[TANKS] Re: brushless motor questions
Can't say I truly understand the brushless nomenclature (i.e. KVA) because nobody ever talks about the controller side. Brushless motors are basically steppers and without the controller are inert chunks of iron and copper. What I don't get is the KVA ratings (rpm's per volt) of these motors. In my mind, the controller dictates rpm by how fast it is energizing the phases, not by how much voltage is being applied. Voltage would affect acceleration and torque or am I getting this wrong? ST On Tuesday, July 28, 2015 at 12:07:45 AM UTC-4, RocketMan wrote: Hello – We’ve had a few discussions regarding brushed vs brushless motors. The most important point I remember was that brushed and brushless ran at similar energy efficiencies under load. I’m wondering about efficiency with respect to size and weight. Let’s compare this brushless motor http://www3.towerhobbies.com/cgi-bin/wti0001p?I=LXLWY0P=7 to this brushed motor http://www.andymark.com/CIM-motor-FIRST-p/am-0255.htm Both are in the 300 watt range. At 12v, the unloaded brushless motor, rotates at 32k rpm and the brushed motor at 5.3k rpm. Of course, the brushless motor would need a lot more gearing to make it usable in a tank. That aside, could I expect roughly the same performance from both motors ? It’s hard for to believe that because the brushless motor is 1/14 of the brushed motor weight and 1/7 of the volume. Is there another factor (besides cost) I need to take into account when comparing a brushed to a brushless motor ? Thanks, Doug -- -- You are currently subscribed to the R/C Tank Combat group. To post a message, send email to rctankcombat@googlegroups.com To unsubscribe, send email to rctankcombat+unsubscr...@googlegroups.com Visit the group at http://groups.google.com/group/rctankcombat --- You received this message because you are subscribed to the Google Groups R/C Tank Combat group. To unsubscribe from this group and stop receiving emails from it, send an email to rctankcombat+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [TANKS] Re: brushless motor questions
I haven't looked at brushless motors in detail, but from a couple years of Physics in college I learned that when you increase voltage/current in a coil, you increase the strength of the magnetic field generated by the coil. So, I suspect that the RPMs per volt rating for brushless motors tells you how much voltage needs to be applied to pull the armature hard enough for a given speed. Presumably, that rating is for a 100% duty cycle (i.e., max speed). Indeed, the controller pulses the voltage for two purposes (a) to spin the motor one way or another and (b) to regulate the speed (i.e., decrease the average voltage seen by the coil). With regard to torque, for a given duty cycle, if you decrease the input voltage the torque will also decrease. But, if you maintain the same input voltage, while decreasing the duty cycle, the torque will remain relatively stable while the speed decreases. That's why really big earth movers and locomotives use diesel-electric drive systems ... maximal torque across a range of RPMs. On 7/29/2015 12:18 PM, TyngTech wrote: Can't say I truly understand the brushless nomenclature (i.e. KVA) because nobody ever talks about the controller side. Brushless motors are basically steppers and without the controller are inert chunks of iron and copper. What I don't get is the KVA ratings (rpm's per volt) of these motors. In my mind, the controller dictates rpm by how fast it is energizing the phases, not by how much voltage is being applied. Voltage would affect acceleration and torque or am I getting this wrong? -- -- You are currently subscribed to the R/C Tank Combat group. To post a message, send email to rctankcombat@googlegroups.com To unsubscribe, send email to rctankcombat+unsubscr...@googlegroups.com Visit the group at http://groups.google.com/group/rctankcombat --- You received this message because you are subscribed to the Google Groups R/C Tank Combat group. To unsubscribe from this group and stop receiving emails from it, send an email to rctankcombat+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [TANKS] Re: brushless motor questions
I use brushless motors in my tank-And it seems to work well: https://www.youtube.com/watch?v=-MlTcjFC61E And nobody can beat the price-http://www.hobbyking.com/hobbyking/store/__8490__Turnigy_4258_Brushless_Motor_800kv.html?strSearch=4258 Den onsdag den 29. juli 2015 kl. 22.04.24 UTC+2 skrev RocketMan: Presumably, that rating is for a 100% duty cycle This is my understanding, too. Thanks for the responses, everyone. I think I'll stick to brushed motors for now. Frank's points make a lot of sense to me. One more thing that concerns me about the outrunners is that most of the housing I've seen are open. That's good when you're flying a plane and want to use the air flow to cool the motor. It's bad when there's dust and dirt everywhere and Will is trying to shoot paint up my tank's ass ! - Doug -Original Message- From: rctank...@googlegroups.com javascript: [mailto: rctank...@googlegroups.com javascript:] On Behalf Of Frank Pittelli Sent: Wednesday, July 29, 2015 3:09 PM To: rctank...@googlegroups.com javascript: Subject: Re: [TANKS] Re: brushless motor questions I haven't looked at brushless motors in detail, but from a couple years of Physics in college I learned that when you increase voltage/current in a coil, you increase the strength of the magnetic field generated by the coil. So, I suspect that the RPMs per volt rating for brushless motors tells you how much voltage needs to be applied to pull the armature hard enough for a given speed. Presumably, that rating is for a 100% duty cycle (i.e., max speed). Indeed, the controller pulses the voltage for two purposes (a) to spin the motor one way or another and (b) to regulate the speed (i.e., decrease the average voltage seen by the coil). With regard to torque, for a given duty cycle, if you decrease the input voltage the torque will also decrease. But, if you maintain the same input voltage, while decreasing the duty cycle, the torque will remain relatively stable while the speed decreases. That's why really big earth movers and locomotives use diesel-electric drive systems ... maximal torque across a range of RPMs. On 7/29/2015 12:18 PM, TyngTech wrote: Can't say I truly understand the brushless nomenclature (i.e. KVA) because nobody ever talks about the controller side. Brushless motors are basically steppers and without the controller are inert chunks of iron and copper. What I don't get is the KVA ratings (rpm's per volt) of these motors. In my mind, the controller dictates rpm by how fast it is energizing the phases, not by how much voltage is being applied. Voltage would affect acceleration and torque or am I getting this wrong? -- -- You are currently subscribed to the R/C Tank Combat group. To post a message, send email to rctank...@googlegroups.com javascript: To unsubscribe, send email to rctankcombat...@googlegroups.com javascript: Visit the group at http://groups.google.com/group/rctankcombat --- You received this message because you are subscribed to the Google Groups R/C Tank Combat group. To unsubscribe from this group and stop receiving emails from it, send an email to rctankcombat...@googlegroups.com javascript:. For more options, visit https://groups.google.com/d/optout. -- -- You are currently subscribed to the R/C Tank Combat group. To post a message, send email to rctankcombat@googlegroups.com To unsubscribe, send email to rctankcombat+unsubscr...@googlegroups.com Visit the group at http://groups.google.com/group/rctankcombat --- You received this message because you are subscribed to the Google Groups R/C Tank Combat group. To unsubscribe from this group and stop receiving emails from it, send an email to rctankcombat+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
RE: [TANKS] Re: brushless motor questions
Here is an in runner that is very much like similar sized brushed motors. They don't have excessive rpms like a lot of brushless motors, and they have loads of torque. Two of these are going to be utilized in project Duece Duece. http://www.allelectronics.com/make-a-store/item/dcm-459/3-phase-brushless-dc-motor/1.html -- -- You are currently subscribed to the R/C Tank Combat group. To post a message, send email to rctankcombat@googlegroups.com To unsubscribe, send email to rctankcombat+unsubscr...@googlegroups.com Visit the group at http://groups.google.com/group/rctankcombat --- You received this message because you are subscribed to the Google Groups R/C Tank Combat group. To unsubscribe from this group and stop receiving emails from it, send an email to rctankcombat+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
