Crazy idea: 6mm motors octopter


#41

Here’s a sketch of what it could look like. No ducts, 31mm regular tiny whoop props, and a frame weight ideally less than 10gr


#42

hehehe thanks. If i only kill the fc board, no big deal


#43

did u make that, looks really neat. the best I would do is a google drawing :joy:


#44

i was a graphic designer


#45

cool, good luck on the build


#46

yeah, lets see if i can figure out how to create a frame like that under 10gr without spending money, or too little money
If i can, and even if the e010 fc doesn’t work, i can always invest in a octo brushed alienflight fc board http://alienflight.com/f3-brushed-octo/


#47

I would think the mosfets on most of the recent F3 boards from eachine and the likes would be able to cope with the draw of 2 motors, at least 6mm ones. Older ones like the scisky and most F1 boards have lower rating mosfets in the style of a black rectangle with 3 legs, newer boards have 10A rated ones that are square style with no visible legs, instead having pads on the underside.
The biggest risk to mosfets is stalling the motor while still feeding power to it, even high quality ones can sometimes only last a second or two of that.
If thinking about pairs one above the other you would need to include some landing gear to allow clearance for the lower, inverted prop, adding to weight.
Let’s see some experiments :+1:


#48

To me that sounds like a big YES! :smile: i thought about several configurations, one of them setting the 8 motors in a circle (as the above graphic shows), but the problem with this is the creation of a light weight frame. A custom homemade frame with cheap materials wont be so light… And don’t have a 3d printer. I even thought about ordering a carbon frame cnc custom cut, but that would be expensive.

The other possibility would be adapting a e010s frame to hold two motors in each mount. Or, if i use 2 tiny whoop stiffeners, i just leave some space in between and each one will hold one set of motors. It would be great, because i have everything i need, and i’m not adding more weight than motors, props, and a heavier battery (and a landing gear, of course, as you mentioned). But in this case i have a lot of questions.

  • If i put two CW motors in the same place, one facing upwards and another one facing downwards, then i have two motors spinning in opposite directions, so that will make both motors work as a coaxial rotor, wouldn’t it? I know that configuration should allow for a stable flight, at least when there’s only one coaxial rotor, but don’t have any idea how will that thing fly when setting up 4 of them… Shouldn’t it cause some yaw issues? And don’t know if it’s more powerful because of the combination of thrusts…

  • Another possibility would be using a CW motor, and below it a CCW one facing downwards, so both spin in the same direction. Both of them using CW props, so they also push in the same direction. But here i have two uncertainties. First, how would those two propeller manage the air flowing throught them? Is there more power, or the bottom propeller doesn’t add much thrust? Second: The spin direction in a brushed motor is in the motor, so i guess that when connecting together a CW and CCW motor in the same pads in the flight controller, both of them would spin in its own direction, and the only info they receive from the flight controller is the speed.

So… what configuration of motors do you think is best? I’m really curious about the airflow between the two propellers in both cases. Is there double thrust? or just a little bit more than with one propeller?


#49

Option 2 is what I’m considering. The motors will work out fine as far as cw and ccw on the same pad. That’s the x8 configuration I talked about earlier. Usually there are two different prop sizes/pitches in a larger model. Maybe a 2 blade on top and a 4 blade below … or maybe the opposite of that - I’m not too sure. But that’s where all the fun comes in. I still think your frame stiffeners will be perfect for that. Sandwich the fc between them and find some sort of standoffs to brace the separation. Just search x8 multirotor to dig up some more info on how they do the specifics on props. Excellent brainstorming so far!


#50

Thanks, man. My research was limited to youtube videos so far, didn’t have the time to research further, but i will. The octocopters that i saw i think that every pair of motors were spinning same direction, and with same propellers.

The whole idea of this project is to have fun, of course, but also to achieve a powerful machine. Not just something like the 42gr octowhoop that barely lifts from the ground

My fear is that the combined thrust of both motors, one on top of the other managing the same air flow, wont be the same as every motor separated and managing clean air. But, in the other hand, i’m saving a lot of weight by using a 3gr frame for the whole setup of motors…

What you said about different blade count in every pair of motors is also very interesting.

Anyways, it will be fun testing every possibility, i just want to collect all the info that i can to save time and money in the whole process.

Thanks again!!


#51

Hopefully this will be enough material for a series of videos, to share all the things i’m learning in the process of building and testing. That’s the idea, lets see if i have the time to do it


#52

Awesome! I came across this thread yesterday and thought - yeh, I can do that :stuck_out_tongue:

It doesnt fly all that well, but if DOES. So if anyone is keen, Im sharing the print file:
OctoWhoop.stl.zip (224.1 KB)

Printed with around 30% infill using high-impact ABS, the frame weighs around 7g.
There is a lot of frame blocking the airflow.

To make it better, the frame material needs to be distributed more vertical. Currently, my beam width is so wide, because its super-simple to design this way, and Im a very amateurish designer using the buggy FreeCAD. Making up this one has cost me around 5 minutes (2 circles, pad, then one 3.05mm circle, octo pattern with 41.81mm radius, pocket).

To make the frame narrower, I need to spend a few hours on the design.
It doesnt fly THAT well that Im motivated to do that right now.
But maybe on a rainy day…


#53

Nice, decided to help and make my own design, if you would like to transfer all that to this frame since I don’t have motors and stuff to make builds whenever I want. Didn’t know the exact dimensions but made the motor holes 6.1mm cause when I measured your model it was about that so hopefully that’s the right tolerance :sweat_smile:
octo.zip (181.9 KB)


#54

Wow that’s beautiful, and strange too!! hehehe. Super interesting design. If the reason of it not flying so good is just the frame blocking the airflow, it’ll be easy to improve it. And 7 grams as it is now is just great, that’s just the weight of 2 light weight tiny whoop frames.

Of course i know nothing about frame designing or 3d printing, and sadly i don’t own a 3d printer (but i’m considering it…) Don’t want to spend much time with this, but i’m so curious about it that made these designs. Of course they’re 2d, and i don’t really know by that picture how is the inner part of your frame. Maybe i can contribute with some ideas

Love it, Benedikt, Thanks fot sharing!

By the way, motor mounts are 9mm wide (so 1,5mm of material surrounding the motor) And the frame itself is 2,5mm wide. I don’t know if that’s too thick or too narrow for a 3d printed frame


#55

that’s really nice xeran! My designs look like shit when comparing, hehehe


#56

So… it wasnt raining, but I still spend some time yesterday to slim it down.
Looks like this now:

and weighs just over 3g :smile:
motor shaft distance is 82mm.

The major challenge in EVERY frame design that includes the motor mounts is,
guess what… the motor mounts!
The obviously need to be wide enough to get the motor in, but they also need to be tight enough to keep the motors in. There are all sorts of fancy design techniques one could apply to make that happen, but I like to keep it simple and just keep them plain round.
If you designing frames for your own printing, its already a good strategy to test-print a series of individual mounts first. But ESPECIALLY when you design for a remote printer, this will save a lot of time.
E.g. for this frame, I disable all elements but one mount. I set the inner diameter to 3.05mm (very rarely, it needs less) and export. Then set it to 3.06mm, and export. Keep going until about 3.15mm, so 10 samples.
Load them all into the printer and go.
Then test which of the 10 samples fits the best around the motor.
Set that diameter for the complete frame and print.

My frame does not have an inner section. That takes the bounce out.
Without an inner section, its a flexible ring. It does not break as easy as when its stiffened up with support.
The electronics will be suspended in the middle with transparent silicone hairbands.
I do have generic pieces for that from the DreamCatcher frames, but I will probably make a dedicated center piece for this one :wink:

I will post more details and a print file here when its working!


#57

Can’t wait to see it flying. Hopefully it will be much better performer than the previous one. Love the concept of the empty inner section. Maybe the silicone bands will add one more gram to the frame, maybe less. It’s going to be really light.

Righ now having a 3d printer would be a pain in the ass for me. There’s so many things about tolerances, materials, hours of testing… A lot of time and money to invest in it that i don’t have. But eventually i would like to try it.

Very nice work, Benedikt, and also from Xeranthecat


#58

3D printing is a complete hobby in itself. A VERY time consuming one.
But the possibilities are endless. We are printing so much crazy stuff…
My son is 7, I showed him thingiverse.com, and every Saturday he can pick something that we print. Unless dad prints copter parts :wink:


#59

If you ever think about getting a 3d printer then you should start designing models, cause you will soon realize thingiverse rarely has exactly what you want. And there are also websites like shapeways that you can pay to print models, don’t know how expensive they are but probably cheaper than getting a custom carbon frame cut :smile:


#60

I love to learn, that’s my motivation, and 3d printing has endless possibilities, that’s what i think about it. I’d love to dive into it, but my 2 month daughter and managing lipo batteries are taking most of my time (don’t know what’s first…) And then my job and flying fpv. When my baby is a little bit older maybe i can do the same with her, and print fun stuff every saturday, right before going somewhere to fly fpv, of course