Exceeding max RPM on castle 1650 1717 on 6S??

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dk10438

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Arrma RC's
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Hi
I'm running a 1650 1717 can with an X8S ESC on 6S and I was looking at the data logs and I saw that my max RPM was 66,000 RPM but according to the Castle spec sheet max RPM is 56,000? I was thinking that the theoretical max would only be 24x1650= 39,600 RPM?
1. Am I missing something?
2. Any risk of damaging the motor if I really am exceeding the max RPM?
 
That's wrong,once in logging go to edit top left corner,change it to 4 pole motor an type in 1650kv...it's probly on 2 pole..
 
At 27volts the 1650 is at 44550rpms

Screenshot_20220728-234537.jpg

I thought RPM= KV x Voltage??
Kv+volts=rpms
 
That's wrong,once in logging go to edit top left corner,change it to 4 pole motor an type in 1650kv...it's probly on 2 pole..
yeah
was on 1100 KV 2 pole
do I need to change the gearing info as well? not sure what "specified gear ratio" is or "pinion/main gear" but I notice if I change these values then RPM changes as well....
 
yeah
was on 1100 KV 2 pole
do I need to change the gearing info as well? not sure what "specified gear ratio" is or "pinion/main gear" but I notice if I change these values then RPM changes as well....
Just set it to 1:1 or direct drive.
 
At 27volts the 1650 is at 44550rpms

View attachment 232663

Kv+volts=rpms
Here's a different formula for RPMs that takes into account the main gear ratio:

TOTAL RPM = (Motor KV x Total Volts) / (Spur Gear / Pinion Gear)
So for example with the 1717-1650KV on 6S (22.2 volts) with 46 spur and 22 pinion:
1650 x 22.2 = 36,630
46 / 22 = 2.09
36630 / 2.09 = 17,526 RPM
 
Here's a different formula for RPMs that takes into account the main gear ratio:

TOTAL RPM = (Motor KV x Total Volts) / (Spur Gear / Pinion Gear)
So for example with the 1717-1650KV on 6S (22.2 volts) with 46 spur and 22 pinion:
1650 x 22.2 = 36,630
46 / 22 = 2.09
36630 / 2.09 = 17,526 RPM
???
This makes no sense at all.
 
???
This makes no sense at all.
Same RPM calculation but it divides it by the center gear ratio to account for gearing changes. The plain RPM (KV X Volts) would be if you used 1 to 1 gearing. When you change the gearing on the center diff this formula takes that into account. Maybe it looks a little confusing cause I'm no mathematician but its really. Maybe I could've explained it better I guess
 
Tbh
I don’t understand how gear ratio would affect motor rpm. Seems to me gear ratio should only be relevant in calculating speed
 
As you gear up the rpms will get lower while speed gos up.voltage drop will go lower,amps, watts,ripple,heat will go up
That’s all true and gear ratios would be relevant when using measured RPM to calculate estimated speed OR measuring speed to calculate RPM

Seems to me the esc should be measuring rpm so gear ratios should be irrelevant
 
Same RPM calculation but it divides it by the center gear ratio to account for gearing changes. The plain RPM (KV X Volts) would be if you used 1 to 1 gearing. When you change the gearing on the center diff this formula takes that into account. Maybe it looks a little confusing cause I'm no mathematician but its really. Maybe I could've explained it better I guess
Ok, I see what you're trying to do but, that's not really how this works. If you just put the car up on a stand with the wheels free standing, the motor is going to spin up to or very close to Volts x KV, irrespective of gearing. The only thing that will change is the wheel speed. As @K-BASH was pointing out, as you gear up the RPMs go lower but not for the reason you're pointing out. The RPMs go down due to load, voltage sag of the batteries as they try to cope with the increase in load, wind resistance and a host of other factors.

Think about your formula in the following scenario: Reverse the pinion/spur tooth counts of the calculation you presented. That would be a gear ratio of 0.478 (an incredibly tall gearing which, in reality would result in much lower RPM than Volt x KV) which, by your own formula, should produce 76,631rpm...and it just won't. Don't take this the wrong way, I'm not trying to be a🍆 but, this is why I said that your calculation doesn't make any sense as it will break down at every turn and not align with anything you observe in the real world.

Just to flesh this out a little more, I was running my Infraction with a TP 4080 2022KV motor on 4S parallel with 20/46 gearing. When I ran the numbers from my data log, I was hitting 1960KV (divided peak RPM by voltage). This was due, in large part, to the over geared nature of a 2.3:1 center gear ratio which makes it very easy for the motor to turn resulting in much lower top speed which in turn produces much lower load resulting in much lower voltage sag in contrast to a severely under geared scenario as illustrated above.

I hope this makes sense and makes clear what is wrong with your formula and how it doesn't have any predictive capacity to what you'll find IRL. Again, I'm not trying to :poop: on you or be a Richard, just trying to help you understand where you've taken a wrong turn :)
 
I'm going to run car now on 5s,which is 21v fully charged..I keep it at 15v cause that's the voltage I expect it to hold during pull.on a good pass car will do 130-135mph..but yes I use calculator to see what mph gains gears will do an give

Screenshot_20220729-090737.jpg

That’s all true and gear ratios would be relevant when using measured RPM to calculate estimated speed OR measuring speed to calculate RPM

Seems to me the esc should be measuring rpm so gear ratios should be irrelevant
When my gps was down I used rpms to get a round about speed by using rpms...xlx2 rpms are very accurate..my mmmx8s an xlxare NOT accurate..I always confirm speed this way even with gnss.i drop volts on calculator to match rpms,then see is calculator speed matchs gnss speeed
 
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Ok, I see what you're trying to do but, that's not really how this works. If you just put the car up on a stand with the wheels free standing, the motor is going to spin up to or very close to Volts x KV, irrespective of gearing. The only thing that will change is the wheel speed. As @K-BASH was pointing out, as you gear up the RPMs go lower but not for the reason you're pointing out. The RPMs go down due to load, voltage sag of the batteries as they try to cope with the increase in load, wind resistance and a host of other factors.

Think about your formula in the following scenario: Reverse the pinion/spur tooth counts of the calculation you presented. That would be a gear ratio of 0.478 (an incredibly tall gearing which, in reality would result in much lower RPM than Volt x KV) which, by your own formula, should produce 76,631rpm...and it just won't. Don't take this the wrong way, I'm not trying to be a🍆 but, this is why I said that your calculation doesn't make any sense as it will break down at every turn and not align with anything you observe in the real world.

Just to flesh this out a little more, I was running my Infraction with a TP 4080 2022KV motor on 4S parallel with 20/46 gearing. When I ran the numbers from my data log, I was hitting 1960KV (divided peak RPM by voltage). This was due, in large part, to the over geared nature of a 2.3:1 center gear ratio which makes it very easy for the motor to turn resulting in much lower top speed which in turn produces much lower load resulting in much lower voltage sag in contrast to a severely under geared scenario as illustrated above.

I hope this makes sense and makes clear what is wrong with your formula and how it doesn't have any predictive capacity to what you'll find IRL. Again, I'm not trying to :poop: on you or be a Richard, just trying to help you understand where you've taken a wrong turn :)
No harm...no foul. I appreciate learning new things which is why I'm on the forum. I took this formula from an old article on RC RPM when I first started paying attention to motor KVs and gearing so I could try to go faster. I don't really use it to predict anything in detail but more of a guideline to determine what motors to try and what my gearing limits might be based on the motor spec max RPM. Hell...I need ALL the info I can get. I'm not one of these new young folk who are so damn sensitive they can't learn something new from somebody who knows better or has more experience. I'll be 51 soon so life has taught me quite a few lessons. An old saying I've picked up along the way is "A FOOL THINKS HE'S WISE WHILE A WISE MAN KNOWS HE'S FOOLISH" which I interpret to mean you can never be so smart that you reject learning new things. I appreciate you taking the time to explain it to me.
 
No harm...no foul. I appreciate learning new things which is why I'm on the forum. I took this formula from an old article on RC RPM when I first started paying attention to motor KVs and gearing so I could try to go faster. I don't really use it to predict anything in detail but more of a guideline to determine what motors to try and what my gearing limits might be based on the motor spec max RPM. Hell...I need ALL the info I can get. I'm not one of these new young folk who are so damn sensitive they can't learn something new from somebody who knows better or has more experience. I'll be 51 soon so life has taught me quite a few lessons. An old saying I've picked up along the way is "A FOOL THINKS HE'S WISE WHILE A WISE MAN KNOWS HE'S FOOLISH" which I interpret to mean you can never be so smart that you reject learning new things. I appreciate you taking the time to explain it to me.
All good brother, we're from the same generation and you clearly understood where I was coming from :) If I had taken you for a snowflake that melts at the first sign of dawn, I don't think I would have taken the time to explain it. It's just that after more than two decades of text based online communication I'm all too aware of its shortcomings and just try to reinforce my intentions in an attempt to head off misunderstanding before they occur. While I'm not always successful, my hit/miss ratio has improved considerably over the years. We're all here to learn and I'm always happy to share what I think to know and make clear when I'm spit balling, inferring, speculating or making pre-/as-sumptions.

"A FOOL THINKS HE'S WISE WHILE A WISE MAN KNOWS HE'S FOOLISH" << This could not be more true. We're definitely on the same page (y)
 
yeah, Diem Tuner is right
set the gear ratio to 1:1 or direct and the motor to 1650 4 pole
I did a couple of runs on 4S and pulled the logs
max voltage 16.1
max rpm was 25850 or something like that
16.1x1650= 26565

If I mess around with the gearing I get an RPM number that makes no sense.
 
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