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I would like to make my ebike to have the minimal look, so adding big hubs or mid drive motors isn't really an option since it also costs more. I found this Keda brushless outrunner 2000w 190KV motor on hobbyking and wondered if it can move my bicycle? It's 2000w so it should easily move it yes? Or do RC motors work differently, will it overheat? Do I have to use zippy battery packs or can I build my own 10s battery? And finally, if it can't move me on its own could I make it pedassist?

Here's the link https://hobbyking.com/en_us/kd-53-30-high-voltage-brushless-outrunner-190kv.html

Thanks.

  • 1
    Been there, done that. What will happen is that either your motor is going to overheat or simply break ... for reasons already listed in the answer of @mattnz. For me the biggest challenges were getting the transmission and mechanical setup right, though. And you also need some wiring for your ESC, since you most likely want to control the RPM in some way. – Num Lock Jul 10 '17 at 10:35
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    Depending on your location in the world, 2 kW of power is an electric motorbike and needs to be registered and insured as a motorbike. Having pedals doesn't make it a pushbike. In my country the limit is 300W and in others it may be a maximum speed permitted by the motor. 2kW is ludicrous levels of power. – Criggie Jul 11 '17 at 0:45
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    Another thing that will give it away would be the uprated brakes - there's no way normal bike brakes are up to the task of stopping you from speed. So you will be needing a massive un-subtle downhill-style rotor on the front wheel minimum – Criggie Jul 11 '17 at 0:50
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    @Criggie any set of good brakes should easily be able to stop you from highway speeds, albeit a bit slower than a car. – Daniel Vestøl Jul 11 '17 at 9:21
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    @AidenP If you're looking for torque, then you need to look at the motor's torque, not its power. I'd expect a motor designed to turn the prop of a model airplane wouldn't need to be very torquey. – David Richerby Jul 11 '17 at 9:53
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Its designed to attach the prop of a model aircraft directly, i.e its designed to drive a fan that cools it. It has little (or none) weather protect, and would be destroyed on a bike in months. Another concern I would have with that motor is the shaft size- its one thing to deliver 2000W to a prop, but to connecting it to a mechanical drive train that can load it with sudden changes in forces is likely to destroy it, you would need to get very creative with shock isolation from the drive line.

As far as costs, I doubt the basic motor part of the bike kit costs all that much more, after all, its only a few coils, a shaft and bearings.

The very best current commercial mountain bikes come, despite a lot of frame design and engineering, with a a huge, ugly and heavy mid drive motor. With all the R&D, and money to be made creating the perfect E-Bike, do you honestly think if the big boys could add a 2000W motor weighing 670gram and the size of a bottom bracket, they would not have done it already?

As far as battery packs, with the right controller you can roll your own easliy enough.

  • I thought of all that just wanted to be sure. I want a small motor that would fit inside the bottom tube of the bike. Like specialized did here. electricbikereview.com/wp-content/assets/2017/01/… Could there be a similar motor that is small enough? – Aiden P Jul 10 '17 at 11:43
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    The issue is that even if you find a similar motor, you'll need to engineer a gearbox to make it work, then figure out the batteries, the weather-resistant solutions, the mounting points, the throttle/activation system, the reliability and safety matters, etc. That's a tremendous amount of work for a somewhat satisfying result. This is a job that would require years of work and developement for sure. – mtdp Jul 10 '17 at 13:44
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The important number is not power, but torque. The linked page doesn't say it, but that 2000W is probably achieved at a huge speed (thousands of rpm). To get enough torque to drive the bike (and to step down the speed to usable levels, i.e. in the region of 50 rpm), you'll need a reduction gearbox.

Finally, regulations for ebikes usually specify a max. power of 250 W and a cutout speed of 25 km/h, so your motor would be illegal/would require registering your bike as a motorbike (depending on country. In the Netherlands, there's a moped category for 350W/45 km/h max, anything above that is a motorcycle).

  • As a moped*. There is no rpm rating but there is KV which is rpm per volt. – Aiden P Jul 11 '17 at 9:49
  • 190 kv, 90 A at 2000 W is 22 V, so ~4200 rpm max. – Hobbes Jul 12 '17 at 10:43
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These RC motors are made to be used on much smaller and lighter objects than a bike+human combo. So even if it delivers 2k W, it will most likely just surge and either overheat, break its inner components, or at worst explode. Another issue you'll have with such a motor is that it's not waterproof so first water encounter and the thing is fried.

Regarding the battery, I would highly suggest you not to go with a custom made one for this kind of setup. You don't want an overheating battery coupled to an overheating motor just under the seat. Plus 10S lipos aren't that expensive, I wouldn't cheap out on this.

What would also be hard to figure out is power management. With this kind of motor you would need to throw it to full throw to expect the smallest assistance, which is far from being efficient. Running that way will get your batteries dry in no more than an hour (and I'm being generous) for an at best tiny assistance. Worst case you won't feel any difference with or without the engine. And using it as a pedassist would actually be letting the motor run freely for not effective improvement. Considering how tiny the thing is and the power your lower body can develop, you'll easily outrun the motor even with the tiniest effort. Not only you'll outrun it but you'll destroy it also. It is design to deliver power but not to resist to any received force.

Commercial E-bikes look the way they do because at this point, that's what we need to have an efficient setup. To get to these levels of efficiency you'd need some massive engineering and incredible costs (for reference, check out this doc from a french tv). This isn't really doable for us mortals...

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This is a supplementary answer. You're concerned about your conversion screaming ebike. I'd like to challenge this premise.

Some of the new geared hub motors are small enough to hide behind rear disc brakes and/or look like an IGH hub and are hardly noticeable. You can then hide the controller in a seat bag and hide the battery in a water bottle for the total stealth look.

rear hub ebike

  • Looks cool. How much watts is that hub if you know maybe? – Aiden P Jul 11 '17 at 9:51
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I did this. It is not impossible and very fun, some electronics skills required.

Derate the motor: if the maker says "10Kw @ 100V" you know that the max admitted Amperes are 100. Cut that down to 40-50.

Use a sensored Drive: RC motors` rotors position is determined mainly by reading back-emf. That doesnt work fine when you need to start the motor with a heavy load on it.

Use (or build as I did) a controller with CURRENT LIMITING. That is the key not to burn it.

Have fun!

  • Pics? I'd like to see it if possible :) – Aiden P Jul 11 '17 at 9:52
  • What gearbox did you build? – gschenk Jun 14 '19 at 22:26
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You could use one but to avoid damaging the motor you would be better off using a one way bearing on the shaft so if there's any sudden stopping there wouldn't be any load on the shaft and motor

  • Could you give more detail? Most of the existing answers say that this motor is completely unsuited to powering a bicycle so, if you're going to contradict that, it would be really helpful to explain why the motor is appropriate to this application. – David Richerby Jun 15 '19 at 12:48
  • Welcome to Bicycles. We recommend that new members take the tour to make best use of the site. As David Richerby says, details are important, details and pictures are even better. – David D Jun 17 '19 at 15:48

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