P2 Supercharger Thread

Just got back in from testing in the garage. I posted in the VESC forum, but I'll copy and paste the same post here (too much data to re-type):

"Just got back in from the garage. We're making some progress. And it's starting to look like Frank was right (sorry for doubting you, Frank). With the new gearing, running the compressor into choke (i.e. max load) we were able to hold 9.1 kW and hit 18,900 impeller rpm (72,917 eRPM to be specific; 6 pole motor = 24,305 motor rpm * pulley ratio of .778 = 18,909 impeller RPM). Voltage was pretty solid at 58.5 volts (my batteries are monsters - at 60lbs (27 kg) they should be - unloaded voltage was just under 62). Battery current was holding steady at 155-156 amps. The motor current was the limiting factor - I had it set at 300 motor amps, and it got there and just sat there. Duty cycle was also pretty stable at 61%. The only thing that got above ambient was the belt. As I would expect pushing 9kW of energy through it. And it was just a little warm to the touch (maybe 20-25* C).

I'm not too concerned about the performance with the compressor in choke - it'll never run there on the car; so this is just a durability test. Just out of curiosity, what's the max I should run the motor current at? At 300 motor amps, it's a little high for the motor. At 95% duty cycle, however, that would put us at 285 motor amps, which is about it's rated max. Obviously, the best thing to do would be to find the optimal pulley ratio that's the best compromise on the running car. But that I need to test on the dyno - testing on a public street is far too dangerous. I probably should also machine the bore on the 16 tooth pulley and see if that gives us better on car performance; but once again, right now it looks like the 14 tooth pulley is our friend (also Frank's suggestion). Especially since there's so little voltage drop."
 
That's running the compressor into choke. With the 1" restrictor, we were already able to hit 30,000 impeller rpm with just 150 battery amps. On the running engine, it's somewhere between the two. I'll likely do a few more tests with the restrictor in place (though 30,000 impeller rpm in the garage is terrifying, even with the blast shield), and then hook up the arduino with your code in it and test that and then put the whole mess on the car.
 
I'm still missing one data point to be able to know what the running engine "equivalent" restriction size is. That's knowing what rpm we hit with the 14 tooth setup on the running engine. Then I can play with restrictor size until I find a match. Then we can really dial things in. And then it'll be easier to test the MGM/LMT setup too.
 
FWIW, just got it up to 90,000 eRPM with the restrictor in place. Using much less power - only about 4.5 kW. And seeing 69% duty cycle. I ran into current spikes again. Raised the observer gain from 350 to 500. Seemed to solve the current spike issue. I chickened out at 90,000 eprm. There's some issue with the mechanical aspect because it makes a noise at a certain part of the travel when turned by hand. I think it's related to the offshore sourced belt. I need to find a Gates 260mm belt. I'll take a closer look to be sure.
 
That's running the compressor into choke. With the 1" restrictor, we were already able to hit 30,000 impeller rpm with just 150 battery amps. On the running engine, it's somewhere between the two. I'll likely do a few more tests with the restrictor in place (though 30,000 impeller rpm in the garage is terrifying, even with the blast shield), and then hook up the arduino with your code in it and test that and then put the whole mess on the car.
my direct drive setup needs to hit 60,000 rpm.. which the thought of scares me.. i need to have 120kerpm then.. i hope my china one can do that
 
It might. The VESC does a lot of calculations for each firing of the coils; regular BLDC control is much simpler.
 
Lol - as an admin I can see your deleted post, cmoalem. The bigger VESCs are soon to be released - there's already a number of them made. A sensored motor is definitely a benefit for startup, but once it's spinning, the sensor isn't used past a certain (relatively low) rpm. The VESC's id function and messing with observer gain goes a long way towards not needing a sensored motor. If using an MGM ESC, then a sensor would be almost mandatory, I would guess. But the 75/300 VESC seems to be plenty powerful, as long as current spikes are kept in check. I was able to run at 400 motor amps at about 42% duty cycle without the VESC getting warm.

In any event, I was finally able to get the thing up to max rpm/duty cycle. I posted the same thing in the VESC thread. I'll copy and paste it here just in case someone misses it over there:

Two nights ago I was able to get things up to about 125,000 eRPM. I raised the frequency to 40kHz, and played more with observer gain. We hit 94.4% duty cycle (max is 95%). This is with the 1" restrictor in the discharge. The motor pulley and the belt get the hottest. This was with a 14 tooth motor pulley and 18 tooth impeller pulley. Impeller RPM is 32,400. Now I just need to make sure it's repeatable and can accelerate quickly - then time to install it.
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The downside of the belt drive is starting to show up in the form of heat. The motor pulley gets rather warm pretty quickly; the belt does too, but to a lesser extent. I spoke with Jon at Jon Bond Performance (they rebuild superchargers). We briefly spoke about the old Powerdyne BD-11 blowers that used an internal belt drive. Apparently what they discovered is the teeth in the belt drive itself would compress the air between the belt and the pulley as it spun, causing heat build up. Their solution was to cut grooves in the pulley around it's diameter to give the air more room to escape. I'm not sure in our applications it's as big of an issue, since our setups aren't spinning all the time and they're not totally enclosed. But I did hit the pulley with compressed air from time to time between runs to keep the pulley temp down just to be safe. Also, at lower speeds, it's significantly less of an issue. Like not really at all when I was running the max load tests (no air restrictor, running into choke, much lower rpm; even though motor current was much higher).

I think with a real Gates belt this issue would be somewhat alleviated; and if necessary, we can do the groove thing too. We're not pushing a lot of torque, but we are pushing a lot of rpm.
 
yep ... I have seen those groved Powerdyne pulleys (for rebuilds) on ebay some time ago. The grooves supposed to help with the noise as well! (wheeeEEEEE)

and yes ... the sensors on a emotor are more for the low rpm AND STARTUP sync! BUT ... even if you play with the throttle curve (to limit abrubt start stress) ... I predict you want to minimize lag and will need an aggressive/progressive throttle curve. And here the sensors might come in handy 😉
 
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cmoalem - I do have to say that for the most part, the startup with the VESC is much better than any other ESC I've used with this motor. The bigger concern I'm having is consistency. I'll try to do more testing this weekend and see if it's stable.

MakingStuffAwesome - I could attach a fan, and it has crossed my mind, but I'm concerned if anything gets on the belt when it's not running. Let's wait and see f it becomes an issue in actual use. Right now I'm just trying to be cautious and I am running it more often and probably faster than it will on the car. Plus, there's always the groove thing to try.
 
That, sir, is a brilliant idea. Even if it's warm from compression, by the time it leaves the nozzle, it should be very cold. Simple & effective - like I like my women!

j/k


sorta.
 
2028 800kV sensored. I bought it because they told me the price was going up. Ironically, still cheaper than the TP Power motor. The Castle Creations tech guy told me he's run that motor at 20kW for short bursts. And I learned all about RC drag racing and it's sanctioning body...

We'll see.
 
I didn't know Castle offered that. But no. And in my case, I don't really feel it's necessary. I'd rather use water cooling if I need any cooling. But I don't think I will. FWIW, the motor showed up today.
 
Hey Alex,

Is there any way you can take the dimensions of the P2 for me?
If you go here:

and scroll down to "Dimensions" ...
 
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