Sensored RPM Limit

[Powdersummit]

I'm planning on building a Mid drive unit with a brushless outrunner and a 10:1 planetary gearbox. I would like to go with a sensored controller and fit the outrunner with halls. I am having a hard time finding what the electrical RPM limit is of the sensored controllers on retrofitted turnigy outrunners. I would like to run at least 12s Lipo if not 18s or 20s to keep the torque up in the higher speeds but not run it so fast that it is annoying. If I know the limit for the motor/controller I can adjust my gearing to make it somewhat equal to the pedal speed. Any help would be appreciated.

Carl

 

[thepronghorn]

Well thud tested a 14 pole motor past 11K rpm's on a modified ecrazyman/infineon controller at the bottom of this thread
http://endless-sphere.com/forums/viewtopic.php?f=28&t=18578&start=30
so that's about 7*11000=77000 erpm.

The Kelly's with the ultra high speed firmware can supposedly go up to 100K erpm, but others may be able to shed some light on the validity of that claim.

 

[parabellum]

Your out runner could be the limiting factor if it has skirt bearing. Which one do you want to use?

 

[Powdersummit]

I was really looking at the SK3 6374 motors in any of the given kv values. I know they don't have as much mass to remove the heat but if you were to run high rpms and gear down to keep the amps down I would think it would be able to handle the heat. If hall placement won't work on the stator I could do some kind of external hall placement. If that doesn't fit the bill I would consider the 8085, but the build quality doesn't seem to be that great. I could rebuild the 8085 but would rather not.

The bike will be a downhill frame, boondocking trail bike. I don't need a ton of speed but would like the ability to climb a tree.

Carl

 

[parabellum]

I was really looking at the SK3 6374 motors in any of the given kv values. I know they don't have as much mass to remove the heat but if you were to run high rpms and gear down to keep the amps down I would think it would be able to handle the heat. If hall placement won't work on the stator I could do some kind of external hall placement. If that doesn't fit the bill I would consider the 8085, but the build quality doesn't seem to be that great. I could rebuild the 8085 but would rather not.

The bike will be a downhill frame, boondocking trail bike. I don't need a ton of speed but would like the ability to climb a tree.

Carl

sk3 6374 as well 8085 has skirt bearings, they usually limit the speed of the motor. It gets really bad with bigger diameter bearings. My old sk2 80-100 gets really unhappy and bearing heats a lot after 9000rpm (and tends to fall apart in short time), recommended limit for long operation is up to 7000rpm. 6374 will probably take more rpm but you need to know bearing size to know the limits.

 

[toolman2]

Well thud tested a 14 pole motor past 11K rpm's on a modified ecrazyman/infineon controller at the bottom of this thread
http://endless-sphere.com/forums/viewtopic.php?f=28&t=18578&start=30
so that's about 7*11000=77000 erpm.

The Kelly's with the ultra high speed firmware can supposedly go up to 100K erpm, but others may be able to shed some light on the validity of that claim.

the kellys do a bit over what they say, ive had 12000+ measured rpm from a 14 pole and that was just a 70 000erpm kelly and you can get 100 000erpm upgrades.

and the skirt bearings have grease in them as standard, nearly all bearings do, but grease is unsuited to high rpm so wash it out, use thin watery wd40 type oil and the bearing drag drops from 150w down to below 10w. -i measured it b4 and after. :wink: just oil then once a month and they'll be sweet.

 

[gwhy!1]

for information im using SK3 6374's with halls to power a full size motorcycle, a pit bike and a bicycle

 

[Powdersummit]

Well considering I don't want to tear things up too much on my first build I think I have to keep motor speed below 7k. I should be able to hit close to that with a standard the small standard Kelly. Is the sk3 6374 a 12 or 14 pole motor? I thought they were a 12 pole motor which could give me 6,666 rpm on a 40,000 erpm controller. Running the higher voltage should keep the torque higher thruout the entire rpm range up to the limit of the controller?

Also what kind of torque do you look for at the cranks or rear wheel when designing a mid drive? I set up a spreadsheet and figured the kt value of the motor and gearing to find my top speed in high gear and what torque I would have in low gear. I can play with the numbers and gearing in there to get whatever I need but I don't know what I need for torque at the cranks to get 300lbs of rider, bike and gear up some steeper stuff. Another option I could have is to add a front derailer for even lower speeds/higher torque but I don't know if that's too much stuff to worry about.

Carl

 

[thepronghorn]

The turnigy's are 14 pole motors, 12 slot stators. If you look at the link below they set the 170kV motors to a max of 75% throttle on the basic speed kelly's to prevent the motor from exceeding 40,000 erpm.
http://scolton.blogspot.com/2011/10/okay-tinykart-frightens-me-now.html

 

[liveforphysics]

Don't count on getting any useful torque control at speeds over about 700hz from the fastest Kellys, it's only switching just a couple of pwm blocks per commutation event at those speeds. It's fine if your pack isn't too much higher in voltage than you need to achieve the speeds you're after, but quite a problem if you're not.

 

[toolman2]

Don't count on getting any useful torque control at speeds over about 700hz from the fastest Kellys, it's only switching just a couple of pwm blocks per commutation event at those speeds. It's fine if your pack isn't too much higher in voltage than you need to achieve the speeds you're after, but quite a problem if you're not.

at the risk of sounding stupid, why is that? i mean at full rpm ive worked out that the kelly would only have about 4 pwm cycles before the next phase arrives,
but even then would reasonable control not exist. -im thinking the last bit of on or off is gonna get cut short and there could then be say a 20%total error, but what else causes drama?