12 grams:

And 41g ready to fly (without battery):

And now I have a nice row of micros above my desk:

Landing gear

One failure point is hitting the bottom of the motors and damaging them. I tried to design a more robust motor mount that protected them better and served as a landing gear:

Unfortunately it coupled vibrations too strongly into the frame and resulted in bad attitude estimation (not hovering level). I went with the original design for the motor mount and a landing cup that clips onto the arm and protects things.

They do pop off in crashes, but that's fine since it still saves any serious damage. I want to get my friend to try printing these in different materials - abs or flexible material - and see if it works any better.

BOM

Here are the parts I'm using for my preferred assembly. You can either buy all the parts from multirotorsuperstore or in pieces.

• motors:
• 20$ http://www.multirotorsuperstore.com/cl-0820-17-coreless-motor-set.html
• 30$ micro-motor-warehouse.com/collections/all/products/cl-0820-17 precrimped with connectors
• props
• 3$ for 4 colored: http://www.multirotorsuperstore.com/propellers/propellers-nylon/hubsan-prop-set.html
• 9$ for 20 clear: http://www.amazon.com/dp/B00RE5US38/ref=sr_ph?ie=UTF8&qid=1427170689&sr=1&keywords=hubsan+clear
• camera
• 30$ http://www.multirotorsuperstore.com/micro-600tvl-120-degree-camera.html (nice FOV)
• 50$ http://www.getfpv.com/lumenier-cp-520-pico-520tvl-nano-camera.html
• VTX module
• 10$ http://www.banggood.com/FPV-5_8G-200mW-Wireless-Audio-Video-Transmitter-Module-TX5823-p-84780.html (Boscam E band)
• 14$ http://www.rangevideo.com/58-ghz/57-tx5200m-58ghz-200mw-5v-transmitter-module.html
• VTX antenna:
• RHCP 10$  http://www.fpvhobby.com/231-8-ghz-micro-cl-antenna-.html
• LHCP 5$ http://www.banggood.com/FPV-5_8G-Circular-Polarized-LHCP-VTX-Antenna-p-961731.html
• battery:
• 5$ http://www.multirotorsuperstore.com/battery/1s/1s-380mah-35c.html (note these are 35C)
• 3.50$ http://hobbyking.com/hobbyking/store/__33260__Turnigy_nano_tech_750mah_1S_35_70C_Lipo_Pack_Fits_Nine_Eagles_Solo_Pro_180_US_Warehouse_.html (750mAh)
• charger and miscellaneous:
• charger: http://www.banggood.com/4-In-1-X4-Battery-Charger-For-Hubsan-X4-WLtoys-UDI-JXD-Syma-Quadcopter-p-933932.html
• use this for attaching. it is magical.

Video

I'm really happy how it flies as well as the video quality (which the Dom V2 built in DVR doesn't do justice to). I started playing around in acro mode too and got some flips in, as well as a number of crashes. It takes abuse quite well, typically in a really bad crash just cracking the motor mount which takes about 2 minutes to replace.

 (Update) I also got telemetry on the Taranis via the TauLinkModule S.Port

Playing with #BrushedSparky Taranis telemetry. RSSI, voltage, current, flight mode, altitude, vario all on screen. Also speech warns of low voltage or RSSI, as well as signal disconnect. AndroidGCS is great but sometimes you just want minimal info.

A video posted by peabody124 (@peabody124) on Mar 29, 2015 at 7:36pm PDT

BrushedSparky: Sparky2 + Microquads

Update: see the next revision here 

Also you can purchase Sparky2 here

This is a new TauLabs board I just finished making.

I am now really into microquads for a number of reasons. They are much cheaper and relatively easier to build than full sized ones. They are great for testing things indoors while being quite safe. They make FPVing around a small space an adventure. Finally they are extremely easy to transport and then just quickly throw in the air.

The last month or so I've been on an adventure to build the best microquad I could. The photo above is my latest and greatest creation. It is essentially the guts of TauLabs Sparky2 integrated into a single PCB with an integrated VTX and radio module on the bottom. This is a writeup of how I ended up there.

Sparky2 based micros

Sparky2 has some transistor buffered outputs. I've previously demonstrated these to control LEDs via PicoC to create a visual compass. However, their real goal was to control brushed motors on a microquad. OsoGrande finally motivated me off my butt to actually try this the other day. We both got some of these brushed motors that can draw a few amps and supposedly generate 40g of thrust each.

Here is his:

and mine (actually with a frame of his):

I hate wiring

To get this ready for FPV, it is really annoying to add the 1S to 5V step up, not to mention dealing with the cables and adding a VTX. To make this easier, I made a board that takes care of some of the details (compatible with both Sparky1 and Sparky2)

This adds the voltage boost, VTX, channel selection and connectors for standard motors. Before this even arrived, though, I was already on to a more fun idea (and want to redo it with 6 outputs for 3D printed hex's) ...

About this time OsoGrande received a really nice little PCB frame that has pads for a Polulu step up and a VTX module for doing FPV as well as mounting holes compatible with Sparky2 (and AlienWii):

These were just too much fun to fly, but I really hated the wiring and ugliness of cobbling all these parts together.

BrushedSparky - A.K.A. Let's build a lot of these!

These tiny things are so much fun to fly, that I really wanted to make it easier to build them up and get rid of all the annoying wires and such. They are also great for micro FPV (see OsoGrande having fun) but soldering up the wires for the camera seemed like a giant pain. 

I designed a board that should double as a frame. It's a little less than 100x100 mm. It is basically Sparky2 has the RFM22b module for control and telemetry without an additional receiver, integrated 1S to 5V step up, TX5200M VTX and a full suite of sensors (so can do altitude hold and even navigation). It also has voltage monitoring and the digital to analog converter from Sparky2 goes to the audio input on the VTX so we should be able to send sounds to indicate low battery and such.

Specs:

• Runs TauLabs
• STM32F4 process (168 MHz, floating point unit) so lots of horse power
• MPU9250 gyro / accel /mag chip
• MS5611 pressure sensor
• RFM22b radio module (so hopefully this can be made OpenLRSNG compatible)
• TX5200M VTX module with DIP switch for channel selection
• 4 6A buffered outputs

Soldering and testing

DragonCircuits was awesome enough to make these four layer boards quickly and at a great price! The boards looked as good as I hoped they might.

Here is one fully populated:

Here are the motor mount files I designed:

To save weight I used pegs on the mount instead of holes with hardware. This seems to work quite well, although I add a drop of loctite to keep them in place. I uploaded the files to thingiverse.

A few things I already want to change

• Fix some small mistakes I made :)
• Adding holes for the camera and motor connections to make it easy for the headers to be optional.
• Add current sensing
• The buzzer I used is really not loud enough so I'll be looking for another one of those. 
• Finally I really need to add a power switch for the VTX and camera so you can have it off when it isn't desired.
• VTX channel selection routed to the F405 to avoid carrying the DIP switch
• Few other fun surprises

Here is one that is populated to be a bit lighter. I'm soldering the motor wires directly to the pads and used a solder bridge to select the video channel instead of using the dip switch. It comes in at 43g.

Here is an image of the bottom. You can see the radio module in the middle (RFM22b) and the VTX a bit further forward. The velcro on the VTX module is for when I want to carry a keychain camera.

They are small enough I kept losing them, until I realized a little velcro could easily secure them over my desk:

Control Module

Since every gram counts on these things, I'd prefer to use  RFM22b control instead of a satellite. I've already been using TauLink for this but it is a annoying to jury rig into a JR socket with a bluetooth relay module. I ended up designing a module that should fit into a JR socket and also has a bluetooth module to relay telemetry. This should allow me connect android (or even iphone is someone wrote code) to the quad without any additional wires. This uses a HM-10 bluetooth low energy module (which is actually compatible with iPhone as well) and the RFM22b module used on Sparky2 and TauLink.

It plugs in quite well and fits into a JR socket easily. I'll probably make it a touch bigger just to give a few more mounting points for stability, but it fits well as it is. Plugs in nicely and smoothly into the socket pins.

And of course the important thing is that it of course connects well to the quad for telemetry and PPM control. It was a bit of work to add support for this type of bluetooth low energy module to the androidgcs but it is also working. Gives me nice audio alerts for things like a low battery voltage and verbally tells me the flight mode.

And a quick 3D printed mount to secure my phone over the transmitter to make it easy to use at the field:

One thing that is annoying right now. The BT LE module doesn't work as simply as standard serial modules so I'll have to see if it is possible to relay to computer. This might be a reason to change modules, although with laptop it's easy enough to plug in USB cable since I'm normally inside rather than in field. This might not apply as well for everyone else, though.

The other important goal of this module is actually to pump information back into the Taranis, so even without a tablet or computer you can see things like battery voltage, RSSI and LinkQuality. I'll update more about this later.

Flight testing

Overall I'm really happy with how they fly. The VTX module gets fairly hot (as do the motors) but so far nothing too much so. The video is pretty good, although not great. I think my receiver module is not on the same frequency bands as this module (it is on Boscam A frequencies and I think my stuff is on ImmersionRC frequencies). Alternatively, maybe a small circularly polarized VTX antenna will help since my breaking up seems to be at strong angles.

With a 750mAh battery it will hover for around 5 minutes at about half throttle. It weighs 65g in this configuration.

Of course, here is the video (same as above):

Here is OsoGrande out testing his using some people as obstacles:

It will also fly with a keychain camera attached to the bottom, but that adds another 19g and
 takes most of the spare thrust so I don't really enjoy flying like this. Ground side recording for now it is.

Future fun

• The Pico camera I'm using right now is a bit heavier than I'd like, so I want to try out this one from multirotorsuperstore.com that also has a wider FOV for exploring the furniture (update: tried it and I like it!):

• I also wanted to see if this would behave well for navigation, so spun it a few times while logging and threw the data into the python calibration script:
  
  
  
  
  The nice round circle shows that the magnetometer is a beautiful round circle, so with a GPS it should work great for navigation.
• Get Taranis input straight from telemetry with the TauLinkModule so basic things (e.g. RSSI, Battery voltage) are shown on transmitter without even needing phone or tablet.
• I really need to join up with OsoGrande (who I made one of these for as well) and do some FPV racing in the garage near him...

Fun for you too?

Also since I know the inevitable torrent of questions about this is going to be "where can I get one", I'm working with someone to try and get them manufactured. In the mean time I'll likely make a few for friends and developers for testing purposes, but not too many. Keep an eye on my Instagram/twitter account and I'm sure you'll know not long after I do.

OneShot125: Quantitative Testing

Note: this original spoke of the sensor rate being 666. However, this was a mistake and the sensor rates were 500 Hz and 1000 Hz.

There has been a lot of talk about OneShot125 mode for ESCs and how much better you can tune your quadcopter with it. Briefly, this is a mode that uses a pulse width of 125-250 µs instead of the typical 1000-2000 µs. This shorter pulse width allows a higher update rate (up to 2khz). In addition, the recommendation is to update the output as soon as you calculate a new value. This improves the latency of sensor to ESCs in two ways: the synchronous update reduces the latency due to two independent loops and the shorter pulse duration saves another 1.5ms waiting for the falling edge of the pulse. With an update rate of 400 Hz on the PWM outputs that latency has a worse case of 2.5 ms so ultimately you are talking about 4ms latency reduction.

It sounds somewhat unlikely that such a small time delay would make a difference, but at the same time the ESC latency is the ultimate performance bottle neck for quadcopters. With ESC response times getting into the 10-20s of ms, this communication latency can become an appreciable component.

Back in December ernieieft wrote Tau Labs support for it and with autotuning got higher PIDs and felt like it was quite locked in.  Here you can see the outputs from the four channels as well as the interrupt from the MPU9250 on Sparky2. This shows that each time there is a sensor update, shortly after it there is a pulse on the output channels (synchronous updates).

Zooming in, we can see what the latency is from the MPU9250 indicating a sample is ready to actually completing the pulse, and it is about 300 µs. Much better than the worst case 4 ms described above. This is with a short output pulse so in reality the time could go as high as 450 µs.

However, I wanted to quantitatively compare how much specifically OneShot125 mode really makes a difference. Luckily, we have our autotuning algorithm which actually allows monitoring the time constant of the delay from a change in the output to a change in the gyros.

Normal PWM mode

So first I ran autotuning with Seeing Spark and Sparky2 using KISS ESCs in traditional mode. This is with the sensor running at the default rate for Sparky2 (500 Hz).

After three repeats, this is what I got:

OneShot125

Then I cracked SeeingSpark open and soldered the JP1 bridge to enable OneShot mode.

Note: per request I have put the files to make this power distro board on OSHPark. I'll try and make a BOM and assembly guidelines and upload that soon.

Here you can see the outputs running at 500 Hz synchronously to the sensor.

Then popped in a fresh battery, and did a few more sessions of autotuning.

OneShot125 - 1000 Hz sensor rate

I also wanted to see if increasing the sensor rate to further reduce the latency would cause more improvement, so I set it to 1 Khz.

 and ran another three rounds of autotuning.

Statistics

So of course the punchline. Is there a significant difference between traditional PWM and OneShot mode as measured by the time constant of the response? Yes. Anova shows p < 0.01 for an effect of output type:

Anova results

And the multiple comparison shows that both OneShot tests were significantly different than traditional mode.

Conclusion

Using OneShot mode on this quad results in about a 20% reduction in ESC latency. Even before OneShot, these KISS ESCs were pretty damn fast so it already flew really well. I'm not sure I'll be able to tell the difference in rate mode, but I do believe a better acro pilot than me could. I also didn't run these parameters through the system models to start seeing what the difference in effective control bandwidth will be for the outer loops (e.g. attitude).

It also remains to be seen if there are similar benefits with BLHeli and I believe SimonK has support coming soon for OneShot. I'll probably repeat these tests once I have the right hardware.