GWS Tiger Moth with EPS100C
04-29-2003, 06:06 PM
#1
GWS Tiger Moth with EPS100C
In and effort to correct my mistake of converting my TM to a 280 direct drive setup, I endowed it with an EPS100C with the S-1 gearing, threw a 9070 prop on the deal, and cut a battery tray out of the cockpit to avoid adding ballast. Finally got around to flying it last night... 
... 
... 
. The first flight with a 9047 prop and six cells was......disappointing. It could barely maintain altitude. CG shifting gave me either a powered lawn dart or squirrely prophanger. I was beginning to doubt my powerplant choice, but a quick battery and prop change and the thing almost climbed OOS at full throttle!!! It still flies at a high AoA (from the little added weight, I guess), but I can live with it. Anyone else have any similar experiences with this setup?
... ... . The first flight with a 9047 prop and six cells was......disappointing. It could barely maintain altitude. CG shifting gave me either a powered lawn dart or squirrely prophanger. I was beginning to doubt my powerplant choice, but a quick battery and prop change and the thing almost climbed OOS at full throttle!!! It still flies at a high AoA (from the little added weight, I guess), but I can live with it. Anyone else have any similar experiences with this setup?
04-29-2003, 07:38 PM
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TM
Hi Buzzbomber
If it is flying at a steep AoA it sounds as if your CG is a little too far back AND that you need a little more thrust. You don't say which prop you used for your successful flight - on 6-cells both 9047 and 9070 are going to be about equal in terms of thrust (since thrust is a function of diameter not pitch), but a 1047 would boost it about 20%. What about going to 7-cells and the 1047 for close to 45% increase in thrust - and if you move the 7-cells forward you might resolve the CG problem.
Cheers, Phil
If it is flying at a steep AoA it sounds as if your CG is a little too far back AND that you need a little more thrust. You don't say which prop you used for your successful flight - on 6-cells both 9047 and 9070 are going to be about equal in terms of thrust (since thrust is a function of diameter not pitch), but a 1047 would boost it about 20%. What about going to 7-cells and the 1047 for close to 45% increase in thrust - and if you move the 7-cells forward you might resolve the CG problem.
Cheers, Phil
04-29-2003, 07:47 PM
#3
GWS Tiger Moth with EPS100C
My sucessful flight was with the 9070 prop. It does far better than the lower pitch one, even on the same cell count. I know the dogma for slow flyers is to add dia. and decrease pitch, but this is what seemed to work best in my case(any bigger than 9 in. prop and ROG is out because LG legs too short). I suppose I could carefully trim down a 1047 to 9-1/2" I moved the CG around quite a bit, and in retrospect, I think it was more of a trim issue. However, moving the battery 1/2" fore and aft made a very noticable difference in flying characteristics. Overall, I'm happy with it, although the next one will remain stock.
I moved the CG around quite a bit, and in retrospect, I think it was more of a trim issue. However, moving the battery 1/2" fore and aft made a very noticable difference in flying characteristics. Overall, I'm happy with it, although the next one will remain stock.
04-30-2003, 02:47 AM
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Thought for TM
Though the static thrust figures are much the same for 9047 and 9070, the 9070 is probably better for your TM because it will make it fly a little faster in the air - faster flight will let your aerofoil (wing) provide more lift and thus permit a lower AoA. QED - improved flight performance!
I still reckon 7-cells would be a smart move, though.
I just had a flash of inspiration - why don't you try one of those GWS orange 3-blade 9070's! That would, effectively, be the equivalent of using about a 10" x 5.3" 2-blade prop - that would load your motor a little more and thus get more power through it, and more thrust from it, yet still allow ROG 'cos it's only a 9" prop.
If you do try it, let me know if that works any better, Cheers, Phil
I still reckon 7-cells would be a smart move, though.
I just had a flash of inspiration - why don't you try one of those GWS orange 3-blade 9070's! That would, effectively, be the equivalent of using about a 10" x 5.3" 2-blade prop - that would load your motor a little more and thus get more power through it, and more thrust from it, yet still allow ROG 'cos it's only a 9" prop.
If you do try it, let me know if that works any better, Cheers, Phil
04-30-2003, 12:31 PM
#5
GWS Tiger Moth with EPS100C
I haven't yet tried the 3 blade, but my brother has on his TM with the stock power system, and he didn't like the way it flew. That, however, is entirely his opinion. I may try it still. BTW, 7 cells definitely do help. These 280 size motors don't really seem to wake up on 6. Since no one else has checked in here, I must be the only one at RCU runnig this setup...or the others have been so frustrated by the experience they don't want to talk about it!
Since no one else has checked in here, I must be the only one at RCU runnig this setup...or the others have been so frustrated by the experience they don't want to talk about it!
04-30-2003, 07:15 PM
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3-blade
Hi buzzbomber - Your brother's "stock" motor was an IPS I presume, and (unless it was geared at 6:1 or more) a 3-blade 9x7 would simply have been too much for it. Even the twin-IPS motors at 3.5:1 or 4:1 don't have enough torque to turn that size prop to advantage. Your 280 size should be able to deal with it a lot better.
Cheers, Phil
Cheers, Phil
05-06-2003, 02:50 PM
#7
GWS Tiger Moth with EPS100C
Phil,
The motor my brother was using is indeed the IPS-A drive. It would seem that if it were overloading the motor, it simply would have burned it out (I've seem it enough to know when to expect it now!) What it SEEMED like was running a prop with too little thrust, ie ineffiecient. Maybe its the extra rotating mass, who knows? Where did you get specs on the 3 blade? Just from the GWS site, or do you have another source? I try to educate myself as much as possible about my hobbies so I'm learning and not just flailing around blindly. I know that in theory, 3 blades are less efficient than two blades, and that, again in theory, you can drop ~ 1" dia. same pitch on a three versus two blade. However, I have also learned several lessons that taught me not to rely entirely on theory
. A 280 geared 2.5:1 on an 8x6 prop and 8 cells, according to published specs and simple calculations, should not pose a problem. This combination and propeller changes inc. 9x4.7 and 9x7 has killed two 280 motors within about 25 flights, and worse, doesn't even offer great performance due to the added weight. (these results were on another flyer's planes, not mine. I use an EPS-100C S-1 with 9070 prop and 7x270NiCD with good results. He uses a wattage 2.5:1 with 8x6 or 9x4.7 prop and 8x720NiMH). Anyhow, I'm just rambling at this point. I'm not doubting your knowledge of the subject, just curious to see if you have had similar experiences where theory and reality don't jive 
On another note: Isn't anyone else other than the 3 guys I fly with running modded moths? Just want to see what everyone's got.
The motor my brother was using is indeed the IPS-A drive. It would seem that if it were overloading the motor, it simply would have burned it out (I've seem it enough to know when to expect it now!) What it SEEMED like was running a prop with too little thrust, ie ineffiecient. Maybe its the extra rotating mass, who knows? Where did you get specs on the 3 blade? Just from the GWS site, or do you have another source? I try to educate myself as much as possible about my hobbies so I'm learning and not just flailing around blindly. I know that in theory, 3 blades are less efficient than two blades, and that, again in theory, you can drop ~ 1" dia. same pitch on a three versus two blade. However, I have also learned several lessons that taught me not to rely entirely on theory
. A 280 geared 2.5:1 on an 8x6 prop and 8 cells, according to published specs and simple calculations, should not pose a problem. This combination and propeller changes inc. 9x4.7 and 9x7 has killed two 280 motors within about 25 flights, and worse, doesn't even offer great performance due to the added weight. (these results were on another flyer's planes, not mine. I use an EPS-100C S-1 with 9070 prop and 7x270NiCD with good results. He uses a wattage 2.5:1 with 8x6 or 9x4.7 prop and 8x720NiMH). Anyhow, I'm just rambling at this point. I'm not doubting your knowledge of the subject, just curious to see if you have had similar experiences where theory and reality don't jive On another note: Isn't anyone else other than the 3 guys I fly with running modded moths? Just want to see what everyone's got.
05-06-2003, 04:24 PM
#8
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GWS Tiger Moth with EPS100C
I modded my Moth with a 100C-S1 and tried 9x7, 10x4.7 and 10x8 props with the 8.4V QC LiIons. The 10x8 would shut the pack towards full throttle. Since performance didn't really improve, I reverted back to the IPS-A.
Overall, I wasn't too happy with the performance. I think a larger gear ratio would make it better, as will using the Kokam 2x1020 or ETech 2x700 LiPo's will be better to compensate for the weight gain.
Overall, I wasn't too happy with the performance. I think a larger gear ratio would make it better, as will using the Kokam 2x1020 or ETech 2x700 LiPo's will be better to compensate for the weight gain.
05-06-2003, 04:43 PM
#9
GWS Tiger Moth with EPS100C
Electrifan:
Thanks for the reply. How has your motor life been with the IPS-A? That was the reason I went right to a bigger motor--everyone I know flying the moth has been through more than one motor, and those little suckers get expensive. I now know it was probably a mistake, but oh well, right? I actually can live with the performance of the moth on the EPS-100. All things considered, the moth climbs better now, and is more stable in wind, but duration is definitely down, and less than perfect returns to earth have a higher damage potential with the added mass. I still think the IPS motor life issue is odd because I have a pico cub with hundreds of flights using 6/7 x 150 and 6/7 x 270 packs and I'm still on the original unit.
Thanks for the reply. How has your motor life been with the IPS-A? That was the reason I went right to a bigger motor--everyone I know flying the moth has been through more than one motor, and those little suckers get expensive. I now know it was probably a mistake, but oh well, right? I actually can live with the performance of the moth on the EPS-100. All things considered, the moth climbs better now, and is more stable in wind, but duration is definitely down, and less than perfect returns to earth have a higher damage potential with the added mass. I still think the IPS motor life issue is odd because I have a pico cub with hundreds of flights using 6/7 x 150 and 6/7 x 270 packs and I'm still on the original unit.
05-06-2003, 06:01 PM
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Motor life etc.
Hey Matt, I imagine your IPS A longevity in the Pico Cub is due to the fact that you cannot suck more than 1.5 - 2amps out of a 6/7 cell 150 or 270 pack, but on 8-cells you may be pulling 3 - 4 amps, which the IPS motors do not like! In one test of my S1 with a 9x7 using an 8-cell 950KAN NiMH pack, I managed to draw 4.5A and 162g (5.7oz) thrust - far too much unless one wanted to fry eggs on the motor.
Do you think you could put a 280 into the TM? If you reckon it could handle the weight increase (72g for 280 with a 5:1 g/box and 11" GWS prop v. 35g for the IPS A with a 9" GWS prop) you'd get a heck of a lot more thrust. An IPS A will give you, realistically, no more than say, 5oz (140g) on 3A, whereas a 280 geared 5:1 with an 11x4.7 could get you a sustainable figure of 7oz (200g) or more, on about 2.5A.
The other possibility might be a GWS dual motor (RXC-1, 4.14:1 - system weight 52g) - with a 9x4.7 and 8-cells you can get 8oz (225g) thrust out of one of these at 4A [that's 2A to each motor so they are not being overloaded].
As they say, the only way to really find out what works is to "suck it and see".
Cheers, Phil
Do you think you could put a 280 into the TM? If you reckon it could handle the weight increase (72g for 280 with a 5:1 g/box and 11" GWS prop v. 35g for the IPS A with a 9" GWS prop) you'd get a heck of a lot more thrust. An IPS A will give you, realistically, no more than say, 5oz (140g) on 3A, whereas a 280 geared 5:1 with an 11x4.7 could get you a sustainable figure of 7oz (200g) or more, on about 2.5A.
The other possibility might be a GWS dual motor (RXC-1, 4.14:1 - system weight 52g) - with a 9x4.7 and 8-cells you can get 8oz (225g) thrust out of one of these at 4A [that's 2A to each motor so they are not being overloaded].
As they say, the only way to really find out what works is to "suck it and see".
Cheers, Phil
05-06-2003, 06:49 PM
#11
GWS Tiger Moth with EPS100C
My father (one of the people I fly TM's with) has tried the exact IPS-dual you have described and he blew that, the single IPS-A, and the described wattage setup, (which, BTW seems lower quality than the GWS) too. Since he's an electrical engineer, I chalk it up to knowing too much 
, or evil spirits, maybe bad kharma even. j/k. What really puzzles me is that this has all involved a GWS ICS-50 ESC which is rated at 2A cont. and 4A max. Obviously those ratings are conservative if he keeps losing motors and not the ESC. That, or something is very seriously out of whack with his ESC. You have a point about the higher capacity cells and the lower internal resistance allowing a higer draw. I forgot about that in the 7 to 8 cell jump. I believe that my father ordered new motors for the dual to wire in series..we'll see how that goes. As for myself, I'm going to stick to the EPS-100C for now. To answer your query about the 280, the motor in this setup is identical to a graupner 280 6 volt in case dimensions and I imagine in performance specs also. GWS calls it an EM100. Link: http://www.gws.com.tw/english/product/motor/motor.htm
Later,
Matt
, or evil spirits, maybe bad kharma even. j/k. What really puzzles me is that this has all involved a GWS ICS-50 ESC which is rated at 2A cont. and 4A max. Obviously those ratings are conservative if he keeps losing motors and not the ESC. That, or something is very seriously out of whack with his ESC. You have a point about the higher capacity cells and the lower internal resistance allowing a higer draw. I forgot about that in the 7 to 8 cell jump. I believe that my father ordered new motors for the dual to wire in series..we'll see how that goes. As for myself, I'm going to stick to the EPS-100C for now. To answer your query about the 280, the motor in this setup is identical to a graupner 280 6 volt in case dimensions and I imagine in performance specs also. GWS calls it an EM100. Link: http://www.gws.com.tw/english/product/motor/motor.htm Later,
Matt
05-06-2003, 07:07 PM
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GWS Tiger Moth with EPS100C
Guys - don't forget that the Moth can only take so much weight. Sure, the extra thrust may even make it hover for a bit, but then the LG and wings are being taxed.
Dr. Phil is right, the tiny IPS motors can only take so much. Even keeping the current low, I have read reports of varied mileage from them. I probably have put in about 30-35 hours on mine and performance is lagging a bit.
I think the RXC combo with the ETech 2x700 LiPo's sound like the best choice w/o having to change the mount stick and maintaining weight.
Dr. Phil
is right, the tiny IPS motors can only take so much. Even keeping the current low, I have read reports of varied mileage from them. I probably have put in about 30-35 hours on mine and performance is lagging a bit.I think the RXC combo with the ETech 2x700 LiPo's sound like the best choice w/o having to change the mount stick and maintaining weight.
05-06-2003, 07:44 PM
#13
GWS Tiger Moth with EPS100C
Oh, believe me you, I know aaalllll about added weight...that's why I don't post any pics of my cub (the LG has been toasted several times from sloppy landings). You are absolutely right though. I should know better than to try turning these *****cats into fire-breathing tigers, but sometimes the "bigger, better, faster, more!" mentality is irresistable, you dig? I am leery of the LiPos at this point. More questions, more cash. I am aware that greater performance gains are almost universally aquired from weight reduction as opposed to power increase accompanied by weight increase, but like I said, more more more! Besides, my moth hasn't yet suffered from the few odd grams I added (not that a diet would hurt it). Geez, I meant to repsond with a quick two lines. Sorry for the long post
05-06-2003, 08:43 PM
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GWS Tiger Moth with EPS100C
BTW, at the recent RC Expo in South Cal, GWS is apparently planning for a larger version of the Moth. The pic I saw wasn't the greatest, but it seems that they now have a steerable tail wheel, stronger struts, thicker wings, foam cowl. The prop in the pic appears smaller, so they may have it on a DD motor. The wings also seem to have less dihedral and hint of an aileron. LG/wheels still look 'skinny'.
05-07-2003, 09:14 AM
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GWS Tiger Moth with EPS100C
I upgraded my TM to a m100 280 size motor
I built a small box motor mount out of 3/32 lite ply. The TM takes off from the ground quite well and has more flying capability than the stock ips 100. there is a TM version with a 280 motor but they are hard to find, special order from LHS. The M100 has a gearbox and a prop saver, at $25.00 including gearbox it is a good deal.
The m100 can be found at http://65.108.69.130/jetset/sub/motor.htm
I built a small box motor mount out of 3/32 lite ply. The TM takes off from the ground quite well and has more flying capability than the stock ips 100. there is a TM version with a 280 motor but they are hard to find, special order from LHS. The M100 has a gearbox and a prop saver, at $25.00 including gearbox it is a good deal.
The m100 can be found at http://65.108.69.130/jetset/sub/motor.htm
05-07-2003, 11:17 AM
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GWS Tiger Moth with EPS100C
I'm scratching my head trying to figure out why you guys are going to all this work hopping up a Moth.
Why don't you just get HL's Fatty Sparrow? A biplane, the same size as a Moth, but it's designed to handle the 350 motor that comes with it (insert Tim Allen grunts).
Why don't you just get HL's Fatty Sparrow? A biplane, the same size as a Moth, but it's designed to handle the 350 motor that comes with it (insert Tim Allen grunts).
05-07-2003, 01:04 PM
#21
GWS Tiger Moth with EPS100C
Goofup: very simple--because I can, and I know I shouldn't.
Woodduck: I actually looked into the M100, but it wasn't available locally, so I couldn't get an up-close look at it (I like to see unfamiliar things in person before I buy)-as a sidenote, I used to live about 2 blocks away from the company that markets it, and never even knew they were there! :stupid:
Electrifan: I just saw that on the GWS website. Looks nice! For some reason, though, GWS still insists that I go to Du-bro to get a decent set of wheels. I just automatically pick up a set of 1-1/2" mini-lite foams when I buy a GWS kit. What would be really nice is if the wing is not undercambered on the bigger version, and can easily be configured w/ or w/o ailerons. One of the local TM flyers actually built up a balsa center section (top wing only) with spruce stub spars and added ailerons with a bellcrank setup. As expected, it turned out to not be worth the effort in flying qualities, but it sure looks cool.
To update, I put a few flights in last night with the EPS100C setup, and again(apparently the laws of physics are unwilling to change in order to please me) the flight on six cells was mostly an effort to remain in a shallow climb just above stall speed, but the seven cell flight was far better than that. It just wants to climb and easily maintains or gains altitude, it rolls to both sides easily and gracefully, can do consecutive loops, and with throttle set for a slight climb after 3-4 min. of mild aerobatics, I got about 8 minutes on a 7 cell 270 maH pack. (I'm not exactly sure, since I just glanced at my wristwatch at launch and landing to estimate) Not too bad, thought I.
Woodduck: I actually looked into the M100, but it wasn't available locally, so I couldn't get an up-close look at it (I like to see unfamiliar things in person before I buy)-as a sidenote, I used to live about 2 blocks away from the company that markets it, and never even knew they were there! :stupid:
Electrifan: I just saw that on the GWS website. Looks nice! For some reason, though, GWS still insists that I go to Du-bro to get a decent set of wheels. I just automatically pick up a set of 1-1/2" mini-lite foams when I buy a GWS kit. What would be really nice is if the wing is not undercambered on the bigger version, and can easily be configured w/ or w/o ailerons. One of the local TM flyers actually built up a balsa center section (top wing only) with spruce stub spars and added ailerons with a bellcrank setup. As expected, it turned out to not be worth the effort in flying qualities, but it sure looks cool.
To update, I put a few flights in last night with the EPS100C setup, and again(apparently the laws of physics are unwilling to change in order to please me) the flight on six cells was mostly an effort to remain in a shallow climb just above stall speed, but the seven cell flight was far better than that. It just wants to climb and easily maintains or gains altitude, it rolls to both sides easily and gracefully, can do consecutive loops, and with throttle set for a slight climb after 3-4 min. of mild aerobatics, I got about 8 minutes on a 7 cell 270 maH pack. (I'm not exactly sure, since I just glanced at my wristwatch at launch and landing to estimate) Not too bad, thought I.
05-07-2003, 01:23 PM
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M250/M100
Dear Buzzbomber - your indication of an interest in an M100 motor, and particularly your wish to see the goods in person before you bought it, gives me the opportunity to share with you an e-mail I sent to Jet Flyer mainly about the M250 (but with a side note on the M100) relating to what I consider to be "unrealistic performance claims = misleading advertising". They have not deigned to reply, so I guess I'm free to share with you guys my thoughts on the subject.
Jet Set/Parkflyers M250 Pro spec motor gear drive:
I became interested in one of these M250's because it had been touted on the websites of mantaplane.com and parkflyer.com as being capable of producing 9.5oz (270g) static thrust, using an 8x6 APC prop @ 5100rpm using a 7-cell (8.4V) NiCd pack. The further implication was that this could be achieved at a current draw of 5.4 - 6.0amps at a nominal 8.4V (i.e. 45 - 50W input).
With a view to establishing these remarkable claims, I purchased an M250, ran it in carefully, then proceeded to test its performance on my standard test stand - with digital scale, Whattmeter and Hobbico optical tachometer. [In recent months I have tested dozens of motor/prop combinations ranging from Wes-Tech Micro DC 5-2.4 up through GWS IPS, IPS Dual and EPS 300C, and Graupner Speed 280, 300, 400, to a variety of brushless motors including MP Jet 25/25-26 and 25/35-20, Mini AC 1215/20, AXI 2808/20, and Phasor 15/4 - in most cases the data I have obtained correlate fairly well with the information available from motor manufacturers and from the various computer programs available for deriving static thrust from parameters such as power input/prop size/rpm].
I do believe that the M250 is a well made motor and it probably does out-perform most other basic "can 280 motors": the fabulous video clips on the www.mantaplane.com site indicate that an M250 has adequate power for an aircraft of the Mini Manta's size. However, the performance figures quoted in the promotions and in the documents which accompanied the motor are plainly unrealistic.
Yes, one can extract the magical "9.5oz" thrust figure from an M250, but not with an 8x6 prop, and certainly not at only 5100rpm (the Laws of Physics and Aerodynamics would need to be rewritten if that combination could produce that thrust figure).
Let us look at each of the components: In each test run, the "peak" value I obtained was for a momentary run at the start of the test, with a freshly charged battery pack. The 7-cell NiCd pack used was 600AE, the 8-cell NiMH pack was KAN950.
8x6 prop: on 7-cells the best I could achieve (momentary peak) was 7.1oz (202g) static thrust at 6.6A/7.8V (51W) and 4920rpm: on 8-cells it was 9.1oz (258g) at 8.1A/9.3V (78W) and 5400rpm. Neither combination could achieve 9.5oz!
5100rpm: 7-cells cannot spin an 8x6 at this figure. On 8-cells, 5100rpm produces only about 7.5oz. To achieve 9.5oz an 8x6 prop needs to spin in excess of 6200rpm!
5.4amps: At this current draw, voltage on 7-cells had dropped down to about 7.3V and the input power of about 41W gave only about 6.5oz static thrust. At 5.4A draw, voltage on 8-cells had dropped to 9.0V and 50W gave 7.3oz static thrust. To achieve 9.5oz thrust with an 8x6 appears to require at least 80W input, so one would need to draw about 15A through the M250! One promotion mentioned 6A as the maximum current draw, but even at that one would need a battery voltage of 13V or so to obtain the 80W figure!
Note: Since a nominal voltage of 8.4V appears in all the promotions, it seems to me that a constant voltage source of 8.4V must have been used to obtain your bench test figures. Now that in itself is unrealistic, as it is obvious [as noted above] that battery pack voltage diminishes under load, typically moreso in NiMH than in NiCd.
Now, one CAN achieve the 9.5oz thrust figure by using larger props:
I tested the M250 with a variety of APC SF props and obtained the following results.
9x4.7 APC SF: on 7-cells, the maximum which could be obtained was only 8.5oz (240g) at 4.8A/7.8V (39W) and 4950rpm. On 8-cells, 9.5oz (270g) was achieved at 5.3A/9.3V (51W) and 5340rpm.
10x4.7 APC SF: on 7-cells, 9.5oz (270g) was obtained at 6.4A/7.6V (49W) and 4200rpm. On 8-cells, 9.5oz (270g) was achieved at 5.1A/10.0V (51W) and 4200rpm.
11x4.7 APC SF: on 7-cells, 9.5oz (270g) was obtained at 5.7A/7.3V (43W) and 3600rpm. On 8-cells, 9.5oz (270g) was achieved at 4.9A/9.4V (46W) and 3540rpm.
One other note in the booklet accompanying the motor caught my interest: - it is suggested that, using a 7x5 APC prop (on a 7-cell NiCd pack), one can draw 5.1A through the M250. You can't!
Using 7-cells the maximum current draw achievable is 3.0A/8.4V (27W) for a thrust of 4.5oz (128g) at 6420rpm.
Using 8-cells one can draw 3.6A/9.4V (36W) for 5.8oz (166g) at 6810rpm.
Finally, in the booklet accompanying the motor, the comparison with a geared Speed 280 is not really a fair example. Of course, if one used, say, a 4:1 geared 280 with an 8x6 prop the thrust output probably would not exceed 4oz [I don't have other than a 5:1 geared Speed 280, and on 8-cells its peak output with an 8x6 was only 4.2oz (120g) at 2.0A/10.4V (22W) at 4470rpm]. However, using the appropriate gear ratio and the correct prop the standard Speed 280 can be prevailed upon to produce far more than 4oz of static thrust: - with an 11x4.7 APC SF prop on 8-cells, my 5:1 geared 280 produced 9.0oz (256g) static thrust at 2.8A/9.8V (33W) at 3480rpm. Now, due to its higher gear ratio, that is actually better than the M250 can achieve at the same current draw, and more efficient in terms of output in g/W (7.8g/W for the 280 v. ca.6.0g/W for the M250).
Comparison with a 5:1 geared Speed 300, using an 8-cell NiMh pack, indicates that, with an 8" prop (8x4 Slim), the 300 produces a little more thrust than the M250 at the same power input (8.4oz v. 7.3oz @ 50W), and is capable of drawing a higher peak current [8.4A/9.3V - 81W] to produce a maximum static thrust of 386g (13.6oz) @ 8850rpm.
With 9x5 and 10x7 props the 300 will pull around 10amps [for 90-100W] and produce as much as 400g (14.1oz) static thrust - again, rather more than the M250 can manage.
You compare the "system weights" for the M250 and Speed 280 in the booklet accompanying the motor: here, you do your M250 a disservice, since it actually weighs less than the figure of 2.3oz (65g) given. My M250 with an 8x6 APC SF prop [and wired with 18g wire and a Dean's Ultra connector] weighs only 2oz (56g). With the same prop, my Speed 280 with MP Jet 5:1 BB gearbox weighs 2.46oz (70g) [your figure is 2.2oz (62.5g)]. To round out the comparisons my Speed 300, with an MP Jet 5:1 BB gearbox and the same 8x6 prop, weighs 2.75oz (78g). The M250 clearly has some weight advantage, but the Speed 300 more than compensates for its 0.75oz (22g) higher weight by being capable of producing several ounces more thrust.
Performance figures in the advertising for the M100 also reveal some apparently unrealistic numbers: the quoted figure of 7oz (199g) static thrust with a 7.2x4.2 prop @ 4800rpm CANNOT be obtained in the real world - I do not have an M100 to test but the reputable LCRC Thrust Calculator indicates that, to achieve 7oz thrust, that size prop would have to spin at no less than 7400rpm! The figures I gave above for the slightly smaller 7x5 prop on the M250 give a rough indication of the rpm needed to reach the quoted 7oz figure [since 5.8oz (166g) required 6810rpm - extrapolation of these test data indicates 7oz would require close to 8000rpm - indeed, the predicted figure from LCRC (7800rpm) correlates pretty well].
Please understand, I have not produced this document to criticize your product. I do acknowledge that it is an excellently engineered motor/gearbox system, and I am proud to have one to use on my various aircraft to which it is clearly suited. I am only concerned that people in the R/C hobby, having read the performance claims for the M250, will have unrealistic expectations for the product and attempt to use it in aircraft which are too heavy for it in its stock form (a suggestion for use of larger props, to obtain greater thrust, with the caution that one should not demand TOO much from the motor, in terms of excessive current draws - would be welcomed).
Yours faithfully, Dr Phil Millener (Chattanooga, TN).
Jet Set/Parkflyers M250 Pro spec motor gear drive:
I became interested in one of these M250's because it had been touted on the websites of mantaplane.com and parkflyer.com as being capable of producing 9.5oz (270g) static thrust, using an 8x6 APC prop @ 5100rpm using a 7-cell (8.4V) NiCd pack. The further implication was that this could be achieved at a current draw of 5.4 - 6.0amps at a nominal 8.4V (i.e. 45 - 50W input).
With a view to establishing these remarkable claims, I purchased an M250, ran it in carefully, then proceeded to test its performance on my standard test stand - with digital scale, Whattmeter and Hobbico optical tachometer. [In recent months I have tested dozens of motor/prop combinations ranging from Wes-Tech Micro DC 5-2.4 up through GWS IPS, IPS Dual and EPS 300C, and Graupner Speed 280, 300, 400, to a variety of brushless motors including MP Jet 25/25-26 and 25/35-20, Mini AC 1215/20, AXI 2808/20, and Phasor 15/4 - in most cases the data I have obtained correlate fairly well with the information available from motor manufacturers and from the various computer programs available for deriving static thrust from parameters such as power input/prop size/rpm].
I do believe that the M250 is a well made motor and it probably does out-perform most other basic "can 280 motors": the fabulous video clips on the www.mantaplane.com site indicate that an M250 has adequate power for an aircraft of the Mini Manta's size. However, the performance figures quoted in the promotions and in the documents which accompanied the motor are plainly unrealistic.
Yes, one can extract the magical "9.5oz" thrust figure from an M250, but not with an 8x6 prop, and certainly not at only 5100rpm (the Laws of Physics and Aerodynamics would need to be rewritten if that combination could produce that thrust figure).
Let us look at each of the components: In each test run, the "peak" value I obtained was for a momentary run at the start of the test, with a freshly charged battery pack. The 7-cell NiCd pack used was 600AE, the 8-cell NiMH pack was KAN950.
8x6 prop: on 7-cells the best I could achieve (momentary peak) was 7.1oz (202g) static thrust at 6.6A/7.8V (51W) and 4920rpm: on 8-cells it was 9.1oz (258g) at 8.1A/9.3V (78W) and 5400rpm. Neither combination could achieve 9.5oz!
5100rpm: 7-cells cannot spin an 8x6 at this figure. On 8-cells, 5100rpm produces only about 7.5oz. To achieve 9.5oz an 8x6 prop needs to spin in excess of 6200rpm!
5.4amps: At this current draw, voltage on 7-cells had dropped down to about 7.3V and the input power of about 41W gave only about 6.5oz static thrust. At 5.4A draw, voltage on 8-cells had dropped to 9.0V and 50W gave 7.3oz static thrust. To achieve 9.5oz thrust with an 8x6 appears to require at least 80W input, so one would need to draw about 15A through the M250! One promotion mentioned 6A as the maximum current draw, but even at that one would need a battery voltage of 13V or so to obtain the 80W figure!
Note: Since a nominal voltage of 8.4V appears in all the promotions, it seems to me that a constant voltage source of 8.4V must have been used to obtain your bench test figures. Now that in itself is unrealistic, as it is obvious [as noted above] that battery pack voltage diminishes under load, typically moreso in NiMH than in NiCd.
Now, one CAN achieve the 9.5oz thrust figure by using larger props:
I tested the M250 with a variety of APC SF props and obtained the following results.
9x4.7 APC SF: on 7-cells, the maximum which could be obtained was only 8.5oz (240g) at 4.8A/7.8V (39W) and 4950rpm. On 8-cells, 9.5oz (270g) was achieved at 5.3A/9.3V (51W) and 5340rpm.
10x4.7 APC SF: on 7-cells, 9.5oz (270g) was obtained at 6.4A/7.6V (49W) and 4200rpm. On 8-cells, 9.5oz (270g) was achieved at 5.1A/10.0V (51W) and 4200rpm.
11x4.7 APC SF: on 7-cells, 9.5oz (270g) was obtained at 5.7A/7.3V (43W) and 3600rpm. On 8-cells, 9.5oz (270g) was achieved at 4.9A/9.4V (46W) and 3540rpm.
One other note in the booklet accompanying the motor caught my interest: - it is suggested that, using a 7x5 APC prop (on a 7-cell NiCd pack), one can draw 5.1A through the M250. You can't!
Using 7-cells the maximum current draw achievable is 3.0A/8.4V (27W) for a thrust of 4.5oz (128g) at 6420rpm.
Using 8-cells one can draw 3.6A/9.4V (36W) for 5.8oz (166g) at 6810rpm.
Finally, in the booklet accompanying the motor, the comparison with a geared Speed 280 is not really a fair example. Of course, if one used, say, a 4:1 geared 280 with an 8x6 prop the thrust output probably would not exceed 4oz [I don't have other than a 5:1 geared Speed 280, and on 8-cells its peak output with an 8x6 was only 4.2oz (120g) at 2.0A/10.4V (22W) at 4470rpm]. However, using the appropriate gear ratio and the correct prop the standard Speed 280 can be prevailed upon to produce far more than 4oz of static thrust: - with an 11x4.7 APC SF prop on 8-cells, my 5:1 geared 280 produced 9.0oz (256g) static thrust at 2.8A/9.8V (33W) at 3480rpm. Now, due to its higher gear ratio, that is actually better than the M250 can achieve at the same current draw, and more efficient in terms of output in g/W (7.8g/W for the 280 v. ca.6.0g/W for the M250).
Comparison with a 5:1 geared Speed 300, using an 8-cell NiMh pack, indicates that, with an 8" prop (8x4 Slim), the 300 produces a little more thrust than the M250 at the same power input (8.4oz v. 7.3oz @ 50W), and is capable of drawing a higher peak current [8.4A/9.3V - 81W] to produce a maximum static thrust of 386g (13.6oz) @ 8850rpm.
With 9x5 and 10x7 props the 300 will pull around 10amps [for 90-100W] and produce as much as 400g (14.1oz) static thrust - again, rather more than the M250 can manage.
You compare the "system weights" for the M250 and Speed 280 in the booklet accompanying the motor: here, you do your M250 a disservice, since it actually weighs less than the figure of 2.3oz (65g) given. My M250 with an 8x6 APC SF prop [and wired with 18g wire and a Dean's Ultra connector] weighs only 2oz (56g). With the same prop, my Speed 280 with MP Jet 5:1 BB gearbox weighs 2.46oz (70g) [your figure is 2.2oz (62.5g)]. To round out the comparisons my Speed 300, with an MP Jet 5:1 BB gearbox and the same 8x6 prop, weighs 2.75oz (78g). The M250 clearly has some weight advantage, but the Speed 300 more than compensates for its 0.75oz (22g) higher weight by being capable of producing several ounces more thrust.
Performance figures in the advertising for the M100 also reveal some apparently unrealistic numbers: the quoted figure of 7oz (199g) static thrust with a 7.2x4.2 prop @ 4800rpm CANNOT be obtained in the real world - I do not have an M100 to test but the reputable LCRC Thrust Calculator indicates that, to achieve 7oz thrust, that size prop would have to spin at no less than 7400rpm! The figures I gave above for the slightly smaller 7x5 prop on the M250 give a rough indication of the rpm needed to reach the quoted 7oz figure [since 5.8oz (166g) required 6810rpm - extrapolation of these test data indicates 7oz would require close to 8000rpm - indeed, the predicted figure from LCRC (7800rpm) correlates pretty well].
Please understand, I have not produced this document to criticize your product. I do acknowledge that it is an excellently engineered motor/gearbox system, and I am proud to have one to use on my various aircraft to which it is clearly suited. I am only concerned that people in the R/C hobby, having read the performance claims for the M250, will have unrealistic expectations for the product and attempt to use it in aircraft which are too heavy for it in its stock form (a suggestion for use of larger props, to obtain greater thrust, with the caution that one should not demand TOO much from the motor, in terms of excessive current draws - would be welcomed).
Yours faithfully, Dr Phil Millener (Chattanooga, TN).
05-07-2003, 01:37 PM
#23
GWS Tiger Moth with EPS100C
Dr Phil:
I commend you on having really done your homework on this one. Far more scientific than my typical "look at the specs to get a ballpark figure, then do it to see if it works" approach. The M250 specs claimed above seem like fantasy even to me!
I commend you on having really done your homework on this one. Far more scientific than my typical "look at the specs to get a ballpark figure, then do it to see if it works" approach.
The M250 specs claimed above seem like fantasy even to me!
05-08-2003, 01:43 AM
#24
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GWS Tiger Moth with EPS100C
this might be waaayyyy out in left field or something,but, seems to me the 'moth flies fabulous dead stock with reccomended battery. since it seems to be everybodies favorite thing to hop-up,maybe GWSwill come out with a new version with a jeti phasor 45/3 in it or something.
05-08-2003, 12:38 PM
#25
GWS Tiger Moth with EPS100C
It's only way out in left field because its sailing over the fence! You're exactly right. I mainly got started on this crusade because I was given a DD conversion kit (I couldn't just NOT use it, could I?), and it just sort of snowballed since then. I left the powertrain in my GWS cub bone stock, and the planes have two distinctly different personalities now. The tiger moth is actually more stable in wind, what with the higher wing loading and all. The cub I just lope around with on calm nights and fly the moth when its a little gustier. They're both great. If I had to do it all over, I'd probably leave the IPS in the moth, and stick to 7 cell batteries for the added boost. I know a lot of electric planes come with less than stellar drive systems, but, IMO, GWS probably picked the ideal setup from the get-go on these. Or......we could put a norvel .061 up front and watch it disintegrate in midair