Time to skarper?

[Ajax Bay]

Skarper: seriously interesting and great engineering.
Click and play and now ready to pre-order.
@T4tomo previewed this 2 years ago: https://www.cyclechat.net/threads/skarper-conversion-kit.286034/
Uses (an adapted) disc brake rotor (same centrelock or 6-bolt fixing) to transfer the power to a 'normal' bike
https://skarper.com/tech-page/

View: https://www.instagram.com/p/DBwFl_mMLSp/?img_index=1

 

[wafter]

Doesn't personally appeal since I think these new-fangled electric things are a corruption of the purity of our beautiful rides, however it looks like a nicely-executed, innovative idea

 

[Drago]

It costs more than a halfway decent full ebike.

 

[MichaelW2]

£1,495.00
A bargain at half the price.

 

[Ajax Bay]

A bargain at half the price.

Dad joke! Used intra-family my children don't laugh.

 

[IanSmithCSE]

Good morning,

Looks to me like someone had an idea in a pub after a few pints and for some reason didn't leave it there.

Who is it aimed at?

As a conversion kit for an exisiting bike the price rules it out for a lot of people and if the price doesn't rule it out then surely you are likely, space permitting, to buy something made as an ebike.

What type of bike would it fit on, I would also worry about chain stay wear on a CF frame where the plastic stabilty clip is, there are very few classic bikes with discs and it seems to big for foldables

This seem to leave modernish aluminium road bikes and mountain bikes, but would the rotor mounts on the hub be up to the alternating brake/accelaring loads? We got through axles because Q/R could undo because of twisting forces from one sided discs and if the rotor becomes even slightly lose it will bind and the swinging 4.5kg weight could easily strip the rotor mount threads as these are normally the same softish aluminium that the rest of the hub.

In a test environment it is easy to do maintainance and ensure that the rotor is tight, but in a normal usage case?

Having done around 6,000 miles on my X35 ebike and lost around 10% of battery capacity I would also have concerns about this unit's battery capacity. 250Wh sounds a lot, but the last 10%-15%(ish) can't be drawn at a sufficient voltage&current to be much use even when new.

There is an I dislike Shimano thread around here somewhere, but one really good thing about most Shimano stuff is that it works after 6 months hard use and no molly coddling

So overall a plaything, fine if you take home £10k plus a month?

Bye

Ian

 

[PaulSB]

£1,495.00
A bargain at half the price.

The eco range is 50km (30m). Personally I can't see the point in spending £1500 for a two hour ride! My usual meet point is a 30 minute ride each way from home. That would leave me an hour of assistance riding with my buddies and another 3-4 hours of pulling extra weight around.

 

[Drago]

"Range" is a pointless measure. It goes as far as it goes, utterly dependent upon how far and hard it's used.

 

[Ajax Bay]

As a conversion kit for an exisiting bike the price rules it out for a lot of people and if the price doesn't rule it out then surely you are likely, space permitting, to buy something made as an ebike.

What type of bike would it fit on, I would also worry about chain stay wear on a CF frame where the plastic stabilty clip is, there are very few classic bikes with discs and it seems to big for foldables

. . would the rotor mounts on the hub be up to the alternating brake/accelaring loads? We got through axles because Q/R could undo because of twisting forces from one sided discs and if the rotor becomes even slightly lose it will bind and the swinging 4.5kg weight could easily strip the rotor mount threads as these are normally the same softish aluminium that the rest of the hub.

Clearly at the price, buyers/users will need to afford it. You'll be saying that the price of bikes costing >£3000 "rules them out for a lot of people". NSS I shall not be a customer.
The niche this might fit is a rider who has a couple of nice bikes who wants e-assistance but doesn't want a (£2600) heavyish e-bike
https://www.merida-bikes.com/en-gb/bike/archive/2179/escultura-400
or give one space in their stable (shed/garage). They can enjoy a ride on their bike, unassisted. Or for utility trips, clip it on.
Multi-bike benefits.
I guess there's also a security angle of cyclists who can't lock an expensive bike up with sufficient security but by unclipping the Skarper reduces the vulnerable value.
Makes the charging easy too eg for commuters: quicker (not much) than removing a battery pack.

would the rotor mounts on the hub be up to the alternating brake/accelerating loads?

I'm going to take a stab here and say that the torque the Skarper can deliver via the special for purpose rotor is tiny compared to the effective torque of braking and the fact that the direction of torque differs will be irrelevant. But idk.
Why would one allow a rotor to be "even slightly loose"? You are identifying risks which are very small and easy to mitigate. In any case if there is friction caused in this way the forces from and on the Skarper are small and the effect would be resistance to the bike's forward motion.
X-35; https://velomotion.net/2020/08/new-ultra-light-e-bike-drive/

 

[Tom B]

The eco range is 50km (30m). Personally I can't see the point in spending £1500 for a two hour ride! My usual meet point is a 30 minute ride each way from home. That would leave me an hour of assistance riding with my buddies and another 3-4 hours of pulling extra weight around.

It says in the original article that the target prices was "under £1000". Which is still twice the price of the bike i would fit it to.

 

[IanSmithCSE]

Good afternoon,

............. I'm going to take a stab here and say that the torque the Skarper can deliver via the special for purpose rotor is tiny compared to the effective torque of braking and the fact that the direction of torque differs will be irrelevant. But idk.
Why would one allow a rotor to be "even slightly loose"? ..........

Do you remember when disk brakes were introduced, they were nearly always on Quick Release wheels?

Then there started to be reports of Q/R skewers just undoing themselves, the forums, “letters page”, bike sites and manufacturers all said Rider error.

Now Q/R has been replaced with through hubs, why, because it was worked out that there is "sweet spot" where the wheel feels tight enough to the user but is just loose enough that certain twisting motions that occur when a disk brake is applied slowly undoes the skewer.

So the people with a loose rotor could be the same people as those with loose Q/R skewers.

The way that I understand the Skarper motor is that most of the 4.5kg weight is either in the rotor or hung off the rotor rather than being rigidly mounted to the frame.

So when going round a corner and leaning the bike over, some of this weight will now be pulling the rotor away from the hub which is a direction that is not seen with a standard disk brake.

Powered or unpowered applying the brake will try to move the rotor clockwise in relation to the wheel hub, by the spare space between the mounting bolts and the holes in the rotor and as it can't move much we have braking. (viewed from the non chainring side)

With an unpowered bike if the rotor does slip slightly on the first application of the brakes there is nothing to force it back to its starting position.

If you add this motor, accelerating will try and rotate the rotor anti clockwise back to its starting position, starting a cycle or rotate/unrotate.

These bolts are usually quite lightly done up, typical torque setting for these bolts is 2Nm-6Nm and with the motor weight trying to bend the rotor outwards the friction between the bolt head and the rotor surface has been greatly increased. Possibly making overcoming the clamping forces between, bolt head, rotor and hub more likely and undoing the rotor bolts

Of course this won’t happen and if it does we can all blame the rider for not checking his rotor bolts often enough.

Bye

Ian

 

[Ajax Bay]

The way that I understand the Skarper motor is that most of the 4.5kg weight is either in the rotor or hung off the rotor rather than being rigidly mounted to the frame.

To make clear, I am not a shill for this. I'm just interested in the engineering.
Thru axles at 135mm OLD seem an entirely sensible bet. And centrelocking rotor at that (40Nm).
I also wouldn't install it on a wheel with only 24 spokes (see image) but whatever.
The duck footed rider might find their left heel bashing it, but I think its outer edge is not much (?<20mm) proud of the chainstay, horizontally.
https://skarper.com/tech-page/
To comment (if not answer) your 'understanding', the unit is supported in two places: at the rotor and hung from the chainstay, but not hung off the rotating rotor with the effects you deduce.

From the images, it looks as if the main lock/drive interface is into the working (non rotating) central element of the rotor, the outer 2cm of the rotor rotates through the brakes caliper.
This central element is secured (see above) to the hub and the hub is locked into the frame.
"4.5kg, with an added 600 grams for the DiskDrive® brake rotor"
The Skarper's part weight (the proportion not supported by the chainstay 'clip') is acting in line with the inner face of the dropout (near enough) so there is 'no' torque in the vertical plane: a extra (?post Christmas) stone of rider mass would have same effect.

Cycling Weekly: "When compared to other e-bike conversion kits, Skarper is one of the more expensive options at £1,495 (£1895 to upgrade to the dual bike kit). The obvious comparison is to the Swytch Bike Kit [tiny 90Wh battery = 1kg], or with its largest battery option [weighs more], comes in well under half the price at £599.
"That said, there are very few e-bikes at this price point, and certainly not ones that would be as light or refined as Skarper. Its nearest full bike rival would be something fitted with a Mahle X35 hub, with these typically starting at around £2,600."
https://www.cyclingweekly.com/revie...ent-and-12-8m-of-investment-its-finally-ready