Introduction to Hachidorii XL

The Hachidorii XL is my personal take on a larger whoop frame while incorporating some characteristics from the Hachidorii XS and V2. Some frame specs can be found in my video discussing the frame. If you'd like to support me and my future projects, the carbon fiber parts and some hardware are available here [Link to be added - estimated to be available by end of May] in CNCDrones and all the files for the frame will be available in Thingiverse and Printables here [Link to be added]. A build guide for the entire Hachidorii family of frames will be released soon too including PID tunes, guides, recommended parts, and tips.

The frame, while not the best in any aspect, is more of an experimental platform - something that people can play around different design ideas without worrying too much about weight or space limitations. In my case, I wanted to focus on using the DJI O4 lite - in which I had three goals in mind:

1. Make a frame that fits the DJI O4 lite
2. The frame is easy to build up and performs like a whoop
3. and lastly, to have minimal to no jello in the video feed/recorded footage even in non-deal conditions (bent prop, windy, etc)

Though I'm using the DJI O4 lite, I will also be providing variants of parts that will fit other transmission systems, including analog. Rest assured that the only components that will vary depending on the parts you choose (such as the VTX system) are 3D prints. Though the Top Mount and Bottom Mount variants (more on this later) use a different top plate, everything else should be accessible to anyone who has access to a 3D printer. This also means that modifying the frame will be relatively easy - my gift for those who'd like to experiment with the frame.

Like the Hachidorii XS and V2, the XL's construction is also similar to building up a toothpick - easy to build up and easy to repair. This is a non-negotiable for me as I want to advocate for people to learn how to build and repair. Building and repairing can be very rewarding and extends even outside of FPV. I want to give people a smooth and rewarding experience with (likely) their first digital whoop build. I also want to mention that I am not entirely the best at PID tuning but rest assured that the PID setup that I will be including in my Hachidorii Build Guide will get you around 85% there. Certainly flyable but can still be improved on.

Furthermore, with the components that I recommend in this article, I want the Hachidorii XL to perform like a whoop. This means that it can be used for both cruising and freestyle. Again, this isn't meant to be a top performing setup, but I want it to be capable enough where I can have fun and not be too bothered by the added weight.

Because of these goals, I have made several design choices which will be discussed throughout this article.

The Hachidorii Design

Before we discuss the new features of the XL, let's talk about its similarities to its older smaller borthers, the XS and V2. The Hachidorii design has two main distinguishing characteristics that make it different from the conventional whoop build.

First, the frame is a skeletalized box-style carbon fiber main plate paired with ducts. As mentioned in my Hachidorii V2 article [https://rotorbuilds.com/build/32429], the main advantage of this layout is the mode of vibrations coming from the motors. The conventional X-style frame handles bending fairly well but struggles with twisting modes. On the other hand, the box-style format handles twisting better while still reasonably handling bending. I also want to mention that the Hachidorii family of frames manage to have thin skeletalized arms because, in majority of the crashes they experience, the ducts and canopy are the first to make contact and are generally what absorbs most of the energy in an impact - which is something I discussed in my second material testing video where I did my crash testing [https://youtu.be/RCvcAElcARI?si=M985JYpxM4FyKWWp]. Though ducts will break, this sacrificial piece will keep your electronics safe.

As I've mentioned earlier, I also want Hachidoriis to be easy to build up especially for those who are using the frame in their first build. This characterstic will also allow it to be easily repairable and maintained down the line. Because of this, the second characteristic is its toothpick-like build process. I've been flying toothpicks for several years now and they will (and honestly, will always be) the easiest type of drones to build. The Hachidorii family is the same build process with the exception of a few steps regarding the ducts.

These two characteristics make up the general design language of the Hachidorii family, including the XL. Though the Hachidorii XL does not prioritize weight as much as the V2 and XS, it prioritizes other aspects such as its focus on digital builds and minimal jello in recordings.

The Twins

I've split the Hachidorii XL into two configurations depending on how builders would want to fly it. These are the Top Mount (TM) and Bottom Mount (BM) configurations. Both configurations use three GEPRC vibration dampeners [https://geprc.com/product/gep-camera-damping-ball-6-pcs/] but use a different top plate and a different set of 3D printed components to hold the camera.

Hachidorii XL Bottom Mount [BM]

The BM is your standard digital whoop layout. It has a bottom mounted battery, motors are pointed up, and the camera is mounted above the propline at the center of the whoop. This is your typical digital whoop and will fly similar to a digital Mobula 8 - great at cornering, some ducts in view (ducts in view with camera angles less than 25 degrees), and better camera protection. I've also mentioned in my video that the camera, even when pressed to its lowest point, will not reach the VTX. However, if you want to lower that risk even more, I will be providing a spacer to increase the space between the camera and VTX. This was the first Hachidorii XL I developed and tested which has been beta-tested by a good number of local pilots - some who even managed to fly it in their trips outside of the country. This is the variant of the Hachidorii XL that I find is most fun doing freestyle with.

Hachidorii XL Top Mount [TM]

The TM was the original goal of this project. I wanted something that can cruise nicely, nothing in view (vibration dampeners in view with camera angles less than 10 degrees), and defintely a top mounted battery for that smooth flight. I've also not seen too many whoops at this size that were were both non-pushers and had a top mounted battery. The TM is definitely more fragile than the BM, given the camera position, but I genuinely like the TM more than the BM and have brought it with me in the few trips I've had the past few months. The battery placement also makes a significant difference in the flight feel - making rolls (and therefore, also turns) feel so much smoother. I occasionally freestyle the TM and you can definitely feel the difference between the TM and BM when doing Split-S maneuvers.

Vibration Dampening

One of the key components of the Hachidorii XL is its vibration dampening. I did some testing with different types of vibration dampeners and ultimately chose the GEPRC dampeners for their size and stiffness. Despite being the best among the dampeners that I tested, I did still have some vibrations in the initial stages of my testing. I actually consulted some of my professors regarding this matter and they suggested offsetting the mounts of the dampeners to apply some sort of pre-tension. I played around with the idea and managed to have minimal to no jello in my recordings on the newer prototypes. If you check out my video or some of the photos on the hachidorii XL, the dampeners are actually slightly stretched or tilted which is a result of my professors advice (which works......sooooooo I won't question that HAHAHAH). In my video, I show a mix of footages - some are stabilized in gyroflow while some are either DVR or Raw recordings off the O4 lite.

3D Printed ducts

The 3D printed ducts were the main issue I was handling the past four months of the Hachidorii XL's development. My initial tests all ended with broken ducts but I've made several design changes to the ducts's geometry to give them a better survival chance and I also have two additional recomendations. The first recomendation is to use nylon standoffs and screws to hold the ducts. Nylon hardware has enough flex that acts like a cushion which lowers the instanteneous forces acting on the duct - thus reducing the chances of them sheering off at the mounting points. Nylon hardware is also lighter than metal so that is a nice bonus. This solution actually works fairly well for the testing I've done with PLA ducts (the most brittle material).

However, my second recomendation is to print these ducts in ABS, ASA, or PETG. Based on my testing on 3D printed ducts, ABS and ASA were one of the best materials to be used for ducts because of their physical properties and PETG is also a good alternative if you cannot print ABS or ASA (perhaps for health reasons or 3D printer limitations).

I do want to be honest here and mention that 3D printed ducts will break especially as you increase weight. My digital Hachidorii XL builds have ranged between 45-60g dry weigths and I do still occasionally need to replace them. Rest assured though that, in many cases, the ducts will take majority of the impact in crashes and that it will protect your motors and electronics.

Power Chains

One thing I'd like to mention that I am proud that I found and something that I plan to incorporate into my future micro frames are...Power chains!!

Anyone who has had braces knows what power chains are. They are the chain-like elastics attached to your braces to apply a force between your teeth. It is an unconventional elastic to use for tinywhoops but I found them to be extremely cheap and very accessible in my local online stores. Generally, they will sell power chains as a long strand that you can actually just cut a piece and use as a battery strap. Aside from their cost and accessibility, they have several other benefits that make them really useful for carbon fiber whoop builds.

• Power chains are lightweight. On my Hachidorii XS and XL, two 10-hole strands weigh 0.09g.
• Adjusting tightness is as easy as shifting which hole is hooked.
• They do not degrade (I've used the same pair on the XS for 7 months!)

Personally, I think power chains are convinient and hold batteries well for these small drones. Just like any elastic, its best to file down the frame to dull the corners of the hooks they'll attach on to give them a lower chance of being cut by the sharp edges on carbon fiber frames. If you guys want more information about them, I have a full post about them here http://youtube.com/post/Ugkx9iiOGjpOspvb_5uOGyF3H7I31Q_93osh?si=tqBG2d19hbhwkMJO.

Recommended Parts

When it comes to the recommended parts, I made the Hachidorii XL pretty flexible with what components you can use. However, because this platform isn't necessarily strict with weight, the components I will mention are primarily chosen for their performance, durability, or compatability with other parts.

My build focused mostly on the DJI O4 lite but, as I've mentioned earlier, I will also include files that will allow you guys to use other video transmission systems like walksnail. For an analog build, you can actually just use a standard TPU canopy since the mounting dimensions of the Hachidorii XL is the same as any other whoop canopy (25.4mm by 25.4mm). I do have plans on having a specific vibrationally dampened mount for the Runcam Thumb Pro - but as of now, it's not a priority. For the AIO, I have used BetaFPV's 20a V5 BMI Board, BetaFPV's 12a V3 Board, Happymodel's X12 (with motor connectors), NamelessRC's AIO412T, DarwinFPV's 15a F411, and JHEMCU's GHF435AIO 20A - and I have had absolutely no problems with using them. I think any aio with atleast 12a ESCs is fine given that the DJI O4 can operate directly on 2s. Even the AIO's of BetaFPV's Pavo series can fit the Hachidorii XL - albeit, your usb port is blocked by a standoff.

I primarily used Mepsking's SZ1103 11000kv motors because they were powerful enough but still fairly efficient - getting 3 mins and 30 sec on a 380 mAh GNB battery (which has a bt3.0 connector). I also like the fact that they have a PCB on their motor which makes it convinient to swap motor wires. I have also tried BetaFPV's 1103 11000kv motors which were not as powerful and punchy but definitely more efficient compared to the SZ1103 motors - 6 min on a 550 mah 2s LAVA battery while doing casual freestyle. If you are looking for a more efficient setup, I recommend going for 1202 or 1202.5 motors with around 10000kv motors (or just get higher KV motors and lower throttle output). They won't perform as well as the 1103's for freestyle but they will definitely fly longer which is what I found when trying the Aeolus 1202.5 11500kv motors.

As much as I want to recommend some props, I genuinely only had the opportunity to use Gemfan's 45mm props. They work fine in my opnion but are extremely fragile. There is a very helpful video made by ButterflyFPV about 45mm propellers [https://youtu.be/crKrlwHEF6s?si=gPDKT2MQPyCUblsf&t=98] which I think you guys would appreciate. Based on his findings, I think the HQ props would be a great candidate for the Hachidorii XL.

Other Notes To Consider

Lastly, this section is just some random things I don't really know where to put but would like to mention - either as a neat fact or for some of you who have questions.

• The original frame I played around with earlier this year was Spezilover's Spezilicious 75 RST [https://rotorbuilds.com/build/33863]. I highly suggest checking him out and his store [quadview.eu]! the Hachidorii XS is also available in his store!
• The frame is open source so feel free to check out the files in Thingiverse or Printables if you'd like to experiment with the frame or make some custom parts to make your build cleaner or more convinient.
• I was taking my Controls Engineering and Vibration Engineering classes while developing the Hachidorii XL. I've actually implemented some concepts I learned at university to this frame. Though it is not perfect, I am proud that I've managed to apply something I learned. I even showed some professors and they found it cool.
• I wanted to use printed dampeners but I've had absolutely no luck with the results I got earlier this year.
• You can use lens modded DJI O4s with the Hachidorii XLs but note that the camera guard does not account for the added length of a new lens. I do have my own design for the lens mod which can be found here [https://www.thingiverse.com/thing:6985062] or here [https://www.printables.com/model/1235923-dji-o4-lite-lens-mod-for-m8-and-m12-lenses].
• I have tried to add an ND filter mount on the Hachidorii XL but gave up as the results wasn't as good as I was hoping. The O4, in my personal opinion, is not that great for getting cinematic footage. It is good enough for sharing but definitely not on the level of the O3 or O4 Pro - unless you color grade as amazingly as Shauny_D [https://tinyurl.com/c7eweeew]
• There was supposed to be a third configuration (a pusher) which was meant to hold the DJI O4 Pro. I did not think that it was going to fly good so the idea was scrapped. However, with some slight adjustments to the duct's design, the O4 Pro does fit the Hachidorii XL BM. Alternatively, I think a pusher like BetaFPV's Pavo drones (with the vtx and camera module on top) can be implemented on a pusher variant of the Hachidorii XL.
• I'm like....extra broke HAHAHAHHA I destroyed two DJI O4 lites during my initial month of testing
• I have no shame - heres an affiliate link to Mepsking's store [https://tinyurl.com/mr3ypscw]. You can also use "RICE10" at the checkout for a 10% discount.
• I have no shame again - heres an affiliate link to BetaFPV's store [https://betafpv.com/ricebowl]
• Definitely don't need to use these but I just wanted to put them out there. Thank you so much if you do!
• Thank you so much if you've reached this end!