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HomeAircraftHelicopterLow Head Speed Helicopters › Model Aviation Article LHS
02-02-2016 03:50 AM  29 months agoPost 1
turboomni

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East of the Equator

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Nice article in the AMA mag about low headspeed heli's. Of course it was linked to the guru of low head speed Gary Wright and rightly so.
I suggest you read it ,,I guess I should really put this on the main discussion section to get more airplay.
Last summer I did basically the same as the article but with a different older heli. I had a Align 550 Pro. It also came with a 830 kv motor as used in the article but from Align. I stretched it also with bigger 600mm blades[boom was already equipped for 600;s from the factory]
Instead of a HUGE 16 t pinion I went with a 10 T pinion and max head speed was 1800. I also used the older tail gears which upped the tail ratio,,which is needed for anything much under 2000 head speed.
Talon 90 and 95mm tails. 9 minutes with no gov at WOT. This is with one 6 cell pack and a Talon 90 just like the article. Do not think I am gloating in any way as it was just a logical step at the time. Also I learned most all about LHS from Gary anyways!! Gary does have a lot more up his sleeve but this is a great way to start. Congrats Gary for getting more news out of LHS to the masses.

Setup is everything, All my heli's can fly far better than I can pilot them

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02-02-2016 04:21 AM  29 months agoPost 2
Ace Dude

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USA

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I just read it yesterday myself. Great job Gary & Chris. I do hope you do a part two on how go about selecting the proper pinion size and Kv motor for the application at hand.

  

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02-02-2016 04:27 AM  29 months agoPost 3
turboomni

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East of the Equator

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Well as far as pinion size goes you can calculate the max head speed with the KV and gear ratio at wide open throttle and go from there.

Setup is everything, All my heli's can fly far better than I can pilot them

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02-02-2016 04:44 AM  29 months agoPost 4
gologo

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Sedalia, Mo USA

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Yep, just read this and great to see another potential 'convert'.

And yeah, what better one to consult w. for the article!

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02-02-2016 04:46 AM  29 months agoPost 5
Ace Dude

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USA

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I've gone through the process a few times and put a spreadsheet together that I use. I thought it would be good for those readers who don't know all the remaining details can be found here on RR.

  

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02-02-2016 02:58 PM  29 months agoPost 6
gwright

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Champaign Il

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There will be more coming. Chris kept bugging me via lengthy texting sessions so I wrote something for a future MA article. dunno if we got it in early enough for the next month to followup on this one. It's like a 3 or 4 month lead time on those things

It's not immensely detailed, and in no way the gospel,I'm not a guru... It's just my thoughts and processes. I tend to be rather verbose, so it took longer to pare it down to the 2500 word limit than it did to write

Ace Dude, you're not alone,.. I'm such a nerd I had spreadsheets for lots of things. i had them with all the available gear ratios for the TT machines I flew and now the Synergies. I could just plug in motor KV and cellcount. Also had one with calculated tip speeds, and with disk areas. Had another that calculates the force on the blade bolts at various rpms. You plugged in blade weight, distance from bolt to CG of blades, distance between blade bolts (head spacing varies greatly among different machines) and it gave you newtons and pound force at the blade bolt.I also had one where you plugged in a known value of power usage at a known rpm and it would calculate power and flight times in 100 rpm increments going up. It's pretty eye opening when you see the flight time at 2300 on a given heli is 5 times what it is at 1300. We actually confirmed those numbers a few times and they're scary accurate. The above numbers were my E700 and Tom Rolfsonn's. Yes, I flew 12.5 minutes and he flew 2.5 minutes on the same machine. 1300/2300. The last spreadsheet I did was last year when FP came out with the new battery cells. Dimensions/weight/capacity of all the cells and computed cells for power density and energy density. It was very informative. When you see watt-minutes per gram (energy density) of the various packs there are some outliers that are so much better it appears to be magic. Many packs were in the 8 to 8.3 watt minutes per gram area whereas the 4350 packs I'm now using are 9.5. Doesn't sound like much, but that's more than a 10% difference. It compounds when you add in the increased efficiency of the lighter heli in flight. I should have kept copies of all those files, might be interesting to others. I'll have to look for all of them.

Gary Wright

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02-03-2016 02:08 AM  29 months agoPost 7
Ace Dude

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USA

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There will be more coming.
That's great news Gary! This is what spreadsheets were made for. Mine is kind of basic, but it gets the job done and allows the results of several different combos of gear ratios and Kv motors to be displayed at once for comparison purposes. The only gray area for me sometimes is what the best options is when there is some overlap. IIRC in one of your posts you mentioned some benefits of lower or using the lowest Kv motor that works?

  

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02-03-2016 02:12 PM  29 months agoPost 8
gwright

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Champaign Il

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I think I understand what you are saying regarding "overlap". I think you mean something like you have 400 and 450kv motors, and various pinions available. Say you want 1750 headspeed and the 450 with 12 tooth pinion computes to 1750, or the 400kv with 13 tooth computes to 1750,..how do you choose. the only answer is that "it depends". If you don't necessarily manage collective smoothly, and power is your ultimate goal, then I'd use the higher KV and smaller pinion. If you're priorities are like mine, and flight time trumps maximum power,.. then I'd go with the lower KV motor and larger pinion. In reality,the higher KV motor with small pinion is probably going to give you more than you need(what I would refer to as wasted overhead ) because our batteries hold higher than the 3.7V/cell we use in calculations. What I would really do personally is go with the lower kv motor, and also the smaller pinion, then increase timing a few degrees at a time (which slightly raises KV on the motor), till I had the "perfect" setup for flight time efficiency.
Currently, my 700 has a 400kv motor which is the lowest available from the Hackers that I like to use. Calculations (400*44.4*12/121) result in 1761 rpms and I use 1750. No loading down of the head,..i.e. it never runs out of power,.. and I even run some pretty high pitch ranges (haven't measured in a while and I'm constantly tweaking setup but at one time it was +/-16 with 12/12 cyclic, in lowest rpm mode).ESC logs show that I occassionally have a peak current over 70 amps (when in high rpm mode). If I had a slightly lower kv motor (375~380 just guessing), I could get those spikes down a touch more and maybe get the average currents down a fraction of an amp in each rpm. That's sort of splitting hairs as it probably wouldn't be but a percent or two difference in flight time, but it still irks me that it's not truly optimized for flight time with "appropriate power"

Gary Wright

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02-03-2016 03:30 PM  29 months agoPost 9
prototype3a

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Christiansburg,VA

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IF.. I can get my hands on some logo600se stretch parts, I'm planning on doing some theory to practice testing on my motor efficiency curve calculations which, in theory, could increase your flight time by as much as 20%.

This might make choosing a motor a bit easier and allow you to get much better flight times.

The gist is that it looks like most motors are very inefficient at low power and especially so at higher voltages (10s/12s etc).

~Drew

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02-03-2016 03:55 PM  29 months agoPost 10
Ace Dude

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USA

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I think I understand what you are saying regarding "overlap". I think you mean something like you have 400 and 450kv motors, and various pinions available.
Thanks Gary, your post above is exactly the information I was looking to confirm. I'm interested in maximizing my flight time vs. power.

  

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02-04-2016 01:25 AM  29 months agoPost 11
gologo

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Sedalia, Mo USA

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Prototype, are you looking to stretch TO 600se, or to stretch an existing
se?

Sorry for the off-topic.....

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02-04-2016 02:50 AM  29 months agoPost 12
prototype3a

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Christiansburg,VA

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Stretch from 600-3d to se. I used to have an se but I shrunk it to 3d several years ago. Actually, these days, I have a 500-3d, 500se and a 600-3d all using the 25mm booms. The 500-3d is my ultralight low headspeed 550.

~Drew

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02-04-2016 03:23 AM  29 months agoPost 13
gologo

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Sedalia, Mo USA

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Cool! That is my plan w. the 500se; it will get the 25mm boom in SOME length, not sure yet Already has had a 600 head on it for years, and 600
motor/pinion/maingear now. Will eventually make it a dedicated LHS'er like
what Gary does, w. low kv motor and high voltage. Good stuff!

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02-04-2016 03:10 PM  29 months agoPost 14
gwright

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Champaign Il

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I don't think of my setups as "dedicated LHS". i think of them as "appropriately powered for a wide range of headspeeds,.. and one end just happens to be pretty low . my 700 is currently setup for 1250 to 1750 and gps has shown over 90mph at 1750. Not "fast",.. but definately not slow.

Proto,.. I understand what you want to play with for efficiency, and you can do a lot better than my setups, but you'll be locked in to a single rpm. I sacrifice some effic. to allow for a wide range of rpms. With that in mind,.. deep gearing and low Io are the important things. If we could somehow change gears in the air and get multi rpms while always at full throttle that would be utopia,.. but I think the added weight for the gearing assembly would hurt worse than the electronic efficiency gains. Hi Io is the real killer when at very low power levels and high voltage.

Gary Wright

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02-04-2016 04:00 PM  29 months agoPost 15
prototype3a

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Christiansburg,VA

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I just wish we could convince motor manufacturers to make lower kv 4025 class motors. A ~480kv 4025 would be fantastic.

Deep gearing == high ratio or low ratio. Because at just 6s and 560kv, you need a ratio around 8:1 for ~1250rpm.

I don't mind the dedicated setup at all but the fact that I'm probably going to have to run a weird Lipo size (6s6000) is slightly annoying.

~Drew

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02-04-2016 04:30 PM  29 months agoPost 16
gwright

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Champaign Il

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I don't mind the dedicated setup at all but the fact that I'm probably going to have to run a weird Lipo size (6s6000) is slightly annoying.
May want to look at Xnova. They have some lower kv motors in the physical size we normally use. Forget the numbers,..been a while since I looked at the specs, but i think they go down to 350kv.

Gary Wright

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02-07-2016 01:30 AM  29 months agoPost 17
Chuck Bole

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Tulsa Ok. U.S.A.

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Nice read Gary.

Kept you in mind with my 766 setup. didn't have a 400Kv motor so i went with a 500Kv. On 12s we tached it last weekend at 1200 to 1750 in 1,2,3.
Just my sport flying some loops,flips, tic tocs, etc.. Got 8+ min and took out 2549 from a 12s 5000 pack.

chuck

Team Synergy Field Representative / Thunder Power

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02-08-2016 03:03 PM  29 months agoPost 18
gwright

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Champaign Il

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Nice Chuck! Wow,.. 1200 on 12S with a 500kv motor. That thing must have really really deep gearing available.

Gary Wright

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02-08-2016 09:14 PM  29 months agoPost 19
Chuck Bole

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Tulsa Ok. U.S.A.

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139T main and 12 or 13T pinion can't remember which off the top of my head.
Using a HK 4530-500, Hobbywing 160Hv ESC. 50% 65% and 75% on the "curves".
Haven't tested it but the Kv might be off. We used a Miniature Air optical tach. When i go to Idle up 1 it sounds like i shut the motor off i know that much.

chuck

Team Synergy Field Representative / Thunder Power

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02-09-2016 12:13 AM  29 months agoPost 20
CSpaced

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Oak Ridge, NC

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The next two issues will feature Gary's article on low head speed. It was a little longer than our typical articles, so rather than edit it down I chose to split it in two. It makes for a good read!

The reason I am hooked on low head speed is because of Gary, he was like a crack dealer giving me that first flight for "free" He's also been a tremendous teacher in getting me up to speed (see what I did there?) on low head speed flying.

Chris Mulcahy
Team Futaba
Team KDE Direct

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