Brushed vs Brushless for the Oset

[Oded]

What made Oset's engineers choose brushed motor over brushless?

Almost all e-bike alternatives run brushless. 

 

Is it because these motors are less expensive? Better low speed characteristics (RC crawlers have brushed motors for that reason)?

 

Starting to think about an Oset 24 conversion. So many brushless controllers and motors options as opposed to brushed...

[arthritic]

I believe Kuberg use brushless motors, but I haven't seen any of their trials versions in competition. Maybe worth finding an owner for comment.

 

[Oded]

Electric motion use brushless as well, and of course all the others - Alta, KTM Freeride, Zero...

[tjums]

Short answer - Price...
It is mere expensive to use a brushless motor in your electric bike, than to use a brushed motor.
Also, it will need a more complex controller, than the brushed motor.

[gwhy]

brushed tec if very old tec but also very easy to understand. brushelss is a much better/lighter tec but very hard to get to grips with if you not have a understanding of how they work, Price is comparable to be honest as controllers are much better spec/priced now than what they were 2-3 years ago, brushelss motors however can be a mine field to source one that would be suitable for a given application they are not cheap enough to take a gamble unless you know what you are looking for. 

[kaarelj]

On 9/12/2021 at 7:52 PM, arthritic said:

I believe Kuberg use brushless motors, but I haven't seen any of their trials versions in competition. Maybe worth finding an owner for comment.

 

I've seen few in noncompetitive situation on training.

Quite bad to be honest. Geometry is weird, distance from handlebar to foot peg is longer than on 125/250cc fullsize bike. But Kuberg is meant for smaller crowd. Buti t is a long bike, compared to Oset 24 it seems allmost a foot longer. Kuberg Challenger has 14" rear wheel. 

Yes, powerful motor, but the ~13yo beginner had a serious struggle there. Small rear wheel with huge amount of power caused it to just spin everywhere. It was a struggle to lift the front wheel. Seemed to be almost impossible to climb slowly on soft terrain. And the ride height is quite high hence loosing some balance there already

It seems to be cool ride for freeride in forest or fast MTB/FullSuspension trail. But it does not seem to be good fit for Trials. Don't get me wrong, it looks cool and it would be really cool to freeride and have fun with it.

I made a real quick mockup for comparison with Evo80jr and Beto FullSize. Although the Kubergs commercial image makes the rear wheel a bit larger IMO. IRL it is actually smaller I would say.

 

 

[bikerpet]

Brushed motor controllers are inexpensive and one of the key features is that the throttle response from even the most basic brushed controller/motor combo is virtually instant, even from stalled. The same cannot be said for a lot of brushless controllers, many of them are perfectly fine for 99% of uses, but the tiny bit of lag, particularly as they first spin the motor or from very low RPM, can be a problem in trials.

I'm guessing, but I'd also expect that as most brushed controllers are fundamentally analog rather than digital, then it was far easier to find a controller that could use easy to understand twist knobs to adjust settings.

Digital brushless controllers have to read the rotor position from sensors, then calculate & send the appropriate AC power to the correct motor windings, that happens fast, but depending on the software and hardware there can be delays. An analog brushed controller just ramps up the voltage and the motor spins.

My guess is that Oset found that for the money there wasn't much out there that had the same response & control inputs in brushless designs.

Brushed motors are slightly less efficient, but really in trials is it going to be even measurable or significant? Brushes are going to last nigh on forever in trials use and are cheap and simple to replace anyway (I don't know the detail of Oset motors, this is a generalisation).

Yes, a good brushless setup will be a bit more efficient, probably lighter and maybe more tuneable, but you'll likely be paying a pretty decent premium to get one that actually rides as well as a sorted brushed setup.

I've got an analog brushed controller here that costs around US$15 and works really nicely for trials. I've also got a $500 brushless controller that does pretty much the same job. I've certainly heard of people spending well over $100 on a controller and getting something that is perfect for golf carts, scooters etc but is almost useless for trials because of the throttle lag.

No question a quality brushless setup is the gold standard, but in the real commercial world there's a lot to be said for the older tech.

[sectionone]

My biggest complaint about my Oset brushed motor is how hard it is to back the bike out of my garage! The instant throttle response is worth the trouble and my ebike has a long lag and the surron lightbee I tried also has an annoying lag. The solution would be a brushless motor with a clutch.

[Oded]

interesting.

I ended up replacing the stock Oset controller with a 1500w basic brushed controller.

it was a mistake as the response and power were brutal (instant but brutal). no way of taming down this basic controller. 

also, there was no current limit on this controller, so blew the 100A fuse.

will try a more subtle 1000w controller.

[bikerpet]

6 hours ago, Oded said:

interesting.

I ended up replacing the stock Oset controller with a 1500w basic brushed controller.

it was a mistake as the response and power were brutal (instant but brutal). no way of taming down this basic controller. 

also, there was no current limit on this controller, so blew the 100A fuse.

will try a more subtle 1000w controller.

Without some degree of programmability in the controller I think you'll struggle to get the feel you need.

There are cheap brushed controllers with basic programming for max power, acceleration and throttle start/end points. They work just fine although you need a USB to serial dongle and windows PC to adjust settings.

7 hours ago, sectionone said:

My biggest complaint about my Oset brushed motor is how hard it is to back the bike out of my garage! The instant throttle response is worth the trouble and my ebike has a long lag and the surron lightbee I tried also has an annoying lag. The solution would be a brushless motor with a clutch.

Yes, it's a small but sightly annoying feature. On the plus side it does offer a little rollback resistance when you lose it on a hill :-)

A clutch is almost pointless without some significant flywheel mass. With a lightweight brushless rotor the motor simply stalls instantly if you don't have enough power on, and with too much the bike either spins or takes off. It's flywheel inertia that makes a clutch work, one without the other is at best pointless and at worst a nightmare.

Hence EM having adjustable flywheels on e-pure bikes with clutches.

[sectionone]

Brushed motors run hotter than brushless? When I trail ride my Oset 24 the motor overheats and goes into limp mode after 20 minutes with the dials all the way to the right. My 2000 watt electric mountain bike never has an overheating problem.

This guy sells an electronic Oset clutch and I'd like to try something like it on my emtb that has a throttle.

https://sites.google.com/pretoriaengineering.com/osetclutch

[Oded]

Mine overheats as well. Not the best bike for trail riding 

[bikerpet]

3 hours ago, sectionone said:

Brushed motors run hotter than brushless? When I trail ride my Oset 24 the motor overheats and goes into limp mode after 20 minutes with the dials all the way to the right. My 2000 watt electric mountain bike never has an overheating problem.

This guy sells an electronic Oset clutch and I'd like to try something like it on my emtb that has a throttle.

https://sites.google.com/pretoriaengineering.com/osetclutch

I don't believe there's any significant difference between the two motor types when comparing apples to apples. Motor heat is simply the result of the amount of current you stuff through the copper windings less the the heat shed through the motor body. There would be a very slight contribution via the friction and arcing of the brushes, but I don't think it would be significant. So overheating is basically a result of a (possibly deliberate) mismatch between the power output of the controller and the ability of the motor to shed that heat. Oset probably decided that it was a better trade-off to use a lighter, cheaper, smaller motor and drive it hard, given the target is trials where the duty cycle is typically very low so the motor has time to shed the heat from the short bursts of full power.

Your MTB motor/controller was probably designed with a far higher duty cycle in mind, the motor just isn't driven as hard so it can shed the heat adequately. Throw a controller on it that can push more current and it'll overheat just as quick.

I'd be interested to hear how the e-clutch works out on the Oset. My expectation is that it will be fairly underwhelming. It won't change the peak torque at the back wheel one iota, only very slightly speed up how quickly it builds - assuming the controller can ramp up as fast as the lever can move. It will give a nice cutout against whiskey throttle and possibly the alternative throttle control via the clutch finger could be more controllable in some situations. The e-clutch is really only a "finger throttle", it's not at all the same as a "real" clutch. On most controllers it's relatively easy to hook up a "reverse throttle" in series with the normal one, which is all the e-clutch is.

FYI my dob e-trials bike doesn't overheat pretty much whatever I do to it and it's a brushless motor too. It certainly gets too hot to touch if I work it hard up a long steep hill but it's never missed a beat.

[Oded]

The excessive heat damages a brushed motor much more than its brushless equivalent. The brushes will need replacement.

Brushless motors tolerate the heat better.

[bikerpet]

I just had a quick look at the Oset wiring diagram (if in doubt read the b****y instructions). There is a temp sensor in the motor that feeds back to the controller, which in turn shuts down the output if the motor gets hot. So there's little risk that the motor is getting damaged in any significant way.

There is also an Oset Technical Bulletin which says the sensor has had some failures on some 2017 bikes, is not needed and can be safely disconnected.

I leave it to you to find, read and decide if you want to act on it.

5 hours ago, Oded said:

The excessive heat damages a brushed motor much more than its brushless equivalent. The brushes will need replacement.

Brushless motors tolerate the heat better.

I don't know that I'd consider a bit of extra brush wear "much more" damage. Brushes wear - faster if they are are worked harder. Brushes are also cheap and usually pretty straightforward to replace. Not such a big deal I'd have thought. I don't know how often Oset owners have to replace brushes?

Also it may not be the motor that is overheating, it could be the controller. In which case there is probably little if any damage occurring anywhere. If it's the controller then presumably it's a self-protection function kicking in. Just an annoyance. Try adding some cooling to the controller (more/better heatsinking or a small fan perhaps?).

My understanding is that the main issue with excessive heat in any motor is

1. The winding insulation breaks down
2. Magnets can be demagnetised by excess heat, particularly when combined with high currents.
3. Solder joints can melt

Brushless motors also have electronic components within the casing (hall effect sensors), these can be damaged by excessive heat.

So bottom line is that too much heat is bad for any motor, I'm not sure it makes a great deal of difference if it's brushed or brushless in the real world.