Hi everyone -
For those of us that build and fly scratch built park jets, we have probably all experienced some significant differences in quality control and performance, even with the same component. I guess that is part of the risk/reward of using mass produced inexpensive components from various online manufacturers and distributors.
Early on in my park jet career, I went through a run of bad luck with frustrating/inferior ESCs. I found Grayson Hobby to be the absolute worst. I bought 3 of their 50A ESCs to go with my SMJV2 motors, one never worked properly, one lasted about 10 flights and magically I got about 100 flights out of the third one before that packed it in. Less than stellar quality and performance! I also went through a myriad of the Red Brick and HobbyKing SS ESCs, many of which were very heavy, a pain to set up and often required the use of a UBEC which made the setup even heavier and bulkier. Fortunately about a year ago I switched to Turnigy Plush ESCs and have not looked back since, maybe I just got lucky, but they have all worked extremely well, some for hundreds of flights.
Servos are another component that can be hit and miss. While I find the RC Timer servos to be superior to the HK servos I have used, even then I occasionally get one that just chatters like crazy or doesn't work as expected. Into the spare parts bin with those!
Batteries have also been an adventure for me, awhile back I bought a bunch of the Turnigy Nanotech high discharge batteries that I figured even with my NTM setups would be indestructible. http://hobbyking.com/hobbyking/store/__11951__Turnigy_nano_tech_2200mah_3S_45_90C_Lipo_Pack.html When I first bought them, they were about $17, they are now $20! Some of these batteries used to get warm with my Focal Price motors which draw just over half the amps of the NTM motors! I will be hard pressed to buy another Nano Tech battery for a very long time, I have been very disappointed in their durability and performance for the price. I have been having great luck with these batteries for the last few months, they even work really well with my NTM setups http://hobbyking.com/hobbyking/store/__9942__ZIPPY_Flightmax_2200mAh_3S1P_40C.html I do find that they take a little bit longer to fully balance charge, but they run very cool and give nice, even discharge and are only $13.60.
So this leads me to motors, sometimes you get cold ones, sometimes you get average ones, and sometimes you get lucky and get a "hot" one. And I don't mean hot in that it gets hot when it runs, but gives just a bit more power than it's peers. I found quite a few differences between motors and ESCs when I did a bunch of field and bench testing of several motors last fall/winter. I started a thread here http://www.rcpowers.com/community/threads/parkjet-motor-bench-testing.15685/ If you go to post #127 of that thread, you can download the most current version of the spreadsheet I maintained through the bench testing.
So I had dropped a completely new Focal Price motor into my RCP Mig29 V4 NAMC2, ready to see how fast it will go compared to the V1 since the first motor I put in it was running rough. So I was excited when I got to the field today to do a "fly off" to see if it was faster since I built it about 0.7 oz/20 grams lighter and expected great things... :/ You can read more about my "fly off" comparison here http://migsrus.blogspot.ca/2014/09/rcp-mig29-v4-namc-v1-and-v2-fly-off.html
So as I got into the flying, I noticed immediately that the V2 even with the new motor was slower on the "hole shot" and at top end. I didn't even need to clock them to be able to tell it was slower. So swallowing my disappointment, I started to wonder what was going on....?! Of course being overly self critical and self deprecating (probably more than you want to know about me... :) ), I immediately thought it had something to do with how I redesigned the tails that was causing drag or other speed problems.
So after a brief "pity party", my inner "Bill Nye the Science Guy" kicked in and started to look at things more logically. So since all the control surfaces were dead centre, no trim, there can't be that big a difference in drag, I started to look at other components. Both ESCs were set up exactly the same, props both the same, both balanced.
So luckily I had my "park jet dyno" with me at the field (my handy wattmeter... :) ) and decided to check what was going on with the two motors. As a side note, I find a wattmeter a valuable little tool for evaluating what is really happening with a power setup. I use this one from HK. http://hobbyking.com/hobbyking/store/__10080__Turnigy_130A_Watt_Meter_and_Power_Analyzer.html It is probably big overkill for what I might ever need and I am not smart enough to really use all that it tells me, but it gives good precise feedback on how many amps a power system is drawing and how many watts are being produced.
So, interesting results, both motors have the 6x3 EMP prop and I used a freshly charged 40C discharge 3S battery when I tested each motor.
The new motor in the V2 draws 32A and produces 356W. This is pretty normal for most of the Focal Price motors I have tested.
The older motor in the V1 draws 36.5A and produces 413W... :), this is what I call a "hot" motor... :)
Good thing I switched to a 40A ESC a long time ago for use with this motor...a 30A ESC would get beat up pretty badly over time with those amp draws... :/
Interestingly enough, when conducting the highly scientific and reliable "finger touch test", both motors run about the same temperature, but one produces quite a bit more power.
So I think from now on that I will do this watt meter test on every setup I have to see what is going on so that my expectations don't exceed reality! I have also noticed big discrepancies in a couple of my NTM motors, one draws about 48A and produces 488W (lower than it's rating) and another draws 61A and produces 600W (higher than it's rating). So like I said, I think I will check each power setup now and try to keep the really "hot" motors for planes that I really want to scream... :)
Anyway, just another interesting lesson that I have learned in this exciting park jet journey... :)
Cheers,
Scott
North American Mig Consortium (NAMC) was formed to share ideas, build techniques and test results in pursuit of a park jet that suits our flying styles. This additionally will be a forum to freely post and share ideas and have a lot of fun! If you don't have gmail or google accounts and want to send us questions, please do so at scott@migsrus.com. Your e-mails may be re-posted in the blog to benefit other followers. Puto, Consilium, Test et Convalidandum; Think, Design, Test, and Validate
Scott,
ReplyDeleteI've noticed the differences between motors as well and always blamed overheating or wearing it out. I need one of those watt meters, I don't have one of those.
Great stuff as always,
Stephan
Hey thanks, Stephan, I'm sure that maybe the "hotter" motors might not last as long as ones that run at advertised or lower rating. But what the heck, it is fun while it lasts and these are park "jets", so "speed is life".
DeleteI also put just a few very small drops of light sewing machine oil on the back where the bearings are and tried to get a little bit in the front where the bearings are. Next time I make an HK order, I'll get some of those super fine CA applicator tips to try to get a little oil in there. I noticed it makes a difference in the "hot" motor and when I tested it again in the NAMC V2 after a bit of lubrication, it is actually running the same amps but kicking out about 15 more watts. That could also be because of the different ESC, but I'll take the extra power regardless, sometimes you just don't look a gift horse in the mouth!
If there is any weak or inconsistent part of these motors it is in the quality of the bearings. Other than when a motor is pushed really hard with lots of full throttle or run on 4S, much of the heat build up comes from the bearings, you probably notice when you do the "finger test" that the motor is much hotter at the base right against the motor mount where the bearings are, then that heat migrates out to the bell and stator.
I know some guys have gone to the trouble of upgrading using Boca or other high quality bearings. The bearings cost about the same as a new motor and it takes some delicate handling and tools to make the swap. I am going to try and remember to put a little lubricant in each of my motors now every so often to help them run smoother and longer.
Of course fixing the motor mount on the V2 made a huge difference in performance and noise, I was probably loosing a large amount of energy through vibration with an insecure motor mount. Got her in there good and solid now with some Gorilla Glue, she isn't going anywhere unless I drill it into the ground!
The wattmeter is a handy little tool for sure, gives solid feedback on what a prop/motor and ESC combo are doing. I'm not sure if playing around with timing on a motor that is "cold" or not running to specs might kick it up a notch or two.
For the motors we like to run, the FP and NTM 2700s, low timing I think is the best choice, the NTM actually performs worse on medium or high timing. The FP will give a little more "oomph" at top end on high timing, but it's mid range power and efficiency are way down on medium or high setting, so best to run that one on low timing as well for best overall performance.
I'm still trying to wrap my head around how the whole timing thing works, sometimes you just have to adjust it, hook it up to the wattmeter and see what you get. I know it makes my motor spreadsheet seem very complicated and overly detailed, but I wanted to test both at full and 50% throttle to be able to assess the results and choose what would give the best overall performance, even if it meant compromising a little bit of top end performance.
Nothin' like cold hard data over conjecture to help a fella figure out what is going on!
Cheers,
Scott
Hi Stephan -
DeleteI was poking around a bit more on the Deal Extreme (DX) website today and found a watt meter that looks like it will do the same thing as the one I have from Hobby King, but it is $5 cheaper and free shipping. Of course it will take until Thanksgiving to get to you probably... :/ But the price is right I think. I'll keep poking around there, looks like they have a more robust selection of RC stuff than Focal Price. Most of their stuff they say is for RC helicopters, but it is usable for planes if need be. Good price on a prop balancer too if anybody needs one of those http://www.dx.com/p/maglev-propeller-balancer-essential-for-fixed-wing-aircraft-red-black-219603#.VCw8CGddXkU Currently 20% off, so the price is $5.99, again shipping free, but slooooowwwww.... :)
Cheers,
Scott
Found out I have another "hot" little motor amongst my Focal Price 2700 collection, I putt the watt meter on the motor I have in my stock Mig29 V4 yesterday, got 36.5A and 430W... :) I'm starting to wonder if these motors don't need a good break in period just like a car does to fully reach their potential. As I mentioned, the one I put in the NAMCV2 (which has now been replaced by the hot motor from the NAMCV1) was brand new out of the box and was more efficient, but less powerful.
ReplyDeleteLike I mentioned, something to check more often to see how the motors may or may not change over their life span. No matter, I'll take the extra horsepower anyway I can get it... :)
Cheers,
Scott
Scott, I admire your approach to studying components for optimal performance and cost. Every time I've raised the cost of what I put into the air I've increased the crash anxiety (e.g. I have so much money in this plane), that I fly a little more carefully and that caution limits my fun and I don't push myself to fly faster or try a new maneuver.
ReplyDeleteThanks, Dave... :) I guess I started to really pay attention to dialing in the gear and components I used in the summer of 2013 when the V3s were released. That is when I decided to try and do some testing with motors to really find out what the capabilities of the components I had on hand. The claims of the vendor/manufacturer compared to what I sometimes saw at the field were not lining up. That coupled with some of the crazy numbers people on the forums would claim certain motors were capable of led me to just do my own testing.
DeleteESCs were also one area that used to cause me some stress until I just stopped fooling around and went with the Turnigy Plush line. I know there are lots of other great ESCs out there, but the Plush ESCs just work awesome for me. The other less expensive Red Brick and Hobby King SS were big, heavy and I was never sure if they were programmed correctly trying to follow all the beeps and squeaks while programming them through my transmitter. Now I just connect the Plush ones to the programming card and in about 10 seconds I can see what settings I have, makes me much more confident in what is happening.
It did take me awhile to get to the point where I am with the components I like to use after trying many different options. Even though much of what I use is less expensive than other gear available, it just plain works! Maybe you have seen it already, I put a "laundry list" of links to all the components I currently use along with some of the materials in this post http://migsrus.blogspot.ca/2014/10/my-park-jet-workshop-video.html
I have a couple of Focal Price motors with about 400 flights on each of them and they are still running strong, not bad performance and durability from a $12 motor... :)
Thanks again for your kind words.
Cheers,
Scott
Dave,
DeleteWelcome to our Blog.
Foamies have taken away 99% of all the stress of the flying RC for me. I'm always nervous about the first couple of flights, but then I let it rip. Once I start building our next prototype, then I fly the wings off of the planes. Push my limits, crash, fix it or trash it. Then I recycle the parts. No more post crash depression lawn darting a 6 month balsa build for me.
Stephan