Brushed vs. Brushless Drivetrain Questions

[ekline309]

Hello Everyone!!

This question has to do with RPM reduction for brushed vs. brushless motors. My current system is a 36V 1000W PMDC motor with a 5:1 belt reduction in order to operate at the target efficiency RPM.

First, what would happen if you had no RPM reduction and just connected a high RPM brushed motor straight to the drivetrain?

Second, if you use a brushless motor do you still need an RPM reduction scheme??

I am trying to overcome this problem so I can have a motor that I can connect straight to the drivetrain, like a derailer. Can you recommend a low RPM motor for this, or would it have to be a gearmotor?

I have pretty much settled against hubmotors, because I feel like they won't provide the torque I want(just guessing). Also, I want my motor to be removable.

Thanks in advance for your help, I have been searching for threads on this topic for days and have had no luck.

 

[Anonymous]

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[Link]

If you had no reduction, you'd overload the motor. You'd might go really fast for a while if it's got a lot of torque, but it would fry in short order.

The only difference between brushed and brushless motors is how they're commutated, so, yeah, you'd need a drivetrain.

There are pretty much no motors that will spin slow enough on decent voltage to connect directly to the drive train. Well, there are, but you wouldn't be able to fit them on a bike. You'd have to use a geared motor for a suitably low RPM.

FYI, you can get some really crazy torque out of hubs. Doc's crazy X5 setup gets 120Nm, which is near 90lbs/ft.
But how are you planning on making the motor you do plan on using removable, anyway?

 

[John in CR]

I'd have to disagree with Link on this one. I've been looking around to try and secure motors directly from the factories and there are a number new quite efficient and powerful brushless motors coming out that are designed to run and are rated in the 700-1500rpm range that weigh less than the X5 range of hub motors. With a remaining reduction from 2:1 to 4:1, it seems relatively easy to do directly in a drivechain. Once you go to something more powerful than you have, then running it through the bicycle chain is going to be problematic, so putting the motor on its own chain drive becomes easy and efficient for a single step down. The biggest problem is going to be finding these motors at a low price, since the latest and greatest coming out seem to have a premium attached.

Something I'm going to give a go is to use the 90° gearbox from an angle grinder. The ones I've gotten my mitts on have a 3-4:1 geardown, and those things are designed for both high speed and abuse. That way I can run a big higher speed motor in line with the bike and just attach a 2 sprockets and a chain or pulleys and a belt to whatever final ration I want. It will be a month or so before I can report any results, since I have 2 hub motor projects to wrap up first.

Good luck finding what you need.

John

 

[Link]

Wait...I'm being retarded, seeing as how the X5 IS a brushless motor of suitably low RPM to connect directly to the drivetrain.

EPIC FAIL. :?

 

[John in CR]

Wait...I'm being retarded, seeing as how the X5 IS a brushless motor of suitably low RPM to connect directly to the drivetrain.

EPIC FAIL. :?

Not really. Finding low rpm, but powerful without being heavyweight industrial size isn't an easy task, except for hub motors. Ooooh!, Imagine an X5 not in a wheel, but instead running through a variable set gears. A low gear for efficient low amp climbing, regular gear 1:1, and overdrive...yeehaa!

John

 

[Link]

We refer to that as a "Stokemonkey" setup. :wink:

 

[ekline309]

link- the motor will bolt into a mounting plate which will bolt directly to the down tube and seat tube.

john- who are you thinking of getting these low RPM brushless motors from?? I would definitely pay a premium for the simplicity of running the motor directly to the drive train.