Re: [TANKS] brushless motor questions
The no-load RPM value doesn't tell you much by itself. The stall torque and current are better properties to know, but they still don't tell the whole picture. What you want to know is how fast the motor will turn (RPM) and how much current (AMP) will be used for a given workload (Torque). In other words, it would be best to look at the RPM and AMP draws for each motor over the expected range of workloads for your application. Back in my warship days, we spent many an evening measuring motor performance/cost to find just the right drive and pump motors for our fleet of ships. (Which is why I still have a couple boxes full of different types of motors in the workshop.) In general, I would expect that any motor designed to efficiently spin an airplane propeller (such as the Great Planes motor) would not work well when used to spin a pump impeller or move a mechanical load. Yes, you can add lots of gearing to make it move the load, but the gearing significantly reduces the overall efficiency. Also, motors designed to spin an airplane prop don't have to be overly concerned with over-current problems, which allows them to be made lighter. That is, since the prop is not expected to hit something hard (unless you've really had a bad flying day), stall currents will never be experienced. If you adapt them to workloads that are capable of causing the motor to stall, they could generate more heat than the motor parts can handle. For example, door lock actuators are cheap little motors that are mechanically stopped when the arm reaches the extreme position. They work very reliably for their intended purpose. But, if you keep applying the current for even just a few seconds, the motor winding wire will simply melt. A classic case of designing the motor to work well only within a given performance envelope to save money. So, in addition to examining the RPM/AMP/Torque performance curves, you should also consider the intended purpose of the motor to determine if there could be design limitations. On 7/28/2015 12:07 AM, Doug Conn 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 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 mailto:rctankcombat+unsubscr...@googlegroups.com. 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] brushless motor questions
The max power spec for the CIM motor is for normal operation. It is capable of drawing almost 1600w when stalled. Ohms law... 12v and 133A. However, generally speaking the CIM motor is very inefficient, ~65% or less. An outrunner style brushless motor can produce the same torque at much higher efficiencies, ~75-90%. Copy link below for a motor that can easily produce more torque than the CIM and is almost definitely more efficient in normal operation. It just needs to have its 6mm shaft adapted. http://hobbyking.com/hobbyking/store/__18174__Turnigy_Aerodrive_SK3_5055_320kv_Brushless_Outrunner_Motor.html The higher RPM of a geared brushless system should minimize cogging. Where the motor has trouble analyzing its own position. Which is a problem in direct drive low RPM circumstances. Mike On Jul 27, 2015, at 9:07 PM, Doug Conn dwconn...@comcast.net 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. -- -- 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.
[TANKS] brushless motor questions
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? http://www3.towerhobbies.com/cgi-bin/wti0001p?I=LXLWY0P=7 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.
