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Eachine RedDevil Review

29/7/2019

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The Eachine Red Devil is available exclusively from Banggood
Introduction
​The Eachine Red Devil is a 120mm "toothpick"class quad: an ultralight micro that is capable of swinging 65mm bi-blade propellers. This quad is very similar to the Happymodel Sailfly-X (which I reviewed here) but with a bump in specifications, particularly around the FPV camera and VTX. You can actually think of this as an updated Sailfly-x much like the Eachine trashcan (reviewed here) is actually an upgraded Mobula7 (reviewed here). Is it better than the sailfly-x though? Mostly less but it does feel like it needs a little extra to take advantage of this. Read on to find more.
What's in the pack?
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Like the Eachine Trashcan (and unlike the Sailfly-x) the Red Devil ships with a nice protective zipper case that you can store the quad, some simple spares and batteries in. It also ships with a simple but useful selection of spares as listed below:
The quad itself
  • 3 full sets of propellers (12 props) (spares here)
  • 3S 11.4v 300mah 30C/60C battery (spares here)
  • Propeller disassemble tool
  • Screwdriver
  • Eachine Handbag
A closer look at the specs:
  • Crazybee F4 v2.1 board - The quad is build around this very familiar all in one board. It has a F411 processor that is capable of 8k/8k Gyro/PID loop with all dynamic filters and features. It also includes a 4 x 5A esc that is capable of 2-3s including a very useful current sensor. Lastly it has a built in recevier (Flysky, FRsky or DSM) which makes it compact and light.
  • EX1102 8700kV motors - Nice light motors with 2 bearings, identical to the Sailfly-x's motors but supposedly a slightly higher kv.
  • Caddx EOS2 FPV cam - A polarising camera this one... I've had good and bad experiences with this cam. Superior to an AIO cam at day but surprisingly doesn't handle the low light as well
  • 25-200mW vtx - This is a welcome addition that means I can run more that the 25mW I'm limited to on AIO cams like those on the sailfly x. 
  • 2s 300mah 30/60c battery - Nice lightweight battery that suits the Red devil well. Same as the one included with the Sailfly-X
A closer look at the quad itself
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Same light but flimsy canopy as the Trashcan
There are a few surprising element to this quad that you wouldn't pick up on from specs alone. Firstly you'd expect that with heavier cam and vtx the quad would weight more than the Sailfly but surprisingly it doesn't - this is because the canopy is much lighter than the hefty 3d printed unit on the sailfly meaning that it comes in at a very familiar dry weight of 38g. This does come at a cost though as noted later in the flight review (jello).
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Also interesting is that they have flipped the flight controller right side up - this means that the motor plugs and USB ports are pointing down rather than up. My guess is that this is to allow the canopy to sit lower and tighter but it does mean than foam tape is needed on several of the connects to protect them from the insertion and removal of the battery. My concern is that this will compromise durability over time.
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Red Devil (left) has a stronger frame
Other than the cutouts for motor plugs and USB access the frame is the same design as the sailfly-x. It is however interesting to note that the frame has more material around the motor screws... a significant improvement over the known weak spot on the Sailfly X.
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New standalone VTX
Lastly the VTX is surprisingly not the same triangular unit from the Eachine Trashcan that is bolt-mounted above the crazybee board - it is instead a small rectangular standalone unit that allows the canopy to be mounted lower down. Here is the page for the VTX for a closer look
Pre-flight setup
Unfortunately like most other crazybee boards released at this time, this board ship with a nightly 4.0 build of betaflight that is not fully compatible with the latest version of betaflight. I'd recommend updating to a release version of betaflight 4 and transfer the key data in as I've done with my sailfly x here. The only real difference is the board orientation set up and motor mapping which is captured in the diff all files below:
Here is the original diff (4.0)
eachine_red_devil_default_diff_all_4.0.0.txt
File Size: 2 kb
File Type: txt
Download File

Default working diff for 4.04
eachine_red_devil_default_diff_all_4.0.4.txt
File Size: 2 kb
File Type: txt
Download File

QuadifyRC diff for 4.04
eachine_red_devil_quadifyrc_diff_all_4.0.4.txt
File Size: 3 kb
File Type: txt
Download File

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​Flight performance
Honestly the flight performance is indistinguishable from the Sailfly-x. To summarise it does actually 'feel' like flying a 5 inch quad due to the control and linear throttle response but obviously not the speed. In addition it is hugely efficient, offering long flight times on small cheap batteries. Relevant quotes from my sailfly-x review are below:
2s flight performance
Straight up this is a quick little quad even on just 2s. It feels about as fast as a good 2.5 inch on 3s, easily. But the speed isn't even the best part. Control is something else. To me micros have always lacked the control feel of a 5 inch quad, you feel less connected but the Sailfly-X feels a lot more predictable. I found myself able to fly more comfortably even on the maiden flight and throttle control tasks like flying close to the ground felt a lot more natural. My guess is something to do with the very low disc loading that may be more in line with a 5 inch.

Better than both of these those is simply stunning efficiency. Other than the 2s battery that shipped with this quad the only batteries I had immediately available with a standard connector were GNB and Tattu 2s 300mah batteries. I was astounded that these batteries consistently gave me 4-5 minutes of fairly hard flying, it is difficult to fathom. Bob Roogi talks about the ideal maximum weight of a toothpick build being 72. With a 2s 300mah battery is is 58g which may go some way to explaining the efficiency. From my estimates the current meter is well calibrated and the maximum draw I saw at 100% throttle was just 7A total. So what does this mean? Lots of time in the air and very cheap batteries. Also minimal weight means less damage but more on this in the durability section.
Lack of weight does have one minor disadvantage which seems logical - lack of chuck-ability. When you try to throw a quad over and obstacle or in a split-s or power loop it doesn't seem to hold momentum at zero throttle. You can see this in the DVR above where most of my split-s and power loops look poorly timed. This may be a feel things since I am not used to the format but time will tell.

The tune feels precise which seems surprising given dynamic filters are off. Furthermore there are no oscillations and motors are cool even after 4+ minutes of vigorous flying.

UPDATE: After spending more time on 2s 450mah (which yield a 5-6 minute flight time) I feel the extra weight isn't worth it. My recommendation is to stick with 300mah and staying light if you stick with 2s, I've listed a few options at the bottom of the page

3s flight performance
3s on the HappyModel Sailfly-x is fast, the strong feel of control as mentioned in 2s really comes into play here because 3s really tests your limits (mine anyway). Whereas I feel the 2s suits small to medium parks I feel 3s suits medium to large parks. To use the same analogy as before this feels like a fast 2.5 inch micro on 4s  from a speed perspective (like the skystars bolt reviewed here)  but with better control due to the lighter weight.

One advantage that 3s cannot maintain over 2s is the crazy efficiency. It feels like the top 20% or so of the throttle on 3s really starts to taper off - whether motors are getting beyond their peak efficiency or motors are starting to flatten out there seems to be more current draw with little improvement in thrust. For this reason I prefer to run a 20% throttle cut on 3s. I got around 3.5 minutes from the stock 3s 300mah battery on average but found the variation  on flight time based on throttle management to be larger which makes perfect sense given my earlier thoughts on peak efficiency.
FPV performance
This is the major departure from the Sailfly-x. Firstly the Caddx EOS2 camera which is a fairly well known quantity now really offer just middling performance. It's looks nice in directly light but in many conditions the red hues become super-saturated and look unrealistic. Low light performance is average. My main complaint of this particular cam in the trashcan review when in 16:9 format as it is here was the lack of vertical field of view making it tricky to fly. I've personally since gotten used to this but it is something to be mindful of.

I'm pleased to say however that the VTX does tend to make up for the camera shortcoming in that it does appear to offer a better signal the the 25mW sailfly vtx (most AIO vtxs don't actually put out 25mW) and that at 200mW it is vastly more powerful. For me 100mW feel like a good setting - not a lot of heat but a signifant improvement when flying behind trees. Like any modern VTX all settings can be accessed in betaflight OSD via smart audio control.
Now for the major downside... on first glance the trashcan canopy looks great - it is very lightweight AND offers adjustable camera angle. Firstly the angle isn't really adjustable because all the efforts make to make the profile low means the camera board fouls on the other components. Next the light weight it false economy - either by design or lack of material the canopy vibrates and moves in flight which means jello (wobbly video) during mid to high throttle especially. I can get around the camera but the jello is really off putting. You can fly through it like most things but it does detract from the overall experience.
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My props actually fouled slightly on the canopy first flight
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See the zip ties holding the canopy down? This was a community 'solution' to the traschan's jello that Eachine adopted for the red devil. It does not work very well!
Conclusions and what next
The Eachine Red Devil is a hard one to pick - it offers wonderful value for money and amazing flight performance but is let down by the FPV experience. Although the frame looks to have been strengthened compared to the sailfly-x there are question marks in my head about the long term durability of the plugs in the way they can rub against the battery - even when protected by foam tape.

As a standalone product I do actually prefer the Sailfly-x... the heavier (uglier!) 3d printed canopy offers a sturdier mount which minimises unwanted movement. This means that even though it has an inferior camera and VTX that the FPV experience is more enjoyable. 

This isn't all doom and gloom though - like the sailfly-x pricing is MUCH more competitive that any other offering in the toothpick category but it does offer a distinct advantage: potential. I have already ordered and received several low cost upgrades the will help realise the true potential of this powerful ultralight quad. As a hint:
  • Eliminating Jello
  • Improving FPV camera image
  • Improving VTX signal
  • Better control link with more range
  • Better propellers
  • Improved durability
  • Optimal tune.
​​I have a day job where I am well looked after so don't need you patreon money nor your deposits to my bitcoin or paypal accounts. I recommend you keep that money for yourself and your family. I do use affiliate links at no cost to you to help fund the parts I need for articles like this - tips, tricks, ugrades and reviews. If you like this or other articles I've written please click on these product links to help me keep this going. Click on the links below to like or share on facebook and spread the word. Thanks :)
Parts
​Here are all the parts specific to the red devil including my recommended batteries. Click through to take you through to the page
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Replacement 3s 300mah lipo
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GNB 2s 300mah value pack - my recommended 2s
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GNB 3s 300mah value pack - my recommended 3s
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Replacement props
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Replacement frame
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Replacement frame and canopy kit
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Replacement Crazybee f4 V2.1 board
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Replacement VTX
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Replacement 1102 motors
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Replacement power lead with capacitor
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Replacement camera in 4:3 - much better FOV than stock 16:9
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