Thoughts on the UrbanX eBike kit and other complete-wheel kits

[Swytch Bike]

Hi all - we are interested to start a conversation about the UrbanX and some of the other kits out there that are designed to be self-contained kits packaged in a way making them quicker to fit.

https://www.kickstarter.com/projects/934648866/urbanx-convert-any-bike-to-an-electric-bike-in-60

It's a relatively new eBike kit on KickStarter with the battery and controller built into the wheel.

Other similar kits that it is compared with are the Copenhagen Wheel and also the Geo Orbital Wheel:
https://www.geoo.com/
https://www.superpedestrian.com (Copenhagen Wheel)

The advantage of these kits that is advertised is that they are self contained kits that are appealing because they are so-easy and quick to fit (due to the self contained design)

Our view is that if you select the right battery type for your bike, the only tricky part of fitting an eBike kit is replacing the wheel. So these kits are seeking to solve a problem that isn't there - you still have to do the process of swapping out the wheel, and if anything it is more difficult because of the beefy design of some of these motor wheels.

Furthermore there are two huge disadvantages:
- The battery capacity is massively limited because of it all being packed into a wheel. E.g. the Urban X is only 125Wh and it is optimistic at best to think this will get the 30 miles range advertised
- The weight balancing of the bike is terrible due to it all being in the front wheel


What does everyone else think? Will these gimmicky conversion kits fade into irrelevance or is the novelty of having only one replaceable part really that useful that there will be more uptake than conventional kits?

 

[Deleted member 4366]

That's a lot of rotational inertia to carry in the front wheel. I can imagine the rim brake in the photo having a lot of trouble to stop it. At 20 mph, I give it 5 miles max.

Fitting is not as straightforward as they say. We all know about fitting hub-motors to front forks. It only works on certain types. On most, you need to deepen the drop-outs and fit a torque arm. Theirs looks like a normal 12 x 10 axle with a large flanged nut. That's a recipe for disaster on most alloy forks, especially as it has the power for 20 mph.

No mention of how to fit the pedal sensor, and that can bring all sorts of problems. Nobody has yet come up with a PAS that can fit all bikes. The same with the throttle. Where do you put it? That's the big thumb-throttle, which is always a struggle to find room for.

In summary, they should have designed it with a 10mm round axle and a separate torque arm that would be anchored with a clamp around the fork. The throttle should have an option of left-hand half-throttle or the small thumb-throttle, and they need to think about a true universal PAS. Even with all that, the inertial will affect the steering and braking, so not ideal.

I'm not voting because it won't be any more simple to fit than a normal front motor kit. The only thing it saved is the battery fitting, which is probably the easiest part to fit anyway.

 

[Danidl]

That's a lot of rotational inertia to carry in the front wheel. I can imagine the rim brake in the photo having a lot of trouble to stop it. At 20 mph, I give it 5 miles max.

Fitting is not as straightforward as they say. We all know about fitting hub-motors to front forks. It only works on certain types. On most, you need to deepen the drop-outs and fit a torque arm. Theirs looks like a normal 12 x 10 axle with a large flanged nut. That's a recipe for disaster on most alloy forks, especially as it has the power for 20 mph.

No mention of how to fit the pedal sensor, and that can bring all sorts of problems. Nobody has yet come up with a PAS that can fit all bikes. The same with the throttle. Where do you put it? That's the big thumb-throttle, which is always a struggle to find room for.

In summary, they should have designed it with a 10mm round axle and a separate torque arm that would be anchored with a clamp around the fork. The throttle should have an option of left-hand half-throttle or the small thumb-throttle, and they need to think about a true universal PAS. Even with all that, the inertial will affect the steering and braking, so not ideal.

I'm not voting because it won't be any more simple to fit than a normal front motor kit. The only thing it saved is the battery fitting, which is probably the easiest part to fit anyway.

.... And you could have added that any weight in the rotating wheels as an effective weight exactly double its actual weight. There is the actual weight and there is the rotating weight moment of inertia , which by a quirk of the maths provides the equivalent mass ...

 

[Woosh]

the immediate benefit of such systems is no wiring or very little wiring,
These systems are intrinsically low power, reducing risk of mechanical or electrical failures.
There is nothing to stop the designer adding a port for an additional battery.

 

[Woosh]

Believe it or not, that kit weighs 7kgs according to the web page.
if you build a similar kit using a front XD motor plus a box on the handlebars to house the controller and a 10S2P battery, the total weight is about 4.5kgs.

 

[Danidl]

.... And you could have added that any weight in the rotating wheels as an effective weight exactly double its actual weight. There is the actual weight and there is the rotating weight moment of inertia , which by a quirk of the maths provides an equivalent mass ...

... Thus doubling the effective weight ...

 

[jollyDodger]

... Thus doubling the effective weight ...

Rotating weight make a small amount of difference and only when accelerating. Admittedly the weight difference here is huge, but a Copenhagen Wheel, compared to a traditional rear hub is not that much difference in weight (and comparable to on-line tests of bicycles with heavy vs light rims). I would guess that either rolling resistance, regenerative braking or aerodynamic design would more than make up for rotating weight.

I like the complete wheel concept a lot and may invest and see if it really does work. Admittedly it's not the right bike for those that it's marketed at i.e. 'lazy americans', I want a lightweight bike just to give me a little bit of help home up a hill. My current dutch electric bike on doing a 14mile journey everyday has more that 50% battery but also weights 30kg.

 

[Deleted member 4366]

Rotating weight make a small amount of difference and only when accelerating. Admittedly the weight difference here is huge, but a Copenhagen Wheel, compared to a traditional rear hub is not that much difference in weight (and comparable to on-line tests of bicycles with heavy vs light rims). I would guess that either rolling resistance, regenerative braking or aerodynamic design would more than make up for rotating weight.

I like the complete wheel concept a lot and may invest and see if it really does work. Admittedly it's not the right bike for those that it's marketed at i.e. 'lazy americans', I want a lightweight bike just to give me a little bit of help home up a hill. My current dutch electric bike on doing a 14mile journey everyday has more that 50% battery but also weights 30kg.

Read carefully what I wrote above. Fitting such a device is not straight-forward, especially as a front motor. You can put yourself in a lot of danger if you don't get it right.

I think it's very bad of them to show videos of assembling to the one type of fork it does fit without much trouble and saying how easy it is, then leaving the punters to get it all wrong on their bikes with different forks.

 

[jollyDodger]

Its the "thus doubling the effective weight," that is misleading not your post d8veh.

From how i have grasped the explanation of the physics behind this, the extra rotational weight would be on acceleration not deceleration. However as you have clearly pointed out any extra weight on front forks that are not designed for that sort of load bearing is dangerous.

What are your thoughts on the now shipping Copenhagen wheel?

 

[Danidl]

Rotating weight make a small amount of difference and only when accelerating. Admittedly the weight difference here is huge, but a Copenhagen Wheel, compared to a traditional rear hub is not that much difference in weight (and comparable to on-line tests of bicycles with heavy vs light rims). I would guess that either rolling resistance, regenerative braking or aerodynamic design would more than make up for rotating weight.

I like the complete wheel concept a lot and may invest and see if it really does work. Admittedly it's not the right bike for those that it's marketed at i.e. 'lazy americans', I want a lightweight bike just to give me a little bit of help home up a hill. My current dutch electric bike on doing a 14mile journey everyday has more that 50% battery but also weights 30kg.

.. I will explain again. .. all weight on the bike irrespective of where it is .. on the person or in the frame or carrier increases the mass of the bike and reduces acceleration and deceleration. It makes it slower to accerate and slower to stop. It means that going down hills is faster and going up harder.
Any mass added to the wheels , must also rotate and it therefore has rotational inertia. By a quirk of the maths, the added inertia is exactly the same as the mass, small wheels have to rotate faster to cover the same distance than large wheels. If the battery is put inside a rotating wheel, it will contribute to this inertia
The only difference is that the wheel inertia does not contribute to the rolling resistance.
Regenerative braking is generally not effective on ebikes, as the total inertia is small and the speed relatively low.
People pay a small or large fortune to buy bikes weighting marginally less than competitors, putting a battery in a rotating wheel negates that advantage, By the weight of the battery.

 

[Deleted member 4366]

Its the "thus doubling the effective weight," that is misleading not your post d8veh.

From how i have grasped the explanation of the physics behind this, the extra rotational weight would be on acceleration not deceleration. However as you have clearly pointed out any extra weight on front forks that are not designed for that sort of load bearing is dangerous.

What are your thoughts on the now shipping Copenhagen wheel?

I probably didn't explain very well. I don't care to much about the physics of the situation, but what I do care about is how easy they make it look to fit the thing. They choose the ideal bike in their videos and practice that everything works first. Fitting a front wheel motor of any type is fraught with dangers and difficulties. They don't do any explanation of what they are, nor the problems you're likely to encounter