P2 Supercharger Thread

Oh the other thing is that if YOUR at 100% duty if you didn't have enough "power" you could get more power out of the motor by increasing the load "motor slow than impeller" If your already at 100% and dont want to change the gearing then you'd have to increase voltage or KV which both cost something.

Form an efficiency point of view it would seem that "loading" the motor and running at say 50 Duty is about the worst thing you can do... your better off to unload the motor ( say 1-1 ) and run at 100% duty ... If you can get there at say 75% then youd be better off to to gear it the other way ( motor faster than impeller )

The question does remain though......... in a drag car does electrical efficiency even matter ( probably not )
 
I think I dont really understand the part of duty cycle, load, the KV thing. That's part of my language 🤪 can someone explain in one simple line? I think im lost
 
I think I understand now. You have more chance to get your 30k impeller rpm by unloading the motor with a 1-1 gear then hoping the motor have enough torque to run a 1-1.25 gear. Is that it?
 
You're on the right track. By giving the motor a "gear reduction" (small motor pulley, larger impeller shaft pulley), we can raise the RPM of the motor. And raising the RPM of the motor increases duty cycle. And as MakingStuffAwesome says, the worst place (hardest on the ESC) to run is at 50% duty cycle. Right now, with the compressor running at max load (choke), as you see in the screen shot on the previous page, we're only at 45% duty cycle - the hardest zone for the ESC to live in; it also keeps the "total system power" down. As duty cycle increases, motor amps and battery amps get closer together. At 50% duty cycle, motor amps are double battery amps. And that limits max power into the system as a whole. If we could get to 100% duty cycle (not really possible, but 95% is; but let's use 100% for the sake of clarity), then motor current and battery current are the same.

Let me put some numbers to it: at 50% duty cycle, 50 volts and 100 battery amps, you'll see 200 motor amps. But total power in the system is "only" 5,000 watts (volts X battery amps = watts). If we change nothing but the duty cycle to 100%, the motor's spinning twice as fast, and you'll see 200 battery amps AND 200 motor amps. Total power in the system is now 10,000 watts! Before you had 50 volts x 100 amps = 5,000 watts; now you've got 50 volts x 200 amps = 10,000 watts.

That's important because we need to get to maximum duty cycle to maximize power in the system, and therefore maximum impeller speed.

Towards that end, I ordered an assortment of pulleys and belts to play around with and see what that sweet spot is. And every setup will be a little different because every engine has different airflow characteristics. That's really one of the great things about the P2/belt driven setup. You can tune it precisely for your needs and to minimize load on the ESC.

Oh, my MGM/LMT stuff showed up today. Just a little side note.
 
"duty cycle" is a nerd way of saying throttle percent.
"KV" is now much RPM you get per volt.... so 1000kv gets 1000 rpm per volt so at 50v that 50,000 rpm ... a 2000kv motor at 50v gets 100,000. HOWEVER this is an Unloaded Motor ... Free reeving... nothing attached to the end of the motor ( no load )
100% loaded would be if it was bolted to a immovable object.. and that despite giving the motor 100% power/duty cycle / throttle percent .. the object doesn't move.

Now one of the observations from my previous post was ....

If a 1000kv motor gets you 50,000rpm at 100% throttle that would theoretically be the same as a 2000kv motor at 50% Throttle.. 2000*50/2
While this is theoretically true both have 50,000rpm ( unloaded ) The efficiency it not the say.. The first motor running at 100% has a greater efficiency and therefore longer runtime and less heat.


The next part was ...well what if we need 75,000rpm .. Which neither of our examples can achieve at 100% 50k or 100k. What is more efficient to take the motor that can only spin to 50k and gear it to allow the impeller to turn at 75k (motor slower impeller faster). or the opposite.. take the 100k motor and gear it to the same 75k (motor fast impeller slower)

Both are theoretically the same again as both get to 75k but from an efficiency point of view it seems the second one where the motor spins faster than the impeller (less load) will result in better efficiency.
 
Oh to be clear im talking about electrical efficiency.. defined by.. the amount of electrical power (watts) sent to the motor V that actual amount of torque applied to the load...greater the efficiency the longer the run time ( lower amount of electrical power required to apply the same torque).. And as i have said before it probably doesn't matter to Alex as all he needs is 10 seconds

Im not at all talking about what would give you the most electrical power consumption. Or which applies the most Torque to the load.

For the direct drive group guys this can all be summed up with... make sure you dont have a KV that is to high and your throttling it back. This will be less efficient than getting a lower KV and running it at 100%.
 
Now I totally understand, wow thanks guys! In the mgm datalog, I've never see duty cycle. But I saw motor AMP and battery AMP.. so will take a look at this!

I ordered my pouch cells yesterday! They will show up this year AHAHAH long stoey for the shipping.. I had to chose between 450$ shipping for 5days or 170$ shipping for 50days.. I take the low shipping cost 😂
 
Wow... even $170 shipping is crazy.

I had a question, so I wrote this stuff below. Going through the process of writing it, I figured it out. Rather than just delete it, I figured I'd post it anyway, since it might help someone understand this stuff better (or make it more confusing, but hey - it's data and analysis; that's always useful):

"Going back to the duty cycle thing; the one thing that I'm still not really understanding completely is that duty cycle and KV don't really correlate. What I mean by that is that in my case, my actual RPM doesn't match my expected RPM based on duty cycle and KV.

Going back to the VESC log:
vlcsnap-2022-02-10-02h59m17s249.jpg

This one is with the restrictor in place. Battery voltage is 56.3. Duty cycle is 62.4%. eRPM is 70,931. If we divide eRPM by the number of pole pairs (3), we get 23,644 motor rpm. If we multiply battery voltage times duty cycle, we get 35.13 volts. My motor's kV is 750. If we multiply kV by actual voltage based on duty cycle, we get 26,347.5 calculated motor rpm, for a difference of 2,703.5 rpm less.

Now let's apply the same math to the unrestricted datalog (where the restrictor was removed and the load increased dramatically):
vlcsnap-2022-02-10-02h59m41s217.jpg

Here we're seeing an actual motor RPM of 14,413. But based on the duty cycle/voltage, we should be seeing 19,347 motor rpm; for a difference of 4,934 rpm less.

I realize that kV represents unloaded speed, and we've seen a much larger drop going from less load (restrictor plate) to more load (no restrictor plate); both numerically and a much larger drop proportionally (~10% vs ~26%). That makes sense.

Duty cycle should correlate directly with actual rpm, shouldn't it?

But looking at the two graphs, only kinda-sorta. Looking at it from a "per-percent duty cycle" vs RPM, the heavier loaded graph is lower by about 20%... oh, nevermind; I get it now..."

So what I've realized at this point is kV isn't a fixed number and I wasn't taking that into consideration. Unloaded kV is one thing (and what you see when you're buying your motor); lightly loaded kV is a bit lower, and heavily loaded kV is lower still.

Let's look at these graphs and put some kV numbers to them.

The motor's advertised kV: 750
The motor's lightly loaded kV: 673
The motor's heavily loaded kV: 559

On one hand, this seems obvious. On the other hand, we now have actual numbers to put to the theory, and it also explains a lot. So if I go with a step-down ratio on the motor, rather than a step-up ratio, that should lessen the load on the motor as well as allow for much more RPM and a higher duty cycle. At least that's the current theory and why I think cmoalem was right and I was wrong. Also, keep in mind that I'm over-currenting the motor by a good bit. The motor's rated for 283 amps; we're pushing 400 amps in both tests. One thing I don't know is if that 283 amp rating is an absolute number, or an average. In other words, if we're pushing 400 amp pulses through the motor at a 50% duty cycle, does that mean (from a manufacturer's rated current perspective), we're pushing 400 amps or 200 amps?

So now it's finding the optimum balance; which we can get somewhat close to with bench-testing, but until it's on the car, we won't be able to find the optimum balance for that particular engine. That's why I ordered 16, 14 and 12 tooth pulleys, and a 255, 260, 270mm belt. Watch - with my luck, I'll need an 18 tooth pulley, and optimum will be 1:1 - where we started with version 1... that would be my luck.
 
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There is another question - why is it stuck at 150 battery amps in both graphs? My battery amp limit is set to 220 in both graphs.
 
it is interesting that the Motor current is so much higher than the battery current ( Average ) though that makes sense since motor current is alternating. Apparently really High AC current relative to DC current is a function of having to higher KV and throttling it back (lower efficiency).. which for this example is the case 45% duty = the 400amps... ( interesting test but wont be achieved on the engine )

So that raises the question ... when ESC's are rated are they rated at the DC or AC load.. I would think most people would assume the DC load but their probably not as.. the peak current of the mostfets is probably in reference to AC load.... but without this kind of real time data whos to know what the current AC load is......

The filer ESC's ere problayb massively overloaded lol

The loaded testes .. they were all low battery currents and not at 100% duty .. not sure why you didn't man up and run them at a higher duty.. which surely has to be the goal ? ... i assume the idea is to apply 400DC amps at red line at WOT..
 
I think there's a bug in the VESC that's limiting the battery current to 150 amps after I doubled the observer gain to prevent the current spikes (I think doubling the observer gain had a bigger impact on the current spikes than anything else, to be honest). I may have to run this setup with the MGM ESC just to prove a point.
 
AlexLTDLX said:
I think there's a bug in the VESC that's limiting the battery current to 150 amps after I doubled the observer gain to prevent the current spikes (I think doubling the observer gain had a bigger impact on the current spikes than anything else, to be honest). I may have to run this setup with the MGM ESC just to prove a point.
Click to expand...
yeah have you found out what that is meant to do lol ? (that gain )
 
It's got something to do with how it estimates the position of the rotor using FOC mode. That's as much as I know.
 
AlexLTDLX said:
It's got something to do with how it estimates the position of the rotor using FOC mode. That's as much as I know.
Click to expand...
... and if you feel comfortable to dive in here the wizards were discussing the topic 2 years back ... just before the version 5 frimware:

Factors of VESC motor detection and operation with 3rd Party Hardware | VESC Project

vesc-project.com vesc-project.com
needs really fresh memories of some electrical/physics classes ... ahhem

btw ... paltatech are working on real high power versions of the VESC

oops ... this belongs into the VESC thread 🤒
 
Oddly, it's really not *that* foreign to me (it would've been a month ago). As far as the observer gain issues are concerned, they're what I've found - larger motors and a lot of inductance in the power cables tend to give erroneous readings. The other stuff doesn't really apply to my setup. The biggest issue is that Frank and I are having a "disagreement" via email about the 150 battery amp limit. Given all my data (not just from VESC, but also from the APD logs), doubling the observer gain for whatever reason is capping battery current at 150 amps. He thinks (pretty solidly) that the motor's torque limited. I'm sure it is at some point, but before I doubled observer gain, I was actually able to go above 150 battery amps (then I got spikes - but I could hold 160 amps without spiking; above that it would spike.) That was also reflected in higher duty cycle (by 6%), higher eRPM (by a bit over 2,000 eRPM) and less motor current for the same gains.

Nevermind that verson 1 (the Vortech based unit) hit the same impeller RPM while boosting my engine as this one can with a 1" restrictor - much less load, relatively speaking.

This can easily be proved. All I have to do is try the MGM ESC with the P2 setup (see how I'm bringing this back around on topic? Slick, huh?) Of course, I don't want to risk hurting the MGM ESC, but if I'm careful, I should be able to do it. And I'm going to bet that it blows past the VESC. Of course, I'd do a video on that, but I really don't want to make anyone look bad. Another option, which I haven't looked into the details of how to do it, is to simply try running the VESC in BLDC mode. That should give me more RPM anyway (potentially 5% more; since FOC is capped at 95% duty cycle, and BLDC can hit 100%). The APD setup was pretty consistently around 90% duty cycle. And that I think was actually torque limited.

I'd be much faster with all this experimentation if it didn't carry the risk of destroying hundreds if not thousands of dollars worth of stuff... besides, I still have to shoot the MGM/LMT unboxing video.
 
yeah ... somehow my gut feeling is telling me the MGM/LMT combo is less complicated to "dial in" on the P2. (unscientific for now ... would take some time to explain and might be subjective here and there)

But what I am particularly interested in would be a VESC/LMT combo on the P2... how THAT would get along 😛 ... and does "sensored" actually help dialing in FOC and can it keep up with those relatively high erpms (well ... the 2pole LMTs would give you eRPM==motor shaftRPMs, but still)

To be honest: despite the "technicalities" and "cognitive complexity" with the VESC: I still beleive it is a bad ass ESC ... the impemented protections/failsafes have so far prevented desintegrating the power stage (I love those errors being triggered shutting down the power stage in your videos ... my inner eye saw always a smoking and arcing pile of Flyer remains)... and your time spent digging and discussing parameters with Frank certainly have added to your knowledge and insights!
(yeah ... still needs a high end "end user"!)

Having said that: check with Frank if BLDC mode does have all these watchdogs in place monitoring and protecting the power stage ... from the discussions I read on the VESC forum I had the impression "not quite!"!
 
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Im with cmoalem... the VESC seems awesome .. Better than the MGM .... But it is the most expensive so thats to be expected...
It seems like you can take assurance that it wont catch fire.
Also i personally love all the nerdy stuff with it...

The APD seem to be the worst .. because despite their high price they are still garbage.. They make the flier ones look good... and im sure they might still be ok for lower power systems with short cables
 
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All of this (particularly at this power level and these rpms and not in proprietary systems) is still very new tech. I actually like APD a lot. The first ESC performed exceptionally well, esp. given it's size. It's apparent there were some teething problems. But what makes APD stand out is the people behind them. I really, truly, sincerely would love an opportunity to try out some of their new products. None of these are perfect yet (I haven't tested MGM yet, and the delay in getting it was really out of their hands, so I won't pass judgement - they could very well be #1).

Right now it's becoming more an more apparent that VESC is still a work very much in progress. The links cmoalem finds on the VESC forums are gems of knowledge (how does he find those things? I try and I don't come up with stuff that good). Frank and Benjamin are doing their best to be evangelists for VESC, but right now they're failing on the user experience front, which will kill their ability for mass-market penetration (speaking from a professional point of view - I was in advertising, as per my university degree - heck I used to do VW and Mercedes commercials - "Drivers Wanted" anyone?)

That doesn't mean it's a bad product or that Frank or Benjamin are anything other than good people. They're really trying. But they went big too soon and without the necessary resources. Their situation is actually a bit worse than Megasquirt's. The FOC side of things still, quite frankly, needs a lot of work. It's very impressive, but if you read the last thread cmoalem linked to, they're still finding fairly significant calculation errors and other not-yet fully formed things that prevent it from being a real star. The more I learn about FOC, the more I'm beginning to think that is has no benefit to our needs and is, in fact, a hinderance (95% duty cycle limit, and generally less power, apparently; and what it does bring to the table - low-speed control and slightly quieter running are non issues for us).

Even if we throw VESC's FOC away and use it purely as a BLDC controller, it still has a lot of appealing points for us. It's price point for what amounts to a premium, feature-packed unit (features that work as intended) can't be beat. All of those features - real-time data, multiple control options, excellent current limiters, 900 amps worth of good quality MOSFETs are all major pros. It seems to be a really good match for the 650hp and under crowd. The real-time stuff and current limiters are the real stars for us. Testing the way I've been doing it - using the actual cables and such in the car - is something we really couldn't do before; certainly not to this degree of precision. I really need to do some BLDC testing, because that's something well understood at this point, and hopefully will result in the performance we're looking for.

The MGM/LMT stuff should be like a diamond-encrusted sledgehammer (in fact, "sledgehammer" is what I intend to call the MGM/LMT/Vortech setup). Expensive, but it should just work. It's my machining and fabrication that's likely to be the weakest link there. But again, very expensive. But also very powerful. The MGM/LMT setup costs triple what the VESC/TP Power setup does.

But we will all find out as soon as I can get this stuff together. If I didn't have life getting in the way, development could easily be twice as fast. I LOVE THIS STUFF.
 
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