Cyclicscooby Posted March 19, 2012 Share Posted March 19, 2012 The motor in my Bipe is drawing too much current, even tho, its about the same spec as a similar plane which runs fine on the same Lipo's, and similar prop (Edge - 8x4, Bipe - 8x3.8sf)... I had it in my mind, that it was a 1200kv motor, but its actually 1900kv, and i'm pretty sure thats the problem.. It being too high for my requirements, that is.. To clarify.. Both Depron home-made, Both using a 1300mAh 3s.. Plane 1- 36" Edge profile foamie - 325g (440g inc 3s) Fusion 2826/12 1380Kv (100W) - 8x4 prop Never had any issues, never got hot, draws 700-800 mA from 8-9 mins flight Plane 2- 31" Full bodied Depron Bipe - 440g (555g inc 3s) Overlander 2826/09 1900Kv (150W-260W.? says both ) with an 8x3.8 SF A 6 minute flight uses 900-950mA.. Way more than the Edge.. I've already cooked a motor, and have limited this same-spec replacement to 53% max throttle using the Watt-meter, to keep it in limits.. I know I could try a 7x5 prop, to lower the current draw, but i'm concerned that wont give enuf lift, or change the 'slow-fly' abilities of the Bipe.. Before you ask, I got the motor cuz my LMS has limited range, and it looked like it was right.!!.. Not that thats important now, cuz I realise i'm gonna have to replace it anyway.. Anyone confirm my thoughts... I should add, that the Bipe flies fine as-is, but needs sorting before I nail the motor.. again.. Luv Chrisie.. xx Edited By Cyclicscooby on 19/03/2012 22:57:58 Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted March 19, 2012 Share Posted March 19, 2012 Er yes, 1900kv is too much for a 8 x3.8 on a 3s, you could try it on a 2s battery though, that would have the same effect as limiting the throttle, get a slightly larger 2s battery. Also thats probably why Overlander quote 2 power ratings, 2s and 3s battery limits (its all down to the amps) Quote Link to comment Share on other sites More sharing options...
Seamus O'Leprosy Posted March 20, 2012 Share Posted March 20, 2012 you need a what meter! Quote Link to comment Share on other sites More sharing options...
Allan Bowker Posted March 20, 2012 Share Posted March 20, 2012 I think Chrisie already has one Seamus, I had to re-read the post to realise. I would agree that the kv rating seems high for that size prop. I would recommend that you need to buy a motor that will give the wattage you need within the prop size you wish to swing. 100watts per lb will give you lots of power, usually no need to go over that. Look at the motor spec and the recommended prop sizes, they normally list wattage output for a given prop. Giant Cod is a good source and Hobby King have a motor size selector thingy. If you prefer the LMS route, I would recommend giving BRC Hobbies a call, they would be able to sort you out with something at a good price. Edited By Allan Bowker on 20/03/2012 13:00:10 Quote Link to comment Share on other sites More sharing options...
PatMc Posted March 20, 2012 Share Posted March 20, 2012 Seamus & Allan, I think there's a clue in the OP Quote "I've already cooked a motor, and have limited this same-spec replacement to 53% max throttle using the Watt-meter, to keep it in limits." Edited By PatMc on 20/03/2012 12:58:57 Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted March 20, 2012 Share Posted March 20, 2012 I’m not sure if I’m confused or not, which probably means I might be, but this line - I've already cooked a motor, and have limited this same-spec replacement to 53% max throttle using the Watt-meter, to keep it in limits.. - from the OP seems to me that Chrissy already uses a wattmeter? PB Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 20, 2012 Share Posted March 20, 2012 Chrissie Surely changing a prop is much cheaper and quicker than risking a motor. At the higher revs the 1900kv unit is capable of the 7x5 (or even a 7x4) may give the thrust and keep within the amps limit. At the ultimate I doubt you will be able to exactly match the lower kV motor/prop set up but you should get quite close. As an example a 7x6 took my motor a bit over it maximum rating so I fitted a 7x4 and it flew very nicely. As an experiment I fitted the 7x6 and took care to only use fullpower when in the air. It flew rather better and to my surprise for rather longer as well. Obviously the coarser pitch prop was a bit more efficient at part throttle. Moral? Try it and see! Edited By Simon Chaddock on 20/03/2012 15:22:31 Quote Link to comment Share on other sites More sharing options...
Cyclicscooby Posted March 21, 2012 Author Share Posted March 21, 2012 Thanks for the replies guys... Yes, I do have a watt-meter... I built the bipe specifically as a slow-flyer, not a bat out of hell, so I think (correct me if i'm wrong) that a 7xX prop wont do what I want.. A lower Kv motor and stick with the 8, or even 9" prop... I have got a 'spare' E-flite Park370 in the non-flying tailwind, which is a 1320Kv... Might give that a go before endulging in a new motor... Thanks chaps.. Luv Chrisie.. xx Quote Link to comment Share on other sites More sharing options...
Seamus O'Leprosy Posted March 21, 2012 Share Posted March 21, 2012 Tell me what I already know ......... You need a what meter......... Keep up lads Quote Link to comment Share on other sites More sharing options...
Allan Bowker Posted March 21, 2012 Share Posted March 21, 2012 My meter reads 4 what's in this thread Chrisie is doing the right thing by changing the motor to a lower KV for that size prop. Edited By Allan Bowker on 21/03/2012 17:56:18 Quote Link to comment Share on other sites More sharing options...
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