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Motor specs for DIY project

ComikzInk

Soft and Foofy
#1
Hi all :)

First time posting, apologies that it's not the usual post around these parts. I usually do this sort of thing solo but after all the planning I've done so far I don't want to end up spec-ing my project wrong so was hoping for a second opinion or if not alternative suggestions.

I feel I'll be requesting the help of the chaps across the pond at the moment as I think my fellow crumpet and tea lovers are sleeping or hibernating through the harsh weather in their RC sheds waiting for the better weather to come back around like myself.

Long story short I'm building a OneWheel with some brushless motors that I'll be welding some brackets to mount inside a GoKart wheel that I have sitting next to me with bright eyes and a bushy tail.
OneWheel1.PNG

There will be 1 brushless motor each side inside the hub, There's just enough room in the wheel I have for them to fit snuggly inside without extending out beyond the rims and adding unnecessary width.
OneWheel2.PNG

The motors I've got planned are 2x 270Kv 1820W Outrunners (https://www.ebay.co.uk/itm/152558299902) And I'll be using the absolute max these boys will take being 8s packs (or a few smaller ones dumped in series, depends on availability and space)

From my A-level physics and Maths I've attempted a rough estimation of the acceleration these will give me as I don't want to hop on, tilt the board and find myself nosediving into the pavement because the motors are not up to snuff. That and I'm concerned if they can do it will they accelerate fast enough to even bother having it.

Equations I've used (most likey in the wrong application) are below and using 2 of these motors with a total weight of 70Kg (my weight plus the board assuming it is around 11Kg) I'm getting around a measly 0.5M/s^2 which I would find laughable if not for the fact I might be right :(

Power = 3640W
RPM/V = 270Kv
Wheel Radius = 0.14m
Total mass = 70kg


RPM Calculations
RPM = Kv x Voltage
270 x (8 x 3.7) = 7992RPM

Torque Calculations
T = P x 60 / 2 x Pi x RPM
3640 x 60 / 2 x 3.14 x 7992 = 4.35Nm

Force Calculations
F = T / r (Radius of my wheel)
4.35 / 0.14 = 31.07N

Acceleration Calculations
a = F / M
31.07 / 70 = 0.44m/s^2

With something as small as less than half a meter per second per second I'm doubting the feasibility and might opt for dicing the wheel and welding an E-Bike hub motor in there. Are my calculations correct / utilization wrong or am I correct in thinking even 2 E-Skateboard rated motors are not up to the task?

Any help would be much appreciated, I'm more than happy to share the plans and if anyones interested actually update the thread with my progress :)

Kind regards
Lia ~ <3
 
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ElectriSean

Eternal Student
Mentor
#2
I'm definitely not a physics guy, so I won't comment on your equations though they look accurate to me. I did look at the specs on the original OneWheel, which brags 2HP of power. 1 HP = 746 Watts, so you are nearly 5 x that with the power system you've chosen. They do use custom (probably sensored) brushless motors, so the comparison won't be direct, but I would think what you have will be ample bordering on overkill :)
 

ComikzInk

Soft and Foofy
#3
I did look at the specs on the original OneWheel, which brags 2HP of power. 1 HP = 746 Watts, so you are nearly 5 x that with the power system you've chosen. They do use custom (probably sensored) brushless motors, so the comparison won't be direct, but I would think what you have will be ample bordering on overkill :)
>.>

<.<

I didn't notice the horsepower when checking the specs of the original, only the wattage (500w) and wondering how they were doing it. In that case I'm doing something wrong in that equation (Torque part most likely). With blissful ignorance and a helping of confirmation bias I'll pretend it'll work so I can move onto the rest of it :p

Thanks for pointing that out. I had spent ages looking for a spec sheet but as always I'm looking in the wrong places :eek:

As for the sensors I'll probably rig up some hall effect sensors on the hub. I've seen a few motors with them in but that might be an upgrade for the future when I've got some extra cash to splash.
 

ComikzInk

Soft and Foofy
#5
Thanks :) I'll post updates when I start building it. So far the frame is designed with room for the components.
OneWheel3.PNG
OneWheel4.PNG

After some thought I'm thinking Aluminium for the frame instead of steel so I can cut, shape and weld it easier.

As for controlling it I'll opt for a 200A esc (with Y-splitter) to give me headroom then an Arduino uno for the brains I have laying around plus a decent gyro sheild. The pads either side of the board will contain pressure sensors to tell if I'm on it to stop it running away when I'm not on it god forbid I fall off :p

Many thanks ElectriSean for being so welcoming and interested. I hear all the time that this community is one of the best and you've certainly proven that. Certainly a pleasant first experience on the forum :)
 

ElectriSean

Eternal Student
Mentor
#6
You've certainly got me interested :) I've been tinkering with Arduino off and on for the last year, just starting to get into servo and motor control. I'd love a peek at your schematics and code when you get to that point. Thanks for posting your project here, even though it's not flight related. Do you fly as well? I'm surprised Jim hasn't popped in to pump you for a more detailed introduction ;)
 

ComikzInk

Soft and Foofy
#7
I've messed about with them a bit, All my 3d Printers have used some revision of Arduino so you get used to it a bit, I'm just not much of a programmer xD I attempted to rebuild my old FXD Flamestrike with an arduino but got burnt out on the project as my printer gave up.

I'll be sure to share them, I've noticed there isn't any hub motor based designs on the net. The only thing I found is an old Instructable post I bookmarked years back that looked kinda cool (http://www.instructables.com/id/Self-balancing-one-wheeled-electric-skateboard/)


I was a bit on the fence if it was suitable posting this here but being as it uses some RC parts and I've seen the FT Team using a OneWheel it might be cool to share the experience of a DIY one :)

I do fly actually which is what brought me here really. I got a Parrot Bebop a few years back, then a Vortex 285, Inductrix FPV, FT Gremlin and finally a Mavic. Sadly it's cold and windy here in England so it's a bit too brutal to fly right now albeit the Vortex doesn't seem to care about wind. I did a little compilation of some of my flights where I hadn't already used the footage


How about yourself, any projects you've got going?
 

ElectriSean

Eternal Student
Mentor
#8
Cool video :) I know what you mean about the weather, we're expecting our first real dump of snow this week, 20-25cm :( Freezing fingers kinda takes all the fun out of flying for me. I have a couple of LED projects on the go, one with RGB LED strips, and one for a buddy with WS2812 addressable LEDs. He is a photographer and uses the strip for light painting in long exposure shots. The 2812's I think will give him some cool effects. I'm also waiting on a 4WD tank chassis to begin my foray into RC + Arduino fun.I have a feeling it's going to be a long winter, so I have a few plane builds planned as well, once I get a proper workbench figured out.
 

ComikzInk

Soft and Foofy
#9
Thanks :)

I can't remember the last time we had real snow where I am, it gets miserably cold and wet but snow is usually in short supply regardless. To be honest I wouldn't mind trying a flight after it had snowed however I know I'll be going in blind with cmos fpv camera's not picking up any terrain detail.

That sounds pretty cool, I assume the LED's will be multiplexed in some way so you won't need an output per LED. The light painting alone sounds really cool so I can imagine with addressable led's it'll be even better.

Have fun with the tank chassis, sounds like a pretty fun project and one that you could probably unleash into the snow xD How big are you planning on building it? I'd love to see how that turns out :)
 

ElectriSean

Eternal Student
Mentor
#10
You can have all of our snow... Come and get it ;) Flying FPV in winter is not fun at all, even with a decent CCD camera, especially on a cloudy day. Not to mention the ghost branches everywhere.

The WS21812 LED's are pretty cool, in that you only need one signal pin to control the whole strip. These are the same as the Betaflight LED system uses. Using the FastLED Arduino library, you can do pretty much anything you can think of. The main challenge for me is coding the user interface to change programs and color settings. Trying to do it all with 3 push buttons and an LCD screen is a good challenge. I made a quick video of the FasLED demo code to show my buddy, it's pretty neat stuff - https://www.youtube.com/watch?v=YFu198jjgPg

This is the tank chassis I'm starting with - https://www.banggood.com/6-12V-CNC-...Crossing-Crawler-With-4-Motors-p-1178264.html Kind of a gamble with no reviews or anything I can find on the net, but it looks pretty solid. I may have to beef up the suspension, the springs look a little weak, but it should be a good start. It may eventually become an FPV snow plow lol :D I'll probably start a thread here once I start building it. I think a few of guys here are into surface RC stuff, though it doesn't get talked about too much.
 

ComikzInk

Soft and Foofy
#11
I've only had one run in with a ghost branch. If I were going slower I may have seen it but full tilt with a stock Vortex 285... well I didn't stand a chance xD

Oooh wow those are so cool. I can certainly see that being a challenge, I think the chaps that make the LED cubes on Instructables might have some code you'd be interested in as some made presets and menu's that I'm sure would work with some careful program surgery :p

Risky but I'm sure it'll pay off. Other than sanding the edges and maybe a few do-overs on some holes I'm sure most of that will be fine. Certainly looks the part. I've heard a few members are into ground based RC so I'm sure they'll be pleased to see the thread you've got planned for that frame. I'll be sure to look out for it when I familiarise myself with the platform.
 

ComikzInk

Soft and Foofy
#12
After some careful consideration I've decided to put this one on hold till I get some bigger and better power tools of which I need a bigger garage for.

By the looks of it the motors will not be up to it afterall, the calculations are correct however what is letting this down is the high KV rating, on EBikes I've found they're about 2-5KV so for 500W at 24v you can get nearly 100Nm which is well over an order of magnitude what I can get out of the brushless RC motors without gearing it. If I were to gear it I could convert the high RPM to low RPM + High Torque but that's too easy and honestly doesn't look nearly as cool as a wheel that seemingly rolls itself.

Hope is not lost though. I just need more tools than I have (always need more) i which I can cut out the central section of the wheel and weld a bike hub motor in there much like what I assume Onewheel did just more gracefully then what I plan on doing to the poor GoKart wheel and tire sitting beside me >;D

If I ever do get back into this hopefully I remember to edit the OP and this reply to where I've posted the updates to rather than necro-ing this thread later on :p I'll still be active here, been needing a reason to create an account and this gave me one.

Cheers for reading :)
Lia ~ <3
 

ElectriSean

Eternal Student
Mentor
#13
My last day flying I thought I'd killed my Wizard on a ghost branch, I disarmed way too high and it took a nasty tumble. Turns out I only killed the battery, which was on it's way out anyway. That poor copter has taken so much abuse... Keeps on going though, gotta love it.

I have the UI framework for the LED controler basically there, I just have to implement a sub menu system. The main thing holding me back is laziness of course ;) My buddy just moved to Manitoba, and they get even more snow than I do, so I doubt he'll need it any time soon anyway.

Sorry to hear you're putting off the one wheel project, I guess squeezing a gear box in there would be a little too tight ;)
 

ComikzInk

Soft and Foofy
#14
Ouch sounds nasty, at least it was only the battery. I've killed about 7 batteries in 3 years. 3 cheap parrot bebop batteries that swelled due to being left fully charged a whole half year (whoops), and 4 cheap as cheap gets Chinese off-brand 2s batteries for my Gremlin which all died because they wouldn't balance charge correctly (weak cells). Saved one by manually charging individual pairs through the balance lead manually in the end xD

That's pretty cool, at least it's lazyness and not external limitations :p I kinda miss the snow, if it's gonna be cold I at least wish it would be pretty outside :D

It's okay, Ive seen alternative parts that will work but what I need to do is cut a large slice completely perpendicular in the middle of the wheel hub and weld an e-bike hub motor, going to aim for 1000W or more just for giggles as the price difference per wattage after the initial cost isn't too steep. One thing I need to look out for is a sensor based reversible motor and controller combo. Sadly just swapping the contacts still leaves the hall effects sensor timing out and reversed.

Thankies for sending a friend request too *yay* Didn't know that was a feature.