DIY (Mini) ebike/moped -> square tube frame, hoverboard motors - does this look reasonable? Any obvious oversights?

[ziddan]

The glass transition temp of PLA is about 60c, i live in Sweden (hottest day measured around this part of the country was 36c, back in 1975), the tabs are out of the sun under the seat+clamped tight against the frame and separated from the batteries by about 5cm vertically.
The issues ive seen people have with PLA prints sagging have been when inside parked cars on hot days, essentially saunas.

I guess can will print something beefier, possibly in PETG or incorporating some metal strips to replace the tabs, on the new printer which should be arriving next week, but i highly doubt it will be necessary.

 

[lnanek]

I've strapped heavy things to my bike before with these metal zip ties:

https://a.co/d/7FVJEcm

And of course plumbing hose clamps with screws to tighten them. Grin has some videos of those and torque arms holding up even when axles broke under torque. Something like 500 pounds of force.

Might be more trustworthy than 3d prints unless you use the kind that has metal in the material and you can bake off the plastic.

 

[ziddan]

Got a battery clamp designed and printed, the oval stud slots into the place where a locking pin would go if using the original mounting system of the bicycle.

That stud holds the clamp centered and the hooks clip over the battery mount by flexing them a little when attaching, seems like it should be secure for most normal use cases.

Ill be attaching some heavy string to the clamps and tying them through the bottom center hole so they dont get lost, even if they stay relatively well even when a battery isnt installed.

Ill also look at those metal zipties, they seem quite interesting even if i dont expect they will be necessary.

 

[Tony01]

View attachment 368911
Here is a product shot for the rotor ive got.

Also, since your posts are mostly know-it-all put-downs, id like to officially inform you that you very welcome to bow out of this thread permanently. Either way ive put an ignore on you and i wont be seeing whatever further put-downs you still feel like making.

Looks like it’s manufactured by a Chinese company that ripped off a brand name product thinking rotor design is for ‘style’. What a surprise.

What company is that? Oh but you blocked me. Insulted then tried to guilt trip me. But this is a forum, you still see that I’ve posted on it, and you’re going to read it anyway too. And then you’ll hit the report button like a proper *****.



If you’re going to ignore discussion on the physics of parts on a technical forum, don’t go appealing to authority with no-name Chinese brands. Or it would have been printed on the disc along with the size like a real Shimano, Hayes, Avid, whatever name quality rotor.

your posts are mostly know-it-all put-downs

Wow, got some real butthurt!! Now THAT’S a put-down (go read “mostly” all of my posts). I have seen too many people die or get seriously hurt due to shoddy builds or unsafe riding habits, and I’m not going to sit by this inaccurate and dangerous misinformation without speaking out.

Let’s do this the easy way… here’s a few of my builds, let’s see yours?

Knowing how to draw in 3D doesn’t make you an engineer, and assembling a 2-stroke motorized bicycle engine kit in an old bicycle and fixing it continuously for three years doesn’t make you a seasoned builder. Your overinflated ego is going to get you hurt and you should be counting your blessings like all the front bicycle tires you didn’t blow at speed. Good luck!

 

[ziddan]

Today ive switched the connector on one of the batteries and while i had it open i looked at the fuse, its 30a.
As well as making the extensions for the sensor+phase wires for one of the motors.

Its after dark and ive yet to install any lights but i couldnt resist taking it out for a first short test drive around the block, it lives!

It doesnt do uphill very well, as ive been half expecting, looking at the display i was seeing the voltage meter dropping down from five bars to two before it stalled, then going up again as i let go of the throttle.

Gonna do up the second battery with another XT60 and make a parallell Y harness to connect both, that should hopefully improve uphill a bit as the C will be doubled.

 

[ziddan]

As i was going home after a second test drive, this time with the batteries paralleled, drive cut out just into start of the uphill bit leading to my door and the reported speed on the display shot a lot higher than actual.

The connected motor was warm, but not hot, to the touch, so i turned the controller off, lead it up the last bit and brought it back inside.

Back inside i found the motor was noticeably warmer, going on hot, indicating to me that the stator was likely a quite a bit warmer than what had managed to transfer into the shaft, through the bearings and into casing itself when i first touched it.

It was to the point that the printed rim adapter on that side was starting to deform due to tire pressure, as recently noted PLA has its glass transition point at around 60c, and i could no longer keep a finger on the casing or motor shaft on that side .

I deflated the tire, unbolted the wheel from the frame, removed the screws securing that side, popped it open and was met with the smell of too hot electronics.

After letting it cool down a bit i got my multimeter to confirm what had become my expectation.
Measured the resistance between the phase wires, .6 ohm, okay, thats probably just the wires.
Then phase wires to the motor shaft, .6 ohm again, same.

So yea, one fried hub motor.

Guess ill look for some another option, either a hub motor designed to be part of a scooter, or a motor to do chain drive, perhaps the latter option is the better one as it would allow for easy retrofitting to other use cases as well.

 

[amberwolf]

As i was going home after a second test drive, this time with the batteries paralleled, drive cut out just into start of the uphill bit leading to my door and the reported speed on the display shot a lot higher than actual.

Was it just the drive cutting out, or did power actually shut off?

What voltage did you see on whatever monitoring device (wattmeter, etc) you're testing with?

If power didn't shut off, what is the controller LVC?

(based on the other info in the post I expect it is none of those things causing it, but rather a destroyed controller that then shorted out the battery. It may have left the BMS intact, or it could have blown the output fuse or even FETs; note that blowing the FETs usually means shorting htem, so the battery would be stuck on permanently and unable to turn itself off to protect from overcurrent or overdischarge).

Back inside i found the motor was noticeably warmer, going on hot, indicating to me that the stator was likely a quite a bit warmer than what had managed to transfer into the shaft, through the bearings and into casing itself when i first touched it.

The actual windings could get VERY hot (even damagingly so) in the event itself, then the heat spread out into the rest of the motor over the time and appear to be much lower than it actually reached.

After letting it cool down a bit i got my multimeter to confirm what had become my expectation.
Measured the resistance between the phase wires, .6 ohm, okay, thats probably just the wires.
Then phase wires to the motor shaft, .6 ohm again, same.

So yea, one fried hub motor.

If the phase windigs read shorted to the axle, they're shorted to the stator, which probably means shorted to each other. Even if it's just the phase wires themselves that melted their insulation, rather than the windings, and shotrted to the axle/each other, the result is effectively the same***. That means the controller was probably damaged or destroyed as well (it's very rare for a controller to survive this event unscathed).

***


Sounds like you need to determine the amount of power required to do the job you need it to do under the conditions you have, and *then* look for a drive system that can do that job. You can use the simulators at ebikes.ca to do this, by experimenting with setups until you find one that can do it without overheating, and then use the chart results to see how much power it took under each condition, whcih will also give you approximate battery currents required, and approximate wh/mile (which lets you estimate battery size required for a given range requirement).

 

[ziddan]

Was it just the drive cutting out, or did power actually shut off?

Just drive, the display was still on and the kph reading went way up.

What voltage did you see on whatever monitoring device (wattmeter, etc) you're testing with?

Only had the battery bars on the display, i dont recall them being in any odd state.

If power didn't shut off, what is the controller LVC?

LVC is set at 31v, ive previously tried to raise it to 32 in order not to drain as deep but the value seems to be locked dependant on set nominal input voltage(36, 48, dont recall if this controller does 60).

The batteries seem okay to me, they respond when pressing the report button, still on blue, which is the highest of the three report colors.
When i had the batteries open yesterday i tried hitting that report button with the fuse removed, no light up at all, put the fuse back in, reporting.

So i guess its an easy indicator that the fuse is okay, id think the BMS likely is too.

If the phase windings read shorted to the axle, they're shorted to the stator, which probably means shorted to each other. Even if it's just the phase wires themselves that melted their insulation, rather than the windings, and shotrted to the axle/each other, the result is effectively the same***. That means the controller was probably damaged or destroyed as well (it's very rare for a controller to survive this event unscathed).

I hooked in the other motor just now, the display/controller turns on fine and the throttle responds as expected, guess ive got a rare controller?

Either that or it was some sorta thermal shut down due to motor temp, which seems unlikely because it was so hot and its now reading short between phase wires and stator.
Also there are five wires in the sensor lead, i think a sixth would be the temp wire?

 

[amberwolf]

Just drive, the display was still on and the kph reading went way up.

The speed reading probably went up as the phases were being shorted to the hall sensors before things failed, so the sensors were reading the phase PWM or commutation frequencies.

Only had the battery bars on the display, i dont recall them being in any odd state.

LVC is set at 31v, ive previously tried to raise it to 32 in order not to drain as deep but the value seems to be locked dependant on set nominal input voltage(36, 48, dont recall if this controller does 60).

It's uncommon to be ablet o adjust the LVC, so I'm not surprised. Mostly you find that in FOC controllers where you already have to setup up a bunch of manual tuning parameters to get it to work with your system at all.

The batteries seem okay to me, they respond when pressing the report button, still on blue, which is the highest of the three report colors.
When i had the batteries open yesterday i tried hitting that report button with the fuse removed, no light up at all, put the fuse back in, reporting.

So i guess its an easy indicator that the fuse is okay, id think the BMS likely is too.

Probably.

If it's a 30A fuse it probably means the battery and BMS are capable of less than that, perhaps 20A. Could be good up to the 30A, but usually they use higher rated fuses than actual intended usage. If you're not sure of it's intended usage, it's safer to assume lower current capability, and use lower current limits in your controller (if it's adjustable).

If you can place a current-controlled load on it and monitor voltage drop, then the results can show you at what point it's safer to run it for max--wherever voltage drop begins increasing dramatically, go with less than that current.

I hooked in the other motor just now, the display/controller turns on fine and the throttle responds as expected, guess ive got a rare controller?

I guess so--it means that either random chance caused system shutodwn before damage occured, or that damage isn't obvious (yet), or that the system can detect phase currents and shutdown for overcurrent very fast. I've had shorts that have blown controllers in wierd ways (see my BLDC powerchair motor thread for one example) where they still 'work" but "aren't quite right in the head", so to say.

If it still works--good, but I would never count on the protections (though you *should* be able to, if you know it has them from documetation describing them) always keeping it safe.

Either that or it was some sorta thermal shut down due to motor temp, which seems unlikely because it was so hot and its now reading short between phase wires and stator.
Also there are five wires in the sensor lead, i think a sixth would be the temp wire?

You can test for a temperature sensor by measureing resistnace between it and ground or it and 5v. It'll be different at different temperatures. Most are 10kNTC which means at room temperature around 72F they're 10000ohms, and decrease at higher temps, increase at lower. The beta of the sensor tells you how mcuh they change per degree, but you'd have to determine that experimetnaly with existing sensors, as it's not marked on them (if you need a specific beta for a particular usage you order them with that beta).

 

[ziddan]

If it's a 30A fuse it probably means the battery and BMS are capable of less than that, perhaps 20A. Could be good up to the 30A, but usually they use higher rated fuses than actual intended usage. If you're not sure of it's intended usage, it's safer to assume lower current capability, and use lower current limits in your controller (if it's adjustable).

As the bicycles these 36v batteries are for are 250w, id think they should cover those 7 amps easily, likely with capacity to spare.
I mean 7a out of an 11.6ah battery is 0.6c and that seem pretty low to me.

With the two ive got in parallell id think i should be able to do 20a, the max continuous of controller i have and still below 1c per battery.

I had the controller set to 12a when on the two test runs, thats its default value.

 

[MxusMick]

You are dreaming big, but be warned, you need to simplify, things go wrong often in the DIY world, and if something fails you will be bummed. For instance, one of the motors dies, I am always challenged with obstacles on my builds, I just switched to a higher voltage battery, ride around the block, stoked by the additional speed, then the throttle quit. It's Murphy's Law bro, I had done a shunt job and the solder rattled loose and fried a Mosfet. The point I wish to make is too many variables can cause a massive can of worms and disappointment, not to mention it your bike stalls in the middle of the woods. Frames have to be professional, the weight of rider, battery, and motor combined with a pothole at 20 mph can go bad. The Hoverboard motors are a bit janky bolted together and McGyvered to a front fork, I would be fabricating it belt drive to the rear wheel. Please don't consider me negative, I have bunches of Hoverboard motors, treadmill motors, Razor motors, etc., so I really understand how you are thinking and wish you success. Find a solid frame for starters. You will need to focus on the build, loose wires, brakes, and be able to identify problems as they arise, as your ebike gets shaken apart from use.

 

[ziddan]

I honestly think ive been going pretty simple with this build. Wont be going 20mph with it, more like 12 mph

Hoverboard motors are a bit janky

Yeah i sorta knew going into it that the hoverboard motors might be a bust but worth a shot since they were really cheap and there are hardly any vibrations when spinning them at full throttle/reporting 40mph on the display so i got alignment pretty close to spot on just carefully using a hand drill.

McGyvered to a front fork

Front end, both the suspension and brake, did fine on the two test drives.

I would be fabricating it belt drive to the rear wheel.

Belt drive? Now that is a can of worms i wont be opening.
Im looking at chain drive tho.

Find a solid frame for starters.

I dont get what you, and others, have against the frame, ive welded it and ground some of the outside surfaces flat, the metal is homogenous under the ugly bead. Welding is most of what ive spent time doing during this build.
Brand minibikes fit for engines with multiple HP mostly have less frame than what ive put together.

At time of the test drives there were no lose wires, i ziptied them all against the frame and collected any spare length together under the seat before trying to ride it.

As for shaking, ill probably try a bit less air in the rear tyre next time, i had it all the way up to 25psi, so it was quite firm, in order to minimize rolling resistance.

 

[MxusMick]

If you remove the tire off the hoverboard motor it becomes a pulley, for belt drive, or with the tire intact could be used friction drive against bicycle wheel. I wonder how you plan to secure the pancake motors to your forks. When I am going above 20mph I am concerned with losing the front wheel sometimes or a blowout, so don't let that front wheel fall off, make some torque arms for it. I wish you luck and you will be stoked once you get up and running!

 

[ziddan]

I never intended to and wont be driving the front wheel, before i took the rear end apart after frying one of the hovermotors, i had them clamped in using the original clamps cut out of the hoverboard chassis, the motor shafts have a flat one one side and the clamps fit those perfectly.

As the hovermotors have proven not to be able to handle the power im now looking at doing chain drive to the rear wheel, very much like a standard minibike but with an electric motor, checking parts and options currently,

 

[ziddan]

A new motor has arrived.

It is a vevor 48v 1800w with a 9 nine tooth sprocket prefitted.
Surprisingly it also came supplied with an 11 tooth sprocket too, which wasnt advertised.

Would have preferred the 36v version but it didnt seem to be available when i ordered.

The extra 11t means im going to have more options than just switching between the 64 and 74 tooth rear sprockets ive also ordered.

Going by the example given for the motor on 48v, it would turn a 16" wheel with 9->64 gearing to 36mph/almost 60kph under load.

The motor is probably overkill and obviously im both undervolting and underamping it with my 36v batteries and 20a (this assumes just 0.85c with the paralleled batteries) but since im only aiming for 20kph i dont think that will be an issue.

Calculations, assuming a linear drop in RPM according to voltage and having the same loaded percentage of rated RPM as their example, tells me my first try will be 9->74, which in theory will give about 25kph.
Im hoping that the lower final gearing from a smaller wheel and larger rear sprocket will allow it to spin up well enough on the lower amps.

Ive verified that my controller turns the motor.

Hopefully the reported progress of the packages containing the sprockets and the rim is accurate, if so they will be getting here tomorrow.

Ive got thursday off and i think im likely to try figuring out the new motor mount/drivetrain/rear end situation.

 

[amberwolf]

FWIW, if you can use it, the 11 tooth on the motor will have better chain wrap, less wear, less noise, though less torque and higher speed, vs the 9 tooth.

The lower voltage will give proportionally lower top speed, the lower available current will give lower torque.

 

[ziddan]

Ill give the pre-installed 9t a whirl first to see what results i get and how i feel about noise.
The decrease in torque due to less amps is part of what im hoping to alleviate with the lower gearing, doing 11->74 would be a bit higher than the given example for the motor, though my smaller wheel lowers it back down to just under it again.

 

[glennb]

Really enjoyed following your build.

Your into interesting territory with can motors and #25 chains.

The motors are a sizeable lump, good 5kg, so plenty of copper and you needn't be shy with dumping current into them. All things considered, it's preferable to extreme single stage gear reductions.

The ability to mount tiny sprockets for large reductions is irresistible, but whereas for high road speed applications the noise they make is kind of "hell, yeah" , and the rapid wear is "the price of fun", for low speed applications and utility vehicles ... not so much.

11-74 is passable, I've been guilty of worse. Only on tiny vehicles though, where there was no room for a double reduction.

Another thing. You can relieve stress on the motor bearings by mounting the sprocket further inboard. The shafts are soft, a file is your friend. Probably unnecessary with the 9T, but in all likelihood you'll come to the conclusion that 11T is a bare minimum, and 13T preferable, in which case it's worth considering.

 

[ziddan]

This motor for sure is a lump

For the equiv of around 100 bucks i couldnt see a better option which would be as over spec as this, i figure erring on this side should mean reliability as with the low gearing and undervolt its not going to be anywhere near its rated stress limit.

I guess i could do a jackshaft for two smaller reductions, instead of a single large one but thats added complexity so i hope this will be alright with just a straight chain as my wheel is only 13".

At 20kph id say this is almost a low speed utility vehicle

You mention tiny, ive actually already started to consider making it shorter by taking some out between the front and rear triangles, would entail shortening the seat as well as refiguring the battery mount tho is im going to try it as i have now.

Received the rim, chain and sprockets today and im worried that the rim is too skinny, will see when i try to get the tire on it.

I was looking a lot and it seems its hard to find rear rims that are just the right width and have hubs in them.

Havnt been able to understand the bolt in hub variants so didnt spring for one of those.

 

[glennb]

Smaller? Yeah, I suppose, shorter wheelbase is great for manoeuvrability, and backflips aren't a concern with low CoG.

Can't remember what your vehicle's purpose was though. Why you only want 20km/h. Why 36V? Why starve the motor with only 20A? Was it for economy? As in long range with a small battery, and long drivetrain life?

The thing about using 36V on the 48V wind is it won't draw big amps from stall, and with a big gear reduction the current draw will level out pretty quickly as BEMF rises. You can consult the manufacturer charts.

So, you don't really need to starve the motor, you can let it draw however much current it wants. It'll draw half from stall what it would at 48V, and naturally settle, on flat roads, I'd guess at around 15A.

There's a bit of weight in your vehicle, so your 20A will be lacklustre for takeoff, and not do your motor any favours up inclines (which will cause it to bog down in low RPM).

Anyway, there's plenty you can play around with, and you have a good platform to do it with - more motor than you need, one that's easy for any controller to drive, and for which chains and sprockets are cheap.

I don't know too much about 16" rims and tyres. 305mm rims?

 

[ziddan]

Smaller?

Just because it would be easier to store or fit in the trunk of my car if i want to bring it to my moms place in the countryside, or something.

Can't remember what your vehicle's purpose was though.

This whole project is just because i got a bug to build something for fun, i like building stuff, computers, rc planes/drones/cars, tabletop miniatures and i also like riding mopeds.
If this works right/proves reliable im probably commuting to/from work on it, about 16km/10 miles each way, weather permitting.

Why you only want 20km/h.

20kph is because im aiming to have it in the no license "elsparkcykel"/e-scooter bracket within the regulations here, basically the same rules as for bicycles.

Why 36V? Why starve the motor with only 20A? Was it for economy?

I guess economics would be the closest fit, initially i was aiming to use a couple of 36v hoverboard wheel/hub motors bolted together in a dual motor hub "frankenrim" using 3d printed spacers, it worked but was severely low on torque and on the second test drive one of the motor burned up. Hence my reason for erring on the side of going for a beefier motor than is probably strictly needed for the application.
(and i might try electrifying my Crescent 2000 using it or similar at some point)
I snagged two 36v, 11.6ah batteries for 50 bucks each.
20a for now because thats what my controller will do sustained and that comes out to whatever C draw (something like .85?) i mentioned earlier when running the batteries in parallel, i expect that these batteries arent high draw specced as they were made for ebikes with 36v/250w motors.

There's a bit of weight in your vehicle, so your 20A will be lacklustre for takeoff, and not do your motor any favours up inclines (which will cause it to bog down in low RPM).

Not targeting burnouts or drag racing, im hoping the small motor sprocket, large rear sprocket and relatively small wheel will allow it the torque to maintain RPM and, at least some of the already low, speed when climbing as there are a few hills on the way to work.

I don't know too much about 16" rims and tyres. 305mm rims?

16" tyres with 9t->64t gearing giving about 50kph at 48v were in the example given for the motor and ive seen people reporting it to be relatively accurate.

Im using 13" tyres on 6" rims, 33cm outside wheel diameter, this build is essentially a slow electric version of the classic simple 60ies/70ies US style minibikes, a type of vehicle which ive always thought neat but that arent a thing here in Sweden.

48v to 36v gives -25% so 37.5 km/h, which is total loss from decreased power but
Then 64t to 74t gives +15% in torque at the lower speed of 32.5km/h
Then 16" to 13" gives +19% in torque at the lower speed of 25.6km/h
Coming out to a speed which is about 25% above my targeted 20km/h, which i would limit down to using the controller.

With the extra torque from gearing+smaller wheel im hoping this is reasonable, but i wont know until its together.

Im gonna get it together with the parts ive got now to see how it does but im already itching to pick up a VESC to enable regen breaking, not because of the regen itself but just for the simplicity of using to motor to brake during regular driving, obviously the front disc brake will be applied for quicker stops.

Last night i got the tube and tyre on the rim, it is indeed a little bit on the slim side but it doesnt look like there will be more than 5mm or so of shimming out the sprocket for it to work so im going to give that a shot.

 

[glennb]

Fair enough, perfectly valid reason to build what you built.

Although ... "fun" and "20km/h" ... cough cough

With the right controller you can sneakily lock/unlock the RPM you know.

I can give you detailed instructions on how to do it with a Votol, so that it defaults to a capped RPM mode, but if you hold a switch closed while booting up the controller the RPM restriction is removed.

Other controllers, you can do it other ways. Even lowly Kunteng controllers are capable of it if you install the open source firmware.

I suspect you got what're commonly designated 6.5" rims. They're common as mud, and have the bolt configuration for cheap 4-bolt sprockets. Either way, 70mm tire should be ample volume to run a comfortable pressure.

Regarding bogging down on hills, you might want to consult Grin's calculator. You could well need more than 20A to keep the RPM up.

Look forward to more pictures ... too much talking in this thread. Sorry, my fault.

 

[ziddan]

The controller i have does have various settings accessible by holding down two of the buttons on the EN06 display it came with, not specifically RPM but wheel size and max speed, which essentially is a multiplication of RPM, as well as max amps.

Id love to know if there are custom firmwares for it, ive not dug into that side of things yet.
The only issue im currently seeing is that the minimal wheel size setting it allows is 2.5" as the thing seems designed to work with hub motors.
Which doesnt work with the gearing i have, id need to get it down to 1.6" for it to report the speed properly, otherwise it will be reporting too high speed.
One possibile "hack" ive though of for getting it to display the right speed with gearing is changing the settings for number of motor magnets, i think that will multiply or divide the speed calculation by whatever percentage i under or over report the actual number of magnets in the motor.

I guess they could be 6.5" rims but they were listed as 6" and the tires ive fitted without too much trouble, are 13x-5.00-6.
As im not all that great with tire/rim and inch sizes i went by the given MM measurements for the rim outside and the tire inside diameters to be sure would be able get them on.

The sprockets ive gotten for it are 3 bolt with 42mm spacing, ive just measured up how to space it from the rim and am just now sitting down to cut the overlength bolts i have down to size.

I did have a look at Grin's calculator but i feel like id need to learn more about this stuff before i could properly use it and whatever results i get wont affect the parts i already have (which should be everything i need to get this running again with the new motor.)

Pics?
Sure, but its mostly a pile of parts on my floor at the moment:

Isnt talk kind of the point at a forum? Well thats mostly what i use them for anyways

 

[glennb]

True. But photos are especially welcome in build threads. And any photo's a good photo. Particularly early on in the build. They're more educational than seeing the finished profuct posing at the beach or on a bridge.

You can use the motor simulator to see gross power requirements for hauling given weights up given grades - you don't need to model your motor in the simulator for that.

If your controller's firmware has the option of selecting 1-6 magnets, then yes, sounds like it was programmed for a geared hub. If there's an option for selecting "external" for the speed sensor, you can use a magnet on your wheel and reed switch on the frame, then program the correct wheel size.

It's unlikely there's custom firmware available, it's only available for Lishui and Kunteng that I'm aware of, besides dedicated mid-drive controllers..

You got 6" rims alright. Wheelbarrow size. Your 5" tire is 125mm. Huge. Going to be a soft ride. Rolling resistance not good though, with only 20A to play with.

42mm bolt spacing? All the ones I have for 4" rims are 34mm. (That's spacing, not BCD. BCD would be 39.2mm by my calculations, which is an ugly number, and I suppose the reason BCD is never used for these patterns). It doesn't matter the pattern, as long as it's easy to source cheap replacements in a good range of tooth counts.

 

[ziddan]

Actually the range for magnet amount goes all the way from 1 to 100, which i think will let me get it to divide down to the correct speed with some calculation/experimentation.

Wheelbarrow size, yep

Asking about 30cm rims earlier, how big did you think i was building this thing? Wheelbase is about 1m so overall length about 133cm from the front of the front to the rear of the rear wheels.

Most cheap tires like this are only specced for 4kph, less pressure and are usually "2pr", which i gather is the amount of layers of reinforcement, these i picked are 4pr.

I did look up the manufacturer specs, dont recall the name but these are specced for 250kg, 30kph and 25psi max so i can pump them pretty firm for decreasing the rolling resistance somewhat, tho i wont be going rock solid as i want some cushioning of the ride.

Got the bolts shortened and the sprocket spaced in place:

Not sure about how bolt spacings are usually measured or what BCD (Bolt center distance is my guess) is but the 42mm was the given measurement from hole center to hole center, not relative to the axle, and there were sprockets listed with those same numbers so i paired them up.

Now working on the "new" mount for the rear axle, re-using the axle clamps form the hoverboard wheels.
Figured that i can use some of the left over aluminium pipe i used to make spacers for the front wheel as shims around the threaded rod axle to make it clamp in firm.
The pipe is only like 1 or maybe 1.5mm wall so it squishes down when the clamp is tightened and as the wheel is on bearings this will be alright. Might make something out of angle iron to bolt in at the back at a later date as it would be more sleek, this is easy for now.

Doing all i can here at home and bringing the bike with me to work tomorrow to weld up motor mounts, unless i get bored and do it later tonight.