Joined: 16 Jun 2004
Posts: 9481
Location: Where you least expect
The Brushless thread
plenty of us are using this technology now so time for a thread me thinks if we could put up experiences of every motor used and controller that would be good!
brushless power has an awesome power to weight ratio (650 gram motor is about 3000 watts at 80% efficiency or so) and are very compact so there very attractive to use as weapon drives.
but they do have some problems -
Cogging
most of the motors and controllers we use are sensorless which means the controller is guessing the position of the rotor (it applies reduced power to one coil and senses the back emf through another i believe).
problem is with a large load such as a blade or drum etc the small amount of power applied to one coil at start up isnt enough to move the motor enough to induce a large enough back emf for the controller to sense.
the only way to get around this is reduce the loading on the motor (reduce belt tension or make the setup more efficient etc) or to gear it down more. getting a motor with less KV (rpm per volt) may also help as the torque from the motor is increased.
some controllers also are better and sensing start up on certain motors then others so its a matter of experience there.
Overheating
sometimes the motors just overheat rapidly under free load and driving an otherwise minimal load..
reason being the controllers we use are more or less generic and made to work with lots of different motors. inrunners, outrunners, 2 pole 4 pole 8 pole motors etc etc. all require different timing settings.
generally the outrunners that use 6 or more poles (poles refers to the amount of magnets in the motor) require medium to high timing settings while the inrunners using 2-4 poles require much less timing.
as an example the KD45 blue inrunners most use on high timing generate approximately 3 times the heat on high timing mode with next to no extra rpm generated. be sure to experiement with your controller settings it makes all the difference in this regard.
probably the best of the cheap motors. proven to be pretty durable mechnically so far and the power is immense.
the end caps are only pressed in and need to be reglued and then a mounting system that holds the ends in devised. its also totally sealed so stops swarf being sucked in
runs very very hot (dumps nearly 600w of heat at full power) and runs great from 18v - 36v although you really have to keep your eye on the temperature.
lots of rpms made so lots of gearing needed. goes great with the new turnigy 100A HV controller from united.
a massive motor probably the best for flat out power and torque. it is the outrunner style so its less durable then the inrunner and swarf can get sucked into it..
low RPM per volt means you dont need much extra gearing as opposed to a inrunner so its good to use when your converting a dc motor robot to brushless.
the magnets are held in poorly tho so definitely a good idea to pull it down and reglue them! also support the motor from both sides for strength
because theres so much torque cogging is not really an issue with this motor.
Sentilon 100A HV brushless controller
works good on most motors. has plenty of settings and all are pretty usefull. also failsafes properly (stops motor when no signal is present)
3 timing settings so its good for the inrunners and outrunners. and constructed pretty average in the new version (small heatsink and weak base..). pretty damn good overall for the money. very reliable so far! _________________ www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz
Fri Jan 02, 2009 4:09 pm
Valen Experienced Roboteer
Joined: 07 Jul 2004
Posts: 4436
Location: Sydney
cogging has NOTHING TO DO WITH THE CONTROLLER!.
cogging torque is the ripple in torque due to the interaction between the iron in the motor and the magnets.
IE when you spin the motor by hand its the "lumps" you feel as it turns.
The problems that sensorless controlers have spinning up motors with lots of inertia attached has nothing to do with cogging. Stop calling it cogging because it just plain isn't.
</rant>
brushless is good mmmmkay _________________ Mechanical engineers build weapons, civil engineers build targets
Fri Jan 02, 2009 9:22 pm
Glen Experienced Roboteer
Joined: 16 Jun 2004
Posts: 9481
Location: Where you least expect
except one is right and one is wrong ;-O _________________ Mechanical engineers build weapons, civil engineers build targets
Fri Jan 02, 2009 9:26 pm
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Thanks for making us COGnisant of the real meaning !
Fri Jan 02, 2009 11:18 pm
cerberus3112
Joined: 05 Dec 2005
Posts: 497
Location: Mt Druitt,Sydney,NSW
Does anyone listen to "COG"? _________________ A journey of a million miles begins with a single step followed by a hell of a lot of other steps so get walking
Sat Jan 03, 2009 12:14 am
andrew
Joined: 16 Jun 2004
Posts: 3110
Location: Castle Hill, Sydney. N.S.W
yeah that band kicks ass, now back to topic
In regards to the outrunner motor glen posted i have tried them and have had nothing but bad things with them, i have yet to see them used successfully in a heavy hitting spinner
The blue inrunners work a treat
Dylon has them in his eggbeater robot which once he gets it reliable will be incredibly nasty
they worked fine in orbit minus proper mounting which caused motor failure (this has been rectified) plus the touro featherweight robot from Brazil which competes in robogames every year uses them at some obscene speed and it seems to perform well. _________________ Andrew Welch, Team Unconventional Robotics
Sun Jan 04, 2009 12:34 pm
timmeh Experienced Roboteer
Joined: 20 Jul 2004
Posts: 2523
Location: Victoria
Just thought id throw in some controllers advertise they have a low torque start feature to save your lil gearbox in your plane which may be why some controllers dont throw enoughf into the motor to start your weapon up.
Also i dont see the 700kv motors on hobbyking? _________________ Tim Team Reaper.
Sun Jan 04, 2009 3:30 pm
timmeh Experienced Roboteer
Joined: 20 Jul 2004
Posts: 2523
Location: Victoria
Cost me bout $25 will see how it gose. _________________ Tim Team Reaper.
Sun Jan 04, 2009 3:51 pm
Glen Experienced Roboteer
Joined: 16 Jun 2004
Posts: 9481
Location: Where you least expect
they call those ones "supersimple" escs, they have heaps more timing features and some other features but the reviews are always half work great the other half are DOA.
the 700kv motors are on a different page (last one i think) so just look and youll see em. they where out of stock last i saw _________________ www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz
Sun Jan 04, 2009 4:01 pm
Rotwang Experienced Roboteer
Joined: 15 Jun 2004
Posts: 1589
Location: Vic
A long long time ago when Brett and I were thinking heavy weight thoughts and Brett was starting to play with the idea of building some ESC’s one of the possibilities we kicked around was using car alternators as blushless motors.
We decided the air gaps were too large to get any worthwhile efficiency but I am tempted to get a controller and try and see if I can get one to motor.
It’s going to take a lot to convince me that these hobby motors are worth using in a feather.
Bit expensive to be considered a consumable. _________________ Satisfaction is proportional to effort and results.
Mon Jan 05, 2009 6:21 am
andrew
Joined: 16 Jun 2004
Posts: 3110
Location: Castle Hill, Sydney. N.S.W
granted, the blue inrunners have a good track record though and if mounted properly with a flange on both sides to assist the press fit then they should work nicely.
Only reason motor died last event was caus my mounting was crapola and the press fit loosened and both ends of the motor flanged out.
Besides that had more than enough power to spin up the 3kg disc at 2:1 ratio and the motor didn't get too hot either _________________ Andrew Welch, Team Unconventional Robotics
Mon Jan 05, 2009 8:59 am
timmeh Experienced Roboteer
Joined: 20 Jul 2004
Posts: 2523
Location: Victoria
question
one blue motor running 28.8v 1-4 gear ratio.
two blue motors running 14.4v 1-2 gear ratio.
Both driving same load.
Am i correct in saying the two motor setup would produce less heat and less stress on the motors?
This is an example i am aware that 28.8v would prob be pushing the blue motor. _________________ Tim Team Reaper.
Sat Jan 17, 2009 7:35 pm
Nick Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
Just remember you need two controllers as well.
Sat Jan 17, 2009 7:48 pm
timmeh Experienced Roboteer
Joined: 20 Jul 2004
Posts: 2523
Location: Victoria
Easy controllers get cheaper when your running lower voltages _________________ Tim Team Reaper.
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