Cheap 3" Drone for taking HD video

Ever since the intern Canadian UAV regulations were released, I've been wanting to put together a relatively cheap, but HD Camera carrying drone that is light enough to be exempt from any regulation. At the threshold of 250 grams, it was actually quite doable at a relatively low price given the extremely rapid developments in the DIY quadcopter industry over the past few years.

This is the second, but much more used iteration of the particular frame. The first had a 4 in 1 ESC and F4 controller which I blew up on a hard crash (did not disarm when it dove into the ground in acro mode), and due to parts I had available it was rebuilt using slightly less optimal (weight-wise) parts but ended up flying very well, so I kept it even after replacement parts arrived.

Before delving into the details, here's a google photos-created video from some footage I took while travelling in Finland for a conference. The small size of the quad means I can carry it easily in a backpack containing my work laptop (13" MBP) without adding too much extra weight.

Here's the finished build "in action" next to the transmitter, out on the field on Aalto University campus:

Parts list and build details

Frame: Realacc RX130 that came with a Matek PDB. (Used to be able to find it for about $13-15 on Aliexpress)

Motors: ReadyToSky 1306, 3100kV (available only on AliExpress from what I can find; example link. They are super cheap clones of the DYS 1306 at half the price, but the latter are much better in quality. Supposedly 4s capable but I've only ran them on 3s so far. Works fine!

ESCs: EMax 12A "BlHeli" which actually had to be manually programmed with "real" BlHeli. They're not super light but can be found for cheaper from eBay and AliExpress merchants. However, I would actually rebuild it with a BS412 (25x25mm) or maybe a RacerStar 4in1 (30.5x30.5mm). The latter is 20A and would work with 1407 motors which could support a larger craft (160mm frame swinging 4" props). A 4in1 (even larger 20A one) would also be considerably lighter than the 12A EMax's I'm using. For discrete ESCs the EMax Bullet series may be better as they're much smaller and lighter.

FC: I'm using a strange Piko BLX clone board that has a curious 23mm!? hole spacing. It fits in between the standoffs of the 30.5mm spaced stack, but is not ideal. I would probably just go with a full size 30.5mm FC for this frame next time... or else go 20x20.

Receiver: FlySky A8S. Tiny, supports failsafe fine despite product description stating otherwise, and no reliability issues that seem to be a problem with older versions that are no longer sold on BG...

Batteries: ZOP power 3s 500mAh 45C. They're not rated for consistency, and of the two I have one seem to work better than the other. Having said that both allow me to zoom around for about 3 minutes or so lugging the HD camera, or do more aggressive manoeuvres without the camera.

Props: DYS 3045. The only 3" props I've used so far. Seems to be a good match and they're pretty, so not too much to write about at this point... ;)

Camera: the trusty RunCam 2 HD. Weighing in at 50 grams with battery and SD card, its not the lightest option but its a nice action camera to boot. I could have shaved about 15 grams off by not using the battery and powering it off the 5V rail of the PDB instead. Another interesting option would be the new Split that weighs about 20 grams or so and has a faster analog signal for realtime FPV feed (requiring an analog transmitter of course), but the Split is pretty much a dedicated flight camera and can't be used elsewhere by itself.

Transmitter: The trusty FlySky i6 which I modded to 10ch, and the i6ab receiver is still working well on the 250 class quad.

The build weighs in at exactly 250 grams with the camera, which is about 15 grams more than when I had the BS412 4in1 ESC and F4 controller with built in 5V regulator which eliminated the need for a PDB. This means I don't have room for a lipo voltage checker/alarm (such as this one), and I have to go by gut feeling and go by experience from more open locations when I didn't need to conform to regulation.

Previously, with the lighter 4in1 ESC:

Here's some raw, unedited zooming-around-the-park footage:

All in all, a very fun quad that gets a lot more action than the 250 (5") one due to the size and legal status. The Canadian regulations have recently been updated to be a lot more reasonable, but anything that weighs over 250 grams (and less than 1kg) is still relatively restrictive in terms of space.

Cheapest Brushed Tricopter Ever? [Detailed Part 1]

[disclosure: some of the banggood links contain an affiliate code, but many products are discontinued or outdated so consider seeking current alternatives!] 

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...

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):