HappyModel Larva-X: Review, SETUP, PIDS

The Larva-X is a new lightweight micro FPV quadcopter made by Happymodel, a company who are very well known now to innovate new trends and hype in micro quadcopters. The Larva-x looks to be a more robust and refined evolution of the "toothpick" class of ultra light weight quads, this time with a more robust frame, better receiver options and a better FPV system, which addresses complaints on some of their earlier models.

The Larva-X is available now from many retailers. Below is the link from Banggood who ship internationally from $0 and up. At time of writing (9 September 2019) they have their big anniversary sale on and have the Larva-X on Special for $83 using the code "BGANLX" and this link: Happymodel Larva X 100mm 2-3S 2.5 Inch FPV Racing Drone

Specifcations
100mm carbon fibre frame - Although a spindly design, this is 3mm thick carbon. It feels rigid and very robust, a big improvement on previous frames which were light but prone to breaking.
Happymodel EX1103 7000KV Motor - An extra 1mm stator height gives 50% volume over the 1102 motors found on the sailfly-x. 7000kV is a good rating for 3s primarily or 2s for smaller areas.
Crazybee F4 Pro V3  Flight Controller - V3 of this flight controller no longer requires the additional capacitor as seen on the sailfly-x and eachine red devil
Onboard 10A 4in1 ESC - The extra current overhead (10a vs 6a) and voltage overhead (up to 4s) means that this should be MUCH more reliable on 3s... it is well away from current and voltage limits with 1103 7000kV motors
Multiple receiver options - Have options to choose onboard frsky/flysky/dsmx which have typically poor range but for the first time they are offering discrete receiver options including XM+, R-XSR and even TBS crossfire!
Happymodel Diamond VTX - Not only does this offer 25mw-200mW OSD selectable transmit power but it also includes an onboard DVR for static-free recording.
Runcam NANO2 FPV Camera - Hooray! A better camera. The rancam nano 2 is currentl recognised as the best price per performance nano size cam at present.

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What is included in the kit (other than the quad as specced above)?

4X Micro Avan Rush Propeller 2.5 Inch ( 4 CW & 4 CCW) - Included are Emax Avan Rush 2.5 and or HQ 2.5x2.5x3. Both are 3 bladed props which are quieter and more grippy but slightly slower and less efficient that the bi blades we've become familiar with in this class.
1X Propeller disassemble tool
1X Screwdriver
1X Battery strap - the crappy kind 😢
1X Spare Canopy - This is an extremely pleasant suprise since it is injection moulded (not 3d printed) but more importantly feels light, robust and is much better designed the previous Happymodel offerings. I can see this becoming my favourite canopy for any tootpick build going forward.
Note: there is no battery which is the first for a Happymodel quad. I'm happy for them to do this in order to keep the cost down as I'd rather choose these for myself. My recommendations on batteries can be found in the review itself.

A closer look at the build
I like the happymodel builds, that are very modular meaning components can be replaced and upgraded very easily. Looking closely at this build I can first see they have finally moved from nylon screws to steel screws to hold the flight controller, vtx and canopy to the frame. This will make it much more robust than the nylon screws used in previous models like the sailfly-x, red devil and trashcan.

Steel screws are a welcome update

Large spacing between FC and VTX allows for cooling

​Speaking of mounting there looks to be a seemingly unnecessarily large amount of space between the flight controller and the VTX. On closer consideration though this makes sense - the VTX has a high power output for it's size and it has a DVR crammed on the same board meaning it likely runs warm. The extra space will not only protect the flight controller but will offer better cooling as well.

The frame looks very spindly to start but being based on 3mm carbon means it actually feels very rigid. This is a welcome relief from the sailfly-x which had a very lightweight but weak frame. It will be interesting to see how the extra rigidity and support spars translate to flight performance. Propeller size is limited to 65mm maximum which is fine - a 3 inch prop is too big for an 1103 motor anyway.

Frame is 3mm thick and designed with multiple spars

1103 is a good increase in motor size but I would have preferred m2 rather than m1.4 screws

Next it's nice to see the switch from 1102 motors on the sailfly-x to 1103 motors here. An 1103 motor offers 50% more stator volume and is a welcome improvement. 7000kV rating is better suited to 3s but will be much more tame on 2s. It's a shame they are sticking with their 3-hole mounting system for the motors as this closes the frame off to any other motor since Happymodel are the only one who runs this 'standard'. Also be ware that motor screws are only m1.4 - combined with the fact the motors are made from fairly soft aluminium, take care not to overtighten and strip.

Setup - a note on binding for SPI receiver models
You'll see in the instructions that you need to press the binding button on the board to bind. Don't even bother - this is located on top of the board beneath the VTX and impossible to access without disassembling. Assuming you have one of the on-board receiver options instead use the betaflight CLI command "bind_rx_spi" which will do the same job as pressing the button.

Setup - a closer look at the betaflight factory settings and the changes I made
Good news, they are finally shipping the Crazybee boards in these quads with a proper betaflight release - in this case betaflight 4.04. Prior to that they had been nightlty builds which have had compatibility issues with the current version of betaflight configurator. After looking at the default setup there were definitely some changes I wanted to make which I have clearly illustrated in the screenshots below:

A note on PID and fliter tune
Since it is a topic that deserves a section on its own I've done so here. I do not like the custom tune that came on this quad with 3s. It has a lot of propwash oscillation and felt loose at the same time. I've chosen to use a PID tune and filter tune based on the community preset for micros developed by Mark Spatz (UAVTech). Most importantly filters are adjusted to better match the high frequency of these micro motors and pids to adjust the level of autority the motors have over the prop. Please see below for my final numbers (click to embiggen):

less P, more I and changes to d set point

TPA increased at high throttle

Changes to the filters to make them more suitable for small motors

Flight performance - 3s
First flights were on 3s 450mah and the quad felt good (if a little heavy) but the factory tune was awful. I since upgrade to the tune above which felt much better. After that fix I'm really enjoying this on 3s: It is fast and due to the relatively light weight and large 3 blade prop the grip is excellent and it is super quiet. All of these factors make it a real treat to fly in areas where larger quads would be frowned upon. It offers greater performance than 2s 1102 or 1103-based toothpick quads but is more of an evolutionary rather than revolutionary step. I think the key performance boost is reliability on 3s given the board is now rated for 4s 10a rather than pushing the limits of the 3s 6a sailfly-x board.

So far as batteries, my 3s 450mah nanotech 40g batteries feel perhaps a hair heavy but have always performed well for me and are cheap at around $7 each from hobbyking. Flight time here was around 4 minutes which is very respectable (landing at 3.78v per cell rested).

If starting from new I'd probably go for the new GNB 3s 300mah 29g batteries which will be more nimble on account of 10-11g less weight. 

Flight performance - 2s
2s is understandable more docile but the level of control and throttle resolution is very nice. I think this would be a great size to run for tight spaces like small parks with lots of trees or carparks. It obviously doesn't have the top speed of 3s but flight time on my tattu 2s 450mah 30g packs was around 5 minutes; great for a gentle cruise.

FPV performance
It's a little bit tricky for me to judge FPV performance because I've just switched to the Skyzone SKY03O goggles (reviewed here) which have a much better screen and receiver than I'm used to. From what I can tell though the runcam nano 2 is similar to the Caddx EOS2 but with improvements where they count - less of the funny red tint the plagued the early EOS2 cameras plus a much better vertical field of view. Reception is good and it's nice to have the extra power options compared to the fixed 25mW vtx of the sailfly-x. DVR is a nice function to have. Quality is no better than your goggle DVR however there is no break up. The Runcam split 3 nano is of course coming but this is pretty useful for a low cost solution. DVR footage from onboard and goggle DVR from the same flight is below for your consideration

Goggle DVR

Onboard DVR from the Diamond VTX

Durability
I sustained damage on my very first flight but it is an easy one to avoid. The linear dipole vtx antenna popped of the UFL connection and was lost. Luckily I had a replacement but would recommend using some E6000 glue to fix it to the board more securely. This glue works well because it is removable like hot glue but wont melt off as a result of VTX operating temperatures.

$3 E6000 glue is super useful

It's looking good so far for the frame but I'm wary of the motors. The Emax Avan Rush 2.5 props are incredibly stiff and I'm worried that a crash will transmit forces back to what is a fairly weak motor. This is the main reason I switched the the HQ 2.5x2.5x3 but the relatively flexible HQ T65mm prop looks like a good option too. Update: I did damage a motor but was able to refix it without noticeable permanent damage so far. I made a note on the Happymodel Facebook group and was happy to receive a response from Jason @ happymodel fairly promptly - see below

Summary and recommendation
Like most of the recent Happymodel products, the Larva-x has hit the model with quite a splash. It is a well thought out unit that follows their mantra for lightweight and yields the desired response of performance, agility, quietness and efficiency at a low price. Their are clear improvements and added features following their learnings from earlier models: a stronger frame, more powerful motors, adjustable vtx with inbuilt DVR, better FPV cam and an ESC with a much better performance overhead.

The only clear deficiency I've found through my own testing is around the motors, not from a performance perspective but from a durability one. Even then they have recognised this issue and as noted in the review look to be working on it already. The other deficiency common to crazybee boards with inbuilt SPI receivers is the poor range but at least this has been recognised with multiple FRSKY and even a crossfire receiver option.

The flight characteristics, FPV feed, efficiency and quietness of this model makes it a lot of fun to fly in places that a larger quad would be antisocial yet still has the power (especially on 3s) to cover a lot of ground in a hurry.

I do think this is an incremental improvement over the other bind and fly toothpick class quads and as per other happymodel releases offers great value for money. It retails for $98 with the inbuilt receiver but over the period 9-12 September it is just $83 with code BGANLX at this link

​Thanks for reading, if you found this article useful please feel free to like or share, the facebook links below directly link/like this article. Links are affiliated and help me buy the bits I need to produce this type of content. If you are looking for quads or parts check out my coupons and discounts page which I keep updated with only the parts and quads I like at a proper discount.

Spare parts

Runcam nano 2 cam

Frame

Screw set

Canopy

Crazybee F4 V3 FC/ESC

1103 motors

Avan rush props

GNB 3s 300mah. Make sure you get this one specifically