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Posted by devinvagt | Jul 12, 2016 @ 10:55 PM | 1,069 Views
While working on our sub-250 gram fixed wing fpv racer, we got into a discussion of what combination of motor, prop, and battery would suit this plane the best. For a motor, we started with the Emax cf2805 1300kv and the Hurc 300 'blue wonder' ; two very similar motors. They're about 29 grams and can handle in the neighborhood of 10A continuous. A little overpowered for our purposes, probably, but a good place to start. Later, I added the power up 250 plus 1400 kv ( tested as 1290 kv), a slightly lighter motor with similar performance, but with a little lower amp capacity.

I wanted to gather some real-world numbers we could rely on, so I tested props with the type of batteries we would likely use in a small model, i.e. small 2 and 3 cell lipos in the 500-1000mah range, at ~80% capacity. I tested static thrust because it's the easiest to measure, and for maneuverability and hovering it's a good guide to what you can expect in flight.
What follows is the results of the testing, sorted by max thrust, thrust/watt ( what most people are interested in ), and thrust per gram. In general, the trend is simply: as thrust goes up, efficiency goes down. The trick is to find the right balance of power, weight, and efficiency. I also averaged out the score for thrust/gram, thrust/amp and thrust/watt and gave each combination a score. it's useful to get an idea which combinations are a good balance.

Some of the standouts that are worth checking out:
Best overall...Continue Reading
Posted by devinvagt | May 05, 2016 @ 12:29 AM | 3,224 Views
I have been testing a new lemonrx receiver+ stabilizer combo in my sub 250 gram plane and I've found it works well in close. BUT... I've been getting a loss of control out a farther, say, past 0.25 mile/ 0.4 km . In two cases, I still had pretty good servo control to land, but no motor response. So I did some range testing in my back yard and I was able to replicate this situation pretty reliably. It comes down to how the receiver failsafe handles signal loss.
When the lemonrx receiver loses the signal, it sets the throttle to zero. No surprise there. But when it reacquires the signal, it does not restore throttle to its previous value. Rather, you have to move the throttle stick up and down for a while, sometimes for as long as 10 seconds, before you are given back throttle control. During this time you have varying amounts of servo control, which is a big help when you're trying to pick a spot for an emergency landing. However, in the most recent case I was flying over a lake and had to land in the water, so there were no good spots to be had (I swam out and fetched the plane -- it's OK now. )
So what to do? A mini-shootout, of course. I ran a range test setup with the diversity lemon rx combo, a diversity lemon rx receiver, an orange rx r615x, an orange rx r620, an old spektrum ar600 with a couple of split-v dipole antennas( a la Ibcrazy) attached, and a brand new spektrum ar610. I should add that my transmitter for this test was a spektrum DX6i...Continue Reading
Posted by devinvagt | Apr 24, 2016 @ 11:36 PM | 1,849 Views
EDIT: added two more cams, corrected some info -DV

I've been trying out some different mini - cams for my sub 250 gram fpv race planes, and I thought I'd share my findings. I checked out six cams, in ascending order of price:

Diatone 600TVL 120 Mini Camera Black $13
Eachine 700TVL 2.6mm Lens 1/3 CMOS 110 Degree $14
RMRC-Pico wide v2 520TVL $15
Aomway HD Mini 1/3'' CMOS 600TVL 2.8mm $15
Aomway 700TVL HD 1/3'' CMOS FPV Camera $30
Tarot 520TVL FPV 1/4 120 Degree Wide Angle Lens $31

and in ascending order of weight ( with cable attached, cam is no good without a cable! )

Diatone 4g
Tarot 7g
Eachine 10g
Aomway 600tvl 11g
Aomway 700tvl 15g

The smallest, lightest cameras tend to be more expensive, with the exception of the Diatone.

The Aomway 700tvl is definitely the best camera overall, a very sharp picture, good color and not too expensive, but also being the heaviest, if you call 15g "heavy". Also, the sticker on the back says NTSC, but it seems to switch between NTSC and PAL for no reason. It also tends to over-expose rather than under expose, which is an asset for FPV flying. I highly recommend this cam if weight is not your main consideration. If it is, the Tarot, RMRC, and Diatone are small and light enough to go on even a micro plane or quad without screwing up the CG or aerodynamics. The diatone is advertised as 600tvl, but the video quality looks more like the other two 520tvl cams. Still, it is a...Continue Reading
Posted by devinvagt | Aug 06, 2015 @ 09:22 PM | 1,627 Views
Accidentally destroyed a surface mount component while changing the 5v regulator on my remzibi OSD to a recom r785.0-1.0. It's a drop in replacement for a standard 7805 with much better efficiency-no heatsink neeeded! I think later versions of this board incorporated a similar item. I tore off part of the trace along with an unidentified surface mount component. Bad bad bad.