electric help

Sam has just bought a Modelisme FURY wt 750. Appreciate suggestions on Motor,Esc......john

John,

Welcolme along this is just what the forum is for, Ive used 2 power systems in this size both to equally good efect

First off the EF2118/900 and airbos 35amp esc from www.freestylerc.co.uk
and secound the Thumper 3548/900 and Tornado 40amp esc from overlander (this one proberbly abit overkill for the fury)

Both systems are fantastic and imo the best out there but in the fury my pick would be the EF2818/900 running 3s1p 1800mah/2000mah lipos

Im sure others will chime in with cheeper Chinc alternatives so have a good look round any more questions just shout

Mark

I would be looking for around 250 Watts in an airframe like that, possibly more if you are trying to unleash the hooligan from within!

Going for batteries at the larger end of the scale (2000mAh or so) will add a little bit of weight, but for the generally gusty conditions found round these parts, the extra weight will help smooth things out a little! This would be a 3s lipo pack too by the way.

An Esc of around 35-40 amps should do the trick quite comfortably, and the prop would be best around the 11" diameter size. The prop pitch shouldn't need to be too high, you are after thrust with this model, not speed. I would aim for around 5" pitch props. The motors Mark suggested would be a good starting point, although the EF one is probably the best of the two. The other alternative which would work well in this model, is a PA Thrust 20 motor, coupled with an 11x5.5" prop. That will pull around 25 amps or so on a 3s pack for over 250 watts.

There is quite an extensive thread on the RCGroups forum here: http://www.rcgroups.com/forums/showthread.php?t=589120

Worth a read if you have an hour or two spare!

Cheers
Andy

thanks Mark and Andy for suggestions.Ive been on Giant Cod web site what would their equivalent be of a
AXI 2217-16 or those that you suggest ?
Also on the motor specs its give,eg,
current capacity 45amp/30sec does this mean the motor will allow draw of 45 amp for 30 seconds ?if so what capacity ESC would be used a 50 amp ?

thanks john

you would be looking for a 50amp esc for that motor which in turn would mean you would need a minimum off 2200mah lipos @ 20c, this is worked out because the motor will pull 45amp, batts will need to be capable of that so 2200mah= 22amp (20c means batts will work double that so 44amp) see what I mean??

This is then driving the weight of the set-up up slightly which in turn up`s the wing loading meaning the plane will need to be flown a little faster, its all very small differantces but it is worth thinking about,

Mindfeild i know

Mark

Don't forget that it is the size of the prop (i.e. load on the motor) and voltage of the battery pack that will primarily determine the current drawn by the motor. Generally, if you increase the size or pitch of the prop, or increase the battery voltage, the current draw will rise (sometimes quite sharply!). Consequently, reducing teh size of the prop, lowering the battery voltage, will cause a reduction in the current drawn.

The ratings for the motors that you quote (a current for a set period of time) are the maximum the motor is rated to work at. If you go over this, you risk overheating the motor, and causing it to expire prematurely. Sizing an ESC is really just a case of knowing what sort of current draw you epect to see, then giving a little bit of headroom. For example, if I know a setup will draw around 25Amps maximum, I will use a 35A Esc. If I know a setup will draw around 45Amps max, I will use an esc of 50 or 60A (depending on what is available). The important thing to do is always use an ESC rated for more current than you expect to draw. Doing that helps keep the magic smoke inside the ESC, where it works best

Regarding the Axi motor replacement, then personally, I would just buy the Axi. They are very nice little motors, and I think they are worth the extra over the chinese stuff. The equivalent motor on the GiantCod website is this one: http://www.giantcod.co.uk/221716t-1050kv-220w-brushless-outrunner-motor-p-402408.html?osCsid=6a0e9a8239ec4a4a686bc62b4028a13e

This looks like a direct replacement. The way I determine this, is to compare a few things between the two. The first is the kV (rpm/volt) ratingm which tells me how fast the motor turns per volt applied. The second is the current ratings. These hsould be broadly similar. Thirdly, the mechanical dimensions/weight. These should also be similar.

You may wonder what the difference between a 12 quid motor and a 30 quid motor is, and at first glance (and reading the specs) it might not look like much at all. Generally the more expensive motors (certainly the Axi's) will be a fia rbit more efficient. This means less battery power is wasted heating up the motor, and more of it goes into turning the propellor. It can often give you a good 10% extra flight time from the same battery packs!

Hope that helps!

Andy

Andy...appreciate your help.This evening after a few stiff drinks Ill try and absorb all the info you and Mark have given.
Give me the good old days,a Mills .75,an egg cup of fuel,4 hours trying to start it,one numb index finger and going home to tea on the table.

john

The best bit of advice I offer Electric newbies, is to get someone who knows what they are doing to spec the power system for you, or copy a proven setup exactly!

If you have any other questions, or something doesn't sound quite right to you, just shout. I can explain most things about electric flight without resorting to a bit of chalk and a blackboard too much

Cheers
Andy