Keep in mind, motor RPM is kV x Voltage so a 200kv motor on 24V = 4800 RPM. We are looking for at best 120 RPM at the crank. So a 34T to 9T is a ratio of 1:3.7 reduction. This brings the RPM down to 1200 RPM. To turn the crank at 120 rpm, we need to run a the speed controller at a duty cycle of 10% and duty cycle of 5% for a more practical 60 rpm. No controller will survive for long pushing usable amps at that duty cycle.urga wrote: ↑Oct 03, 2018 10:39 amThat's spooky because I've just ordered a mini vesc from Flipsky (same one? ) I too am trying to get everything inside a bottle(albeit I'm hoping to custom build the battery from cells) with a socket at the bottom for quick change overs.I imagine the permanent drag is of no consequence on a mtb's fat rubber anyway.Is there any chance you could post a drawing of your mounting method,John? I use Sketchup for my work and could maybe use the pics to draw up a model. The smaller motor seems a good move also as the single chainring doesn't give you as much cover as a 2x.What I love most of your setup is you can hardly tell it's assisted.VERY cool
Scooterman,I'm still tempted to have a go at crank driven setup. I'm not getting why you need a 10:1 reduction on a low KV motor with a 34T to 9T ratio from crank to motor?I also understand that you can limit the throttle settings on the vesc for soft startup and limit the ERPM of the motor. Surely it would be possible to tune the motor to start softly and never go above whatever your natural cadence is? ( mine's 90rpm on the road)I agree though you do need a good bit lower offroad. However,I would be using this for climbing only and asI like to spin up climbs I would be happy with the high cadence. I also think that rather than complicating the design with clutches and gears etc,it would be better to use the assist only where suitable. A bit of a compromise I know ,but I really don't want to just power up climbs as some of the E bikes can.This motor here looks tempting:https://alienpowersystem.com/shop/brush ... 0kv-1700w/
and :https://alienpowersystem.com/shop/brush ... 0kv-1800w/
The latter has huge torque for a 50mm 60KV motor.
If I had more engineering skills...........
Kepler wrote: ↑Oct 03, 2018 7:37 am
Also i have a new mini Vesc to test. This Vesc is half the size of the standard 4.2 Vesc with exactly the same power rating and features. It also has a built in heatsink which should assist with cooling especially in enclosed spaces. This has allowed me to fit the vesc inside the tool bottle together with the battery, Arduino interface, and Bluetooth interface. If I am happy with the overall performance, the plan is to build a second bottle battery with its own vesc built in.
Kepler wrote: ↑Oct 03, 2018 10:38 pm
Mud and water are not a problem. these motor will run under water and the electronics are now perfectly sealed in the tool bottle. Got to say, I think I am close to having all bases covered
With a mid drive design, actually no choice but to mount the motor up high. Looking a bit more closely at the how a mid drive could be laid out it became quickly evident that there wouldn't be enough distance between the chain ring sprocket and the motor sprocket if the motor was mounted under BB.
I have a feeling also that the mid-drive design would be disappointingly noisy. The other day when testing my friction drive off road and coming across the Bosch power MTB, I was really quite surprised how much more quite my drive was compared to the Bosch.
urga wrote: ↑Oct 04, 2018 11:47 amGoogles 'Sprag clutch'
I was thinking of modifying a single speed freehub,but these are much better!
Scooterman, is this the kind of thing your thinking of? http://www.chainreactioncycles.com/hxr- ... d|575489UK
Hmm, 78 rpm @ 1:3.77 would have the motor under 300rpm at max speed !urga wrote: ↑Oct 04, 2018 11:47 am.......14.8V 4S cell on 50KV giving 740RPM with a 1:3.7777 reduction(34T:9T) giving 196rpm at the cranks.Running the Vesc @ maybe 40% duty cycle should have my wee legs spinning @78 rpm ? I could live with that cadence,but can the Vesc live with a 40% duty cycle ? .....
The regen is dependent on the kV of the motor and the set voltage. If I was using a 6S battery or a higher kV motor, I wouldn't have seen the regen happen. You can of course can set the the max regen in the Vesc with the regen then being variable via the ppm signal input.urga wrote: ↑Oct 07, 2018 9:39 amInteresting. Could that regen threshold be modified via the vesc,or it's inherrent to the KV of the motor and V input?
The more I begin to understand about using outrunners the more I can appreciate why you pursued the FD method. The 11:1 reduction circumnavigates the main problem I'm having getting my rpm down. The more I look at using gears etc the more I'm put off . I like the FD system because of it's 'simplicity' and lack of clutter on the bike. It gives me more than enough assist( done a 42 miler with a cat 2 climb @18mph ave with 3850ft climbing ,and still had juice left in a 8AH battery!) for my needs and the bike hasn't taken on the frankenstein look of most of the mid drive/geared systems I've seen.
So although I've given up before I started,I still might be converting my gravel bike to a FD.The terrain I ride on this would suit the FD perfectly.Can I ask whether you have any intensions of producing the mounting bracket with a larger dia for us poor BB30 chaps out there?
No big deal but it would save a bit of time with the Dremel.
A use a similar clamping method on my carbon road bikes. Trek use a BB90 bottom bracket. The clamp is against the carbon outer of BB however the crushing force of the clamp is distributed through the carbon fibre to the bottom bracket bearing so it not actually putting much load on the outer shell of the BB.urga wrote: ↑Oct 07, 2018 1:47 pmYes,I seen that post. I was worried that this wouldn't be suitable on a carbon frameset as they advise against clamping forces here.I loved what he did with the rest of his setup.I used Kepler's mounting bracket which worked fine after some machining,albeit I now have a creaking BB,which ,ironically it never did before fitting the convertor! I didn't use Loctite initialy as I had to mess about with the settings quite a bit,but once I was happy I marked it up and refitted it with Loctite. Stills creaks but hey ho.....it's an old framset so there may be some wear in the interface.