Paralysis by analysis - motor/esc for kyosho optima reissue
#1
Paralysis by analysis - motor/esc for kyosho optima reissue
Hi all. Thanks in advance for the help. Getting back into the hobby after 30 years with a new optima kit in transit as we speak.
I want to utilize the modern amenities so I'll be running it with the belt drive and 2s lipo power. However, I can't make a decision on motor. I want to run a brushless, and would like the car to be a ripper... But I don't want to be breaking it constantly. I've seen the YouTube review in which the guy puts an 8.5t motor in it. On another forum a guy is saying no lower than 17.5t. The whole 2 pole vs 4 pole thing has me flustered too..
I have my eye on the hobbystar motor/esc combos. 3500kv or 3100kv? Or am I on the wrong track completely? Would like to be around $100 for a combo. There won't be any racing, just bashing around. Also trying to avoid soldering cause I sucked at it when it was building kits at 12 years old and still suck at it, ha.
I want to utilize the modern amenities so I'll be running it with the belt drive and 2s lipo power. However, I can't make a decision on motor. I want to run a brushless, and would like the car to be a ripper... But I don't want to be breaking it constantly. I've seen the YouTube review in which the guy puts an 8.5t motor in it. On another forum a guy is saying no lower than 17.5t. The whole 2 pole vs 4 pole thing has me flustered too..
I have my eye on the hobbystar motor/esc combos. 3500kv or 3100kv? Or am I on the wrong track completely? Would like to be around $100 for a combo. There won't be any racing, just bashing around. Also trying to avoid soldering cause I sucked at it when it was building kits at 12 years old and still suck at it, ha.
#2
Tech Addict
iTrader: (1)
The 2 pole vs 4 pole question...based on my observations, the formula for motor RPM is KV * voltage * (poles/2) = motor RPM. So 3500kv 4 pole motor on 2S power spins at 8v*3500*4/2= 56,000rpm.
It seems that the sealed can brushless motors are designed to run right up to 60k rpm.
By comparison, I have a 6.5T 540 motor that turns at ~40,000rpm on 2S. That'd make it a 5000kv 2 pole motor.
I ran a 13.5 briefly on indoor oval, and if I remember correctly, it was running around 20k rpm. But it is a little fuzzy now.
It seems that the sealed can brushless motors are designed to run right up to 60k rpm.
By comparison, I have a 6.5T 540 motor that turns at ~40,000rpm on 2S. That'd make it a 5000kv 2 pole motor.
I ran a 13.5 briefly on indoor oval, and if I remember correctly, it was running around 20k rpm. But it is a little fuzzy now.
#4
Tech Lord
iTrader: (252)
The 2 pole vs 4 pole question...based on my observations, the formula for motor RPM is KV * voltage * (poles/2) = motor RPM. So 3500kv 4 pole motor on 2S power spins at 8v*3500*4/2= 56,000rpm.
It seems that the sealed can brushless motors are designed to run right up to 60k rpm.
By comparison, I have a 6.5T 540 motor that turns at ~40,000rpm on 2S. That'd make it a 5000kv 2 polez motor.
I ran a 13.5 briefly on indoor oval, and if I remember correctly, it was running around 20k rpm. But it is a little fuzzy now.
It seems that the sealed can brushless motors are designed to run right up to 60k rpm.
By comparison, I have a 6.5T 540 motor that turns at ~40,000rpm on 2S. That'd make it a 5000kv 2 polez motor.
I ran a 13.5 briefly on indoor oval, and if I remember correctly, it was running around 20k rpm. But it is a little fuzzy now.
#5
Tech Adept
Make sure you're looking at sensored motors. Sensorless is frustrating and annoying. I would recommend a HobbyKing 13.5 setup. However you will have to solder it. Maybe there is a track or other hobbyist nearby that could help you with it?
#7
Tech Addict
iTrader: (1)
Actually, based on my first hand experience using the data logging capability of my Tekin ESCs....
2000kv 4 pole T8 (4038) on 4S peaks at ~65000rpm. Per data logging data.
1350kv 4 pole T8 (4038) on 6S peaks at ~65000rpm. Per data logging data.
Math:
2000*(4/2)*16.8v = 67200rpm.
1350*(4/2)*25.2v = 68040rpm.
In this calculation I am using the voltage of a fully charged battery, not the nominal pack voltage (i.e. 14.8 or 22.2). This gives the theoretical max RPM, but it is unlikely to reach this number in a driving situation.
Working out wheel speed of my truggy based on motor RPM:
60,000*(16/46)*(10/46) = 4536.8 rpm (wheel rpm)
5.55"*(1'/12")*3.1415 *4536.8rpm = 6592 ft/min
(6592'/1min)*(60min/1hr)*(1mile/5280') = 74.9mph
Now, the big question...how fast is my truggy actually going? Considering the fact that most of the time peak rpms are ~40,000, only occasionally peaking at 60,000+rpm, I'll say that yes, these numbers are completely accurate.
#8
Tech Fanatic
iTrader: (1)
If you are wanting to stick with the whole 'retro' them, while still going with current (BL/sensored) tech., look into the Kyosho Le Mans '240S' 15T brushless motor.
KYOSHO RC MODEL LE MANS 240S Brushless Motor (15.5T/4WD) 37032
There is a similarly marketed Kysoho 60 amp Le Mans '240S' sensored ESC - though personally I don't know who the underlying manufacturer therein is. At a minimum, the 15T motor would be a solid part of this combination.
KYOSHO RC MODEL LE MANS 240S Brushless Motor (15.5T/4WD) 37032
There is a similarly marketed Kysoho 60 amp Le Mans '240S' sensored ESC - though personally I don't know who the underlying manufacturer therein is. At a minimum, the 15T motor would be a solid part of this combination.
#10
Don't get a 4 pole, its too much torque for this buggy.
17.5T is a bit hard to gear right, unless you can custom make a smaller spur. 13.5T is about right. Don't need more motor and sensored of course
17.5T is a bit hard to gear right, unless you can custom make a smaller spur. 13.5T is about right. Don't need more motor and sensored of course
#11
Tech Lord
iTrader: (252)
That 240s retro looks sweet but spendy sompared to some others but I remember when that was the hot motor from Kyosho. Not sure why 4 pole is too much ? 4x4 power hungry I would think a 4 pole would hit the spot but then again last time I ran one I ran a 360pt motor in one with a 6cell nicd lol.
#12
I've tried a few motors in my optimas and think the 13.5t is perfect. Currently running a SP reventon R and SP 13.5. That lemans looks sweet though...
#13
Tech Addict
iTrader: (1)
Are you saying that Tekin is a liar, or that their equipment lies about it's RPM?
The RC world is full of half truths, misconceptions, and flat out false beliefs. Can we abandon the dogma and be enlightened by the facts? When facts and belief contradict, sometimes it is because the beliefs are wrong, no matter how often they are repeated!
The fact is that this definition you are using, which a lot of people believe is true, does not work on 4 pole motors!
1) As I have clearly shown, actual rpm of my 4 pole motors, as recorded by my ESC, is exactly double what the over-simplified definition of KV would indicate.
2) Calculating backwards from actual wheel speed, factoring in gear reductions at the differentials and spur/pinion, confirms the motor RPM indicated by my ESC.
If this was an issue of "some variables", it would be a difference of a few percent, maybe 10%? But if the KV is meant to represent actual motor RPM, it'd take a moron to not notice that his motor is spinning twice as fast as he says it does.
I think it is plainly evident that "kv" represents the strength of the inductance of each pole. So more poles = more rpm. I've proven this.
And contrary to popular belief, torque is actually the same before gear reduction. Torque comes from inductance... The belief in greater torque comes from when the 4 pole is geared down to the RPM of a 2 pole, it effectively produces twice the torque. But it gets that torque through doubling RPM, not by increasing the strength of the inductance of the motor.
This is my understanding based on observable, testable info. If you think it is wrong, please present information to back up your claim.
#14
Tech Lord
iTrader: (252)
Simple question for you. 2wd slash stock 3500kv vxl average 30to35 mph same gearing with castle 4 pole 3800 wheelies more but is not twice as fast. By your theory it should be approximately twice as fast. I am not talking bad about tekin. I have 4 of their esc's. Maybe I'll toss an rx8 in that slash and see what it says.