Wednesday, January 17, 2018

Quad racing motors in park jets, Part 2 - starting to make sense of it all

Hi Everyone -

I will warn you ahead of time, this is a bit of a long post, especially if you watch both the videos from start to finish (if I had one to recommend, watch the second video by Kabab FPV first).  You might want to grab a beverage (preferably caffeinated😉) and maybe a snack or two before you get settled in.😋

It has been almost ten months since I first started experimenting with using a quad racing motor in a single motor, prop in slot configuration in a foam park jet.  This little beauty right here😊
Including this first RC Timer FR2205 2550 Kv motor, I have now flight tested eight different quad racing motors in various sizes and Kv ratings.  I still have four more on the way to test and evaluate that were selected based on what I have learned to this point.

During this time, I have spent lots of time researching motors, watching videos, including many of rcplanepirate's from whom I have learned a lot.  Not only have I learned a lot about quad racing motors, but brushless outrunners in general, so it has been and continues to be a very interesting and educational journey.

I also found Ryan Harrell's website www.miniquadtestbench.com (I wish I had found this a bit earlier) from which I have learned a lot also.  I do find his charts a bit tough for me to interpret, but his writeups on each motor he has tested have been very helpful to understand what might be a good motor or good value for the dollar.

I found his website after watching this video interview between Ryan and Joshua Bardwell who is one of the leading guys on YT when it comes to the technical aspects of quadcopters and all their components.  I admit that I have watched this video several times to try and understand what they are talking about.  A lot of it is still a bit technical for me, but I have still learned a lot from their interaction and Ryan's experience as being one of the leading (if not the leading) tester of quad racing motors and ESCs.

Another video I have watched a few times and found easier to understand is this one from a fellow called Kabab FPV on YouTube.  I found this one a little easier for me to follow as he has several motors apart so it is easier for me to visualize and understand several important aspects of what makes one motor better or different than another.
So I would like to tell you that I have determined exactly the best make, size, Kv quad motor for use in a park jet.  Though some numbers are starting to take shape, like many things in life, there are often exceptions to rules we try to make😕

Maybe now is the time to back up a little bit.  When I first started down this path, one of the main things I wanted to find was a motor that would give me fairly close performance to what I call the "park jet workhorse" the 2212/6 2200 Kv motor, but looking to reduce the motor weight considerably.  You can watch this video to learn more about my thoughts on this most popular of park jet motors.

I was also putting some challenges in front of myself as I would be running these quad racing motors on 3S when most of them are designed to provide optimal power on 4S and sometimes higher.  I would also be spinning more conventional 6" two or three blade props as opposed to 5" quad racing style props.  Although I knew that I probably wouldn't find anything as efficient (low amp draw for equivalent power) among the quad racing motors when compared to the 2212 2200 motor, as long as I didn't have to use anything more than a 40A ESC, I was OK with that.  

As the testing went along and I watched more of RCPP's videos, I also decided that the 6x4 APC gas prop would be my standardized prop for all motor comparison.  Although I will bench and field test all the motors eventually with other props, the 6x4 APC gas prop is now my favorite overall park jet prop for reasons I explain in this video.

It is important to add that the planes I like to fly and the style in which I fly them might demand a much different power setup and performance than others might seek.  I wrote this article which is Quad racing motors in park jets, Part 1 that discusses what I think is important in selecting and building to optimize quad motors for how I like to fly.

If you watch my videos, I don't spend a lot of time flying around slow, I have a pretty heavy throttle thumb and like to have some good punch out power for acceleration and vertical maneuvers.  I also like a motor that when I'm cruising around at about 60% throttle, I can do basic turns, rolls and other simple aerobatics without having to mess too much with the throttle.  I guess I don't ask for too much, do I?!😉

So while I think all the quad motors I have tested have at least equal power in top end speed (perhaps not equal torque) to the 2212 2200 Kv motor, they are certainly lighter, but all are more amp hungry.  Like many things in life, trade offs are required.

Awhile back, a viewer posed a question on one of my field test videos asking me to rank my favorite motors based on thrust, weight and price.  Since then, I have reviewed my notes, watched my videos several times and come up with what is currently my favorites for how I like to fly.  As I have mentioned, I am basing this currently all on field performance as until I have my thrust stand, my thrust test numbers are fairly suspect.  I didn't worry too much about price, I think you get what you pay for and sometimes if you want the ideal power setup, you just have to pay a little extra for it.

I have broken it down into two lists, one with motors of 2700 or higher Kv, the other with motors under 2700 Kv as the difference is noticeable at this Kv point, primarily based on top end speed, not so much torque or other factors.  

I took this picture of the 2700 or higher Kv motors (links to each below the picture).  Prices shown in USD, weight is with all hardware and prop (i.e. ready to go in the plane), amps pulled is full throttle with 6x4 APC gas prop on 2200 3S 40C battery.
 Motors under 2700 Kv.  These motors all produce less top end speed than the 2700 or higher Kv motors, but the first three all produce pretty good torque, equal to (or in one case greater than) the 2700 or higher Kv motors.
So despite putting rankings on them, all of these motors are good, I have not been disappointed in any of them, in fact I was pleasantly surprised with a few of them, especially the two Racerstar motors.  Again, it boils down to what you can get, what you can afford and what works best for you like much to do with this hobby.

Because of how I like to fly, I would probably be in favor of the 2700 or higher Kv motors over the less than 2700 Kv motors, but they would all play their roles depending on the size, weight and performance I was looking for out of a particular plane.

So what criteria did I use for my rankings?

The EMAX 2750 seems to be just that little bit better in torque, top end speed, motor quality and smoothness than any other motor I have tested thus far.  It is also rated as being able to handle 58A, so given the low amount of amps I'm putting through it, I think it should last a pretty long time.  I know it will be difficult for you to see, but based on some of the criteria from Kabab FPV's video above, the EMAX motor has curved N52 magnets, tight air gaps, tight tolerance between the magnets and stator and multi strand windings around the stator arms (supposedly produces more power).  The motor spins smooth, the magnets are strong and "grabby", but not bumpy.  According to the evaluation on www.miniquadtestbench.com, this motor is actually a 2630 Kv motor.
I gave the BeeRotor 2207 2780 and BrotherHobby 2205 2800 motors pretty much equal billing.  I would say they are close to equal at top end, the BH motor is obviously quite a bit lighter, but the BeeRotor motor does have slightly more torque.  This is due to a slightly taller stator, but also larger magnets.  I can't find out if the magnets are N52 (perhaps N50), but they are about 50% thicker than those on the EMAX and BH motors.  There is a bit more air gap between the magnets and the tolerance between stator and magnets is not as tight as that of the EMAX and BH motors.  The magnets are strong and "grabby", but it does run a bit "bumpier", again it has multi strand thin wires wrapped around the stator.  A very strong overall performer.  According to it's writeup on www.miniquadtestbench.com, this motor is evaluated as a 2630 Kv motor as well.
The BrotherHobby motor is about equal in top speed to the BeeRotor and I give it such a high rating because it definitely punches above it's size and weight and at 40 gr is the lightest motor I have tested thus far.  What it lacks in torque is made up somewhat by high Kv.  The magnets are curved with tight air gaps and tight tolerance between the stator and magnets.  It has slightly thicker wire on the stator windings, draws a few more amps and might be capable of higher temps than the previous two motors.  Again, it is unbelievably powerful for it's size and weight.  In a small, light wing or park jet on a calm day it would be tough to beat this little beast😏
The Racerstar BR2306S 2700 Kv is a real surprise and the best value in the 2700 or higher category.  Slightly less torque and top end speed than the two motors in second place, but for the price it is very tough to beat.  Considering it only draws 29A, it could probably be run on a good quality, lighter 30A ESC where the other three would all need to be run with a 40A ESC, so an additional potential weight saving of about 8 gr with a 30A ESC.  The magnets are flat and don't feel super strong compared to the other motors, but the air gaps are pretty decent and the tolerance between the stator and magnets is pretty good considering it's price.  Again, it appears to have thinner multi strand wires wrapped around the stator arms like the EMAX and BeeRotor motors.  A very pleasant surprise in "power for dollar" ratio.😊
For the motors that are less than 2600 Kv, they all have lower top end than the previous four motors.  Normally, if I have a motor that I know is not going to give me blinding top end speed, I opt in favor of best torque so I can fly slower and then be able to hammer through lots of aerobatics confident I can "muscle" myself out of trouble if need be.

The Racerstar BR2406S 2600 Kv motor has probably the most torque of all the motors I tested including those at 2700 Kv or higher.  This would be my choice if I wanted brute force torque for a particular plane or flight envelope.  It has flat magnets, they look about the same size and thickness as those on the Racerstar 2306 2700 with slight more air gap between them (expected I suppose with the slightly larger bell).  Although I didn't measure, I suspect the stator arms are longer, the windings are multistrand and thin, the motor runs smooth and not bumpy, so the magnets are not as strong as some other motors.
The Multistar Viking 2208 2600 Kv motor has the edge in top end speed of all this group of motors, not quite as much torque as the Racerstar 2406, but better than both the RC Timer motors in this group.  It is very hard for me to get a picture of the bottom of this motor without taking it apart, so I borrowed this one from the Hobby King website.  It has fairly thin but curved N50 grade magnets, the wires wrapped around the stator arms are thin and multistrand.  The magnets do feel strong and "grabby" with fairly small air gaps between them.  I would compare it closer to the DYS BE2208/7 2600 Kv motor I have run for quite awhile, but lighter (by 4 gr), slightly better made and more powerful.
The two RC Timer motors in this second group are quite similar in top end speed even though the 2306 size has 100 more Kv, the 2306 motor does have noticeably more torque, but you pay a bit of a weight penalty as it weighs 8 more grams than the 2205 2550 Kv.

As you can see in these pictures below (2306 2650 Kv first, 2205 2550 Kv second), there is a pretty noticeable air gap between the magnets and not a terribly tight tolerance between the magnets and stator compared to other motors I have tested.



In all honesty, if I had to choose between these two RC Timer motors, I would probably go with the less powerful 2205 2550 Kv motor primarily because it is lighter, more efficient and can use a wider variety of props.  I have used this motor the most and have much more flight time with it than any other quad motor thus far, I did a more in depth discussion of my experiences with it in this video.

As mentioned before, there are certainly exceptions to making any rules.  The BeeRotor 2207 2780 and the BrotherHobby Returner R2 2205 2800 (definitely makes up for small size with increased Kv) would be exceptions perhaps as I think for most other brand names, going with a 2305/06 or 2405/06 would be my choice in 2700 or greater Kv motors to ensure that in addition to top end speed there is still good torque.  

In the lower Kv, I don't think I would ever choose a motor below 2600 Kv on 3S anyway, I think 2406 is probably the ideal stator size for what I want to achieve with my planes. 

So of course these are my opinions based on what I like to see out of my planes.  Quad racing motors are a bit of a "double edged sword" when trying to track down what will work the best in a park jet on 3S as the variety of sizes/Kvs/brands is quite staggering.  From what I have seen, EMAX, BrotherHobby, BeeRotor and Multistar brands have certainly done a good job of squeezing the maximum amount of power from their motors.  For best value, it is tough to beat the two Racerstar motors, however.  Their quality control might be a bit of a risk perhaps compared to the other higher quality brands, but tough to beat the "power for price" ratio.

So still more motors to evaluate and much more to learn.  My biggest challenge is knowing when to stop evaluating motors before I "go broke saving money" on motor sales!😟 

Park Jet noise...the "other" sound of freedom😎

Cheers,

Scott


  








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