4 Motors Tested. Look for videos of the tests at youtube.com under the username rcsportflyer.

Transcription

1 4 Motors Tested for Electric Ducted Fan (EDF) Jets BY: Carl Rich E lectric Ducted Fan (EDF) jets are coming on strong in our RC hobby. They are becoming larger and faster as motor systems are being designed specifically for this facet of RC flight. Also, lithium polymer (LiPo) battery technology continues to progress. A continuing issue that EDF enthusiasts face, however, is there is little information available to help them pick the right motor, fan, electronic speed control (ESC) and battery combination for their jets. They may opt to buy a ready-to-fly (RTF) jet, but sooner or later they start to wonder if there is a more powerful fan and motor combination available. If, however, they buy an almostready-to-fly (ARF) jet, they ll need solid performance information before they can pick a power system. In this article, we ve tested four quality motors to find their limits and exactly what their performance parameters were when installed in a standard 70-mm fan. The results were suprising and exceeded my expectations to say the least! The four motors to be tested: Hoffman Magnetics The Beast, Little Screamers Jet Screamer 1400, Medusa s Afterburner V2, and Light Flight RC s ARC The Beast includes long motor wire leads, an O-ring to help center the motor in the fan s motor housing, and four screws. It comes in a plastic bag wrapped in a foam column and placed inside a sharp looking black container. Look for videos of the tests at youtube.com under the username rcsportflyer. We Test We test a bit of everything. There are two inrunner brushless motors with published Kv ratings that are a bit different and would suggest one to perform best on 5S (5 cells in series) LiPo pack, and one to perform best on 6S. There are also two outrunner brushless motors with differing 26 RC SPORT FLYER

2 4 Motors Tested The Jet Screamer 1400 looks Industrial Grade, as though it were machined from a solid piece of metal and could power a car. It comes with long wire leads, a tight fitting O-ring already in place, and four screws. Kv ratings, but both manufacturers recommend a 4S LiPo or 5S LiPo battery source. We re going to test all four motors with three different cell counts to find the best configuration for each motor in the 70-mm WeMoTec Mini fan. This fan was chosen as it has been around for a long time, has great performance, and a reasonable price at only $55. We ll also test each motor to find our own no load current and no load Kv rating. The no load current will give an indication of motor efficiency. The Kv rating tells you how many revolutions per minute (rpm) the motor will produce for each volt supplied. A 4000 Kv motor would spin 40,000 rpm if supplied with ten volts. Some manufacturers list Kv as no load, meaning that nothing was attached to the motor shaft during the test. Others list a Kv taken under load, meaning that the motor was working to spin the shaft against the resistance of a ducted fan rotor or propellor when the Kv was recorded. A no load Kv is expected to be a bit higher since the Kv drops as the load is increased. Unfortunately, some manufacturers list a Kv that is no load and others under load I can t think of any that tell you which system they use. We ll discuss this further after the testing. Four Motors ARC The ARC motor is a four-pole inrunner motor, with an advertised Kv of It is priced at $ Based on the Kv of previous motors I ve tested in the WeMoTec Mini fan and information on the seller s Web site, this would likely make for a good test on 5S LiPo if its maximum rating is an under load Kv. This motor comes with wires that are long enough to reach out of the exhaust ducting behind the fan but not much more. The 4-mm bullet type connectors come already soldered in place. A pair of female connectors and shrink wrap are provided for your ESC too. Like with many motors we buy, there was no information concerning the internal resistance of the motor, its maximum rpm, current, or the maximum voltage it was designed for. So, we started conservative with a 4S LiPo test and worked our way up. The Medusa Afterburner motor is packaged securely and has all the important information printed in the box. It does not come with screws, but the WeMoTec Mini fan supplies them and Medusa offers them on their Web site. The ARC motor comes without information and in an unassuming box. It s the only one that comes with bullet connectors already soldered in place and female connectors with heat shrink for your ESC. Two mounting screws are provided. RC-SF.COM 27

3 All four motors are made to slide right in to the 70-mm Mini fan and will accept the two mounting screws supplied with the fan. The motor is a total of 58 mm long and weighs in at 6.4 oz, including the added heat sink, and 5.5 oz without. The heat sink is available off their Web site. It helps to pull heat from the motor, so be sure to use one when possible as heat kills motor magnets. The shaft diameter is 3.17 mm all the way through the motor, so the shaft bearings are among the smallest of the motors tested. Note that the motor shafts of both inrunners are just large enough in diameter that the fans aluminum shaft adapters must be heated, for minimal expansion, in order to get the adapters to slide on the motors shafts. The fans instructions actually acknowledge this as a normal procedure and mention the use of a lighter as a heating option. The ARC motor comes in a small black box with only the word ARC in red and yellow. If you judged this one by the package you d be sorely mistaken! motor tested. You ll notice from the photos that less aluminum is used on the mounting flange than that of the Jet Screamer outrunner. You ll also notice that the entire standoff is composite. The purpose of the standoff, on both outrunners, is to position the actual motor behind the fan unit. This is done to keep the motor in the fast moving air stream for cooling purposes and because the motor is 35 mm in diameter, so it is too large to fit inside the motor housing. The rear portion of the motor is also composite, which helps to keep the spinning mass low. The Beast has the largest percentage of open cooling area upfront and in the rear by far. It is the only motor that you can actually see through from the front to the back. The Hoffman Beast has the thickest motor winding wire too, followed by the Jet Screamer 1400, which appears to be about the same as the ARC motor. The thinnest wire is used in the Medusa. Most outrunners have a set screw or two holding the rotating can to the motor shaft, as does the Jet Screamer The Beast has no visible set screws, which leads one to believe the composite end is adhered to the motor shaft much the same way as the composite standoff is adhered to the aluminum mounting bracket. Most motor shafts will push or pull a small amount, relative to the non-rotating components, if you try. The Beast s shaft movement is nearly imperceptible. The steel outer casing is polished to a The Beast Hoffman Magnetics The Beast is a $118 four-pole outrunner motor of a different breed. The Beast incorporates a great deal of composite material instead of aluminum to keep it lightweight. It weighs in at a scant 4.6 oz, so it was the lightest The rotating can diameter is basically the same for the Jet Screamer 1400 and the Beast at 35 mm. The Medusa and ARC inrunners are each 28 mm in diameter. Wire thickness varies with the Medusa being the thinnest, the ARC and the Jet Screamer 1400 looking the same, and the Hoffman Beast being the largest by far. 28 RC SPORT FLYER

4 4 Motors Tested A Castle Creations 125-amp ESC was selected for its super smooth throttle response and ease of programming. The new Thunder Power Pro Power 30C LiPos held excellent voltage under large currents and held up under repeated abuse from the tests. The WeMoTec Mini fan is an excellent 70-mm fan that has been used succesfully by many modelers for years and comes very complete with a balanced rotor. Both The Beast and the Jet Screamer 1400 come with an O-ring to hold them firmly in place when installed in the fan. The Beast has two positions for the O-ring and the larger diameter position was used. The Jet Screamer O-ring comes in place and required a little material be removed around the fan s motor housing to create a beveled edge to get it started. Both the Medusa and ARC inrunners used a heat sink that is available from each. Radio Shack s Heat Sink Compound is a paste that allows for better heat transfer, so use it between the motor and heat sink. Clockwise: Medusa s Power Analyzer Pro gathers the data and sends it to the computer. Medusa s Temperature Sensor is attached to a wooden rod so it can be inserted deep into each motor for accurate temperature readings. The Eagle Tree speed indicator is used to give the maximum air speed (efflux) from each test. An infrared thermometer measured the battery pack temperatures and a Castle Creations ESC provided smooth input to the motors. RC-SF.COM 29

5 fine finish and emblazoned with Hoffman s logo. In comparing the Jet Screamer 1400 outrunner to The Beast, you get the feeling that the Jet Screamer could be beat with a stick and never give up, while The Beast is a refined precision instrument both fine qualities but different. This Beast comes with an O-ring and two indentations on the standoff to place it. The location that pushed the O-ring to a larger diameter was used for this testing and it slid snuggly into the motor housing to aid in holding The Beast firmly in place. The shaft and bearing diameters are 3.14 mm, so the rotor adapter slides over the motor shaft without requiring heat. The Beast comes packaged like you d expect a precision instrument to be packed. The motor is in a plastic bag and then placed inside a surrounding tube of foam and finally inside of a hard black plastic box with the Hoffman logo. Included is helpful information calling out the Kv of 4130, the resistance of ohms, weight of 130 grams (4.6 oz), and the use of 4S or 5S LiPo for 70-mm EDF. The aluminum thrust stand transfers force from the fan to Medusa s Thrust Cell, the Power Analyzer Pro feeds the data to the computer, and the Eagle Tree airspeed indicator s pitot tube is centered on and just outside of the exhaust cone. Jet Screamer 1400 The Jet Screamer 1400 six-pole outrunner motor is from Little Screamers. It is sold by Hobby Lobby for $ The box text provides a Kv rating of 3990, with additional details relative to watts, current, and rpm for 4S LiPo power. They also give stats of 1250 watts, 77 amps, 48,000 rpm, and 141 grams (5 oz). Little Screamers also gave us the fabulous Jet Screamer motor for the smaller fans used in the Alpha F-86 and MiG models. That motor really changed the performance of the smaller jets, so the bar was set pretty high for these tests. This motor comes with extra There was a great deal of probing with the temperature sensor. LiPo batteries have a lower resistance at higher temperatures. A new toaster oven was set to heat the LiPos to 90 degrees (F) to get the most from each test and guarantee equal battery performance regardless of room temperature. 30 RC SPORT FLYER

6 4 Motors Tested The 28 mm long heat sink is just slightly longer than the amount of each inrunner motor protruding from the rear of the fan. Notice the white heat sink compound used between the motor and the heat sink. long wire leads, a mounting flange on the front, four mounting screws, and a note stating that you ll want to set the ESC to low timing, no brake, and hard or fast start. The long mounting flange on the front allows the spinning motor case to hang out behind the motor to catch all the cooling air from the fan. The mounting flange has a large O-ring that will assist in holding the motor securely in the fan, as the O-ring fits tightly against the motor housing walls. The fit was so tight that you ll need to use a hobby knife to make a rounded edge around the motor housing to get the O-ring to compress enough to fit. It only took a minute but it s something that makes installation much easier. The back of the fan s rotor adapter must be kept 3 mm away from the face of each motor to keep the rotor from rubbing on the front of the motor housing. Only the Jet Screamer 1400 motor had a stop machined into the motor shaft that allowed for perfect spacing without the need to measure. All of these motors have openings for air to come in and to exit the rear. The Jet Screamer openings are not forward facing but radial around the front of the motor. It has a 5-mm motor shaft, and therefore the largest bearings of the group. The shaft drops down to 3.14 mm upon exiting the motor and allows the shaft adapter to slide into place effortlessly without heat. The motor assembly weighs 5.3 oz. Medusa V2 The Medusa Afterburner V2 is a four-pole inrunner motor that has similar cooling inlet and exhaust openings as the ARC motor. It sells for $ The wire diameter is a bit smaller than the other motors, while the shaft going through the motor and corresponding bearings is a bit larger at 4 mm. The front of the Medusa motor is one piece with the tube that forms its housing. It has a rear plate that presses on, as compared to the ARC that has both ends pressed on the middle tube as separate pieces. The wire leads are the shortest of the group and are just long enough to reach out of the inlet ducting. If your jet requires that your motor wires bend as they exit the exhaust duct due to fuselage clearance, then you ll want to add a couple inches of flexible wire to the V2 motor leads. The motor is held securely in its shipping box with a roll of foam wrap and cardboard on both ends. The box has all of the pertinent information printed on it. The Kv is 2800, the no load current is 2.5 amps at 8 volts, the resistance is ohms, maximum rpm is 60,000, maximum current is 69 amps, and the dimensions are 28x56 mm with a shaft diameter of 3.17 mm. (The no load current is a good indicator of motor efficiency and it would be nice if all motor manufacturers listed this as well as the maximum suggested current and rpm.) The Medusa motor weighs in at 6.5 oz with the 0.9 oz heat sink added, and 5.6 oz without. Like the ARC motor, the mm motor shaft requires that the aluminum rotor adapter receives a little heat to slide on to the motor shaft with a tight fit. I had tested the previous version of this Medusa motor and was looking forward to testing this V2 version at and beyond its suggested limits to see how it would perform. Test Results The goal of these tests was to create as equal a playing field as possible considering the Kv differences involved. The tests were performed using the same WeMoTec Mini fan. I also used the same Castle Creations 125- amp ESC and Thunder Power Pro Power Series 30C 3850-mAh LiPo packs that were fully recharged and heated to 90-degrees Fahrenheit before every test. Using the same gear provided for consistency between tests. The ESC was set per Castle Creations recommendations for inrunner RC-SF.COM 31

7 motors at: Hard cutoff for cut-off type Fixed end points for throttle type Disabled for brake strength High for motor start power Medium for throttle response Standard timing for motor timing 13 khz for PWM rate Insensitive for current limit The only change to this was that the motor timing was set to low advance for the Jet Screamer 1400, per their recommendation, motor start was set to medium, and timing to low advance. Current limiting was set to normal for the Hoffman Beast, per their recommendation too. The tests were administered by the settings I input into the Medusa Power Analyzer Pro software such that the computer controlled the testing from beginning to end and gathered data at a rate of four times per second. Three Tests Performed The objective of test one was to determine the no load Kv of each motor. Each motor was tested using a linear ramp from zero to 100% throttle over a period of 15 seconds to avoid a spike from ramping up too quickly. Full throttle was then held for five seconds to make sure there was no spike. The objective of test two was to determine how many LiPo cells the motors could handle without over heating or exceeding the ESC s capability. The only real way to do this thoroughly would be to run the motors until they die, but that would likely also kill the ESC and the LiPo batteries. So instead we ll watch the temperature increase from the beginning to the end of the test and watch to see if the current exceeds our ESC rating of 125 amps. This test consists of a linear ramp from zero to 100% throttle over 15 seconds and then full throttle is held for a grueling 30 seconds more to allow the heat to build up in the motors, which provides some idea of whether or not the motor is likely to survive Both outrunners extend out behind the fan and take advantage of the high speed cooling air. The O-rings on each of the standoffs help to hold them firmly as a large percentage of their weight is behind the fan. with much more abuse. The temperature is read both by an infrared thermometer and by using a Medusa Temperature Sensor inserted inside the rear vents of each motor. The temperature sensor is placed directly after each test and moved around to find the hottest spot. It is left in place for as long as the temperature continues to increase and then we look for a hotter spot. In every test the sensor gave a higher reading than what the infrared thermometer read from the outside. This test starts with the lowest practical LiPo cell count. Increasing cell count is tested until the motor appears to suffer, or when the ESC has reached its limit of 6S LiPo or 125 amps. Test three analyzes the maximum LiPo cell count (most powerful setup) for each motor, but inside of their limits from the second test. This test allows for the most accurate data readings, as it is a five-step test with each test lasting five seconds. The steps are 20%, 40%, 60%, 80%, and 100% of throttle. This is more accurate as there is some lag time between the ESC requesting a specific throttle input and the motor achieving the rpm of that throttle input. There is further lag time between the rpm reaching the requested throttle input and the thrust cell reading the exact force from that rpm. The lag is less than two seconds, so holding each setting for five seconds allows for accurate readings at these points. In addition to these tests, the ARC motor was also tested with and without the heat sink to see how much of a difference it made in cooling the motor. On the 5S LiPo setup the change in motor temperature ended up being 10.3 degrees F cooler after running test two with the heat sink installed compared to testing without the heat sink. 32 RC SPORT FLYER

8 4 Motors Tested Test One Motor Volts Current Watts No load Kv ARC , Medusa V , Hoffman Beast , Jet Screamer , The motors are listed in order of increasing current with the ARC motor requiring the least to spin freely. There is a big difference between the current of the inrunners and the outrunners, but the outrunners have a higher Kv. The ARC motor is within 1% of its listed Kv, so its rating is based Test Two on no load. The Medusa motor no load Kv is 15% above the listed Kv, so the listed Kv is most likely the loaded value. The Beast is only off by a little over 1%, so it s likely a no load value. The Jet Screamer 1400 motor s listed Kv was 7% higher than the no load Kv observed here. The Kv will only go down once a load is applied, so the Kv listed is off a bit and not all that helpful. I find the Kv rating to be most helpful when it is that under load. You can take the figures provided and multiply it by the applied voltage to determine the approximate rpm the motor will spin a propellor or an EDF rotor. For example, in this case it would be helpful to know the voltage needed to get to the motor to the 55,000 rpm suggested limit of the WeMoTec Mini fan. If you know the under load Kv is 2800 then you can simply divide 55,000 rpm by 2800 Kv to find out you need about 20 volts. That means a 5S LiPo pack under load is not quite going to do the job, as it s rated for 18.5 volts. Motor LiPo Cells Volts Current Thrust (oz) Watts Air Speed (mph) Delta T (F) , Hoffman Beast Jet Screamer , ARC , , ** , Medusa V , , ** An accuracy of +/- one percent for the Speed Sensor and Thrust Cell would explain a 213mph reading for the Medusa motor at 91.3 ounces of thrust and a 208mph reading for the ARC motor at 93.1 ounces of thrust while having basically the same rpm reading. As mentioned before, the purpose of test two was to discover which LiPo and motor combinations appeared to work best and if any appeared to be working too hard. The ARC motor was to be tested up to 5S Lipo, but it proved to be working great so it was tested successfully on 6S LiPo. Even so, it still recorded the lowest temperature change of all the motors. The 5S Lipo setup on the Hoffman Beast appeared to be too much for these tests. A temperature increase of degrees above room temperature after 30 seconds at full throttle seems excessive when compared to all other combonations tested. The current of amps exceeds the batteries continuous rating, as well as the ESC s 125 amp rating. The Hoffman Beast may work fine on 5S LiPo for folks using throttle managment and for batteries that do not hold voltage. RC-SF.COM 33

9 Test Three Results Fan: WeMoTec Mini Fan Motor: All ESC: Castle Phx 125 Battery: TP3850-3S to 6S Pro Power ARC on 6S Jet Screamer 1400 on 5S Hoffman Beast on 4S Medusa V2 on 6S Input Voltage Input Current (amps) Input Power (watts) Thrust (oz) Throttle Position (%) , , , , , Input Voltage Input Current (amps) Input Power (watts) Thrust (oz) Throttle Position (%) , , , , , Input Voltage Input Current (amps) Input Power (watts) Thrust (oz) Throttle Position (%) , , , , , Input Voltage The following graphs are all derived from test three: This graph simply demonstrates that the fan produces a specific amount of thrust at a given rpm, regardless of the motor spinning it. It shows that having the outrunner motors in the airstream behind the fan does not negatively affect the Input Current (amps) Input Power (watts) Thrust (oz) Throttle Position (%) , , , , , thrust a perceivable amount. The Hoffman Beast has its first point (17,100 rpm) before the others, as it is being tested on 4S LiPo and appears to be below the lines of the others simply because the others have no graphing points around Hoffman s first point. They would all follow that similar curve except the graphing software is picking a straight line 1 2 between 0 and the first point for the other motors. This graph shows the watts each motor expends at a certain rpm. You ll notice that the ARC motor is the most efficient at producing rpm per watt. It is closely followed by the Medusa motor and then the Hoffman and finally the Jet Screamer It is 34 RC SPORT FLYER

10 4 Motors Tested also interesting to note that the Hoffman motor s efficiency drops to equal that of the Jet Screamer 1 Static Thrust (oz.) 2 Static Thrust (oz.) 3 Static Thrust (oz.) ARC on 6S Jet Screamer 1400 on 5S Hoffman "Beast" on 4S Medusa V2 on 6S Thrust vs. 0 17,500 35,000 52,500 70,000 Thrust vs. Input Power ARC on 6S Jet Screamer 1400 on 5S Hoffman "Beast" on 4S Medusa V2 on 6S Input Power (Watts) 1400 once they both reach about 1500 watts, which is the last point for the Hoffman motor on 4S. Thrust vs. ARC on 6S Jet Screamer 1400 on 5S Hoffman "Beast" on 4S Medusa V2 on 6S 0 17,500 35,000 52,500 70,000 3 This graph shows a motor s ability to produce thrust with a given amount of power. Not suprisingly, they fall in the same order as the previous graph. Just because it s fun, look at the percentage difference in efficiency at 1000 watts. Because the ARC motor has the highest line on the graph, it has the highest efficiency at producing thrust, so it will be our benchmark. At 1000 watts the motors produce the following thrust: 54.5 oz, ARC 51.5 oz, Medusa 47 oz, Hoffman Beast 44 oz, Jet Screamer 1400 Subtracting each motor s thrust from the ARC s 54.5 oz and then dividing by 54.5, then multiplying the total by 100% yields the percentage difference between each and the ARC. The Medusa is less efficient by 5.5%, the Beast by 13.7%, and the Jet Screamer by 19.3%. Which One Is Best The best motor for your jet will completely depend on the jet. Most jets that are made for a 70-mm fan are too small to handle a 6-cell LiPo pack of 3850-mAh capacity. The pack is just too heavy for most of them. The trend lately is to make these 70-mm-fan-sized jets bigger. Modelers want retracts so the jet looks cleaner and more realistic in the air. The wings need to be larger to handle the additional weight of the plane as well as to create room for the retracts to be mounted in the wing. There are several jets on the market now that are ready for the most powerful setups I tested. Considering the current of each of the two outrunners on 3S and 4S, the Hoffman Beast provides more thrust and efflux but at a higher current. If you have a battery that will handle the extra current of RC-SF.COM 35

11 4 Motors Tested the Beast, then your decision is pretty easy. If you need a smaller battery pack, then perhaps the Jet Screamer s lower current will allow a smaller capacity pack to be used. On 5S the Jet Screamer 1400 delivers more thrust and exhaust velocity than all others on 5S. If the battery and ESC can handle the current and you want to stick with 5S then that s your pick. If you can use a 6S pack of lower capacity then you may want to consider the ARC or the Medusa for the lower current and bump in performance by going to a smaller 6S pack over a larger 5S pack. If 6S will work in your jet then you will not be dissapointed with either the ARC or the Medusa. The Medusa shows a little more thrust and efflux in the final test but the ARC runs cooler and uses a bit less current. Overall, the inrunners are more efficient. It should be mentioned that the ARC motor does not list a maximum input power but recommends keeping the motor cool. The Medusa motor lists a maximum voltage of 5S LiPo and maximum current of 69 amps. The motors seemed to stay fairly cool during the tests, but check the temperatures after flights on any of these motors to make sure they are not pushed too hard. If a motor is reaching 150 degrees (F) by the time the jet has landed, then consider using better throttle management. Whatever setup you decide to use, make sure to use the best battery and ESC possible or you will have wasted your money on the entire setup due to a lack of performance. These new mah Thunder Power Pro Series LiPos will handle any of these setups with authority and the Castle Creations ESC is easy to program and it demonstrates the smoothest throttle response of any ESC I have tested. Now take your 70-mm EDF jet to the next level with one of these incredibly powerful setups! 4 Motors Tested References: ARC motor and Thunder Power Pro Series LiPos Light Flight RC service@lightflightrc.com Web site: lightflightrc.com Jet Screamer 1400 motor and WeMoTec Mini fan Hobby Lobby 5614 Franklin Pike Circle Brentwood, TN Phone: Web site: hobby-lobby.com The Beast motor Hoffman Magnetics, Inc Eton Avenue Chatsworth, CA Phone: Web site: hoffmanmagnetics.com V2 motor and Power Analyzer Pro equipment and software Medusa Research, Inc. 288 Plymouth Avenue Fall River, MA Phone: Web site: medusaproducts.com 125 Amp Castle Creations ESC Castle Creations 402 E Pendleton Ave. Wellsville, KS Phone: Web site: castlecreations.com SuperTigre Now, the way to go in glow is also the simplest way to affordable high-performance electric power, too. Three brushless motors, two ESCs and six LiPo packs make it easy to make perfect choices for most park flyers. Connectors are compatible and pre-installed. And while all products are priced like similar items on the web, they re backed by a name you know and trust: SuperTigre. Look for the distinctive black and red labels at your local hobby dealer. And get ready to soar. supertigre.com/89m Copyright 2009 Hobbico Inc. Distributed Exclusively Through GREAT PLANES MODEL DISTRIBUTORS COMPANY, P.O. Box 9021, Champaign, IL