kkEdlund
1 W
I discovered this forum about a month ago, and I've been amazed by the wealth of knowledge available. I was hoping for a little advice on brushed vs brushless motors, but first a little background on the application. Our robotics club at school has competed for the last several years in the RASC-AL RoboOps competition at NASA's Johnson Space Center (the first pic on that page is actually our rover) and hope to do so again this year. Our current drivetrain uses 4 brushed DC motors and (I think) 47:1 planetary gearboxes to provide direct-drive to each wheel. Steering is accomplished tank-style by driving one set of wheels forward and the other set in reverse to pivot about a central axis. The motors we are currently using are produced by Anaheim Automation and are rated for 30W output (24V at 2.2A). By comparison, the off-the-shelf brushless outrunner on my e-skateboard is rated for >2kW at 37V, although I only run it at 24V.
Our current chassis has become somewhat obsolete and is going to be replaced, and we want to keep it intact for the CS team to test code. Thus the new rover will need a drivetrain, and I have proposed looking into brushless motors as an alternative. Given that we only get 30W per motor (120 in total) and the 45kg rover is still able to move at unsafe speeds at WOT (considering we are driving from several states away
), would it be possible to use 4 Turnigy SK3 28-30 outrunners to power our new chassis (supposedly 150 W each)?
I would like to see 50-60 rpm at the wheels (20" bike tires, lol), so given that the motor in question turns 920 rpm/volt and will run on 12V I'll need ~220:1 gear reduction, and I believe that I can find a gearbox that will do this. However, if I were to rewind the motor just as it is except terminate the windings WYE instead of Delta, I understand it would spin at ~0.578 the speed for a given voltage. Then I would only need 120:1 gearing.
My sensorless longboard cogs severely from a standstill (2.5:1, 90mm wheels, 260 kV 63-54 outrunner on 6s) but is fine once it is push-started. The robot must (obviously) be able to start itself or it would not be much of a robot. Do you think I will need sensored motors to move its mass from a standstill? Also, if it is imperative that the rover hold its position on an incline, will an off-the-shelf speed controller's drag brake accomplish that on a vehicle this large? I'm hoping that with the massive gear reduction involved, the sensorless motors will be able to start the rover from a standstill and will also be able to hold position (via drag brake) on an incline. Am I dreaming?
In your opinion, are we better off with another brushed setup, sensorless outrunners, "DIY" sensored outrunners (add hall sensors), or something else entirely?
Thanks in advance, and sorry for the wall of text,
Kristoffer
EDIT: One additional consideration is the fact the rover will operate in a harsh environment consisting of sand and other generally unsavory mediums. The chassis is partially enclosed, but sand and dirt will enter the chassis and could potentially find their way into an outrunner motor. Our current motor/gearbox assemblies are sealed, and this is not a concern. I'm afraid sealing the motor space in the chassis would prevent the motor from dissipating heat effectively, but failing to do so could lead to debris finding their way between the windings and the spinning magnets and causing serious damage. Is this a valid concern?
Our current chassis has become somewhat obsolete and is going to be replaced, and we want to keep it intact for the CS team to test code. Thus the new rover will need a drivetrain, and I have proposed looking into brushless motors as an alternative. Given that we only get 30W per motor (120 in total) and the 45kg rover is still able to move at unsafe speeds at WOT (considering we are driving from several states away
), would it be possible to use 4 Turnigy SK3 28-30 outrunners to power our new chassis (supposedly 150 W each)?I would like to see 50-60 rpm at the wheels (20" bike tires, lol), so given that the motor in question turns 920 rpm/volt and will run on 12V I'll need ~220:1 gear reduction, and I believe that I can find a gearbox that will do this. However, if I were to rewind the motor just as it is except terminate the windings WYE instead of Delta, I understand it would spin at ~0.578 the speed for a given voltage. Then I would only need 120:1 gearing.
My sensorless longboard cogs severely from a standstill (2.5:1, 90mm wheels, 260 kV 63-54 outrunner on 6s) but is fine once it is push-started. The robot must (obviously) be able to start itself or it would not be much of a robot. Do you think I will need sensored motors to move its mass from a standstill? Also, if it is imperative that the rover hold its position on an incline, will an off-the-shelf speed controller's drag brake accomplish that on a vehicle this large? I'm hoping that with the massive gear reduction involved, the sensorless motors will be able to start the rover from a standstill and will also be able to hold position (via drag brake) on an incline. Am I dreaming?
In your opinion, are we better off with another brushed setup, sensorless outrunners, "DIY" sensored outrunners (add hall sensors), or something else entirely?
Thanks in advance, and sorry for the wall of text,
Kristoffer
EDIT: One additional consideration is the fact the rover will operate in a harsh environment consisting of sand and other generally unsavory mediums. The chassis is partially enclosed, but sand and dirt will enter the chassis and could potentially find their way into an outrunner motor. Our current motor/gearbox assemblies are sealed, and this is not a concern. I'm afraid sealing the motor space in the chassis would prevent the motor from dissipating heat effectively, but failing to do so could lead to debris finding their way between the windings and the spinning magnets and causing serious damage. Is this a valid concern?
