Peeps, I need help with finalizing a choice for a motor, QS205, anything better?

mbgjt1

100 W
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Sep 22, 2020
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Need some advice, I'm building an e-bike with a rear hub motor for a 150 mm frame drop out.

Initially I planned on building with a QS273 motor, but many have advised that this would be too heavy, and would require an upgrade of all other components (frame, brakes, suspension, etc.).

I've been advised that the best option would be a QS205 motor V3 (4t or 5t winding).

Is this the best option for my build? Is there an option between the QS205 and QS273? I worry that the QS205 might not be powerful enough...

I live in a very hilly area (most roads at 10 to 20 degree gradients). Would this motor be able to handle this gradient for extended periods of time?

Max speed I would like would be around 85 to 90kmph. Rider weight would be 72 kg. I plan to push 200A or 250A max out of the controller into this hub motor. Is this possible? Can the motor handle it with a hub sink and fero fluid? What is the maximum power I can push out of this hub motor?

I plan to run 19" wheels.
 
mbgjt1 said:
I live in a very hilly area (most roads at 45 degree gradients).

You do not. Try again.

If you overestimate speed like you overestimate gradient, you should have no problem meeting your criteria.
 
correction , probably more around 10 to 20 degree gradients..

Gets very steep!
 
mbgjt1 said:
correction , probably more around 10 to 20 degree gradients..

Gets very steep!

Can you provide a location on Google maps of some of these roads? The steepest street in the world is a 35% grade, or 19 degrees, and there are several online tools that can measure the actual grade. 10 degrees is a 17.7% grade, which is relatively steep.

https://en.wikipedia.org/wiki/Baldwin_Street
 
These guys judging you for road grade numbers just like to get into arguments. But they don’t know squat.

19” wheels are a bad idea for hills as they result in a too-tall gear ratio for a hub motor. Go qs205 in a 16 or 17”. You’ll be fine.
 
A QS205h50 can climb any hill road. And yes, it will be happier in a smaller wheel, although some very slow windings are available when you have good reasons to prefer large wheels. On the road normally, large wheels are not a must.
 
Tony01 said:
These guys judging you for road grade numbers just like to get into arguments. But they don’t know squat.

I believe it's fact finding. The original 100% grade was ridiculous, and when challenged by Balmorhea , immediately dropped 36%, and while was less ridiculous, it's still not factual. It's probably best to identify the facts up front in order to provide the best advice, unless you're saying a 16" wheel is going to allow him to ascend 100% grades, for extended periods of time, per the question and "facts" originally presented.
 
E-HP said:
mbgjt1 said:
correction , probably more around 10 to 20 degree gradients..

Gets very steep!

Can you provide a location on Google maps of some of these roads? The steepest street in the world is a 35% grade, or 19 degrees, and there are several online tools that can measure the actual grade. 10 degrees is a 17.7% grade, which is relatively steep.

https://en.wikipedia.org/wiki/Baldwin_Street

Funnily enough I actually live in New Zealand, the same country as this crazy street. But I'm referring to hills and mountain sides with very very steep gradients nearly as steep as this hill. It would be nice to get a bike that would easily tackle these, but hopefully this isn't an issue with the QS205 motor 5T running 17" wheels (max power 14.4kW). What do you think?
 
999zip999 said:
Do some research on your wheel size which is very important for hills. Smaller more torque.

Any sources you can point me towards?

I want a wheel size that offers the best balance of high torque and gives the ability to reach speeds of 90kmph. Would 17" be suitable for this?
 
Tony01 said:
These guys judging you for road grade numbers just like to get into arguments. But they don’t know squat.

19” wheels are a bad idea for hills as they result in a too-tall gear ratio for a hub motor. Go qs205 in a 16 or 17”. You’ll be fine.

Thanks mate, 17" looks like a very promising size and used in allot of the other high end ebikes (e.g. Cyklonebike). Would you happen to know if I can reach speeds to 90km h with such a wheel size? I can probably switch to a QS205 4T winding for the higher speeds.

Cheers,
 
MadRhino said:
A QS205h50 can climb any hill road. And yes, it will be happier in a smaller wheel, although some very slow windings are available when you have good reasons to prefer large wheels. On the road normally, large wheels are not a must.

4T QS205 motor paired to a 17" wheel, would that be the best balance of torque and high speeds upto 90 kmph?
 
E-HP said:
Tony01 said:
These guys judging you for road grade numbers just like to get into arguments. But they don’t know squat.

I believe it's fact finding. The original 100% grade was ridiculous, and when challenged by Balmorhea , immediately dropped 36%, and while was less ridiculous, it's still not factual. It's probably best to identify the facts up front in order to provide the best advice, unless you're saying a 16" wheel is going to allow him to ascend 100% grades, for extended periods of time, per the question and "facts" originally presented.

We've got very steep hills around here, majority being between 10 and 12 degrees (around 18%).

Another way to ask the question, with a QS205 coupled to a 17" wheel, what is the worst gradient it can handle before overheating?

Are there any tests that have been done online? I can't seem to find anything.
 
The motor would need to be modeled to run simulations. It's not really the grade as much as how long it will be at high amps or how long the climb is. You can setup thermal roll back as not to over heat the motor. There are cooling mods to help keep the motor cool.

There are a few here that run the QS205 and should have an idea. Surprised they have not chimed in as yet.
You maybe our best test case. Follow all the suggestions. Smaller the wheel the better, keep a Low T motor so you can dump amps into it and then you will need to up the volts to get your speed back up. Around 96V

Just did a quick check on a 45mm motor and it would pull a 15% for 30 min before over heating but would only go 35 mph at 72V.
The QS205 is 50mm so pulling the hill should not be an issue but getting that set up to 50 mph will take more volts 96-144.
 
mbgjt1 said:
MadRhino said:
A QS205h50 can climb any hill road. And yes, it will be happier in a smaller wheel, although some very slow windings are available when you have good reasons to prefer large wheels. On the road normally, large wheels are not a must.

4T QS205 motor paired to a 17" wheel, would that be the best balance of torque and high speeds upto 90 kmph?
Yep. I would use the 30X4, 11.39 kv
 
I am not that convinced about 4t and good acceleration to 90km/h.
But it depends on what voltage you use of course.

I have a QS 205 50h 4t in a 16" wheel, and if I remember correctly it goes about 80km/h without field weakening.
That should be at about 80v I think.
I have had 17" wheel too, but I doubt it reached 90km/h then either.
I am not absolutely sure, top speed was not important to me.

I think it started loosing power somewhere around 60km/h, but it was hard to tell.
 
I have the 3.5t in a 17” wheel, with field weakening I get up to about 85mph. We have hills here too. As long as you keep the speed to a minimum of 25-30mph going uphill you can mostly avoid overheating. Depends how long your hill is. The one next to my house climbs 2000ft in under 8 miles. I have heatsinks and ferrofluid but they’re still in the box; made it through the whole summer without putting them on.

Lots of tires in 17”. I run a 90/90-17 on the back.
 
I have one 30X4t in a 24’’ bicycle wheel. I feed 24s and it does 75 kmh climbing 10% without any risk of overheating. Total riding weight 254 lbs.

Many factors are responsible for the efficiency, acceleration and top speed of a bike. Aero drag, wheel size and riding weight are making a huge difference.
 
Get a 3t in a 13" scooter rim, which works out to a 19.25-20" OD wheel depending upon the tire you buy. That or a fast wind 273 if you want to go spokes and a bit larger wheel like a 17". If all your riding is on roads that are in good condition, then the size of the wheel and weight of the motor don't really matter. I run almost exclusively 13" scooter wheels with motors that weigh 15.5kg before the relatively heavy tire and allow mag rim, and while the tire can skip a bit on choppy roads, the tire size and motor weight are really a non-issue. I too live in a mountainous country and have the fastest bikes on the forum.

You haven't mentioned what all up load (bike+rider), which is of critical importance.
 
j bjork said:
I am not that convinced about 4t and good acceleration to 90km/h.
But it depends on what voltage you use of course.

I have a QS 205 50h 4t in a 16" wheel, and if I remember correctly it goes about 80km/h without field weakening.
That should be at about 80v I think.
I have had 17" wheel too, but I doubt it reached 90km/h then either.
I am not absolutely sure, top speed was not important to me.

I think it started loosing power somewhere around 60km/h, but it was hard to tell.

I am thinking of going with a 17" wheel since it seems to be readily available, I really hope I can reach 85 90 km h without field weakening. I'll be riding this on the road so a good top speed is important!
 
John in CR said:
Get a 3t in a 13" scooter rim, which works out to a 19.25-20" OD wheel depending upon the tire you buy. That or a fast wind 273 if you want to go spokes and a bit larger wheel like a 17". If all your riding is on roads that are in good condition, then the size of the wheel and weight of the motor don't really matter. I run almost exclusively 13" scooter wheels with motors that weigh 15.5kg before the relatively heavy tire and allow mag rim, and while the tire can skip a bit on choppy roads, the tire size and motor weight are really a non-issue. I too live in a mountainous country and have the fastest bikes on the forum.

You haven't mentioned what all up load (bike+rider), which is of critical importance.

Hey mate, all up the weight would be 70 kg plus 60 so 130 kg all together.

I've never considered going down to a such a small size, I wonder if it will look strange compared to the front wheel.

I really would love to use the QS273 but it seems like the added weight causes too many issues especially off road on trails, i'll also have to invest in stronger overall components so the cost may sky rocket.

For a single person weighing 70 kg I would think that the QS205 motor is the best option.
 
Tony01 said:
I have the 3.5t in a 17” wheel, with field weakening I get up to about 85mph. We have hills here too. As long as you keep the speed to a minimum of 25-30mph going uphill you can mostly avoid overheating. Depends how long your hill is. The one next to my house climbs 2000ft in under 8 miles. I have heatsinks and ferrofluid but they’re still in the box; made it through the whole summer without putting them on.

Lots of tires in 17”. I run a 90/90-17 on the back.

Where did you source your motor from? I've heard the 3.5t is not as good due to uneven copper spread which may cause uneven heat distribution. but if your bike is not overheating even without heatsinks and ferro then that is somewhat comforting.

It seems that 17" is the best wheel size, I'd like to keep it standard.
 
MadRhino said:
I have one 30X4t in a 24’’ bicycle wheel. I feed 24s and it does 75 kmh climbing 10% without any risk of overheating. Total riding weight 254 lbs.

Many factors are responsible for the efficiency, acceleration and top speed of a bike. Aero drag, wheel size and riding weight are making a huge difference.

How many amps are you running through it?/
 
mbgjt1 said:
How many amps are you running through it?/

Battery amps or phase amps? :shock:
Peak or Continuous? :shock: :shock:

Don't lose a shoe, btw not his bike ;)
https://endless-sphere.com/forums/viewtopic.php?f=3&t=107820&p=1578042&hilit=build#p1578042
 
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