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Old Jan 23, 2013, 12:39 AM
Jim in the Desert
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United States, NM, Las Cruces
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Are motor names a code for size?

It seems common for a motor to have a four digit designation followed by a dash or slash and then another number, like Towerpro 3520-6 for example.
Or AXI 2820/12.

Bigger motors seem to have bigger numbers. Do these refer to physical size (like width, length), or something? Or do they refer to power (35 amps, something something...??)?

Thanks for any deciphering...

Jim
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Old Jan 23, 2013, 02:00 AM
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Quote:
Originally Posted by cloud_9 View Post
Do these refer to physical size (like width, length), or something? Or do they refer to power (35 amps, something something...??
Numbers like 3520 or 2820 usually refer to the diameter and length of either the outer case (eg. Towerpro) or the stator (eg. AXI). This gets confusing if two motors have similar numbers but different naming methods, eg. an EMP 2826 has outside dimensions of 28x26mm, but an AXI 2826 is much larger at 35x54mm.

The last number usually refers to the number of turns per slot (or sometimes the turns per two slots for a DLRK winding). The higher the number of turns, the lower the Kv will be. However Kv is also affected by other factors such as the size of the stator and number of magnets, so it only has relevance when comparing two motors which are otherwise identical. Some manufacturers make the last number the Kv, eg. Scorpion SII-2215-1127KV.

Just to make things more interesting, some manufacturers designate their motors according to the 'equivalent' glow engine, eg. OS .30, E-Flite Power 60. Others follow Graupner's designations for brushed 'can' motors (Speed 300/400/480/600 etc.) which are loosely based on Mabuchi's designations (RK370/RS380/RS550 etc.). Note that these designations may be chosen to match either the dimensions or the power of a brushless motor to its 'equivalent' brushed motor.

The upshot of these different naming conventions is that unless you know what system the manufacturer is using, you can't be sure what the numbers mean!
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Old Jan 23, 2013, 07:44 AM
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This part of this article may be useful for this topic:

http://www.theampeer.org/e-basics/e-basics.htm#MOTORS
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Old Jan 23, 2013, 08:25 AM
Jim in the Desert
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United States, NM, Las Cruces
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Originally Posted by Ken Myers View Post
This part of this article may be useful for this topic:

http://www.theampeer.org/e-basics/e-basics.htm#MOTORS
Thanks Ken, that's great.

Particularly I am trying to determine how the TowerPro 3520 (don't know if it's a -6 or -7) compares with the Hobbico Electristar motor
http://www3.towerhobbies.com/cgi-bin...P?I=LXPTL2&P=8

All Hobbico says is the size of the can but not the weight, which compared to your measurements on the TowerPro, makes it seem the latter is bigger. I am about to get the motor out of my Electristar kit and compare it to the TowerPro, and compare the TowerPro weight and size to your measurements, to see if I can tell if I have the -6 or -7.

Just thinking when I build the Electristar (if you call six screws building) I might switch to the TowerPro for more power, but I don't want to mess up the CG of the plane.

Jim
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Old Jan 23, 2013, 08:26 AM
Jim in the Desert
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Quote:
Originally Posted by Bruce Abbott View Post
Numbers like 3520 or 2820 usually refer to the diameter and length of either the outer case (eg. Towerpro) or the stator (eg. AXI). This gets confusing if two motors have similar numbers but different naming methods, eg. an EMP 2826 has outside dimensions of 28x26mm, but an AXI 2826 is much larger at 35x54mm.

The last number usually refers to the number of turns per slot (or sometimes the turns per two slots for a DLRK winding). The higher the number of turns, the lower the Kv will be. However Kv is also affected by other factors such as the size of the stator and number of magnets, so it only has relevance when comparing two motors which are otherwise identical. Some manufacturers make the last number the Kv, eg. Scorpion SII-2215-1127KV.

Just to make things more interesting, some manufacturers designate their motors according to the 'equivalent' glow engine, eg. OS .30, E-Flite Power 60. Others follow Graupner's designations for brushed 'can' motors (Speed 300/400/480/600 etc.) which are loosely based on Mabuchi's designations (RK370/RS380/RS550 etc.). Note that these designations may be chosen to match either the dimensions or the power of a brushless motor to its 'equivalent' brushed motor.

The upshot of these different naming conventions is that unless you know what system the manufacturer is using, you can't be sure what the numbers mean!
Somebody should make a law that hobbies must be fun, not complicated
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Old Jan 23, 2013, 11:23 AM
WBE
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Sometimes deciphering all the crazy little details becomes the hobby!

I too heard about the rumor that hobbies are supposed to be fun and relaxing.
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Old Jan 23, 2013, 12:41 PM
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That's why this hobby/sport has never had it better with PNF aircraft... no thinking needed, just money.
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Old Jan 23, 2013, 01:48 PM
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Quote:
Originally Posted by cloud_9 View Post
I am trying to determine how the TowerPro 3520 (don't know if it's a -6 or -7) compares with the Hobbico Electristar motor
http://www3.towerhobbies.com/cgi-bin...P?I=LXPTL2&P=8

All Hobbico says is the size of the can but not the weight,
At 42x40mm the Hobbico C-42 is a bit smaller - and probably lighter - than the TP3520, so you would expect the Towerpro to be more powerful. However if you have the 7 turn version then it should have a lower Kv, and therefore needs higher voltage to get the best out of it.

Here's some test data for the C-42. It appears to be about 800Kv.

http://www.rcgroups.com/forums/showthread.php?t=1033095
Quote:
Originally Posted by reacher10
I measured the current and power using two 7-cell 3000mAh packs and a single 4-cell 3200mAh (20C) LiPo pack.

27amps (190w * 2=380w) w/two 7-cell 3000mAh NiMH packs (30oz total)
30amps (440w) w/single 4-cell 3200mAh (20C) LiPo pack (14oz)
http://www.hobbico.com/reviews/hcaa12-flyrc.pdf:

Hobbico Electristar EP Select RTF
Flight Report by Thayer Syme

POWER SYSTEM: ElectriStar C-42 brushless
outrunner motor, 11x7 prop, ElectriFly SS-45D

NI-MH FLYING WEIGHT: 101.4 oz. (6 lbs., 5.4 oz.)
WING LOADING: 20.6 oz./sq. ft.
FULL THROTTLE POWER: 30.14 amps, 441.2 watts, 4.35 W/oz., 69.6 W/lb.
TOP RPM: 8,595
DURATION: 13 minutes, mixed flying

LI-POLY FLYING WEIGHT: 84.5 oz.(5 lbs., 4.5 oz.)
WING LOADING: 17.2 oz./sq. ft.
FULL THROTTLE POWER: 33.2 amps, 515.6 watts, 6.1 W/oz., 97.6 W/lb.
TOP RPM: 9,015
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Old Jan 23, 2013, 06:10 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by cloud_9 View Post
Thanks Ken, that's great.

Particularly I am trying to determine how the TowerPro 3520 (don't know if it's a -6 or -7) compares with the Hobbico Electristar motor
http://www3.towerhobbies.com/cgi-bin...P?I=LXPTL2&P=8

All Hobbico says is the size of the can but not the weight, which compared to your measurements on the TowerPro, makes it seem the latter is bigger. I am about to get the motor out of my Electristar kit and compare it to the TowerPro, and compare the TowerPro weight and size to your measurements, to see if I can tell if I have the -6 or -7.

Just thinking when I build the Electristar (if you call six screws building) I might switch to the TowerPro for more power, but I don't want to mess up the CG of the plane.

Jim
I googled for the Hobbico HCAG3740 part number listed on the Tower Hobbies tech notes (actual search used was "hobbico HCAG3740") and could find quite a few references to that motor but not a single one of them listed a Kv spec for the motor or a weight.

I found one thread that discussed it here:

electristar motor - http://www.rcgroups.com/forums/showthread.php?t=1033095

and found an opinion stated in there that it is "..just a LITTLE less powerful than the E-Flite Power 46...".

The E-Flite Power 46 is a 670 Kv motor weighing 290 grams by the specs here:

http://www.e-fliterc.com/Products/De...46A#quickSpecs

And that might give you a starting point for comparing it to other motors.

By the classic rule of thumb that typical quality outrunners will handle an input power of 3 Watts for each gram of motor weight, the Power 46 would be a 3 x 290 = 870 Watt motor. Tower Hobbies rates the Power 46 at 925W peak so I would think that 870W is a realistic expectation for the Power 46.

If you get your motor out and find it also weighs about 290 grams you can probably use the E-Flite specs. And if you use the 3 Watts per gram rule it's weight will give you a starting point for upgrading the power (buy a heavier motor to get more power).

You don't mention the prop used or that you want to use, if you know that it will lead you to confirming if the 670 Kv is what you need.

The link that Ken Meyers posted indicates that the difference between the 3520-6 and 3520-7 is the Kv so that won't show much or any difference in weight. The -6 is a 700 Kv motor and the -7 is a 600 Kv motor so that does confirm that the Power 46's 670 Kv is about right. His review also indicates the 3520's are 262 gram motors so they are also falling in line a little below the Power 46 by the 3 Watts per gram rule.

Jack
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