Fast wind motor

[rocketman58]

It is my understanding that 26” wheels normally use a standard wind motor, but 20” wheels normally take a fast wind motor.

I have a Bafang G020 geared hub motor with a standard wind that came off of a 26" wheel. I am using it on smaller 20” wheel, and it seems to work fine. With the smaller wheel, the top speed is reduced from 25+ mph down to about 20mph. However it seems to be quicker off the line, and is a very good hill climber. Overall a decent tradeoff for the hilly riding I normally do with this trike.

I want to build another 20" wheel for another trike. I have a choice between a standard wind or a fast wind G020 motor. The fast wind is stated for use with a 16", 20", 24" wheels. This trike will see longer flat rides and moderate hills. I'm thinking of getting the fast wind motor for this trike. What difference will I see by using the fast wind motor as opposed to the standard wind? I know it will provide a higher top speed, but will hill climbing suffer much? What about battery life? Will the fast wind motor use more battery than the standard wind?

 

[E-HP]

You can get a good idea of the relationships by choosing a fast and slow wind motor of the same model in the Grin simulator, and running a scenario on flat ground, then with a light grade (say 3%) to see the performance and how quickly they overheat on a grade. The G020 isn’t modeled, but you can use another geared motor just to see the impact of a slow vs fast winding. Using the G01 as an example, the fast wind will be faster, but at the same speed will overheat a little more quickly on a climb.

I’m not on my laptop, or I’d send a link of the two modeled, but here’s a link to the simulator (it’s worthwhile to read the whole page and get familiar with the simulator, since it’s surprisingly accurate when replicating the test conditions in real life.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

 

[neptronix]

The fast wind will consume 15-40% more amps, you'll need a heavier duty battery to feed one properly, otherwise the result will be a lot of voltage sag.

Like above, play with the motor simulator, it can teach you a lot.

And yeah, 20" wheels with a hub are a joy aren't they?

 

[rocketman58]

Thanks for the responses. I did play around with the simulator before posting this. I found that differences between the std and fast wind can be significant different depending on the motor. I will go back and play with it some more.

neptronix, can you explain this statement to the electronically ignorant such as myself? "The fast wind will consume 15-40% more amps, you'll need a heavier duty battery to feed one properly, otherwise the result will be a lot of voltage sag." I think I understand the voltage sag, but would this mean I need a different battery or controller? Does this mean the fast wind motor will use up my battery faster (decrease range)?

 

[E-HP]

neptronix, can you explain this statement to the electronically ignorant such as myself? "The fast wind will consume 15-40% more amps, you'll need a heavier duty battery to feed one properly, otherwise the result will be a lot of voltage sag." I think I understand the voltage sag, but would this mean I need a different battery or controller? Does this mean the fast wind motor will use up my battery faster (decrease range)?

The motors will reach maximum efficiency at different speeds due to their wind, so you need to specify for comparison, if you mean when both are running the same speed (and what speed), both WOT, or something else. If you are riding with your wife, maybe model the speeds you would ride together at first. I would try to stick with a bafang motor for modeling since fast vs std may be more similar than how another defines fast or std. Or, you could research your motor specs and try to find something close, but that’s looking at a lot of spec sheets.

 

[neptronix]

Continue to play with the ebikes.ca simulator, it's super useful.

To hit a given speed, a faster winding will use more amps than volts. There will be increased amp usage due to the higher top speed it can produce also. We need to factor this into our battery choice.

If we picked a large battery, this isn't a big problem. We have a big headroom in the battery's output capability; the difference in voltage sag between both motors is small enough to not matter much.



Now if we picked a small battery that is just barely adequate for the standard winding, then switched to the fast winding, we get fairly bad voltage sag on the standard winding, and unacceptably bad ( the battery will overheat and possibly catch fire ) voltage sag on the fast winding. This voltage sag is also bad enough to limit our top speed and torque from a stall.


So if you're going to use a faster winding than usual, your battery will need higher amp hours and lower voltage.
Your controller needs are the same, you need to push higher amps for the fast winding to make equivalent torque as the standard winding.

In the case of a 26" to 20" wheel swap, because we reduced the speed of the motor dramatically with a smaller wheel, the faster winding would give you roughly equivalent speed and torque as the standard winding.

In this case, the grin all axle motor sees an efficiency and torque output increase, because said motor is actually designed with a 20" wheel in mind, and it's in it's sweet spot for power output. We can increase the motor amps beyond what's seen and realize a LOT more additional torque.



A typical geared motor going from 26" to 20", with a winding adjustment to match, will see a great torque potential increase but typically reduced efficiency because it has higher friction in it's gears from the higher RPM. A DD would be the ideal choice instead.

 

[rocketman58]

Neptronix, thank you for your help.

From your last post and playing around with the simulator tool, I have drawn a few conclusions: 1) With the same motor, performance with a fast wind/20" wheel is more or less the same as a std wind/26" wheel. The major difference (at least for me) is the fast wind motor is going to require more power from the battery which will reduce range. 2) A geared hub motor is a better choice for a 26" or larger rear wheel. This may explain why it is difficult to find a geared hub motor in a 20" wheel.

So what to do? On my first trike I pretty happy with the std wind Bafang G020 motor and the 20" wheel. It is a good hill climber and provides power up to 20mph. Since I don't typically pedal faster than 18mph this is not an issue. The logical answer would be to get another std wind motor and build up an identical 20" wheel for my second trike.

All this discussion has opened up other thoughts though. I'm just not sure how much better they would be. Option 1) As discussed, build an identical 20" wheel to the first trike. Option 2) Replace the 20" wheel with a 26" using a std wind Bafang G020 hub motor. I can do this by swapping the rear section of my ICE Adventure's frame. Option 3) Keep the 20" rear wheel but ditch the hub drive and go with a mid drive. But, would I have the same issues with a mid drive and a 20" rear wheel?

For reference, I my 2nd trike already has a complete rear hub drive setup similar to my 1st trike. However the std wind CST motor has issues. It works ok below speeds of 7mph, but above that it gets very noisy and tops out at 16mph. It could be that the CST motor does not like the smaller 20" wheel, or the motor may just have some problems.

 

[Chalo]

Neptronix, thank you for your help.

From your last post and playing around with the simulator tool, I have drawn a few conclusions: 1) With the same motor, performance with a fast wind/20" wheel is more or less the same as a std wind/26" wheel. The major difference (at least for me) is the fast wind motor is going to require more power from the battery which will reduce range.

That's not a sound assumption. Just because a faster motor and smaller diameter wheel can make more power doesn't mean you have to use more power. If it makes the same watts at the same gross efficiency, then the only differences that affect range would be from factors other than the motors (tires, weight, aero, etc).

 

[neptronix]

Moderate hills and you don't require high speeds, but you have the torque advantage of a 20"? check how a given motor responds up hills, but, i'm pretty sure you don't need the additional complexity, expense, or drivetrain wear of a mid drive. You may already have adequate torque.

 

[rocketman58]

Moderate hills and you don't require high speeds, but you have the torque advantage of a 20"? check how a given motor responds up hills, but, i'm pretty sure you don't need the additional complexity, expense, or drivetrain wear of a mid drive. You may already have adequate torque.

I am happy with the G020 I have on trike No 1. It tops out around 20mph which is as fast as I go, and it climbs great. Since this is the case, I will just build another duplicate wheel for trike no 2. Going through all of these posts and the research I did only seems to validate that as the best choice for me.