Idiots guide to rewinding Revolt 120 pro

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Miles   100 GW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by Miles » Jul 07 2017 10:23am

Wheazel wrote:@Miles, what would be your educated guess for improvement by segmenting the magnets?
What magnitude of change can be expected under the current circumstances with larsb's revolt?
It really is a guess but, I would have thought 50% reduction in rotor losses should be achievable... Lars has obviously researched this area but I've attached a paper which gives a desktop analysis on the effects of varying segmentation.
Attachments
Permanent Magnet Loss Reduction in PM Machines.pdf
(255.08 KiB) Downloaded 76 times

larsb   100 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Jul 07 2017 11:50pm

Thanks for the input!

Still thinking halbach..
I believe the biggest factor of using a Halbach array is that it requires more magnet material to give the same field strength. Assembly is also harder since i would need loads of smaller magnets. I am almost wanting to do it since i'm anyway using more segments if i go ahead with the rotor.

I don't like the mild steel option since we use tons of salt on the roads here in the winter. Rotor would be destroyed by rust even if painted well.

I can make a carbon or glass fibre shell myself, the issue would be balancing it, lack of thermal mass and conduction.

Alu rotor maybe? It has really good thermal properties but is more sensitive to eddy currents, if we say losses are mainly in magnets then that is not so important, it is corrosion resistant and cheaper than stainless steel.
Last edited by larsb on Dec 07 2017 3:47pm, edited 1 time in total.
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madin88   100 MW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by madin88 » Jul 08 2017 12:58am

larsb wrote: I can make a carbon or glass fibre shell myself, the issue would be balancing it, lack of thermal mass and conduction.

Alu rotor maybe? It has really good thermal properties but is more sensitive to eddy currents, if we say losses are mainly in magnets then that is not so important, it is corrosion resistant and cheaper than stainless steel.
are you talking about an halbach rotor now?

Recently i reserched hub motors used for solar racing cars, and they often went with the halbach design to increase efficiency, however, from what i have found out those hub motors offer no weight savings and the torque wasn't impressing compared to hub's with iron core.
Probabaly not the optimal design for a Hub drive with high torque requirements (i know it's all about trade offs), but for mid drive things quite likely will look different.
- 10kW belt drive with Neumotor 8057: [url]viewtopic.php?
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larsb   100 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Jul 08 2017 2:20am

I am not so concerned with weight if it is well utilized.
I did some FEMM halbach simulations some years ago and they show that you can reach the same field strengths as normally found in the airgap when using backiron but you need stronger magnets or more magnet material. That comparison was done with true magnetic steels as backiron so it would be easier to top the revolt performance as there is quite some leakage flux and stainless steel used.

Main advantage with the halbach is the lower losses and more even field distribution in sinus form.

It would take 130pcs 50x3x3 magnets and (if true, seems too cheap) costs 60usd at aliexpress :roll:
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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Jul 09 2017 5:15am

I checked the 50x3x3 magnet supplier reviews, they are poor quality supplier as expected 8) , large tolerances on dimensions and sometimes poor magnet properties. This is the only supplier of 50x3x3 i can find, probably since thin magnets like that are sensitive to cracks.

50x5x5 is looking a lot better for supply:
https://m.aliexpress.com/search.htm?key ... +neodymium#/

Then i need a new plug to form the rotor shell around thats around 124mm in outer diameter. If it needs to be done on a lathe i might just get a new shell turned instead of the plug.

I wonder if a 3D print would have good enough tolerances to form a plug.
@wheazel: what do you think? I know my collegues machine is out of question, prints are too poor!
Ride on :D

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madin88   100 MW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by madin88 » Jul 09 2017 7:59am

larsb wrote: Then i need a new plug to form the rotor shell around thats around 124mm in outer diameter. If it needs to be done on a lathe i might just get a new shell turned instead of the plug.

I wonder if a 3D print would have good enough tolerances to form a plug.
@wheazel: what do you think? I know my collegues machine is out of question, prints are too poor!
optimum would be both. a 3D printed jig for mounting the magnets (with gap between N and S), and a new rotor done on a lathe.

btw: is the stock rotor really made of some sort of stainless steel?
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dreamer291   10 µW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by dreamer291 » Jul 09 2017 8:05am

a few time before i found this shop with high quality magnets for motors
http://www.super-magneten.de/Segment-Ma ... eo731.html

larsb   100 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Jul 09 2017 8:41am

Yes, rotor is stainless on the revolt. Salt spray driving for 4 months has not affected it :D

From revolt home page:
All of our motors parts are made of SS or coated (even the screws are made of SS), only the bearings and the retaining rings could suffer
That's one positive thing, apart from the losses :D
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Wheazel   10 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by Wheazel » Jul 09 2017 9:38am

The rotor on my old rv100 is not stainless, my rv120pro might be.

larsb   100 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Jul 09 2017 1:08pm

So you've got two of these buggers? 8)
And what does the non-stainless one look like now?

What do yo think, would it be possible to print a dimensionally correct tube plug to make a carbon fibre shell?
Ride on :D

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Wheazel   10 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by Wheazel » Jul 10 2017 5:47am

It is a bit rusty, but ive polished it once so it is not that bad now. Not in use atm, it sat on my retired winter tilt-trike.
Printing a plug with the right measurement wouldn't be a problem, at least if I can have more than 1 try :D.

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macribs   1.21 GW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by macribs » Jul 10 2017 1:46pm

Man what a forum. There are actually good and decent people in the world. TG.
I salute such behavior.

larsb   100 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Jul 11 2017 5:07pm

Thanks a lot! I'll send an stl file tomorrow.

I think i'll stick with the original magnet thickness of 1/8":
I cannot be sure how the change in the magnetic circuit affects performance if i change magnet thickness -there's a risk of getting a halfway improvement since eddy currents get more volume to build in if i go 5x(5x5mm) magnets instead of 1x(25x3mm) that's in motor today.

My choice will then be comparable to 8x(3x3mm)

I recall that i've seen what looks like metal foil visible between the magnets in the revolt rotor - i think at least some of the magnets are electrically connected in it today.

I honestly wonder who is doing the engineering at Revolt.
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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Jul 12 2017 8:03am

Stats of rewind
Measured phase-phase resistance:
Before rewind:26mohm
After rewind: 15mohm
image.jpeg
image.jpeg (144.95 KiB) Viewed 2038 times
kV before 45.3
kV after 41.5

That's almost half (42% decrease) the copper losses with an 8% increase in torque/amps - pretty good

Noload after rewind:7.2A
Noload before 7A (i am not so sure on this one)
Inductance phase-phase:0.132mH

BEMF shape:
Fil 001.png
Last edited by larsb on Jul 24 2018 1:04am, edited 1 time in total.
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larsb   100 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Jul 12 2017 8:59am

playing a little bit with the bavaria calculator (http://www.bavaria-direct.co.za/constants/) shows:
- If the motor could shed 1000W of heat at 100degC motor temp (i don't say it could, just for an estimation)

Efficiency 91% at 72V/145A and 9kW out

If noload could be lowered to 5A
efficiency 92.3% at 72V/180A and 11.8 kW out

I think i will finish this thread and start a new one with the rotor improvement :D
Ride on :D

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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Jul 12 2017 3:34pm

Rotor improvement continued in this thread as rewind is basically finished.
https://endless-sphere.com/forums/viewt ... 30&t=89473

@wheazel: i have sent some STL:s as well as uploaded into new thread. :D

I plan to post some updates later on from using the motor..
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Wheazel   10 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by Wheazel » Jul 12 2017 3:48pm

Cool ill have look on em.

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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Oct 05 2017 6:50am

I have been testing the motor for some months now and the difference to before is very small in my application.

I run at 100% battery and phase amps, as i do road driving i didn't overheat even before the rewind (after the halls issues were fixed)

'Edit: removed incorrect text on cutoffs. These were found to be caused by incorrect controller connections

There aren't many controllers out there with small size and true high power. I know I won't be using an Adaptto after previous bad experiences with their customer service.

There's a new 200A sabvoton (http://www.cnqsmotor.com/en/article_read_672.html) but the eRPM@72V is slightly too high for the Sabvotons if they haven't improved the eRPM limits of their controllers.

Maybe i'll rewind the old motor to have two separate sets of windings when i do the halbach rotor :D It could be controlled by dual KLS7230 controllers.
Last edited by larsb on Dec 07 2017 3:52pm, edited 1 time in total.
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Buk___   10 kW

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Re: Idiots guide to rewinding Revolt 120 pro

Post by Buk___ » Oct 05 2017 7:14am

larsb wrote:when i do the halbach rotor :D
Does a halback rotor actually make any real-world difference?

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Re: Idiots guide to rewinding Revolt 120 pro

Post by larsb » Oct 05 2017 8:23am

Yes and no. Since i am not at the limit of the motor i won't know the difference if i don't dyno it. But i have started to do a halbach rotor so there will be one :D
it will be lighter, hopefully have better efficiency and a questionmark for the torque output.

I think many mistake halbach motors and ironless motors for the same thing. Ironless motors loses a lot of torque, not so with a motor that has the iron core and a correctly done halbach rotor.

But it is a gamble since i haven't simulated what i will do.
Ride on :D

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Re: Idiots guide to rewinding Revolt 120 pro

Post by Karolis » Oct 05 2017 11:19am

I think that rotor is crap (maybe not good material for rotor) and main loses comes from it. I didn't see any rotor which temperature rises more than stator's and that is at free spining. After one minute of free spin you can already feel it. So imagine what energy it takes to heat that.
My motor at 36V at free spin uses ~ 3,5A battery 4,5A phase.

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