Motrolfly 3625-650 - RC Groups
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Jan 15, 2009, 05:10 PM
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Motrolfly 3625-650

Testing Motrolfly # 14
I got recently from Ken Y. (the official exclusive distributor in the USA one Motrolfly DM 3625-650 sample motor to test. Motrolfly motors are made in Shenzhen (China)

The general aspect shows a very good quality and robust outrunner.
DM3625-650 corresponds to "36x25 mm stator size", 650 Kv
Motor included in a small black card box:
a) Motor delivered in a card black box, good foam protection
b) one prop adapter collet type, 5mm motor towards 8mm/M8 for prop. Conical nut.
c) one alu cross mount and 4 metric screws for fixing the cross on the stator flange
Mechanical :
256 g (without cross, without prop adapter, with 3.5 mm male connectors)
267 g (with cross mount)
Wheel collar retainer (+set screw) on the shaft over-passing stator side 6mm.
Motor fixing via 4 metric M4 screws on 30 mm circle
I dismounted the rotor. I am rather conservative and added some oil on the 3 BBs.

Stator 12 slots, diam. 36 mm, length 25 mm, lams seem 0.35 mm thick
Windings turns, wires ?? number of strands ? I dont know.
Outer diam 45.75 mm, length 50 mm. End bell with 3 spokes, no threaded holes on this old version
14 flat Magnets 25 x 6 x 3 mm, grade ??
Shaft 4.98 mm L = 92.5 mm. Threaded M5 part of shaft over-passing 36 mm the end-bell
Ring wall is about 1.1 mm thick. Airgap is estimated 0.5 mm.

Electrical :
Rm = 0,0234 ohm @ 20C (measured , not "computed by D-Calc")
So Rm is physical, without the ESC internal resistance
No load tests with an ESC 60A, timing auto
Io = 1.8 A @ 8 V , Peakeff in the range 85%
Io = 2.67 A @ 16.1 V , Peakeff in the range 86.9%
Kv = 655 rpm/V very close to indicated on the label (650 rpm/V)

Important remark:
I got an old version of Motrolfly 3625 with a threaded M5 shaft. No problem to fix directly a prop with the wafers and nuts.
However, new version is equipped with a prop adapter (for end bell side) premounted-bolted with 3 screws : BETTER solution. See the new picture showing the three spokes with threaded holes.
Concerning the connectors, I got gold 3.5mm male and female included. New version will be come with 4mm gold bullets pre-soldered. If the customer buys an ESC with the motor Ken will pre solder the connectors on the ESC side as well. At no charge.

I tested this DM3625 with props directly (and easily) tightened to the end bell via the threaded shaft.
** Align 11x6 15V 27A = 405 W providing thrust 1800 gf at 8740 rpm , estimated efficiency 83%
** APC 12x8 E 15V 32.5A = 490 W providing thrust 2200 gf at 8460 rpm , estimated efficiency 83%
(both operation points close to Peakeff%)
Not that I am (some people could say very) conservative with that power (around 2W per gram) but I tested it full throttle 10 minutes.
Final flange temperature was 34.4C (Medusa temp sensor) and windings were 70.3C (temp gun) in 21C air-ambient temperature. No problem.

Motrolfly DM3625-650 will be a good competitor 260g class, specially for planes up to 3000g. A typical prop 13x8 around 41A on 4S LiPo could be right, power 600W.
Next test will be conducted with one 13x8 prop.
Of course if you consider a short running time or some throttle management the prop size could be bigger. Nevertheless IMHO for this motor class 250g a power around 750 W (3W per gram) is close to the limit for long runs. Of course, temperature is function of throttle management, running time and venting the motor on board.
Ken told me that he ran the 3625-650 with a 14x8.5 on 5S LiPo 18.5V 78A 1400 watt for some bursts, but my power supply is not able for that (.. my MRGN-900 is limited to 15V 60A or 30V 30A = 900W). On 20V I could have only 30A (600W)

For info on other Motrolfly results:
1) Thread concerning DM2810-830 (Kv 732 rpm/V) 16 oct 2007
2) Thread concerning DM2810-1200 (Kv 1240 rpm/V) 18 oct 2007
3) Thread concerning DM2820-750 (Kv 640 rpm/V) 19 oct 2007
4) Thread concerning DM2820-950 (Kv 966 rpm/V) 21 oct 2007
5) Thread concerning DM2215-1150 (Kv 1096 rpm/V) 22 oct 2007
6) Thread concerning DM2215-850 (Kv 731 rpm/V) 24 oct 2007
7) Thread concerning DMH2215-3100 (Kv 3200 rpm/V) 25 oct 2007
8) Thread concerning DM2210-1080 (Kv 993 rpm/V) 27 oct 2007
9) Thread concerning DM2205-1350 (Kv 1189 rpm/V) 29 oct 2007
10) Thread concerning DM2810-1000 (Kv 1056 rpm/V) 29 may 2008
11) Thread concerning DM2210-1700 (Kv 1623 rpm/V) 25 sept 2008
12) Thread concerning DM2815-850 (Kv 863 rpm/V) 26 nov 2008
13) Thread concerning DM2815-1100 (Kv 1106 rpm/V) 26 nov 2008
14) Thread concerning DM3625-650 (Kv 655 rpm/V) 15 jan 2009

Look at for future information
Now I have to update the freeware Motrolfly Calculator

Last edited by Fourdan; Jan 22, 2009 at 05:54 PM.
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