I’d up the motor temp start and end cutoffs. Those reachers are pretty durable (well the Radium 6385s are at least). I have mine at 100 start, 115 end
sweet! always wanted to build a in board charging harness and expose the balance leads for easier checking. i didn’t want to perma join the balance leads. dual db15 is a great idea for that. 
W00t. congrats on huslting around that big ol track.
probably 'cause he had one motor. 4 is handicap apparently. 
/s
maybe you’re running into the iron losses thing @Skyart and @Tony_Stark were informing me of over on my v5#1 thread.
rpm based eddie currents from high rpms? though at 12s i’m not sure that’d be it. but if it gets worse with lower gear ratio… maybe? (seems unlikely)
did you record graphs of temps? are they stable or jumping around? maybe just move motor temp cutoffs the f out th eway and risk the life of the motors. 
definitely do that if they are noisy. (tho noisy temp sensors would feel jittery when the power cutts rather than smooth )
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and you are using the watts… so… bringing the heat?
it’s curious to me why you’re using so much. with 4x motors I’d expect some ineffeciency… but for it to tend closer to watts = mass * acceleration * distance. so it’s weird.
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This meshes with what I felt on track very closely, especially after coming off the track.
Very interesting.
Aye, I’d agree…
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With 4wd compared to 2wd total copper heat loss is halved, but copper heat loss per motor is actually 1/4, because P = I^2 * R
Really surprised you heat the motors so much…
Is your acceleration something stupid like 1G+?
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We don’t have a dyno chart for your motors, but it makes me wonder if you’re too far down and to the right on the efficiency map, where the efficiency drops like a rock.
At your top speed of 60MPH you need about 300N of thrust, depending on how much air resistance you’ve got. With your current setup that translates to 1.6N-m torque per motor, round it up to 2N-m for rolling resistance and iron losses.
The 6355 is half the weight of your motor, so that should be analagous to 1N-m on this chart, which would put you about here:
So it might be fine, but it’s close to the edge of the efficiency band. Given the uncertainty here you might be over the cliff, trying to push power through unloaded motors. I’d imagine that just going from 90% to 80% efficiency could get your gourd properly borked.
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welp. elsewhere in chat @tuckjohn mentioned getting temps up slowly to 95c … so. that’s pushing em pretty far. since/if? they aren’t short spikes moving the temp cutoffs out the way is probably not too helpful.
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Okay, so looking at this again after a couple nights of restful sleep.
@s_m_l_s_ is really putting in the work to make my board look good! Thanks man. Your photos are one of my favorite parts of race events.
No data recording on the board at the moment. I’m waiting on the Voyage systems Megan for logging on my board (Autumn 2023? I know It’ll drop when it’ll drop, I’m just too excited 
@janpom)
Unfortunately not. I mean, it’s quick off the line compared to a normie board when the motors aren’t overheating, but not 400 motor amps quick.
Very interesting information, and a promising theory. I can follow the argument that going from 90% to 80% efficiency could be the difference between fine and overheating.
However, efficiency != heat generated, right? Unless I misunderstand the graph, In the condition that the motor is along the bottom of the graph, the current going through it is small, so low efficiency*small number = small amount of heat. Whenever the motor starts to get/output appreciable power, the torque will increase, leading to an increased efficiency.
Would this make “living on the bottom edge” of the efficiency band fine? I also took a look at your “Total losses” graph in your Dyno thread, which seems to say the same thing.
This is really seeming like it could part of the issue, and hope it’s not. I think the best solution would be to get smaller KV motors to reduce the iron losses. That would be an unfortunate purchase I’d need to make. 
Considering the relative cost of pinions and new motors, I’ve bought smaller pinions that should arrive next week. I’m really hoping that the issue is just that the motors are over-geared, and just putting smaller pinions on the motors will solve the issue. Both of your proposed hypothesizes @fessyfoo and @Flyboy suggest that reducing the pinion size is going to make the overheating worse, so I’m excited to put them on and see what happens. For SCIENCE! It’s going to be fun if I’m proven wrong.
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These are 2 different languages for describing the same physical phenomenon, in this case the efficiency would be low because the iron losses are high. I was trying to quantify whether it was happening, and you’re right that I haven’t proven anything other than that the problem isn’t copper losses.
Efficiency IS defined by what fraction of the energy goes to heat, and cruising at 300N and 60MPH you’re looking at over 2kW per motor. 80% efficiency would mean 400W of heat per, but looking at the core losses chart, it actually looks improbable that you’re losing much more than 100W to the core. So maybe idk what I’m talking about lol.
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I have no idea what’s going on here, but i’m almost positive that i’ve seen someone else here say that the 7490 motors run really hot…
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Massive stator has massive losses 
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Easy enough to try it at a lower voltage with lipos isn’t it? Give them the amps at 8s?
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Awesome build! I’m also jealous of your one post build, forum mic drop.
(Get back in here and revise and tinker and post! you know you want to, the mic is right here… just waiting for v2 
)
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What motor kv are you running?
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This thing is insane. You’re like me if I had more money and let my intrusive thoughts win🤣. No fr tho, incredible work bro!
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Ok, here’s my take. @tuckjohn the TLDR, is that you have unusually high iron losses. Your motor RPM doesn’t seem that high, but your ERPM is very high compared to most builds, because you’re running 10 pole pair motors instead of 7 pole pair.
This build is on 265kv, and at 12s that’s only around 10,500 loaded motor rpm. Not crazy high.
Although iron losses will be higher on 20 pole motors vs 14 pole, because higher ERPM. With 20 pole motors you have 42% more ERPM vs 14 pole, at any speed.
- 7 pole pairs * (265kv * 50.4v * 0.95) = 88,817 ERPM
- 10 pole pairs * (265kv * 50.4v * 0.95) = 126,882 ERPM
126,882 ERPM is technically possible for VESC, but it is higher than most of us run.
Switching losses and iron losses could both be significant factors on your rig’s inefficiency. Important to note that iron losses are not linear. At high speed they square, so they increase more than you would expect. Based on the fact that you said these motors are heating up like crazy, this tracks with my theory.
My theory also tracks with your observation above. You’re battling iron losses, not resistive losses, so lowering amps doesn’t do very much.
It will be easy to test this / fix this, but it will cost $$$:
If you acquire 4x 6395/6380 motors at 265kv, everything about your build would stay the same, but you’d immediately lower your ERPM by 42% (and thus iron losses would be much less, and you wouldn’t overheat anymore).
It sucks to spend the money, but that’s what I would do. I don’t think you’re going to be happy long term a with a race board that hits thermal throttle at 85c and let’s others pass you.
For shits and giggles, you could take a video screengrab of VESC tool with your motors spinning up to full speed under no load (wheels removed). It would be interesting to see how many watts you’re pushing just to keep the motors at top speed.
I hope that’s all helpful. If I’ve botched something I welcome corrections.
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Yup, same page with you on everything, it makes sense.
It’d suck to buy a whole set of motors… If I had to do that, I’d probably buy the 7490 179kv or 135kv. Reduce the overheating problem just enough that I can last a full race- and part of me like the absurd motor size
Next time I take this board out to the track I’ll do this.
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