Building a DJI Inspire 2 with Solo Internals - Dev Help Requested! [INSPI-3DR]

Jun 6, 2016
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Forgive me if I'm in the wrong place, but I figured I would start here.

I have purchased a crashed 3dr solo from ebay, in hopes of building a replica (with minor upgrades) of a DJI inspire 2. To do this, I know I will need to do the following.

-replace stock esc's with larger (30a) simonK bec esc's to support larger motors
-figure out how to use a larger 4s 8000 mah lipo instead of the solo's standard battery. This will involve figuring out the SM-bus protocols to maintain smart battery features

and the main reason i am here, I will have to figure out how to use the Accessory bay to control a servo motor that will move the arms up and down once the quad is in the air.

I am a senior at the University of Cincinnati graduating in December with my BBA in Entrepreneurship and a minor in Information Technology. I have worked in several different fields as a development intern, IT intern, and Data analytics intern.

For the most part, Code is not new to me, and I am proficient in Python, JS, Java and SQL.

What I am looking for is any insight on where to begin in regards to the programming of the accessory bay. I will also be documenting this build on YouTube if anyone would like to follow this.

Thanks in advance for any help, It is much appreciated, as I know this will not be an easy task.

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and the main reason i am here, I will have to figure out how to use the Accessory bay to control a servo motor that will move the arms up and down once the quad is in the air
Some people tapped into the accessory connector and were able to control a servo, with the solo controller. Search the forum for servo control. IIRC it is controlled by long pressing the pause button, if that's of help.
figuring out the SM-bus protocols to maintain smart battery features
If you can do this, then you will be the king of Solo....batteries

Will you be using the Solo gimbal or using an alternative? Many are hoping the gimbal code is made open, but no one has been able to crack it to date...i.e. smart shots

Good luck and look forward to your successful project, sounds cool.
Thanks guys, I have been scouring the dev3dr page for the majority of the weekend. Also, I believe I am going to run a stock solo battery in paralell with a secondary 4s battery. I have done a lot of research and even though the one study done on this only netted a 3 minute increase in flight time, I believe with 600kv motors and at least 12" rotors, I will net better results as the test ran a stock solo frame with the stock solo props...
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Update! - So over the weekend I did a bunch of research on how I am going to build this monster, and I have came to the following conclusion, I'm not..... just kidding! haha.

So I decided to stick with Solo's stock motor pods for the esc's as they are 20amp and more than enough for 600kv motors at 4s.

Also I decided per my post above, that I am going to run a stock solo smart battery in parallel with a second 5200mah battery, summing up to 10400mah at 4s. Should be sufficient for my needs as long as the build remains light.

Gimbal, yes, I am utilizing the solo gimbal in order to keep the smart shot functionality. Also, it should be super simple to implement in my design as it is already floating out there in stl form.

Props - probably 12 or 13" - Pitch to be determined. Definitely Carbon fiber.

The most difficult part at this point in time is just the amount of cad/design work required. Also, starting this project from the ground up with no Fusion 360 experience is going to be tedious as well.... the printed part below is 3 hours of design work while watching the damn Pats with the Superbowl last night.

GPS, batteries, and motor pods should be in later this week! Also Stay tuned, I will be posting up a YouTube video of the project in sections throughout the project. Currently editing that. When i am done, assuming the project is successful, I will put it up on thingiverse for all to download.

I also have to pause work on this at some time this week in order to get my large 3d printer back up and running, as you can see the base plate alone barely fits on my print bed!

And I figured out you can indeed 3d print glasses, fell asleep doing research Saturday night and broke my glasses. Easy solution!

As far as printing, I am currently doing all my printing in PLA at a low infill rate for modelling purposes, When complete, ill print everything in ABS with an increased infill, maybe protopasta carbon pla, but then again maybe not as it is heavier than abs.

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Okay, downtime at work today so I started crunching numbers on potential motor considerations
Below are snippets of the excel workbook ive tossed together. I couldn't find stock solo motor statistics, but I found a thread where Roland swapped for a comparable T-motor.

I know my calculations are no where near exact, I simply did a comparision of what I would take for each motor/prop combo to overcome the weight of stock solo. and at what throttle percentage that would occur at.

knowing that this quad of mine is going to be at least 500g (2300g) heavier than solo (second battery) I am aiming for somewhere around 4500-5000 thrust at 100% throttle. This should give me a good balance of performance and longevity as far as that is concerned. Based off of my bastardized math, the solo only has (maybe) 2480g of thrust at 100% throttle. on an 1800g quad, thats not a lot of leeway.

Like I said, I'm no engineer, and I know there are certain variables I am not taking into account, but check out the data Ive compiled below and let me know what you guys think! So far, I am leaning towards either the 3506's with 12x3.8 props or the 3508's with 12x4's .... i guess I will have to calculate the total draw on the electrical system.

3506's - 650kv 4880g's of lift @ 58A and 858w
3508's - 700kv 5540g's of lift @ 64.4A and 936w

Heres the kicker, based on my math, the 3508(700kv) should be more efficient at hover because it will only take around 30% throttle to achieve 1800g of lift with the 12.4 prop running at less than 3.8amps a motor.

The 3506 (650kv) on the other hand, will be hovering around 40% throttle to achieve 1800g of lift, but it will be running a little cooler at 3.1amps

Thoughts? Insights? Am I a complete moron? lemme know !
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Hey Jubalr, thanks for your help! That really is a useful tool and I had no clue about it. It does definitely help calculate a better idea of how the quad will handle!
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Good luck on this project you passion is down right inspiring.
If you eventually run into issues with the stock pods and or propietary nature of the solo gimbal and tx
dont give up.
there are PH2 based carrier boards that are more DIY friendly
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Thanks Pyrate! Since leaving work , I ordered a single MN3508 to start messing with. Not sure if I am going to shell out the $50/pair that T-motor wants for the cf 12x4 props, might shop around a bit, but this seems to be the most efficient motor in the lineup.

I'm currently redesigning the baseplate for the solo mainboard. In regards to tx are you talking about the controls needed for servo operation? I have found like 3 sources so far that have either directly soldered into the header under the PH2 or tagged on a breakout board. My particular mainboard is lacking the header for the breakout board (i have it, but its unattached. However, I would venture to say I could probably find a way to make it work if need be. Current tasks are pretty centric around design. Although I might have to finish my larger printer's repairs before I continue prototyping as my current mainboard baseplate is filling up the whole print area. haha.

IF anyone has any Ideas on extending battery life past doubling the 4s packs let me know. I know 6s is out of the picture as all the solo mainboard runs on it 4s. Either way, the goal is an even blend of performance and efficiency. If I can score 45mph and 20 minutes of flight time ill be happy! haha.
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This is the motor I am going with in my Super Solo.
Tiger Motor MN3110-26 470kv with 15" props and 40 AMP ESC

So far I built my frame and am in the process of flying it on a Pixhawk 1.

Currently my weight is 3.5 lbs (Frame is a bit heavy (First prototype)) and am pulling around 12 amps at hover. I have added 1 2 and 3 lbs of weight, and as obvious the amps go up accordingly. Next step is reducing weight, as my goal is to be no heavier than the Solo is when using the Solo gimbal.
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Glad to hear it drewjet! Yeah I ill look into tarot props. Does anyone know if 3dr ever released any more CAD files than the beauty plate and the battery enclosure? I sent them a request for information hoping for a cad file of the motor pods and the mainboard, but we shall see... It would definitely make my job 10x easier in designing this frame if I could get the mounting of the mainboard and gimbal done already.
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Okay guys, update. Last night after watching some more how-to's on Autodesk fusion, I got a better Idea of how to properly model. I'm still working on getting the standoff's just right on the mainboard holder, but progress is coming along! Also, more parts should be dropping in so stay tuned!

I got my T-motor from Amazon today (love amazon@Cincinnati). So I should begin modifying either blackboxRc's motor pods or Vlad B's Desert Eagle UAV motor pods to fit both a 25mm motor and a Solo ESC with LED's. Should be a fun exercise in Fusion. I still have to figure out the best practice for getting meshes back to solids in Fusion.

Also, printed the Solo beauty plate to get an Idea of the size of the gimbal until I can buy one.... unfortunately, Solo doesn't release ALL of the mounting information for the gimbal, So I am going to have to spitball it until I snag one off ebay. This will undoubtedly be the widest part of the main drone body. Ill probably try to design it similarly to the front of the Inspire 2, where the Canopy Drapes around the gimbal mount that protrudes from the bottom. We shall see.

As far as props, I ordered some cheapo T-style 12x4's CF props from hobbyking. Less than $15 for the set, so Im sure they aren't balanced well... but they will suffice until the project is literally "in the air".

Also still on the hunt for a cheap gimbal. Most have averaged 40-50 on ebay. Eventually Ill have to snag one to finish the design of the body lower portion. On the list for the rest of the week is to finish the main tray and start on the primary battery mount for Solo battery in the stock location. I am doing this to keep the Center of gravity and excess wiring to a minimum. Ill end up having the extra battery connections dropping out below the mainboard as to keep solo battery from getting hacked up. Depending on final flight time, I may elect to strap 2 4000mah 4s's with a higher C rating than the stock battery to the belly. (maybe they will take the load off it a little more?) Research needed here for sure. I wonder if running parallel 30-40c batteries with a 25c will bring the system C rating up a bit?

Anyway. Much more cad modeling to do. Decided to go with 25mm cf tubes for the main arms and 22 for the rotor arms. Identical to the Inspire 2. Seems like people really really like the increase in stiffness on the central part of the drone. Transform arms will be 8mm. Also still need to mock up and probably redesign the arm joints because the center of gravity is different on this than the blackbox setup and Vlad's desert eagle.

I'm sure there are things i forgot, but either way let me know what you guys think. I'm still working on compiling useful information for the first YouTube video of this build.

If you wish to see the print of V1 or V1.5 of the baseplate, Ill link them here. I run a live stream anytime I print something worthwhile.
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Massive Picture Dump this time, so I am only going to put the main ones inline, the rest will remain thumbs!
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I hate backtracking, but after reviewing the specs of the MN3510-13 Shown below, i believe that will be a better motor for my build. So doing as we all do, I am returning the 3508 to amazon. I want to be able to use EXACT inspire rotors. And those are 1345s. Sadly I believe the 3508 doesnt have enough juice to swing those rotors. Luckily. The 3510s can run the 12x4.5's I ordered today, and 1345s giving me the ability to buy new rotors in the future rather than have to do entire motor swaps. Size wise, they are damn near identical, with mounting patterns and motor diameter being the same and the 3510 being only 2mm taller.

Getting damn near 20amps at full go (19.4amps) I may limit them to 95% throttle, but damn, If I can get a 3:1 performance ratio from this quad I will be more than stoked.


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More Progress!! I redesigned the main chassis again yesterday, moving the standoffs and beefing them up a bit. Also adding standoffs to the front of the mainboard chassis.

I also added supports for the front and back of the board, similar to the standoffs. I'm really getting the hang of this modelling thing!
I also moved the side brackets out 1mm and added a third. These will help me judge where to make the cut out for the battery tray cover.

Currently doing a reprint of the main chassis as the current one shifted halfway through the layers. Everything seems to line up well, but I am reprinting just to be safe. Needless to say I am going to have a huge pile of prototyped parts by the end.

Up next is adding the battery tray, and deciding upon where to branch off (or bolt up) the next part of the frame. I would like to print the frame as one solid part, but that may not be a reality in the long run. Only time will tell.

One big concern I have currently is whether or not the 4s 10400mah 25c power system will suffice for the 3510-13 motors. The last thing i want is to kill the batteries with too high of amperage draw. Does anyone know if using a larger C rating battery in conjunction with a lower C rating battery would bring the overall C average up? Or just leave the Lower rated battery dead sooner?

Hoping to crack out V3 of the mainboard today and start mocking up the arm mechanism tomorrow. Need to revise the parts from other builds to support 25mm cf arms instead of 22mm like the inspire 1. My inner arms are going to be 25 and the outers 22, just like inspire 2. Also, holy moly, actually looking at the size of 13" props.....damn. This thing is gonna rip.

I think if my math is right, 10400mah (2 5200mah batts) @ 25C = 260,000Cmah/1000 = 260C/A meaning 260 constant amperage draw.
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So that being said, with the above diagrams,

Once again, Pic dump below.
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Printing frame again, hopefully no layer shift this time.
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Okay, Weekend Recap. Got a lot done!
-Tmotor 3510 630kv showed up. Sent the others back.
-Fixed the design of the mainboard holder
-Realized my ebay mainboard was defective... damnit. Bought a solo combo with gimbal from Best Buy for $300
-redesigned motor pods, twice

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-killed an entire spool of pla
-created battery tray that actually replicated the factory battery tray
-realized that the companion computer on my ebay mainboard was also overheating (no clue why).
-gutted Best Buy Solo, only to have to reassemble it to calibrate the compass
-after 12 hours of troubleshooting multiple controllers, mainboards, batteries and companion computers, figured out which parts were faulty, and or just not okay with the 2.4.2 firmware release.

-FINALLY thrust tested the 3510 630kv motor with a shoddy 3d printed prop and it was TERRIFYING.
Carbon fiber tubing on order. Frame joint design to begin soon. (have to do homework first lol)
Also need to start hunting for a gopro I guess.

Photo dump below and probably the next post as well.... also, if anyone needs a body or motorpods, hit me up, I should have a plethora of unused stock parts shortly.

As always, let me know what you guys think!


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Sorry Guys, been really busy with school! Here's an update though!
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Finishing up the motor pod design and starting on the wiring harness! I decided to use flexible Cat5 (stranded) to control the esc's through the original Esc headers (8 pin). It's lightweight and should be fine as long as I keep it in wireloom mesh.
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I still have to pick up the 4th 3510 and and waiting on the props, but the amount of printing that lies ahead should keep me busy all week anyway. I spent the majority of the last two weeks rebuilding my larger 3d printer, as it is a corexy design and has a titan extruder, which is much much more efficient than my Creatorbox System. However after a few prints with Filament Innovations High Modulus Carbon Fiber ABS, I am running into jamming issues, I am going to attempt to resolve those this week with retraction changes and a rebuild of the extruder. So far, only one successful Carbon Fiber print, but it bodes well for the motor pod design! Also, here is a link to the DBot printing the motor pod (sorry about the camera angle) and another shot filmed on my pixel. Hopefully going to have a lax week at school, time to get some work done on this beast!!!!

Dbot entire print video:
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Pixel Vid of Carbon Printing (50mm/s 50% infill, slight overextrusion)
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