Crank drives and derailleurs.

[hoppy]

I love derailleurs for their efficiency, choice of ratios,speed of gearchange and ease of accessibility. For me they add to the enjoyment of cycling, as a good manual gearbox in a car does to driving.
But with a crank drive ebike derailleurs need very careful treatment. So much so that Kudos have given up on them and Kalkhoff have developed a device to automatically cut the power on changing gear. My Tonaro gears have lasted over three years without problems, but I have been very careful with them! When riding without power the gears change quietly, smoothly and quickly. But surprisingly, even with similar electric power to my pedalling they are immediately more clunky. I wondered why this should be so, and think it's because the motor keeps a constant tension in the chain, whereas even strong pedalling relieves the chain tension as the pedals reach the top and bottom of their rotation. This gives the derailleur a chance to slip the chain from sprocket to sprocket more easily. So perhaps the answer is a motor/controller setup that imitates the pulsing power of pedals. Any comments?

 

[Geebee]

Didn't the early Panasonic crank drive do this?

 

[flecc]

Didn't the early Panasonic crank drive do this?

Yes, the motor accurately tracked the pedal strokes and pressure. In fact even the current models torque sensors follow this arrangement, but the greater power and overhang of power delivery mask it.

 

[Kudoscycles]

I love derailleurs for their efficiency, choice of ratios,speed of gearchange and ease of accessibility. For me they add to the enjoyment of cycling, as a good manual gearbox in a car does to driving.
But with a crank drive ebike derailleurs need very careful treatment. So much so that Kudos have given up on them and Kalkhoff have developed a device to automatically cut the power on changing gear. My Tonaro gears have lasted over three years without problems, but I have been very careful with them! When riding without power the gears change quietly, smoothly and quickly. But surprisingly, even with similar electric power to my pedalling they are immediately more clunky. I wondered why this should be so, and think it's because the motor keeps a constant tension in the chain, whereas even strong pedalling relieves the chain tension as the pedals reach the top and bottom of their rotation. This gives the derailleur a chance to slip the chain from sprocket to sprocket more easily. So perhaps the answer is a motor/controller setup that imitates the pulsing power of pedals. Any comments?

Hoppy,I think you have nailed it,the cycling action definitely relieves the tension on the chain at certain times on the rotation and that gives the derailleur an opportunity to change,the motor keeps constant tension.
Just to add,we have not left derailleur for our hub drive bikes and have a couple with 30 speeds in next years programme,these bikes have been specially specified to be a nice ride with or without power.
KudosDavw

 

[Jimod]

Just to add,we have not left derailleur for our hub drive bikes and have a couple with 30 speeds in next years programme,these bikes have been specially specified to be a nice ride with or without power.
KudosDavw

Dave! More bikes next year? Don't you know I've a wedding to pay for and I was hoping to retire next year? Looks like I'll need to work a couple of overtime shifts and buy a bigger garage.

 

[trex]

I went to see Woosh yesterday to try out their new Big Bear LS and borrowed a Sirocco CDL. I asked Woosh to unplug the PAS so I can test out my theory. Without PAS, no chain crunch. My hands and legs just went through the motion: let go of the throttle, change gear, throttle back up again, without interference from the motor.
Lesson learned: unplug the PAS if you have problems with chain crunch.

 

[dmsims]

I went to see Woosh yesterday to try out their new Big Bear LS and borrowed a Sirocco CDL. I asked Woosh to unplug the PAS so I can test out my theory. Without PAS, no chain crunch. My hands and legs just went through the motion: let go of the throttle, change gear, throttle back up again, without interference from the motor.
Lesson learned: unplug the PAS if you have problems with chain crunch.

Except that will not work going up hill

 

[trex]

I spent an hour testing the theory going up and around Palmeira Avenue, Westcliff, up to the railway bridges then back down to the sea front. You can check on google earth to see how steep it is. Without PAS, the gear change is slower but crunch free. If you want to try, remove the PAS disc, you don't need to access the electrics.

 

[dmsims]

I spent an hour testing the theory going up and around Palmeira Avenue, Westcliff, up to the railway bridges then back down to the sea front. You can check on google earth to see how steep it is. Without PAS, the gear change is slower but crunch free. If you want to try, remove the PAS disc, you don't need to access the electrics.

Doesn't even get to 15%

 

[trex]

no, it's about 11% at the steepest point, about 7% most of the circuit but I could test out various ways to understand why the chain crunch. I think the explanation is the motor runs the chain too fast when going to another gear. As cyclists, we just know how to do this, we can feel the chain in our foot, and apply a lot less pressure, the motor is just too clumsy, too fast, too much force. I was off throttle for about 5-10 seconds (depending on the terrain) for the gear change, the bike momentum was maintained by pedalling. I can't confirm with my BBS01 because the PAS is inaccessable, I will ask someone else to try again to confirm.

 

[Geebee]

Once the motor is throttled off its just a normal bike, if you still cant change gears a derailleur is probably not your ideal system.

 

[jackhandy]

Except that will not work going up hill

Why not?
I don't get your drift.

 

[Kudoscycles]

Why bother....go hub drive...problem solved.
KudosDave

 

[Kudoscycles]

Dave! More bikes next year? Don't you know I've a wedding to pay for and I was hoping to retire next year? Looks like I'll need to work a couple of overtime shifts and buy a bigger garage.

Jim...I think you have a bike stable to cover all your current needs.
My daughter got married last year,one of the best day of my life. Have you got the 'father of the bride' speech ready? Hehe!!
regards
Dave

 

[trex]

Why bother....go hub drive...problem solved.
KudosDave

more people ride crank drives than hub drives, can you explain why?

 

[Kudoscycles]

more people ride crank drives than hub drives, can you explain why?

Once again....statement without any supporting facts?.....my gut feeling if you add up the Cyclamatic,Kudos,Batribike,Roodog,Green Zebra,Tesco,BH emotion,Vita,KTM-Panasonic,Cyclezee plus all the others that I have forgotten, that in the UK Hub v Crank is about 5 to 1.
Crank drive has been perfected by Bosch at great expense,it is complex to get it right and small suppliers just dont have the R&D budget to get it right.
So as your original statement is plainly incorrect I cannot explain why.
KudosDave

 

[trex]

you are right of course regarding the UK sales. Continental sales are very different. If you thesis is correct then Bosch should start making hub motors soon.

 

[Deleted member 4366]

you are right of course regarding the UK sales. Continental sales are very different. If you thesis is correct then Bosch should start making hub motors soon.

They'd be idiots if they don't have one soon. It wouldn't surprise me to get an announcement at Eurobike.

If you're going to include Europe in the sales figures, you'd have to include USA, China and other countries where crank-drives are virtually unheard of.