Left Drive Rear Hub Sprocket Dilemmas

MrHobbitFeet

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I am designing and gathering materials for a bmx ebike.
Should be quite the little beast: 2000 watt motor and controller chain drive to rear hub, diy built 48 V 12 Ah(576 Wh) battery, 13s4p. A bms. Disk brakes. Not fully settled on gear ratio

I need some advice on the drive-train assembly, specifically the sprocket attachment. My plan is to use the original rear tire and the chain motor will connect to a sprocket on the left side hub area.
The problem is exactly how to attach a sprocket there. I cant find a freewheel sprocket that fits the hub. The bearing is 35-15 so 35 mm OD and 15 mm ID. Axle size is 14 mm. The only freewheel sprockets I've found that fit aren't left side driven.

I'm considering welding a sprocket onto the hub itself, or using a ragjoint but these seem risky for bike longevity or loads of work.
Only thing I haven't looked into is the hub adapter clamp things. I'm not too worried about drag from the motor if i end up having no freewheel capabilities.

Anyone one with experience with a build like this have any suggestions?

Here is the hub i have. Will be installing on smaller side
Mission Pace Sealed Freecoaster 14mm
 
I need some advice on the drive-train assembly, specifically the sprocket attachment.
I'd suggest starting with a hub with a LH side (6 bolt) disc brake rotor mount. Sprockets are available to bolt-on.
 

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In times past there were BMX hubs with RH threads on the right and LH threads on the left. There are still LH freewheels available to fit such hubs.

When I made my own very first e-bike more than twenty years ago, I made a 144 tooth sprocket for small pitch #25 chain that clamped around a 16t LH freewheel. I drove that freewheel with a scooter motor attached under the bike's down tube. The single speed pedal drive on the right side was unaffected, so I had two redundant independent chain drives in that bike.

If you don't mind fixed gearing, you can use a fixed/freewheel double threaded track bike hub, and either use a track cog and lockring for the left side, or attach a larger sprocket to the track cog.
 
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In times past there were BMX hubs with RH threads on the right and LH threads on the left. There are still LH freewheels available to fit such hubs.
<snip>
Yes. I used the "ACS SouthPaw" on my Stoke Monkey setup. You'll need to find a hub with the reverse threads, or find a way to adapt a right side Bottom Bracket bearing cup (or is it left side - I forget - one or the other) to the left side of the hub. Mounting a BB bearing cup to a disc brake mount might do the trick.

Here's a photo of a bearing cup mounted to the Crystalyte motor cover and a second photo of the mounted "Southpaw" freewheel.

IMG_20220814_090626227_HDR_SM.jpgIMG_20220814_090954226_HDR_SMcr.jpg

OTOH, if you are driving from the left side with a motor, you could mount a fixed sprocket to the disc flange on the rear hub and use a conventional RH freewheel on the motor. Depending on the motor (like if it were a hub motor) you may have to reverse the motor's drive direction.

Either way, I think you need a rear hub with a disc brake flange as mentioned by @Papa
 
I've had custom disc brake sprockets built by this company before:
REBEL GEARS CUSTOM MADE MOTORCYCLE SPROCKETS ANY SIZE

Good solution, unfortunately they can't help you much with offset, the sprocket will be flat.

Here's your offset; just use the material thickness that does the job. Or stack layers. Put a 110mm or 130mm five hole pattern of 10mm holes, and then you can use a bike chainring for the sprocket.


Disc brake rotors are 6 hole, 5mm diameter, 44mm PCD.
 
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I'm not an advocate of coupling high RPM motors with bicycle chain - been there, done that. My main grip is noise. My second grip is the hassles of cobbling the desired ratio(s), A 16t freewheel cog paired with a common 52t chain ring equates to 3. 25 to 1 reduction ratio. That's unacceptable for a single reduction drive. Short of implementing a two-stage reduction, you'll need at least 9 to 1 ratio (16t/144t) or greater for a measly 3k RPM motor.
 
The chain system design on the recumbent shown uses a 16T ratchet on the wheel with a larger custom modified sprocket bolted to the ratchet.
The larger sprocket was an industrial "blank" likely from Martin like this > link <
The center of the sprocket was machined larger to fit the diameter of the ratchet and mounted with 4 bolt holes (one hole every 4 teeth) to accommodate 5/16" bolts.
Note a series of larger holes cut in the blank spaces to reduce weight.
These days, I would design the sprocket in CAD and have it waterjet or laser cut in aluminum.
> SendCutSend < has been my "go to" lately.
Back when the bike was created brushless motors were rare.
The motor was 24V brushed type sourced from a semi truck cabin climate control fan.
Controller was a custom design from NuSuN.
Competition rules capped the batteries to a max of 20Ah sealed lead.
 
Pre-made 80T sprocket for #25 pitch chain that likely bolts to a 16T left hand thread ratchet
> link <
Amazing what's available in the modern internet world !
 
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Pre-made 80T sprocket for #25 pitch chain that likely bolts to a 16T left hand thread ratchet
> link <
Amazing what's available in the modern internet world !
80t won't cut it on single drives (assuming 406 wheel),... Quality #25H chain 'might' survive 2kW the OP mentioned, but i'm doubtful the standard #25 chain will, for any length of time.

Up to 89t here....

or custom here...
 
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The good news . . .
When building my race winning solar E recumbent there was far less "off the shelf" supplies that could be so easily internet found.
And at such low costs.
No motor specs were stated so we are only guessing at gear ratios.
Anyway . . . MrHobbitFeet has been provided useful info to help decide his build.
Happy trails :)
 
I am designing and gathering materials for a bmx ebike.
Should be quite the little beast: 2000 watt motor and controller chain drive to rear hub, diy built 48 V 12 Ah(576 Wh) battery, 13s4p. A bms. Disk brakes. Not fully settled on gear ratio

I need some advice on the drive-train assembly, specifically the sprocket attachment. My plan is to use the original rear tire and the chain motor will connect to a sprocket on the left side hub area.
The problem is exactly how to attach a sprocket there. I cant find a freewheel sprocket that fits the hub. The bearing is 35-15 so 35 mm OD and 15 mm ID. Axle size is 14 mm. The only freewheel sprockets I've found that fit aren't left side driven.

I'm considering welding a sprocket onto the hub itself, or using a ragjoint but these seem risky for bike longevity or loads of work.
Only thing I haven't looked into is the hub adapter clamp things. I'm not too worried about drag from the motor if i end up having no freewheel capabilities.

Anyone one with experience with a build like this have any suggestions?

Here is the hub i have. Will be installing on smaller side
Mission Pace Sealed Freecoaster 14mm

These guys will have what you need.
 
I did a left side drive but had a slightly different starting point than you. I used the 6 bolt disc mounts to attach my sprocket, and sacrificed the disc brake. I used a fixed cog on the motor so my motor drive was "fixed" to wheel movement, which enabled regen braking.

 
> Link to double sided hub with left hand threads <

> Link to left hand thread freewheel ratchet <

That leaves figuring out the sprocket that adapts to the freewheel ratchet ( there are some sprocket creator online apps )

This bike, created in 1995, has a left side electric motor driving thru a freewheel :

View attachment 361192
I was starting from the same, have die to cut LH 35 mm thread on left side of hub (of a 20" wheel), thread BMX southpaw ratchet on , then 52t chainwheel mounted concentric on that. Since chain goes near vertical (say around seatstay) and is hanging on drive sprocket how small can that be made say 9 teeth? Is that almost 6:1 ratio sufficient for any lightweight 500w motor to help with 1 in 5 grades or must put in another chain reduction stage first?
 
Is that almost 6:1 ratio sufficient for any lightweight 500w motor to help with 1 in 5 grades or must put in another chain reduction stage first?

Chain sprockets are available down to 6 teeth, but I wouldn't use one smaller than 11t and preferably at least 13t. Smaller tooth counts make the chain drive much noisier and rougher, less efficient, and much faster wearing.

I'd look for a motor like Cyclone 500W that incorporates an internal planetary gear stage in the housing.

You should play with the Grin simulator or Kreuzotter power and speed calculator and figure out how much power you need to climb your desired grades at different speeds. You might be surprised how slow you'll need to go to make 500W do the job.
 
Thank you for comments. I hand calculated a lossless 412W for climbing a 1:5 at 5mph ignoring my own arm and leg contributions which can achieve maybe 2.5 mph at best. Please provide link to simulator(s).

A geared motor likely takes too much space and weight 7lbs for Cyclone is borderline , vs adding a second chain stage. Motor would be underneath front of cargo bucket in attached but yawing with front wheel. That yawing mass was manageable with Solex and Motobecane, but I need to test with dead weight
 

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Keep in mind that physical motor mass is also thermal mass to absorb heat from adverse running conditions. If you use a tiny lightweight motor and then run it in almost still air, maybe also in a bogged-down RPM range, it will be very easy to overheat.
 
That yawing mass was manageable with Solex and Motobecane, but I need to test with dead weight
What is the grip-to-grip distance on your handlebar? If less than 530mm, I suggest you widen it to gain additional leverage.
 
Thank you for your help. Please give link to Grin simulator. I calculated 410 ideal watts for 1:5 grade unassisted at 5mph. With my arm as well as leg power I can do 2.5mph for 100' of grade.
Cyclone is a bit heavy 7lbs though just test rode with dummy that weight and no dynamic problems. But I have room for 2 chain stages from hub to rim on 20" wheel. Think gyro effect will be ok as same sign magnitude as wheel. Cut LH thread on LHS of front hub for (BMX) Southpaw ratchet. Bike is highly customised so this seems only option without removing one of many special features Yes handlebars are 20"span=.5m (and don't catch on obstacles. and rock for armpower assist or lock (back for chopper seat))
 

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Keep in mind that physical motor mass is also thermal mass to absorb heat from adverse running conditions. If you use a tiny lightweight motor and then run it in almost still air, maybe also in a bogged-down RPM range, it will be very easy to overheat.
Good point, Thanks. I had only thought location was close to best airflow on bike but no doubt not enough on slow grades.
 
Good point, Thanks. I had only thought location was close to best airflow on bike but no doubt not enough on slow grades.
If you use a double shafted hobby motor, you could put a fan on the unused shaft to help simulate airspeed.
 
Though doing that doesn't do as much as it could when the motor is in it's worst-case slow-but-high-load situation. It would still help, by forcing more air thru during higher speed moments to cool it back down, but having the fan run on it's own motor and suck air thru the motor via a duct would allow it to keep cooling even if the motor itself is near/at stall under load, or when you have to stop but it's still hot.

Often even a small computer-case type fan that moves a fair bit of air (high-CFM) will do the job, and some of those have temperature sensors you can install at the motor so the motor being hot makes the fan run harder, and if the motor isn't hot the fan doesn't run so it's quieter and less power-intensive.
 
Thanks for the suggestion. My computer fan certainly behaves like that. its revving is a sign of overheating
 
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