Revolt Rv-120 Pro Is this motor for real?

[macribs]

The revolt 120 Pro with hall sensors have some amazing specs.
According to the website this is one bad ass motor.

• Voltage: 24v-96v
• Motor Kv: 43
• Continuous Power: 6 Kw
• Peak Power: 15Kw

• Total Length: 191 mm
• Can Diameter: 127 mm
• Shaft diameter: 15mm
• Shaft Legth: 45mm
• Weight: 4.83kg

I must say this motor pretty much beats everything I ever seen - at least on paper. All this in a > 4,8kg package.
So reading this it seems just a little hard to know if this is real world numbers that will hold up or if the manufacturer have been the victim of an eager marketing scheme.

Don't get me wrong, on paper I am crazy in love with this motor. And it seems that it will be able to spin my rear wheel without any additional jack shafts or reduction gear.And that would be a good thing as it can make the build much easier regarding chain line and chain tension.

1: What do you guys think? In the real world, what kind of power could one expect to see from this motor?

2: What kind of voltage would be best for this motor to have the most work done in its highest efficiency range?

3: What kind of controllers would be good match for this motor? I mean many controllers will tap out at about 10Kw, and this promises upwards to 15Kw.

 

[macribs]

I did do the search but all I came over was this thread: Revolt Rv-120/ norco aline ( rc mid drive)

It has some info but not a whole lot. It is hard to tell by reading that thread if the motor stand up to the specs or not.
No info like top speed, acceleration, consumption etc was given in thread.

The revolt is briefly compared to a cromotor - with the scientific approach of "hand down" to feel motor temp.
So I can not really tell anything from reading that thread.

But there was one other thread about the Revolt 100+120 but neither of them runned the PRO version with hall sensors.
And I read that all the way down and on the final post I read this:

The rv-120 is the way to go. No big reduction. No sync problems. Raw power!

You can't get much of it without high rpm. And you don't get more torque by lowering Kv. So lower kv = lower power.

So what is what? Is the specs inflated or does Circuit mean that the RV 120 will need a jackshaft and reduction to deliver?

Can someone understand and explain these charts? To be honest I can't really tell what it means.
But honestly it does not seem to surpass 10Kw ever. Or so it seems to me.

And what about heat? Do I need to make room for water jacket on this motor?
It seems many have bought this motor but no one has done any testing, and only a very few have even ridden their e-bikes with Revolt mounted.

It is hard to draw a conclusion - did they stop updating because winter came along or because the motor was shit or did everyday life catch up and?
Both those threads had good activity and many posts until they both just died.

 

[bearing]

Can someone understand and explain these charts? To be honest I can't really tell what it means.
But honestly it does not seem to surpass 10Kw ever. Or so it seems to me.

If you look to the right in the graph you see ~7A no load current at 72V and ~3225 rpm.

From the graph we can make some rough calculations of performance.
No load losses at 72V: 72V*7A = ~500W
kv = ~3225 RPM / 72V = ~45 RPM/V
At 100A the speed dropped to ~3040 RPM. (3225RPM - 3040RPM) / 45 RPM/V = 4V
Winding losses at 100A: 4V*100A = 400W
Motor resistance is about 4V/100A = 40mohm.

Efficiency at 72V, 100A: (7200 - 500 - 400)W / 7200 = ~88%

Remember, these were just rough/back of an envelope, calculations.

 

[macribs]

Keep in mind that Kv on a motor needs to be pretty low to use it direct drive without any reductions, unless you are wanting a pretty high speed, and/or have a really small tire.

@43RPM per volt, in direct drive, this thing would spin a bike wheel really fast (430RPM) at only 10V. To get that 10kW of power you're talking about out of it at only 10V, you'd have to pour in a lot of current--1000A! I don't know what current it would saturate at, but I suspect it's below that, meaning you'd be producing just heat, not work, with whatever is above it's saturation point (I have no idea what that would really be).

@43Kv per volt I would think 96v would be a more useful voltage. So RPM would be 4128 @ 96v. Meaning you need only 104 A to reach 10 Kw. And that seems doable. And keep in mind we are talking peak power.

If you run it at the 96V they mention as a top voltage, it'd be spinning the wheel (in direct drive) at 4128RPM, more than 10x as fast as I'd want a wheel to be spinning on my own bikes: with a 26" wheel that comes out to a little over three hundred MPH.

Even wtih only a 20" wheel, it's still 246MPH.

A 10:1 reduction on that would bring it down to a bit under 25MPH, which is closer to "normal" for me, with a 20" wheel and that motor in direct drive at 96V.

No idea about cooling/etc., though.

Hm and with 11/52 sprockets like this we are talking a 4.71:1 reduction, right so wheel speed drops roughly by half.

If you swap to 10/72 tooth sprockets you have 35 mph in 26". So using a 19" motowheel I will get about 25 mph according to recumbence drivetrain calculator @ 72 v.

I can pretty much just use moto sprockets and be done with the reduction? So really I can manage without a jackshaft reduction. And that would make for easier build without rebuilding frame.¨

What is not clear to me is if 10/72 sprockets does mean top speed of 25 mph? If so I just geared it too low. As I would like 45-50 mph top speed.

 

[bearing]

You might get longer range if you gear for a lower motor speed. But then you don't get the same power/acceleration. At 36V it's about 180W no load losses, v.s. 500W at 72V. At 96V it would be somewhere around 800W.

There is a tradeoff between winding and no load losses when choosing gearing. Peak efficiency is when no load losses are the same as winding losses. Cruise close to peak efficiency to get the longest range.

 

[Punx0r]

Those no-load losses seem very high?

 

[bearing]

Maybe, depends on what you expect. Depends on the controller as well.
Do you know any motor of this power which have lower no load losses?

I know one motor, but not the same size. The Agni 95 is about twice the weight and twice the power, but has about the same no load losses as this one, according to specs*. So if you could scale it to the same size, the Agni would have half these losses.

*I haven't been able to quite reach the specs on my Agni.

 

[John in CR]

Those no-load losses seem very high?

0.5mm laminations.

 

[John in CR]

Maybe, depends on what you expect. Depends on the controller as well.
Do you know any motor of this power which have lower no load losses?

Pretty good back of the napkin estimate of the phase-to-phase resistance. The one I have is the V1.0, so I don't know what differences there are other than halls and some difference in the skirt bearing end that adds some weight. It's motor winding resistance is 0.027 ohm.

As far as motors of this power, all 3 of my Monster motors are capable of significantly higher power at greater efficiency, so of course the no-load current is lower.

Macribs,

Since the Revolt120 doesn't have top quality stator steel, you'd probably only want to go to 96V if you cared only about maximizing power, efficiency be damned. It's an outrunner, so a water jacket isn't possible. You'd need a centrifugal fan blade at a minimum to draw a good air flow through the stator, and if you leaned on the current you might need to go to an active blower like Toolman2 did with a 70W leaf blower, with which he measured a 1000W savings just due to reduced copper temps.

 

[Miles]

I can add the Rv-120 to the spreadsheet using John's Rm figure.

Here you go:

 

[macribs]

Correct me if I am wrong John but my understanding of an outrunner is that if you anchor down the can the axle will spin? Meaning if can is anchored down it would be possible to use a water jacket as cooling option?

What you think would be the optimum voltage to run Rv 120 regarding getting most work done within best efficiency area?

 

[Miles]

Correct me if I am wrong John but my understanding of an outrunner is that if you anchor down the can the axle will spin?

If you hold the can, the "stator" will spin but it won't make it much past the first revolution

 

[cycborg]

Correct me if I am wrong John but my understanding of an outrunner is that if you anchor down the can the axle will spin?

If you hold the can, the "stator" will spin but it won't make it much past the first revolution

Heh, yeah, if you try that experiment, be sure to get video!

/snark

OK, two problems. First, the axle is fixed to the stator and the stator is connected to the phase wires, so what you're suggesting is a wire-braiding mechanism.

Second, even if you went to the trouble to use a slip-ring arrangement so the stator could spin without tangling the wires, putting a water jacket around the rotor won't do you any good since the stator is where the heat is generated.

 

[macribs]

Ok I see. I guess those water jackets I have seen was for in-runners not out-runners. My bad.

What about cooling in oil bath? Will that work or destroy glue or anything else?
Or is air cooling via fan like those Astro motors from Matt the only way to go to cool RC motors?

Did toolman2 make a thread for his leaf blower fan? I tried to search but could not find any details.

 

[riba2233]

I would say that the fan cooling is only good option. Some larger rc motors like big colosus are water cooled, but they have to have that option from the factory.

 

[John in CR]

Macribs,

Let go of the ICE thinking. Figure out how to make less heat and then the little bit left is easy to reject. Once you have resistance, calculating heat generated is easy. The motors are small and light, so they can't sink away and store much heat like a hubmotor, and temps will increase more quickly. You have no sealed enclosure so forget the oil bath, and even in motors made for liquid cooling there's too much delay in heat transfer from the copper to the coolant for it to allow high performance. OTOH, good tuning can make your electric drive so efficient that a good air flow is all that's needed. You just have to avoid the $%ck measuring contests played by so many who try to stuff as much current into their motors as possible. All that does is make you have to carry a bigger battery.

That's what makes the numbers unreal. Any motor run at its limits becomes inefficient during significant portions of it's usage range. OTOH take the ReVolt120 and run it at 100-125A peak on 60-72V and things look nice, especially if it's geared low so peaks are short in duration. 100A x 100A x .027 ohm is 270W of heat in the copper, but don't forget the hundreds of watts of heat in the iron shown by the no-load current which increases with rpm.

The motors are designed for aircraft where the peak power occurs on launch and during continuous running they have tremendous air flow, so sure in that use 15kw peak 6kw continuous is reasonable. On our bikes the usage is much more intermittent, so power peaks or near peak are frequent. That means efficiency will be lower, and extreme and noisy efforts to prevent heat build up will be required. As you start to run numbers, don't forget that while the motor components will handle a 100°C increase in temperature, the magnets put out less force and the resistance in the copper will increase by about 40%, so even more heat is created at the same current. Stress free should be your operating goal, because that's the route to a more durable and efficient system. Trying to save a few kg with a smaller motor will end up being offset by the cooling system and extra batteries you have to carry. This kind of thing is almost never discussed on ES.

With those types of outrunners, the axle is fixed to the can, so you do have a spinning axle to connect to a pulley or sprocket. The can spins too, and then one end of the stator has bolt holes to affix to the bike so the stator doesn't spin. The axle extends out of both ends of the motor, so it's always a good idea to have dual bearing support.

 

[macribs]

Thx lupus. Maybe we soon will see some real world result from that motor.

 

[okashira]

According to my comparisons, this motor still not close to an astro motor for efficiency and power/weight
But this one is nice because of the high torque makes gearing more simple

The Plettenberg nova motors look insane for power/weight though.

 

[John Bozi]

Macribs,

Let go of the ICE thinking. Figure out how to make less heat and then the little bit left is easy to reject. Once you have resistance, calculating heat generated is easy. The motors are small and light, so they can't sink away and store much heat like a hubmotor, and temps will increase more quickly. You have no sealed enclosure so forget the oil bath, and even in motors made for liquid cooling there's too much delay in heat transfer from the copper to the coolant for it to allow high performance. OTOH, good tuning can make your electric drive so efficient that a good air flow is all that's needed. You just have to avoid the $%ck measuring contests played by so many who try to stuff as much current into their motors as possible. All that does is make you have to carry a bigger battery.

That's what makes the numbers unreal. Any motor run at its limits becomes inefficient during significant portions of it's usage range. OTOH take the ReVolt120 and run it at 100-125A peak on 60-72V and things look nice, especially if it's geared low so peaks are short in duration. 100A x 100A x .027 ohm is 270W of heat in the copper, but don't forget the hundreds of watts of heat in the iron shown by the no-load current which increases with rpm.

The motors are designed for aircraft where the peak power occurs on launch and during continuous running they have tremendous air flow, so sure in that use 15kw peak 6kw continuous is reasonable. On our bikes the usage is much more intermittent, so power peaks or near peak are frequent. That means efficiency will be lower, and extreme and noisy efforts to prevent heat build up will be required. As you start to run numbers, don't forget that while the motor components will handle a 100°C increase in temperature, the magnets put out less force and the resistance in the copper will increase by about 40%, so even more heat is created at the same current. Stress free should be your operating goal, because that's the route to a more durable and efficient system. Trying to save a few kg with a smaller motor will end up being offset by the cooling system and extra batteries you have to carry. This kind of thing is almost never discussed on ES.

With those types of outrunners, the axle is fixed to the can, so you do have a spinning axle to connect to a pulley or sprocket. The can spins too, and then one end of the stator has bolt holes to affix to the bike so the stator doesn't spin. The axle extends out of both ends of the motor, so it's always a good idea to have dual bearing support.

so for a layman are you saying stay away from this motor for an ebike? Just use a hub motor instead?

 

[John in CR]

so for a layman are you saying stay away from this motor for an ebike? Just use a hub motor instead?

That's not at all what I said. I laid out all the considerations for running the motor. I bought one of the early version 1 RV-120's, and wish I'd waited for the version with hall sensors.

For street riding I'm partial to hubmotors due to their silence, ease of installation, and they take up no frame space. Their compromise is weight because the motor rpm is so low. I ignore geared hubmotors, because none exist that run close to the power I demand.

For off road riding hubmotors are inappropriate in my view except maybe for light weight riders or those who stick to fairly easy trails. Off road here is mountainous rocky trails, and with my load and demand for performance more like a motorcycle than just electric assist up hills, any hubmotor would fail miserably. That's because hubmotors are geared too high for high loads at low speeds, and changing the winding to a slower wind does absolutely nothing to remedy the problem (contrary to widespread misconception). Though I do want to try a 2wd with small wheels on a pair of hubmotors as an offroad ebike, mid-drive is the way I'll go for off-road, and as long as you're realistic about current and power I think the big Revolt outrunner is a fine choice.

 

[John Bozi]

Thanks for that clarification,

I am on the market for a new approach after I broke my clyte 4065 axle... yes rocky mountains is what I ride too,

my only solution that worked for some time was the hub and the bafang 750 geared 30t:48t in 20" wheel. The bafang never got hot and climb anything until traction and the vented hub did the rest.

Not eloquent but did the job for me without custom building skills or tools.

appreciate the info John

 

[okashira]

I might have to go with this motor... compared to the NOVA 15 it's quite a performance match.
It's 2kg heavier and longer. But the $2000 less cost means I'll just deal with that LOL. And being heavier it can probably take a little more sustained load.

 

[riba2233]

If only they've used thinner lamination... It can have even more power at higher rpm.