#crossbreaks' midmotor CB120

OLD Topic Name: Custom RV120 for ebike use: group order Rv120-ES edition

If you look for the CB120 go to page 6 https://endless-sphere.com/forums/viewtopic.php?f=28&t=80516&p=1277160#p1277160

The RV120pro looks like a good motor. better than RV160short and RV120short (low Km² motor constant and way too high no load loss). Still, for me the RV120pro design looks not optimal for ebike use, as it does not fit between the cranks, a lot of length is wasted to the complicated bearing design. So I'd like to get rid of the shaft and make things much more simple. We dont need it. Hub drives show us how. This saves quite some space where we need it: length. I know, hubbies run low RPM. This motor runs faster. Unbalance can be an issue. That may be a point to discuss... i hope the bearing config may work at that 1000 to 3000 rpm where it performs best. what do you think?

i also hope that bearing loss can be reduced due the smaller bearing dia of the rear bearing.

in this drawing, i not only got rid of the shaft and replaced it with an axle...i also got rid of those nuts for fastening. I replaced them with bolts so over all length can be reduced further. Another point to discuss. Countersunk screws have drawbacks though...still, multiple Allen bolts are shorter than a nut though

the last drawing of the RV120 is from revolt http://www.revolt.org.il/rv-120/rv-120pro-2/

some spces:

bearings: 16005 (25x47x8mm) and 6003 (17x35x10mm)
Sprocket: custom 13T type 410 (BMX chain), 32mm BCD, 6 bolts M5x10
Phase wires: 5mm dia, shall fit AWG8 with insulation, max bend radius is 6mm
left side mount: single M8 bolt
right side mount: 4x M5 bolts, 18mm BCD

close up of the sprocket attechment

110mm is pretty damn good. The idea looks solid in my book. Planning to mod one and try?

Cool stuff, and that looks like good drawing. So you want to reverse fuction and spin the motor like a hub, but for a middrive? I'm not sure why, although perhaps there could be better cooling but a drawback of larger spinning mass working towards gyroscopic balance? Besides the extra work of course.

I like the look of the 120 (and 160) with the 45kV, and the weight/power ratio.

The bht I use is cropped to almost exactly 5" long by 6" diameter, so the 120's dia of 126mm and similar weight look like a fairly even trade (and/or upgrade) just to use with live axle/output as intended. Probably very similar power handling without goofy heavy mounts to work with on bht. Looks like It wouldn't be hard to get the 120 (or 160) down to about a usable 5" length by shortening one axle and deleting the other (on the 120).

Why does the 120 have a thru shaft like that anyway? Forced cooling?

RV120 * $315 * 4.3 kg * 45 kV


RV160 * $435 * 5.0 kg * 45 kV


Actually, I really like the look of the 160 as an upgrade to bht/bigblock. Similar kV, less mounting BS, and about 2lbs more copper/iron to handle 8kw/15kw cont/peak 8) The extra 1/2" dia wouldn't be hard to squeeze in, and looks like the single shaft could be trimmed to 1" for an acceptable total length of <5".

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So obviously people would be interested in the 120 for a smaller lighter cheaper motor, but why does it have a shaft on the other side, and what are the benefits and drawbacks to making the shaft stationary switching rotor to stator etc?? Is it just the weight and length savings?

What would you plan to run the motor @, and what would you gear the bike for?
Nice job and thanks for the food for thought.

Its actually not about switching rotor and stator, its about just making the axle not rotate.
On stock revolt motors, the bolt interface is the only "external" part that isn't rotating.

nutspecial said:

So you want to reverse fuction and spin the motor like a hub, but for a middrive?

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save space. in particular: length. it's possible to save 10mm
and get bearing loss down. The large bearing of the RV120 induces quite some unnecessary drag. With that spinning shaft there is no other way than using such a large bearing. But with the axle fixed, it is possible to use a much smaller one like the 16005.

A drawback is that the smallest possible sprocket is a 13T for 410, 420 and 428 chains. For belt drives this is no issue, since belt sprockets have to be larger anyway.

Wheazel said:

Planning to mod one and try?

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would be nice..sadly i dont know where to deploy a large lathe. I need a workshop. best would be if Revolt would make a special version. I'll drop them an email.

nutspecial said:

RV160 * $435 * 5.0 kg * 45 kV

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5kg is the short version. this motor is smaller Km² than even the RV120. All short version suck. as written above, they have massive no load loss but weak copper figures. The RV120 is 1.6, the Rv160short is only 1.0 (according to https://endless-sphere.com/forums/viewtopic.php?f=30&t=75494#p1166771), so i think it is weaker in practice, even with its better cooling abilities...plus it wastes more precious battery energy
Your Big block is Km²=0.6, same as the RV120 short. Even a non-pro RV120 would be a huge improvement to your setup. To visualize it clearly: Two RV120short are "weaker" than a single RV120. They have more copper loss than the single one. this is the case, since they have double the end turns and phase wires, which adds up to phase to phase resistance.

Building such a large motor with a tiny stack of only 22.5mm isn't worth it. 80mm can length for 22.5mm stack length tells you that active length is only 28% For the stock RV120 it is 93mm can length for 45mm active material. So active length is 48%. A much better deal if you ask me

So including cooling capabilities this custom RV120 will be over two times more powerful than BHT big block? That will be nice :wink:

Yes, it looks like a big improvement (2.5x less losses?) and not really much length lost with just trimmed axles. . . . If I understand the normal stock operation correctly. . . . And then crossbreak's version would make much better use of the can space for our purposes.

Thanks for all the info crossbreak, it's technical beyond me but a good understandable and informative start.

Am I wrong in thinking the 160 short would outperform 120 pro? sure it has more losses but it has more mass to offset extra heat @ low efficiency (low rpms)? Bht is near 5kg unmodded and close in size so I'm more about getting more power for that size and weight. Seems like the cont and max kw across the revolts are scaled to reflect the km / copper losses you're talking about. 8-15kw for 5kg in that size would prob work well, and am I correct in assuming all extra copper and iron basically add more forgiveness factor when running hard in low efficiency (low rpms)?

I'll have to check some more info and vid to confirm I even understand the normal operation of them.
https://www.youtube.com/watch?v=MeXkpcWoh9U
https://www.youtube.com/watch?v=K5s7zE7WRi8

Oh, I see only the one end is normally stationary. I guess the large bearing and shaft is designed with props in mind. Hmmm It sure would def be nice to not only shorten them but to reverse function so the entire can isn't 'live'. Def mention something to them and let us know if anything comes of it! Thanks for doing the drawings.

This is most important:

Building such a large motor with a tiny stack of only 22.5mm isn't worth it. 80mm can length for 22.5mm stack length tells you that active length is only 28% For the stock RV120 it is 93mm can length for 45mm active material. So active length is 48%. A much better deal if you ask me

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Long motor will have allways better power density than shorter one. So 5kg long stator motor is allways better than 5kg short stator motor. In shorter motor more copper is just wasted on connections between teeth (non-active)

I think the proposed mods would make a revolt motor much more appealing for many applications.
The biggest hurdle I had with the revolt120pro when I built my cargobike, was indeed the placement.
Pedals and feet take alot of space and a too long motor cant be placed inside that space.

Now the motor sits on a shelf, waiting for the next build. This thread has opened my eyes to the possibility to mod it.
I do have access to the tools needed to make it happen.
Making new endbells is the easy part. The more complicated things involve a stator axle and fitting the stator.
I imagine there are big risks I would end up having to rewind the motor.

Same, the modded motor would be more interesting that an stock revolt to me. Mounting still suck on this motor thought, hard to make something really rigid.

Would be interested to get one for a LMX if this comes to life, in 45KV would be ideal.

Adam

*Subscribed"
Need to follow this thread.

Revolt checked the design and they say that they can produce it as is. They want to know how many to produce. Stack is 45mm with .35mm lamination like the RV120Pro. I hope i can tell you the price soon

Who is in?

crossbreak said:

The RV120 looks like a good motor. better than RV120pro

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I have burned 2 Rv-120 and So Far The RV-120 pro on my bike never reach more then 55 degrees...
The Rv-120 pro fins cool the motor efficiently. It takes the abuse and I never feel worried about smoking the motor over long rides.
I had lots of problems fitting the motor to the frame so I had lots of different brackets made. now finally I have the perfect bracket solution witch doesn't require any soldering and modification to the frame. As for the Crank clearance I use A Fat bike Crank :lol:

I dont See the need of using the can instead of the shaft. The Shaft Can be replace easy and it's cheaper.

I forgot to mention that the can of the RV-120 is way to weak to support the load from the sprocket.

yep, that's another reason for the redesign. I meant that package is better for the non-pro, of course performance of the pro version is enhanced a lot due cooling and thinner lamination.

Maybe we should add some holes for cooling...maybe make two versions:
one with holes for those who want better cooling
and one without for those who want a more dirt and waterproof design.

the enclosed version could be a candidate for ferro fluid, to raise continuous power

boisrondevens said:

I had lots of problems fitting the motor to the frame so I had lots of different brackets made. now finally I have the perfect bracket solution witch doesn't require any soldering and modification to the frame. As for the Crank clearance I use A Fat bike Crank :lol:

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good point. to keep q-factor down, i'd like to be able to use normal cranks. Maybe we should design a bracket so people dont start at zero. instead they would have a simple bolt-on device that almost works out of the box and fits most bikes without too much modification

price is approximately $440 if we manage to get a batch of 10 pieces

it will get cheaper if we buy more. About the same price as a RV120pro

Nice crossbreak!!!! I'm super interested.
Mounting bracket wouldn't be a worry with me, and I can add vent holes if needed.

!3t minimum sprocket is fine but Is bmx drivetrain enough? I suppose we can modify and mount up other sprockets -thinking 219 or (prefer) #35. Confirm structural sureness of sprocket and motor mounting area?

Could it be easily explained/shown how normal and modified operation is for those unfamilar with outrunners (like myself :| )?

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A video I watched by revolt suggested an aluminum heatsink and 'ventilator' to run max power ratings well. But even without they can't be near as bad as bht for a similar application? It should be 40% more capable @ the same weight.

I have burned 2 Rv-120

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Boisron, what ride weight and condition were you burning up 120 normal's?
And what power level? Same as the pro120 running < 55deg C?

[/quote] Boisrondevens, what ride weight and condition were you burning up 120 normal's?
And what power level? Same as the pro120 running < 55deg C?[/quote]

going with 125v 120a bat for 10 minutes (24fets controller)

Not enough air flow with the rv-120
https://endless-sphere.com/forums/viewtopic.php?f=28&t=64342&hilit=norco+rv+120

crossbreak said:

... since the Pro version has the better .35mm lamination...

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Where did this info come from? I was one of their first 120 motor buyers and I've prodded them for over 2 years to offer their larger motors with something better than the .50mm lams to no avail, so I have to think I'd be one of the first people they'd contact about a better offering since I told them I'd order a minimum of 10 to help get that ball rolling.

Their high no-load current running thousands of rpm has been the primary indicator of low quality lams and is a loss that keeps me eating the extra weight using the larger high efficiency motors I already have. Km2 is fine for looking at acceleration, but after those few seconds the rest of the time it's irrelevant compared to efficiency, since heat is our limitation.

So the ~5-6a no load current @ 80v of this motor (120reg) indicate a lower efficiency (more heat) @ top speed, probably traded for a more favorable km2 (affecting acceleration)
I think the better km2 would be worth it on my builds, as they're more for the full rpm range and acceleration with less full throttle and taller gearing.

going with 125v 120a bat for 10 minutes (24fets controller)

Not enough air flow with the rv-120
viewtopic.php?f=28&t=64342&hilit=norco+rv+120

Click to expand...

I started reading your build- Thanks, and nice job on it! For reccord I'm pretty darn happy with ~30kv 5kg bht and >6kw. It heats up on aggressive riding with 100a 16s or 73a 20s, but works for me on a light ride with a wild side. I'm using #35 and the 11t and 50t are showing some decent wear for >1000mi- I just don't see a bmx chain being happy with even 6kw for long.

My goal here is to find a good brother or improvement to the bht (which perhaps a 120 could be), and also something more capable of 8-12kw for a heavier build - to me that will mean more iron and copper @ a similar kV and formfactor, and/or active cooling.

https://endless-sphere.com/forums/viewtopic.php?f=28&t=64342&hilit=norco+rv+120&start=100

Page 5 has some very pertinent info for this thread (and for newbs like me).
Awesome job so far on the bike bro! WOW I had kinda given up on keeping pedals (especially parallel) and motor freewheel while approaching 10kw- looks like you're running 12.5kw freewheeled in serial through a freehub???? Again, awesome freakn job. Sure would love to see some video . . . . I'll make some fresh myself in the next few days time permitting. Of 'offroad' of course for full draws

to clear things up, here are the differences between Rv120Pro and non-pro:
nonPro: .5mm lams, Pro: .35mm lams, in theory, the Pro should have around 30% lower no load current, ie 3.5 to 4A. No measured data on this yet.
stack is 45mm for both, as well as Km², its 1.67 N²m²/W - no difference here
The Pro has fan blades in it's side plates that enhance cooling
The Pro is 21mm longer (126mm vs. 105mm) (vs 93mm my design)

i have this info directly from Revolt. Additionally, boisrondevens told us that bearings on the pro version are "enhanced". So maybe this eats up it's advantages of better lamination but we dont now till someone measures no load current of a Pro.

Hm I wonder if a custom version could be wounded as a 6 phase motor? Think that would even yield good result with lower priced controllers. Or work well with dual phaserunners from Grin Tech. Super light controllers and a lightweight motor. Capable of more then 10kw peak. That would be a custom motor I would like to have. And another benefit of the phaserunners are the small size and waterproofing. You can fit them on any e-bike, even on the seat tube if real estate is limited.

Is there anyone else that would like to see a 6 phase version? I've been curios about 6 phase since I first saw John's hubmonster. Then only thing I don't like with the hubmonster is the size and weight. Maybe a custom revolt 6 phase could work well? Even if that motor has low efficiency as some posted in this thread, if run with dual controllers there should be enough current to rebattle some of that - if using a fan blade or maybe even with statorade.

What y'all think, 6 phase revolt sounds hot or not?