The R220 Mini H Quadcopter is Red20RC’s first commercial multirotor frame. Designed using Google Sketchup and cut on the workshop CNC cutter this has been a steep (and often painful) learning curve…
R220 Mini H Quadcopter
So in a break from the normal format, let’s do the video first as it is quite long and I put a fair bit of effort into it…
That’s probably all you need to know. Get over to the store now – www.store.red20rc.org – and buy one today! If however you want to learn a little more about how we got here, read on…
Blackout – the perfect frame?
When I sat down to design my first frame I did my due diligence and spent plenty of time watching videos on YouTube and scouring the internet. The miniquad market is already flooded with cheap frames (I myself was flying an FPV250L from HobbyKing), but a few high-end models were standing out above the crowd. Of these the two that caught my eye was the QAV250 from Lumenier and the Blackout Mini H.
The QAV250 is an awesome frame and their “Team Pilots” on YouTube are pushing the limits of what is physically possible. However, it was the Blackout Mini H that caught my eye (and their pilots are no slouches either). The design was simple and the geometry appeared to give excellent performance. The H style frame gives a very compact wheelbase whilst still allowing for plenty of room for gear.
I’d found my muse, now it was time to fire up Google Sketchup…
Building a virtual frame
I am well aware that there is better CAD software out there but I just find Sketchup so simple to use that I can’t give it up! I started by laying out the geometry of the frame using guides and then adding prop disks so I knew what my limits were. I already had a set of basic requirements to work from:
- 1806 2300kv motors with Gemfan 5030 props
- Naze32 flight controller
- Full-size board camera for FPV and ImmersionRC 600mw VTx
- Mobius HD recording camera
- Full size Taranis Rx and 1300-500mah LiPo
These requirements gave me some basic sizes that had to be adhered to. I used the prop diameter to determine the maximum width for the frame and then eyeballed the shape to something that I liked the look of. The distance between the top and bottom plates has to be a minimum of 35mm to accommodate the board camera so that was an easy decision.
A lot of frames seem to feature a full double bottom plate. Whether this is for strength or not I don’t know. The Blackout is cut from 1mm carbon fiber and has an integrated power distribution board so I suspect the second plate is to reinforce the weaker PDB and the rest of the clones just blindly followed.
I neither wanted, nor had the facilities to produce a PDB, plus I intended to use 1.5mm material, so I shrank the belly plate down to cover the center of the frame only. There would be a minimum of 3mm between this and the bottom plate, giving me at least some space to sandwich cables and a mini PDB to keep the build neat.
Finally, I added my own little flare with the Red20RC logo and name instead of the usual boring slots, squares and holes to lighten the top plate.
Pulling it all together in Sketchup I was pretty pleased with what I had accomplished.
All arms are not created equal
I’ve got a bit of a bee in my bonnet about arm design. Too many “professional” carbon fiber frames out there have arms that are both full of holes and riddled with weak spots.
With the R220 I was really careful to make sure that none of these weak points were present. All curves are smooth and shallow and the motor mounting plates are long enough to protect the motor in a crash.
Next time you buy a miniquad frame, take a look at the arms and you’ll see what I mean.
I had already been following a supplier of fiberglass and carbon fiber products on Twitter for some time and I decided to reach out to them first to see what I could get for my money. Fortunately Merry at XCComposites was very helpful and I decided to start with the much cheaper G10 fiberglass for the prototype.
For my fasteners and fixings I turned to eBay. I got a head-start from my flying buddy Andrew who had sourced similar components for his hand-cut frame and sent me the links. I was lucky enough to find a supplier of quality steel screws and nuts here in Australia. With all the orders in it was just a case of cutting some plates…
CNC Cutting Fiberglass and Carbon Fibre
My process is pretty simple and always follows the same pattern. I export the 2D plans from Sketchup as a .svg file. This then goes into Adobe Illustrator for tidying up and exporting as an .ai file. To generate my toolpaths I use Cut2D from Vetric software. This is where the biggest learning curve came as I worked out the correct way to use end mill cutters and plan feed rates and plunge speeds. As a general guide for anyone just starting out in CNC, for G10 and CF a 1mm mill shouldn’t exceed 250mm/min and a 1.5mm mill 370mm/min. The biggest mistake I made in the beginning was pass depth. An end mill should never cut at more than 50% of its diameter – I got through almost an entire case of drills before I realised I was trying to use a 100% pass depth.
If there is enough interest I’ll do a full article on CNC cutting as it really is an art form in itself…
Putting it all together
Most of the problems I discovered came down to tolerances in the bolt holes and slots being just a little too tight. I did want things to be a tight fit but on the first batch of G10 frames I had to drill out the bolt holes slightly so the screws would go through.
The rest is history. The Naze32 Acro is a perfect fit for this frame and with a little tuning I had it rolling and flipping within its own length. I’ll leave you at the end with some of my first flight videos so you can see what I mean.
The general consensus was that a carbon frame was needed so I took the expensive decision to purchase some very high-end Taiwan 3K Matte CF to cut a “Pro” frame. This was accompanied by a V2 arm design that further reduces stress points and improves motor mounting.
I’m not trying to take over the miniquad market and there will certainly be other frames in the future but, if you want to support a small producer and own something just a little bit different I’d love to see what you can do with the R220 Mini H Quadcopter.
So, I’ve prattled on for long enough. How about some more videos…