How to make Zugo Rhino go a little faster...

[Maciek]

This is basically 2 part question. First would be how to make an existing motor spin a litter faster, second, how to replace an existing, 750 W, Bafang, geared motor to something decent, like QS 205 or similar.
Let start at the beginning. Right now, bike accelerate quite fast to speed 24 mph where it stops. Bar graph which indicates current usage, I think, drops from maximum of 20 bars to 3–4 during sustained 24mph speed. Not so sure what limits the speed at this stage. Internal software of the controller or supply voltage of the battery and construction of the motor? This effect takes place regardless of the stage of the charge of the battery. The bike never exceeds 24 mph, with the bar graph indicating rather small current consumption. The controller is rather small and wimpy, but still providing enough current for decent acceleration. Also, at the current max speed, the motor is quite noisy, running at relatively high rpm.
Taking all the above under account, I would rather go for replacing existing motor into non-geared, more powerful one, around 3kW,
72V battery and new controller. QS 205 would be my first choice, but my bike requires 175 mm drop out, but QS 205 has 150mm.
So here is the question, is there some kind of adapter making this difference? I have a lathe and a milling machine, so probable can make something....
Looking at Alibaba found this, but not so sure about quality of the product. Any opinion would be very helpful.

High Power 2000w 3000w 5000w 20inch E-bike Hub Motor - Buy 20inch 2000/3000/5000w Hub Motor,60/72/96/120v 20 Inch E-bike Hub Motor Product on Alibaba.com

High Power 2000w 3000w 5000w 20inch E-bike Hub Motor - Buy 20inch 2000/3000/5000w Hub Motor,60/72/96/120v 20 Inch E-bike Hub Motor Product on Alibaba.com

www.alibaba.com

 

[Chalo]

It looks to me like the RPM/volt of that Alibaba motor is too high for what you're trying to do. Figure out how much battery and controller you're willing to buy and carry, then multiply battery volts by controller amps and divide by two.

When you have that number, use a speed and power calculator like the one at kreuzotter.de to figure out how fast you can go with that many watts. Be sure to choose the slowest possible bike configuration, because your bike is even much slower than that.

Then take that speed, multiply by 1.5, and that will give you the free motor RPM you're looking for, give or take. You can use 4qd.co.uk road speed calculator to turn speed into RPM.

When you know what free RPM you want, you can order a 2000W fatbike wheel from Leaf Bike and they'll give you a custom winding to deliver that RPM.

If you go with some no-name, no-specific-power rated motor from a no-account seller, more than likely it won't make good on its speed potential, but it will overheat by running at an inefficient fraction of its free RPM.

 

[E-HP]

The voltage and motor winding (kv) determine the speed of the motor. Current/power only comes into play as wind resistance increases at higher speeds above ~20 mph. Motors use less current as they approach their rated speed, which is something you are observing, therefore power is not limiting your speed, since you have enough power.

 

[Chalo]

The voltage and motor winding (kv) determine the speed of the motor. Current/power only comes into play as wind resistance increases at higher speeds above ~20 mph. Motors use less current as they approach their rated speed, which is something you are observing, therefore power is not limiting your speed, since you have enough power.

This is correct. I'll add, if your top speed is capped by being on the diminishing end of the power band (which is good for efficiency), then raising your system voltage will increase top speed even if you don't make any other changes.

 

[Maciek]

...Thank you both for so quick response.

... In this case, I'm afraid, that speed and rpm of the motor are limited by the software in the controller. Speed is limited to 24 mph regardless of battery status, fully charged to 52 volts or partially discharged to 42 volts. Also, acceleration is pretty decisive up to 24 mph, when it's stops.
... Besides that, I'm not very happy with motor spinning very fast making high pitch noise. Replacing it with gearless hub motor would be a great improvement.
... I'm not trying to beat any speed record, just be able to ride the bike with sustained speed of 30 -35 mph and occasionally maybe a little more...
... Recommended website - kreuzotter.de - for sure very interesting, especially for someone working on his doctor's thesis. In my case, I'm looking for more practical advices. After all, not trying to design and build some unusual vehicle, just improve existing one using popular component available on today's market. I think many people already did it and are willing to share their experience.
... For example, what can go wrong by installing QS 205 hub motor, Sabvoton SVNC72150 and 72150 controller and 20S/6P, 30 Ah battery made of INR21700-50E Samsung cells? Controller and cells I already have from privies project, so need to chose correct hub motor, which will fit in my frame, with 175 mm drop out.
... Searching the internet, the closest to my requirement is hub motor manufactured by Chengdu Lunyee Imp. & Exp. Co., Ltd. and sold by Alibaba. At this point would like to ask if anyone has any bad experience with this product?

Thanks for help in advance, Mike

 

[neptronix]

A leafbike 1500w ( 16lbs ) would be more than adequate for your power wants. You really don't need a monster sized QS to go 30-40mph.

There is probably a little more power hiding in your existing motor which could be unlocked with a programmable controller using phase advance/field weakening to achieve higher speed on the same battery voltage.

 

[E-HP]

... For example, what can go wrong by installing QS 205 hub motor, Sabvoton SVNC72150 and 72150 controller and 20S/6P, 30 Ah battery made of INR21700-50E Samsung cells?

Why such a big controller? I guess killing a good pack that can’t provide the current to the controller is one thing that could go wrong. A 60A controller would be easier to find space for.

 

[Chalo]

A leafbike 1500w ( 16lbs ) would be more than adequate for your power wants.

Sure, but it won't fit the obese dwarf frame. I think you gotta get the wide stator version to fit in a chubby kid bike like that.

 

[neptronix]

They make a 170mm model that would work with some minor spacers and i would guess the motor is 35mm wide.

20 inch 48V 52V 1500W rear hub motor - Beach Snow Fat Tire bike conversion kit

Pictures of the motor & specs are not known to be accurate on leafbike's site, so it would be worthwhile to ask if the motor is the expected 35mm.

35mm in an effective 22" wheel would produce more power than the short wheelbased frame could handle without becoming a wheelie machine.

 

[Maciek]

... In any field I was, whenever involved, never was afraid to use components a little larger than minimum required. For instance, the desk top computer I put together needs 700 watts to operate, but I used a 1200 W power supply, so it can run reliably for years without overheating and stressing components.
... Sabvoton controller and QS 205 are also maybe a litter bigger than minimums, which shouldn't shorts theirs lives. So at the end of the day, maybe my bike will be a litter faster. After all, I will still have the throttle control....
... But I notice another problem. In the original frame, the rear fork holding wheel's shaft is not symmetrical, leaving more space for the sprocket set by the chain side. The aluminum frame would be very difficult to bent in, so the solution would be to extend the shaft on the right side of the bike. Not so sure how to do it. Maybe I could to weld a little extension to it...?
... In min time maybe I should try different controller to determent where the speed limit is coming from, software in controller or relation kv...