Optimum crank freewheel revolution speed?

[PowerPedro]

Aloha!!

I am working on a Ebike-setup with a freewheel in the crank like this: http://www.bike-elektro-antrieb.ch/home.htm .... in combination with a Brushless outrunner and a reduction stage. I am trying to find the optimum reduction factor to get the best driving experience. Reducing to less could leed to inefficiency and you cannot paddel fast enought to contribute to the drive at high speeds. I have heared that about 200 revolutions is a maximum that one can paddel. What downgearing do you guys use and what is your experience with it?

Best regards

 

[rhitee05]

200 RPM is really cranking. Have you tried pedaling that fast to see what it felt like? A more normal cadence is in the range of 60-90 RPM. I'm not even sure I believe it's possible to pedal 200 RPM unless you're Lance Armstrong.

 

[nikos7]

I find that I am most efficient at 90 rpm, especially if I'm riding on smooth pavement. If I'm going offroad, it's usually around 60.

 

[rhitee05]

I should have mentioned what the reduction is with my setup. I have a Cyclone motor with integrated gearbox. The motor has a max RPM of around 3400 which gives about 356 RPM at the shaft with the 9.55:1 planetary. The motor has a 14T sprocket and I have a 52T sprocket for the BB, which gives a 3.7:1 reduction. That gives me a cadence of about 96 RPM maximum.

I'd actually like to reduce that further, but 52T is about the biggest I can reasonably do on my BB. I plan to increase the voltage for Mk2, which will require 2 stages to get more reduction to the BB.

 

[bandaro]

im currently building a system like this, waiting for the parts to come into stock and be shipped out, but i plan on having the cranks spinning roughly 65rpm on nominal voltage, so if i really gun it on full throttle i can get some speed up, but it should be a casual pedal speed to assist with. i would recommend making one part of the drive able to take a different sized gear, so you can tune the speed. mine should be running in a month or so, ill post how 65 rpm goes if you like.

 

[PowerPedro]

Yes please post your experience! What motor are you planing to implement? I am using a brushless outrunner (TM685) with 4,5kW maximum and around 6000 rpm.

 

[PowerPedro]

I just searched in the internet and the sprint rekord is 271U/Min. Normal sprints are around 200U/min.

 

[PowerPedro]

Another question in a setup like this is to use a freewheel at the gearbox output or not. If not you would drive against the resistance of the motor when pedaling without electric power. If you do use a freewheel then there is a delayed throttle response in certain driving conditions because when allready driving, the motor has to speed up from 0 to the actual driving speed. Do you guys use a freewheel?

 

[veloman]

You can't effectively apply power for any duration at much above 120rpm. My current bike is set up badly and I have to hit 160rpms or so to assist when going uphill. On the flats, I can't assist it at all with the current crank gearing. I'd have to do 180-200rpms which just makes my feet fly off the pedals and is extremely inefficient. (Note, I am an actual cyclist and did record 242rpms once while on a stationary trainer with no load.) Talk about feeling like a sewing machine.

Ideally you'd want the cranks to be at 90rpm when your motor is full throttle, or 70rpm if you're really looking to put in minimal effort.

Have fun, that's a lot of reduction! 6,000 --> 90

 

[bandaro]

ill be running a 170kv motor on 36v batts, so will also be pumping in the 6000 rpm. thinking of making the gearing 2 1:5 lots and then a final 1:3 onto the sprockets.

going to go to a go kart store and the local mobility scooter/granny scooter store and see what they can get for me in terms of gearing. hoping to be able to make it into a nice tight double reduction setup...

 

[Miles]

ill be running a 170kv motor on 36v batts, so will also be pumping in the 6000 rpm. thinking of making the gearing 2 1:5 lots and then a final 1:3 onto the sprockets.

Sounds ok. That gives you 75:1 You need a reduction of at least 60:1 to the cranks to get a nominal cadence of 90.

5:1 is a large step to achieve, though....

 

[EVnewbie]

I find on my MTB I pedal 80 to 85 RPM for long periods of time

On my recumbent, I pedal at 90 RPM without any problems.

If you want to pedal at higher RPMs, the trick is to use shorter crank arms. Normally, the crank arms are 175mm which is rather long for torque. My MTB runs 165mm arms for extra ground clearance and higher RPMs for the low 32-22 crank and 11-32 rear cassette gearing.

If I wanted to get 120 RPM comfortably, go with 140 to 152mm crank arms. My 165's on the MTB allow me to hit bursts of 150 RPM to limit shifting and give me a broader range out in the slop. Spinning at higher RPMs is nicer to your knees VS mashing long cranks at 60 RPM.

 

[Dingo2024]

Hi, if you take a look at my build log (still on going)

http://endless-sphere.com/forums/viewtopic.php?f=6&t=18130&start=15

you will see how I tackled the cadence issue with 48v cyclone kits.....it runs a 13t to 64t sprocket on the motor and 48t to 13t on the rear hub and this drives through a Nexus 8 speed internal geared hub. The cranks are 162mm trials cranks with a sickbikes ENO freewheel. This gives me a cadence of 88rpm at max motor efficiency and is comfortable..also keeps the heat down on the motor.


Ian