May i ask a silly question please?

[Emma 47]

Please don't shout at me but I am getting a little confused. I won a BH Sputnik in the Christmas super draw and am trying to source the parts to complete it.

The specs ask for an Emax 2826/06 motor.

please could someone explain simply so I can understand what the difference is between a 2826/06 and a 2826/09 apart from the manufacturer and would the 2826/09 be suitable for this aircraft.

Please be gentle this is my first aircraft and I don't want to get it wrong.

Thank you for any light you can shed on this.

[Martin 0]

A 2826/06 and a 2826/09 are both the same size, and will both look the same from the outside, but they are not equivalent motors.

"2826" simply means that the motor is 28mm in diameter and 26mm in length (not including the shaft).

The "/06" or "/09" refers to the number of turns of wire in the motor. This affects the "kV" rating of the motor, which is also often quoted for motors, and refers to the speed (in rpm) that the motor will turn for a particular supply voltage.

Using a motor with a different kV rating may require you to change any or all of the prop size, the battery pack cell count, and the ESC. If you just substitute a motor without doing the calculations then you could end up with insufficient power, or overload your motor/ESC.

If you want to use a different motor, it's better to instead look up the specs of the recommended one, and try to find another motor with the same kV rating. I found the specs of the Emax motor here:

http://www.emaxmotor.com/emax-gt-2826-p ... -1235.html

(Note that the name of the page is wrong - they describe the /06 one as equivalent to a "Power 32" not a "Power 25".)

This page says that the 2826/06 is a 710kV motor. It should be OK to substitute another 2826-size motor with similar kV rating. I had a quick look on the Hobbyking motor finder, but didn't find any, unfortunately - they seem to only sell significantly higher kV motors for this physical size.

If substituting parts (even ones with similar specs) into an electric powertrain, you may also want to check the result with a wattmeter to make sure that your motor, ESC and battery are all being asked to perform within their specified maximum current.

[Emma 47]

Thanks Martin.

I did try google but just ended up getting myself in a tizz.

KV I understand so will use the Emax one for now.

[Bravedan 106]

Hi ChasePlane,

Nobody is going to shout at you, and you have every right to be confused!

One MAJOR problem is that some manufacturers state dimensions by external size (as Martin intimates) and some by the STATOR dimensions (the internal rotor max dimensions). EMax is a case in point as they identify the motor as 2826 by title, but this is not its overall size without shaft, which is variously stated but is on their own site stated as 47.5x39, with a drawing published showing these overall dimensions!

Generically the suffix number does relate to the number (and gauge wire) of the windings, with if there is a range of winds on offer with the SAME SIZE rotor a higher number being more turns of thinner wire, lower number less turns of thicker wire. Generically a 2212 rotor sized motor of 06 wind motor will have a kV (no-load rotation speed) of around 2200kV, and an 09 wind will be around 1400kV!

Lets take an example of a motor I know very well, and have used for many years, the Suppo 2212-6. This motor is/was widely imported and "branded" with re-labelling by a number of resellers like RobotBirds/BRC. For a while it was even anodised in other than gold and sold with other trade names inc by HobbyKing. They may use 2212/6 or 2212-6, same difference!!

If you measure the case you will find it is 28mm x 26mm. Some resellers therefore re-label it and sell it as a 2826-xx, some as a 2212-xx. If you buy a direct supply or Chinese reseller item it will usually have a silver label with black print simply stating (say) 2212-6. and its kV is alternately stated as 2200 or 2300kV.

Speaking for this 2212-06 motor, the prop sizes are around 7x5 down to 6x4, I run either depending on the planes weight and drag.

Now, I also use Suppo 2212-14 motors, bought direct from China and labelled 2212-14. These are the SAME case size, 2826, the same rotor size (2212), but have more windings of thinner gauge (which is really noticeable by observation!), and will generically run a larger 8 or 9" prop.

This is within a single manufacturers range.

SO, looking now more overall all offerings, a 2826 ROTOR sized motor will subject to windings naturally have more power and torque than a 2212 ROTOR sized motor, yet both might be sold as 2826's!!

Yes, I know this may not seem helpful, but it is very important that you understand that there is no single reliable system used to state what a brushless motor is by title, you have to look into the full spec and if possible cross reference as mistakes in print abound!

As an example (in a different sphere of model flying entirely) the widely published tables of FPV Video frequencies available on video transmitters are SO often wrong it's laughable, even to the extent of wrongly copying and publishing two identical rows of data for differing bands.

When you start out it is always best to look around to see what people are actually using on their planes of the type/make/model you want and copycat! Over time you will see through the jungle, and yes, it is worth the effort!!

[Emma 47]

Thank you for the reply.

I think I'll have a beautiful solar panel for a head by the time I've built this aircraft

ok so for the moment I have ordered EXACTLY what it says on the build parts list so have gone for the Emax 2826/06 in the hope that the people who designed the aircraft know what they are doing.

I have 4 Futaba S3003 servos as well as the Futaba RX module and the 2 Futaba TX's as I can't fly yet.

I'm hoping to get the 60A ESC on Thursday and then just need to get the LiPo, the buddy lead, the balance charger, fit them all in the aircraft and get someone to fly it. no problem should have it down the field by Sunday (possibly)

I'm bound to have forgotten more bits I need to get for it anyway but it's all good experience? can anyone think of anything I've missed?

thanks again.

Em

[Bravedan 106]

If not now totally confused, lets deal with the suffix number. Some list this as the number of Poles, but I can assure you (since I have rewound a couple!) that the Suppo 2212-6 has 12 Poles, so Pole Pairs is the nearest to accurate way to describe it.

A DC 5 pole brushed motor has five Poles (not five pole pairs) on the Rotor and a permanent magnet with two Poles. One more pole to create rotation.

The general purpose 2212-6T 2200kV pulsed DC brushless motor has 12 Poles on the wound Stator with pole pieces that are 22mm dia by 12mm long, a sandwich of thinner iron sections, and the rotating magnet outrunner has 14 pole segments. The three wires lead to windings which are more usually delta connected.

[Martin 0]

Bravedan said:

 

One MAJOR problem is that some manufacturers state dimensions by external size (as Martin intimates) and some by the STATOR dimensions (the internal rotor max dimensions). EMax is a case in point as they identify the motor as 2826 by title, but this is not its overall size without shaft, which is variously stated but is on their own site stated as 47.5x39, with a drawing published showing these overall dimensions!

 

 

 

 

Ah! I had missed that in writing my post. That might explain why Hobbyking didn't have any motors matching that size and kV - I did think it seemed odd that the offered ranges (considering both kV and stated numbers of winds) were so far disjoint.

Thanks for the great information. I nearly did write in my original post that you'd really be the person to ask about this!

Also, your mention of "on their own site" made me check again, because I'd posted a link to emaxmotor.com which has no mention of case size being bigger! I have since found the page:

https://www.emaxmodel.com/gt2826.html

which does indeed include the drawing of external dimensions as you say - I assume this is the official site and emaxmotor.com is a reseller? Confusing!

[Bravedan 106]

Motor : Emax 2826-6 (your figure)

ESC : 60A (your figure)

LiPo : Number of Cells(S), Capacity(mAh), and "C" rating (max discharge rate as a multiplier of the capacity)???

Differing manufacturers use differing battery connectors, you may have to change to pair to the ESC, though its more usual for ESCs to come without connectors on the supply pair and you will have to add them/it. This will not normally come with the ESC or battery.

Don't assume that battery manufacturers know what they are doing, for example a "big name" was recently selling 1500mAh 60C 4S race quad packs (so in theory capable IF as stated to be able to discharge 1.5x60=90 Amps, and they were supplying them fitted with red JST plugs. Even if this were an exaggerated discharge claim, they were selling these batteries for 250s that would suck at LEAST 30 amps on full throttle. Now the punch line - Red JST plugs are known to have a max of only 6 Amps continuous, 10A surge, the manufacturer rates them at 3A!!!!

Connectors : Its usual to have bullet connectors between the motor and the ESC on the three wires, these come in many different sizes, and its usual to have the female connectors on the ESC, male on the motor as these can be better insulated. They sometimes come with the motor. You can solder these wires together and heat shrink insulate but its convenient to have connectors for maintenance and reversal when connecting only to find the motor going in reverse to needed, swap any two to get it the right way!

Finally for now, and VITAL..................do NOT repeat NOT have the propeller fitted to the motor until you know everything else works properly, the Tx works the throttle from no rotation upwards, you have fail safe set, and you have a working and easily used throttle cut/hold set to a Tx switch.

[Emma 47]

Thanks again.

Black horse parts list specified the emax motor the 60A esc and a 14.8v 3300mah 20 c 4 cell li poly battery so that's who I hope know what they are doing!

I'm getting so confused and feeling very blonde right now so thank you for your patience with me.

I didn't realise just how complicated it was to get an airplane built and hoped EP would be simpler than IC!

And as for what spares I need to carry to the field with me

Em x

[Bravedan 106]

3.3x20 is 66 Amps. The high sounding Amperage for the motor size is due to the 4S supply voltage "forcing" more current. It all sounds OK to me.

[Emma 47]

Bravedan. Sorry but another silly question!

If it is 66A shouldn't the esc be rated higher?

Thanks for all your help so far.

Em x

[Pilot Ben 28]

As for spares, a lipo checker, spare prop and that's about it. I always take tons of stuff including glues tapes and spare hardware such as a spare clevis, spare bolts, nuts and screws. However the lipo checker, prop are essentials, along with a lipo safe bag and basic tools

[Martin 0]

ChasePlane said:

If it is 66A shouldn't the esc be rated higher?

No - this just means the pack is capable of supplying 66A if called upon to do so. Generally people will allow a bit of a safety margin when specifying ESCs and batteries.

From the motor specification at https://www.emaxmodel.com/gt2826.html , the motor is quoted as drawing 51A off a 4S pack with a 14x7 APC prop, so around 60A capability for ESC and pack seems fair.

Generally, people will select the pack capacity based on size and weight once the number of cells is chosen. The required C rating then comes from the motor's rated maximum current draw divided by the pack capacity - in this case 51A divided by 3.3mAh which is about 15.5C, but to allow a bit of headroom and because no-one makes batteries under about 20C they specify 20C. The required C rating is only ever a minimum requirement - anything higher will be fine though usually more expensive.

[Bravedan 106]

Hi ChasePlane,

A brief explanation as to the "C" Rating(s) of a LiPo Battery.

The "S" rating of a LiPo is a hard thing to disguise or mistake, as the number of cells can in most cases simply be seen and counted!

The two "C" ratings are a VERY different matter. Poetic license abounds, not to mention downright lying!!

"C" Rating applied to CHARGE or current IN. (Usually in the range 1-5)

This is a multiplier applied to the capacity and determines the manufacturers statement as to maximum charge rate. Saying a battery is 5C charge Max is saying for example a 2200mAh battery can in the right circumstances (not always defined!) be charged at 5x2.2A=11Amps. This presumes the charger can deliver 11A into the battery (most could not). Charging at higher than 1C rate (for the example 1C is 1x2.2=2.2Amps) pushes current into the battery faster IF the battery is capable of allowing it.

The problem is that the battery offer resistance to the current flow, which limits current and causes heat, heat that might damage the cell structure/chemistry and in worst case ignite the battery. So, obviously a low resistance (sometimes also wrongly called impedance) high "C" rating is good, right??

Well, not always. Having a very low internal resistance is great for current flow in and out, but potentially bad for long term life and ability to deliver a lower steady current for a longer part of the discharge time. If it CAN deliver current and does the battery voltage will sag earlier.

Which brings us to "C" Rating applied to USE or current OUT (usually in the range 15-150)

This is why some camera drones, where current load is pretty constant and duration time is most needed, actually have relatively low "C" rating for discharge, in the range 15-20C. The motor and prop and ESC are chosen to draw the minimum needed with a safety margin.

On the other hand a Pylon racer or Race Quad needs max possible current or close to it (depending on the motor and ESC being able to take it of course). For example a Race Quad with four 2204 motors and 30A ESCs may ACTUALLY need a current flow of 80A at wide open throttle (WOT), yet the battery will only be around 1800-2200mAh, possibly for sprint racing only 1500mAh. For the middle range as a crude example 80/1.8=approx 45C.

Finally for now, the cell pack discharge "C" rating will often be given as (say) 35-120C. This means the manufacturer claims it will stand 35C current drain CONSTANT, and 120C in a brief SURGE such as when launching, pulling vertical into a loop with wide open throttle, etc.

SO, to sum up.................

1. You cannot trust manufacturers in claiming accurate "C" rating.

2. You cannot ascertain true ability rating before purchase other than by experience or taking account of others experience what any cell packs max charge and particularly discharge "C" ratings are!

As the cell chemistry breaks down over time (as they ALL do eventually), the internal resistance will alter. SOME packs will show this by charging normally at 1C, holding normal voltage, but when asked to deliver current will sag badly after only a few seconds as the pack is asked to give up its charge and cannot because its internal resistance prevents it, i.e, the pack is for recycling and useless.

Rough and Ready Advice......................

CHARGING - Stay at 1C unless extremely pushed for time. IF the pack states 5C charge, its usually OK for 3C.......... BUT whatever you decide upon monitor it and DO NOT LEAVE IT ALONE, keep it in at least peripheral vision sight and with a get me/it out of there backup plan THE WHOLE TIME.

DISCHARGE - While a function of what the motor will take and the ESC handle, take the stated motor max current, and ensure that the cell pack "C" rating is higher with a decent safety margin.

REMEMBER, the current a motor will take is a function of its load, and the load is the propeller. The nearer you prop to the max current the closer to issues/destruction you will get (and again manufacturers are prone to exaggeration as to their motors abilities, and typo's abound too!).

Run out of time now...............more later..................

[Peter Royall 47]

My head hurts

[Emma 47]

Peter Royall said:

My head hurts

Glad it's not just me Peter.

Next time I think I'll just buy a RTF one lol

Thanks for all the help and explanations x