Author Topic: E-Bike developments  (Read 13432 times)

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axman88

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Reply #240 on: September 26, 2021, 04:38:58 am
So when is the NuVinci Hub Motor coming out? They already have the first half of your design package in production.
That's interesting, I hadn't seen that design.  It's pretty amazing how much innovation is going on in the world of bicycles, let alone E-bicycles.

With respect to the NuVinci technology being used in a hub motor, I see a few issues.  As you noted, it's going to difficult to get E-Moto torque levels through what is essentially a friction drive.   

Second, as we can see in these pictures, the spherical balls eat up a lot more internal volume than a planetary gear cage.  Here the planet gears look like nylon.  If they were steel, they could be 1/3 as thick.
https://ebikes.ca/pub/media/wysiwyg/ezeestator.jpg

The NuVinci balls need to be substantial to handle the surface loads.
https://i1.wp.com/www.electricbike.com/wp-content/uploads/2016/06/BeltIGH19.png?w=696&ssl=1

Lastly, again because it's a friction drive, the efficiency is quite a bit less than a gears.  This test showed overall friction loss of 3% for a single speed bicycle chain drive (97% efficient).  With a internal geared (Rohloff) hub that went up to 5.5% average for all gears.  The NuVinci continuously variable lost an average of 16.5% over it's range of ratios.   https://www.cyclingabout.com/speed-difference-testing-gearbox-systems/

Efficiency wasn't so important when internal combustion engines and cheap gas was providing the power, but becomes a bigger factor with limited storage capacity for electrical energy, and definitely when a human is providing the power.

My impression is that the electric motors have such a wide torque band, that in hub form they don't require a lot of ratios to do the job, and don't require continuously variable transmissions at all.  The problem a non geared hub motor has, is that on a steep hill it's being asked to delivery peak torque at lowest rpm and something gets burned up, or at minimum, efficiency plummets.  Maybe all somebody needs to do is create an internal planetary gearing system that has a high ratio planetary, that can also be bypassed for direct drive at high speed, and the controller shifts based on speed and/or power demand?   Seems so obvious, I'll bet it's already out there.

Back to the idea of hub weight creating issues with their unsprung weight, this graphic shows a range of bicycle wheel hub motors.  We can see a weight range from 2.3 to 8.5 kg, quite a variation.
https://ebikes.ca/pub/media/wysiwyg/2020MotorSpread.jpg
I don't know about E-moto hub motors, but wonder if graphing power vs. weight for the bicycle hub motor will result in a fairly consistent factor that could be extrapolated.

It occurred to me that adding a rear hub motor, battery pack and controller, to a pedal moped, would result in a "hybrid motorcycle" that possibly retains eligibility as a non-licensed "low power E-bike".


AzCal Retred

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Reply #241 on: September 26, 2021, 06:59:20 pm
Axman88 - great analysis on the Nuvinci!

Here's how hub motors used to be...check out the starting drill.
Megola - Rotary Engined Motorcycle!
https://www.youtube.com/watch?v=ZghXM9xqCPA

Info from the UK...
https://www.bikesure.co.uk/bikesureblog/2016/05/electric-scooters-and-the-law.html

...and for even more fun, a hybrid scooter conversion kit...!?!
Petrol and Electric Hybrid Scooter
https://www.youtube.com/watch?v=1h4TPIUnYCc

A search for "hybrid scooter conversion kit" brings up a lot of hits. Way more than I would have thought. 4 H8 car batteries and a wounded scooter and you'd be on your way to a fun project.
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derottone

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Reply #242 on: September 26, 2021, 07:49:52 pm

My impression is that the electric motors have such a wide torque band, that in hub form they don't require a lot of ratios to do the job, and don't require continuously variable transmissions at all.  The problem a non geared hub motor has, is that on a steep hill it's being asked to delivery peak torque at lowest rpm and something gets burned up, or at minimum, efficiency plummets.  Maybe all somebody needs to do is create an internal planetary gearing system that has a high ratio planetary, that can also be bypassed for direct drive at high speed, and the controller shifts based on speed and/or power demand?   Seems so obvious, I'll bet it's already out there.


They may need infact just one gear ratio. The AC motors used in vehicles those days are controlled by an inverter that can deliver most any frequency and could be called the "gearbox" or "cvt" of an electric motor. When designing an electric vehicle what you would typically look at is the torque required for a good startability and so that the vehicle is capable of climbing a certain degree of slopes. That would determine your gear ratio that you choose for your motor. The other thing you want to decide upon would be the power in kilowatts, which depends on how fast you wish to go. Once you have selected a gear ratio that permits enough torque for an decent acceleration the inverter will take care of the rest and make the motor spin as fast as necessary sacrificing some torque with rising rpms.

It's all fantastic if there was no such thing as a battery. Although for an electric moped enthusiast the limitations may not be an issue at all. I would still shy away from an hub motor though unless the vehicle was designed for really slow speeds.
« Last Edit: September 26, 2021, 08:06:55 pm by derottone »
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AzCal Retred

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Reply #243 on: September 26, 2021, 09:36:10 pm
"Pure" AC motors draw current inversely (sort of) proportional to the speed. At design RPM they produce enough "CEMF" to limit current in the windings (& inductively coupled rotor) to very low values, roughly analogous to a transformer in a no-load condition. As motor speed slows under load, CEMF decreases, winding currents (& rotor currents) increase, magnetic flux increases, speed increases a bit until the "balance point" RPM for that load on that motor is reached, the "slip frequency" for that load. At start up speeds CEMF is almost zero, so winding & rotor current is quite high, 15x to 30x the design FLA current, depending on winding design efficiency. Higher efficiency (low impedance) motors tend to have higher locked rotor currents. That's why AC motor starting protection looks both at current and time, to prevent motor overheating & damage.

The hub motors normally are permanent magnet motors to eliminate an extra set of brushes, so the attraction/repulsion forces possible depend on available Henrys of flux, rotor/stator spacing, magnetic field proximity, winding wire size & applied voltage, etc., etc.. Starting torque is limited by many design factors. The winding currents are controlled by the electronics "package", so there is some real voodoo going on as relates to motor speed & load control. Some of these hub motors even have regenerative braking/charging features. The package does everything, from protecting the motor windings to limiting max RPM. The fuses supplying them are just to limit damage in event of an internal fault.

Using an ordinary "pure" AC 3-phase motor on a VFD, the rule of thumb is don't exceed 150% of rated rpm. The drive contains various protection curves, and some drives also utilize thermistors embedded in the motor windings for overload overheating feedback. Vehicle drive motors are a pretty specialized design, with the construction blurring the AC/DC motor separation.

I'm with you on the probable need for a transmission, as that keeps you out of the extreme ends of the operating spectrum. We also agree on the limitations of batteries, as weight and limited energy storage capacity are still a problem. And as you point out, slow speeds are less demanding of the system and minimize drag forces, similar to the early days bi-plane flight envelop dictated by the draggy wing cross bracing. At speeds up to about 60 MPH, drag was manageable. For the racing bi-planes of the '30's & 40's, it took a truly huge engine to pull them along at 200+ MPH.
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derottone

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Reply #244 on: September 26, 2021, 09:49:47 pm
 :)...very nice. There is still too much confusion though regarding those motors, some call them AC motors, others DC motors electronically commutated. We agree it's brushless motors that use permanent magnets.
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Richard230

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Reply #245 on: September 26, 2021, 10:48:19 pm
I only know of one "mass produced" electric motorcycle with a transmission. That was the Brammo Empulse that was marketed between 2012 and 2018, when it was sold to Victory Motors, who produced a slightly updated version of the bike for about 2 years before Polaris shut down the Victory brand and the Victory Empulse TT went down the drain, too. That bike was water-cooled and used a 6-speed transmission sourced from a small company in Italy. To my knowledge no other electric motorcycle currently on the market uses a multi-speed transmission. All of the other brands, like Zero and H-D, use direct drive systems, brushless A/C motors, which appears to be the current standard in the industry, which seems to be sufficient to get them down the road. I believe that even all of the electric automobiles on the market also use direct drive power systems, even Tesla. I think Tesla once tried out a 2-speed transmission but that didn't work out for them and they went back to direct-drive.
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AzCal Retred

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Reply #246 on: September 27, 2021, 12:26:20 am
Direct drive eliminates a lot of "excess" components. It also largely removes the "meat puppet" factor, so engineering can just do what's necessary. For flattish ground, modest acceleration and moderate top speeds it works really well. Brammo was basically mimicking an IC engine, which is a LOT more user interactive and fun. Too bad they got shut down.
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Richard230

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Reply #247 on: September 27, 2021, 01:52:20 am
Direct drive eliminates a lot of "excess" components. It also largely removes the "meat puppet" factor, so engineering can just do what's necessary. For flattish ground, modest acceleration and moderate top speeds it works really well. Brammo was basically mimicking an IC engine, which is a LOT more user interactive and fun. Too bad they got shut down.

I have always been a little ticked-off by Brammo. In 2010 they introduced their prototype Empulse with direct-drive. I was one of over 1000 people who put their names on the pre-order list for the bike. Then Brammo took the bike off of the market before it was ever built because the company founder, Craig, wanted to insert a clutch and transmission into the drive train.

After that announcement was made, I saw him at the Sears Point Raceway where they were racing the bike against 600cc ICE motorcycles. I can't recall if that was the direct-drive version or the one with the transmission that was being raced that day. But I had a discussion with Craig telling him that I didn't think much of his decision to cancel the direct drive and go with the 6-speed version.  I thought that having less complexity on a new tech platform was a safer alternative. It would allow them to make sales right away and generate some cash while they worked the kinks out of the transmission version that could have been introduced later. However, he was adamant that motorcycle enthusiasts wanted the fun of shifting and clutching. I responded that I wasn't one of those and just wanted to own and ride an electric freeway-legal motorcycle.

Obviously, I didn't convince him of my way of thinking and it took two years for the new version to be introduced. By then I had bought a 2012 Zero ZF9 and was very happy with its direct-drive and lack of the shifting experience. It had plenty of power, could go 100 miles on a charge and was good for 80 mph up a 6% freeway grade.  Attached are four photos of the direct-drive Brammo Empulse prototype that I took at on February 10, 2011 at Scuderia West (now SF's RE dealer) when it was displayed there one weekend.
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GlennF

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Reply #248 on: September 28, 2021, 12:17:43 am
A truly efficient and simple AC motor would need three phase power.

Just saying :D


AzCal Retred

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Richard230

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Reply #250 on: September 28, 2021, 02:43:17 pm
Here is something that you can do with your e-bike. Turn it into a tie-dyed piece of art:  https://thepack.news/newsflash-ftn-motions-streetdog-collab-with-wellington-airport/
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AzCal Retred

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Reply #251 on: September 28, 2021, 03:55:26 pm
With some painted disc wheel covers you could get that awesome spiral effect as you motored about at the "Doobie Brothers" college...
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axman88

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Reply #252 on: September 28, 2021, 04:26:10 pm
A truly efficient and simple AC motor would need three phase power.
The brushless motors that are used for hub motors are running on chopped up, PWM DC, not true AC.  Some controllers will run at higher frequency to create a waveform that approximates AC, which gives quieter running and more efficiency, but the run of the mill controller just sends subsequent square pulses to the various phases.

There's some information on how this works here:  https://www.integrasources.com/blog/bldc-motor-controller-design-principles/

One could build a controller that had more phases, but I don't see much advantage.  The motors are already constructed with lots of poles which gives more power pulses per rotation.   I count something like 48 on the rather basic, gearless hub motor shown in this picture, split between the 3 phases:  https://www.ebay.com/itm/Voilamart-Electric-Bicycle-E-Bike-26-Front-Rear-Wheel-Motor-Conversion-Kit/322247604604

In this design, the stator is fixed to the axle, while the magnets ( not shown in the picture) are attached to the rotating rim of the motor.
I think it's easy to see why this basic design of hub motor has a hard time developing power at low rpms.

The type with internal gears can spin a lot faster at a given wheel rpm, producing the same power with much fewer poles and in a package with reduced diameter and weight.   http://volto.co.nz/wpvolto/wp-content/uploads/2018/06/motor300w-electric-bikes.png

I imagine that the motors used on the Sol and Sondors machines both use internal gearing, but I haven't seen details of these.


AzCal Retred

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Reply #253 on: September 29, 2021, 06:19:01 pm
New Info from Land Electric Motorcycles -

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Nitrowing

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Reply #254 on: September 29, 2021, 10:10:36 pm
Ugly  :(
No wonder we no longer have a motor industry