RotoMax 150cc review

For those who were wondering about Rotomax 150cc inductance, etc.



Received my rotomax 150cc today. Wires are a lot thinner than my old CA120, almost like 4-6mm². Phase resistance is 12mΩ; inductance 7.55-12.8μH depending on position. Cogging step is a lot smaller. Magnets thinner. Winding wires thinner. Stator slots shorter. It is ∆ wound. Bad thing about it that this part with 6 bolts is not removable, as in CA120.

Calculated values:
Power dissipation at rated 190A current: 433W (trapezoidal commutation, only in winding)
Power dissipation at rated 190A current: 325W (SVPWM commutation, only in winding)
Max RPM at 48V: 6860 (compensated on internal resistance)
Max theoretical power: 8.7kW
Max real power output: ~6-7kW

I did not have the time to look for suitable controller and just that one tiny 3s ESC was lying around. It did run fine at 12 volts.
Battery current 4A at 100% PWM 12V; 3.13A at 50%. Phase current 3.3A at 100%; 11.4A at 50%. Values measured with cheapo clamp meter and can be off.
It runs quite silently, as far as this ESC can drive. Reasonably well balanced. Looks well built.

Electrically 10 eRPM / RPM (however coggs 120 times per revolution). This means that controller has to work up to 70k eRPM to rotate this up to 7k RPM. Kelly with high speed option could be enough.

Magnet thickness 2.0mm
Back iron thinckness 2.0mm
Stator diameter 100.0mm
Air gap 0.5mm
Gap between magnets 3.3mm
Stator/magnet length 37.5mm
Gap between slots 2.5mm
Slot width 10mm.

1734 RPM @ 12V, so 144 RPM/V. Close to 150 as advertised
[moderator edit to consolidate data]

Thanks for the info...
are you planning to dis-assemble for detailed photo's?
re-wind maybe?

Bad thing about it that this part with 6 bolts is not removable

Click to expand...

anything is re-movable....the lathe will wipe it right off :wink:

It will be lying around for some a while, not enough time on my hands... Maybe I'll get very curious and pop it open tonight.

Yes, it is doable with lathe. I do have lathe, so kinda not a huge problem. But still, it was easier with CA120...
Anyway my plan is to use it for controller development. Later on it would be nice to make a small geared motor out of it.

OK, some photos:
http://imgur.com/a/rfQCb#0

And some scope screenshots:
http://imgur.com/a/bmahw#0

I did not have the time to look for suitable controller and just that one tiny 3s ESC was lying around. It did run fine at 12 volts.
Battery current 4A at 100% PWM 12V; 3.13A at 50%. Phase current 3.3A at 100%; 11.4A at 50%. Values measured with cheapo clamp meter and can be off.
It runs quite silently, as far as this ESC can drive. Reasonably well balanced. Looks well built.

Electrically 10 eRPM / RPM (however coggs 120 times per revolution). This means that controller has to work up to 70k eRPM to rotate this up to 7k RPM. Kelly with high speed option could be enough.

Magnet thickness 2.0mm
Back iron thinckness 2.0mm
Stator diameter 100.0mm
Air gap 0.5mm
Gap between magnets 3.3mm
Stator/magnet length 37.5mm
Gap between slots 2.5mm
Slot width 10mm.


BTW, BEMF is very sine-like, so it is not the best solution to drive it with cheapo trapezoidal controller due to noise and efficiency. Here I've adjusted phase and amplitude for a sweet-spot (lowest losses for synchronous control):


1734 RPM @ 12, so 144 RPM/V. Close to 150 as advertised.

I got this in generator mode, hooked to drill.
I did some efficiency calculations based on this, but it's too early to show. Some other day maybe.

hey thx circuit for this great review, a link in the wiki would be worth a lot . sry i could not measure inductance, still got no inductance meter. no load current figures look promising, guess we'll have a lot of fun with this motor series. hope i can come up with some measurement on the 80cc model sooner or later. it runs smoother than the older turnigys 80-100 IMO, nice to hear it's suitable for the kellys!

Pics from the inside of 150cc:
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=46813&start=25#p691522

Gone any further with it? i'm wondering if anyone has got this thing spinning yet..

circuit said:

inductance 7.55-12.8μH depending on position.

Click to expand...

Why does the inductance vary with rotor position (aka, it has some saliency)? I've seen this behavior before for some other BLDC motor reports on this site, too. If the PM's have a relative permeability of 1, and the back iron is a basic cylinder, why does the stator coil's self flux linkage change with rotor position at all, let alone by 70%?

jdb said:

circuit said:

inductance 7.55-12.8μH depending on position.

Click to expand...

Why does the inductance vary with rotor position (aka, it has some saliency)? I've seen this behavior before for some other BLDC motor reports on this site, too. If the PM's have a relative permeability of 1, and the back iron is a basic cylinder, why does the stator coil's self flux linkage change with rotor position at all, let alone by 70%?

Click to expand...

dunno, but i can confirm i got the exact same numbers from a ca120 (but in Y) and the peaks and troughs were found at the rotors natural magnetic centering point, and the 'bump' that was hard to find the centre of and hold for a reading..

How about this hypothesis: Check out the FEMM run for a CA120 by Miles here: http://endless-sphere.com/forums/viewtopic.php?f=30&t=43306&start=50#p667907. Look at the stator teeth in the +/- 45, and +/- 135 positions. Note how the hammerheads are being used to short the flux between the two PMs. Since the heads are driven into saturation, then the circuit inductance for that phase would be lower than the ones at 0, 90, and 180.

Since the phases are wound like Aa, the self-inductance of one phase is driven by the loop that goes down one hammer shaft, across the two heads, and back the adjacent shaft. If the heads are driven into saturation by the magnets, then it effectively increases the gap along that path and also weakens the coupling between coils A and a.

Does that seem reasonable?

Thanks for sharing. I have a 4kwh nimh battery pack that I don't know what to do with and one idea that pondered into my head was to make convert a car into a mild hybrid with a BIG out runner like this. Having it bolted to the crankshaft to take some of the load off the engine and provide a big torque boost during acceleration. It seems both powerful and compact enough for that task

[youtube]oCFW7MHGLjY[/youtube]

This dude has spun it up with a hall sensor addon..

neptronix said:

[youtube]oCFW7MHGLjY[/youtube]

This dude has spun it up with a hall sensor addon..

Click to expand...

This motor is relatively quiet, how do you drive it 6-step or sinus?

This should not be as loud as it is in that video. And there are problems with commutation, one can clearly hear random 'misfires'. Still lots of work until it runs smooth.

circuit said:

For those who were wondering about Rotomax 150cc inductance, etc.

Received my rotomax 150cc today. Wires are a lot thinner than my old CA120, almost like 4-6mm². Phase resistance is 12mΩ; inductance 7.55-12.8μH depending on position. Cogging step is a lot smaller. Magnets thinner. Winding wires thinner. Stator slots shorter. It is ∆ wound. Bad thing about it that this part with 6 bolts is not removable, as in CA120.

Calculated values:
Power dissipation at rated 190A current: 433W (trapezoidal commutation, only in winding)
Power dissipation at rated 190A current: 325W (SVPWM commutation, only in winding)
Max RPM at 48V: 6860 (compensated on internal resistance)
Max theoretical power: 8.7kW
Max real power output: ~6-7kW

Click to expand...

I understand that 190A is taken from battery but how does it get distributed in the coils?
Does anyone know how much current flows through each coil? Or how I can calculate it?
How many turns are there for each coil?

Generator said:

I understand that 190A is taken from battery but how does it get distributed in the coils?
Does anyone know how much current flows through each coil? Or how I can calculate it?
How many turns are there for each coil?

Click to expand...

All RC motor controllers use only two phases at any given time. In this case each phase sees 2/3 of current (127A in average), however total motor current is still 190A.
Battery current is totally unrelated to motor current. Motor current can be 10 times the current of battery current, or more. The only law is battery current is always less. Read up "buck converter".

Hello,

Could you please tell me which diameter is between the 6 bolts? Are the bolts M5 or M6?
The question regards both RotoMax 150 and CA120-70