Woohoo.. we are live with the exclusive new controller for bafang ultra.. and more goodies!

Ebiker33

Well-Known Member
If Pushkar can put Gates/Rohloff/Fenders & Rack on this he will have a very unique Ebike in the industry, the lightest one that's is for sure, and the ultimate hybrid.
I like that it also comes with the slightly beefier 3" tires.
The reviews on this bike from even people that own many Ebikes is fantastic, there is a guy who owns 6 high end Ebikes, he says it's the very best of the bunch.

German video of it
 

pushkar

Well-Known Member
If Pushkar can put Gates/Rohloff/Fenders & Rack on this he will have a very unique Ebike in the industry, the lightest one that's is for sure, and the ultimate hybrid.
I like that it also comes with the slightly beefier 3" tires.
The reviews on this bike from even people that own many Ebikes is fantastic, there is a guy who owns 6 high end Ebikes, he says it's the very best of the bunch.

German video of it

Rohloff and fenders are absolutely doable. Belt for that level of rear travel is definitely a problem.
 

Timpo

Well-Known Member
Pushkar, could this new bike be turned into an all-purpose bike? By all-purpose could fenders be added. Where I live, on Vancouver Island, better know as the wet coast, fenders are really important for at least 6 months of the year. If fenders could be added I'd be interested in this bike.
If there was an innovator award for ebikes you'd surely be the winner. Well done! 👍
Something like this?

 

pushkar

Well-Known Member
You are right that R&M is doing it. There are a couple others that are as well.


Here is my understanding of why this is hard on the Bafang ultra in particular.
  1. Gates updated tension requirements here - https://www.gatescarbondrive.com/~/...arbon-drive-tension-recommendations.pdf?la=en
  2. Using the Bafang ultra with that much torque puts us in the "Punching rough pedaling style" category. (We tension our belts at ~43lbs as a reference)
  3. With FS and belt, we need to be atleast at 45lbs nominal (sitting down on the bike) position to account for belt slack. The drive train will routinely blow through the highest recommended tension with the incredible rear suspension travel.
  4. If we choose to have a lower tension to begin with, we risk the belt falling off and will need a belt guide and other contraptions.

With a smaller motor, like with R&M, we can be in the 35lb-50lb range, and not breach belt tension ceiling. So R&M full suspension will work because it is a smaller motor.

There are 2 ways of making this happen on the ultra.
  1. Have a smaller travel for the rear suspension.
  2. Have a soft tail suspension (another way of limiting travel with rear suspension).
IMO, In both these Ultra-related options, we can get a close enough / reasonable ride experience with the Kinekt seatpost - the standard setup as it stands right now on the UC Pro. I am not super comfortable about breaching limits regularly. I have spoken with Gates to see what options we have, and I will keep looking at designs to be in the sweet spot.
 

smorgasbord

Well-Known Member
It appears Pushkar is on top of the requirements.

For the curious, from Gates' eBike Integration Guide, which doesn't cover the Bafang Ultra: "Gates Carbon Drive components have been designed and tested to handle higher loads than most eBike motors produce. If you are using a mid-drive motor that exceeds 90 Nm of torque, contact Gates Carbon Drive to ensure system warranty."

As Pushkar points out, supporting both high torque AND big rear suspension travel is a tall order.

But, having recently ridden both a Gates/Enivolo hardtail with Kinekt seatpost and a full suspension carbon frame with SRAM 10-50 12-speed, I definitely preferred the ride of the full suspension, even on pavement. That may be due to the hardtail being quite 12 lbs or so heavier. My view is that the Kinekt definitely helps cushion the ride, but full-suspension helps the bike stay more firmly planted on the ground, even on pavement (which is often not totally smooth).
 

Timpo

Well-Known Member
You are right that R&M is doing it. There are a couple others that are as well.


Here is my understanding of why this is hard on the Bafang ultra in particular.
  1. Gates updated tension requirements here - https://www.gatescarbondrive.com/~/...arbon-drive-tension-recommendations.pdf?la=en
  2. Using the Bafang ultra with that much torque puts us in the "Punching rough pedaling style" category. (We tension our belts at ~43lbs as a reference)
  3. With FS and belt, we need to be atleast at 45lbs nominal (sitting down on the bike) position to account for belt slack. The drive train will routinely blow through the highest recommended tension with the incredible rear suspension travel.
  4. If we choose to have a lower tension to begin with, we risk the belt falling off and will need a belt guide and other contraptions.

With a smaller motor, like with R&M, we can be in the 35lb-50lb range, and not breach belt tension ceiling. So R&M full suspension will work because it is a smaller motor.

There are 2 ways of making this happen on the ultra.
  1. Have a smaller travel for the rear suspension.
  2. Have a soft tail suspension (another way of limiting travel with rear suspension).
IMO, In both these Ultra-related options, we can get a close enough / reasonable ride experience with the Kinekt seatpost - the standard setup as it stands right now on the UC Pro. I am not super comfortable about breaching limits regularly. I have spoken with Gates to see what options we have, and I will keep looking at designs to be in the sweet spot.

So are you saying you need higher tension from the tensioner if you were to go Bafang Ultra? 🤔
I'm not an engineer so I may have missed something. 😅

BELT TENSIONER:

Let's say you have two pulleys, one on wheel and one of crank (or whatever power source) and maybe think about pulling something heavy like cars.
The tension will stay on the top part of belt, not the bottom part.

Unless you use the tensioner on top part of the belt to push down the belt, I don't know if you need to add much tension on the tensioner?
For example, without tensioner, the bottom part of belt will be floppy and may come off, but all tensioner has to do is to keep the belt in place.

It's not like motorcycle where you use downshifting (in this case, all the tension comes to the bottom part of belt).
In addition, bicycle's cadence is only like 100rpm or so... it's not like motorcycle revving up to 14,000rpm.
Because motorcycle tensioners need to push down the belt pretty hard, otherwise the belt will come off because of centrifugal force.
However, I don't know if bicycle belts are exposed to much g-force at 100rpm (centrifugal force in this case)

I know simple rpm calculation doesn't say much, because bicycle chain rings and motorcycle sprockets have different sizes and all that, but I still don't know if bicycle belts will expand to outside due to centrifugal force like how motorcycles do on the dyno at full rev.

SUSPENSION TRAVEL:

You said that belt drive will be hard because of the rear suspension travel.
Both of your proposed solutions were to reduce the suspension travel.

Do you think the suspension travel (the travel of, the center of rear wheel) was the problem? or is it the distance from chain ring to rear wheel?
For example, what would be more problematic? 1) rear suspension with 50mm travel, but has 10mm change in rear stay, or 2) 140mm travel with 5mm change in rear stay?

The change in rearstay length will depend on the suspension geometry.
Image result for mtb geometry


For example, I've seen a several MTBs with no change in chainstay length.

Gary Fisher
Gary Fisher Joshua X0 Full Suspension MTB 24 Speed Judy T2 Mavic Clean - $380 Manteca


Klein
Image result for klein mtb full suspension


Schwinn
Homegrown Carbon's?-1998-schwinn-homegrown-all-mountain-lxt.jpg


Now, even if you look at more modern MTBs, some of them clearly have more change in chainstays travel than other.
Depending on the design / geometry of suspension, the travel of chainstays differ drastically.
 

Timpo

Well-Known Member
Also as for the belt, Bridgestone has done 12mm wide belt, which I believe is same as some lighter weight motorcycles.

Goodyear and Continental also make belts too, do you absolutely need to stay with Gates?

I'm not a entrepreneur so I don't know.. I know you have to think about parts availability for customers and all that.


 

pushkar

Well-Known Member
I want to stick with Gates just because of wider availability. I believe continental already withdrew their belt solution. I have not seen Bridgestone but will check it out.

Yes we are at the higher belt tension with Bafang Ultra. This is based on the recommendations we received as part of the certification.

I will look at the other designs and circle back. Thanks for the details. 👍
 

CityExplorer

Active Member
As I understand it, different designs of the tensioner (or dual tensioners) allow for more teeth on the sprocket(s) to be engaged with the belt and thus allow for a reduced belt tension, which can make the design easier. Not to say there are still not challenges. Also we don't really need that full power on the bike, so there is probably a very happy middle ground that can be achieved even if it means running both rear suspension and seat post suspension, It really depends on what the bike is being made for, or to what extremes is it expected to experience. If designing for 1% or even 5% of riders you can make your challenges a lot harder.
 

pushkar

Well-Known Member
Also as for the belt, Bridgestone has done 12mm wide belt, which I believe is same as some lighter weight motorcycles.
Goodyear and Continental also make belts too, do you absolutely need to stay with Gates?
I'm not a entrepreneur so I don't know.. I know you have to think about parts availability for customers and all that.

1. Continental stopped producing belts and wound down that group last year.
2. I reached out to Bridgestone. Not a lot of active effort in furthering the ecosystem. Very limited range of sprockets - none for some of the hubs we need.
3. Goodyear - cant find the right contact.

The regular bikes you described work because the pivot point is the BB itself. IN such cases we wont need tensioner at all (may probably need a snubber to keep the belt in place). The Bafang ultra has a pivot offset of between ~95-125mm (depending on manufacturer).

I will keep looking. Thanks for the ideas.
 

Nutella

Active Member
So are you saying you need higher tension from the tensioner if you were to go Bafang Ultra? 🤔
I'm not an engineer so I may have missed something. 😅

BELT TENSIONER:

Let's say you have two pulleys, one on wheel and one of crank (or whatever power source) and maybe think about pulling something heavy like cars.
The tension will stay on the top part of belt, not the bottom part.

Unless you use the tensioner on top part of the belt to push down the belt, I don't know if you need to add much tension on the tensioner?
For example, without tensioner, the bottom part of belt will be floppy and may come off, but all tensioner has to do is to keep the belt in place.

It's not like motorcycle where you use downshifting (in this case, all the tension comes to the bottom part of belt).
In addition, bicycle's cadence is only like 100rpm or so... it's not like motorcycle revving up to 14,000rpm.
Because motorcycle tensioners need to push down the belt pretty hard, otherwise the belt will come off because of centrifugal force.
However, I don't know if bicycle belts are exposed to much g-force at 100rpm (centrifugal force in this case)

I know simple rpm calculation doesn't say much, because bicycle chain rings and motorcycle sprockets have different sizes and all that, but I still don't know if bicycle belts will expand to outside due to centrifugal force like how motorcycles do on the dyno at full rev.

SUSPENSION TRAVEL:

You said that belt drive will be hard because of the rear suspension travel.
Both of your proposed solutions were to reduce the suspension travel.

Do you think the suspension travel (the travel of, the center of rear wheel) was the problem? or is it the distance from chain ring to rear wheel?
For example, what would be more problematic? 1) rear suspension with 50mm travel, but has 10mm change in rear stay, or 2) 140mm travel with 5mm change in rear stay?

The change in rearstay length will depend on the suspension geometry.
Image result for mtb geometry


For example, I've seen a several MTBs with no change in chainstay length.

Gary Fisher
Gary Fisher Joshua X0 Full Suspension MTB 24 Speed Judy T2 Mavic Clean - $380 Manteca


Klein
Image result for klein mtb full suspension


Schwinn
Homegrown Carbon's?-1998-schwinn-homegrown-all-mountain-lxt.jpg's?-1998-schwinn-homegrown-all-mountain-lxt.jpg


Now, even if you look at more modern MTBs, some of them clearly have more change in chainstays travel than other.
Depending on the design / geometry of suspension, the travel of chainstays differ drastically.

Lol, three of the worst riding fs mtbs of all time......

You can always pivot around the BB like Lenz does.