HDX500RV Prototype Frame with New Main Gear

[Rotorworkz]

Gents,

Here is a prototype pic showing the new gear and frame after testing with this all I can say is WOW!!!
Here is the drive train specs as of now
130T 0.6 Mod. CNC Delrin Prototype
Tonic-X Z20-1470 gives this thing Stupid power WOW!!!!
6s1p 2500 25c New Brand Test pack
12t pinion

OK Drum role.........
I decided to go for 140T main gears as I have more room than previously thought so this opens up many more gear ratio's and motor options

More To Follow

[LITHIUMSTATIC]

:drool::happyd:clappp:happyd

[Ecaf]

Now the big question.....


When?

[booger]

OK
1st question when due we get them.
2nd are they gonna be 130t or 140t
3rd where you get the 12t pinion assuming 5mm shaft on motor

[Ticidytoc]

OK
1st question when due we get them.
2nd are they gonna be 130t or 140t
3rd where you get the 12t pinion assuming 5mm shaft on motor


I talked with Charlie yesterday and he thinks he can make the 140T work. So provided he doesnt run into any other problems, its going to be 140T.

The 12T pinions are available for the T500, so anyone who stocks the T500 should have them.

[666yeti666]

That's good news !

But I was brainstorming about "what is the biggest advantage by using 6cells instead of 4cells lipo ?"

Well, when in both cases the output power is the same , then that would be :
1- less current draw
2- less current losses in the esc. & motor, so better efficiency , slightly longer flighttime

But there are also some drawbacks of using 6s lipo :
A- 6s lipo ESC needed, often higher price , U$
B- often need for external 5V supply (battery or ubec), most 6s ESC don't have a BEC up till 6s lipo. this will have a weight increase and extra cost U$
C- higher voltage, thus switching peaks are larger , potentially more chances of radio disturbance
D- need for 6s lipo charger

Let's do some math :
suppose that the power = 350Watt and one lipo-cell voltage under load = 3.5V
so the 4s lipo=14V and the 6s lipo = 21V

4s lipo :
current draw = 350/14= 25Amps
flighttime with 4s3300mAh = 7.9minutes
lipo loading = 25/3.3= 8C
lipo weight = 350gram
lipo price = 150U$

6s lipo:
350/21=17Amps
flighttime with 6s2500mAh =8.8 minutes
lipo loading = 17/2.5 = 7C
lipo weight = 400gram
lipo price = 215U$


mmm ..... what seemed to be so good on 6cells seems to be more expensive and heavier in practice ...... can somebody convince me of using 6s lipo ?

thanks !

[Ticidytoc]

I think the biggest selling point for the 6s on this size heli is the fact that you can use 2 packs from your 450 sized heli. Other than that the 4s and 5s should be plenty imo.

I will be doing some 4s,5s, and 6s testing in the next week or two. I have some packs that are waiting to be used again.

[666yeti666]

The fact that you can use two 3s packs does have a "hidden downside" ....
Most people use their 3s packs in their t-rex450 SEPARATELY. So in other words, both packs have different cell-voltages and packs have different capacities. Now, when using both packs in series there is a chance that one of the packs is discharged too much, and can be damaged permanently ....

Personally I would be happier with a lower weight with the same amount of power, to get a better power to weight ratio. And that can be achieved with a 4s setup rather then a 6s set-up, as I can judge it by now .

I'm curious about your testresults ...

[WillJames]

I could be wrong, but I think the 4s1p 3700 is about = in weight to the 6s1p 2500.

[666yeti666]

To get same flighttime with 4s , a 3700mAh is needed indeed. Weight is almost the same = 384gram
But with 6s don't forget the external batterypack / ubec .... another 50 grams ...... :-(

[Mikej]

To get same flighttime with 4s , a 3700mAh is needed indeed. Weight is almost the same = 384gram
But with 6s don't forget the external batterypack / ubec .... another 50 grams ...... :-(

I use a Dimension SportBEC on my 4S 3DX-500 and my 6S Hurricane 550 - 13 grams

[666yeti666]

mmm ... indeed ....

The choice for a 6s set-up with a 130T gear seems to be only a selling argument for t-rex450 users (or comparible) so they can easily be 'seduced' to buy a 500 size heli such as a 3dx500 or t-rex500 .... mmm ... smart guys at rotorworkz .... ;-)

[WillJames]

The HDX500 is the product, the 3DX is not a HD/Rotorworkz product.

[altruhtra21]

So you are using the higher rotor hub and your flybar cage is made as a "V". What does this give you in cyclic without binding ?

Harald

[666yeti666]

"The HDX500 is the product, the 3DX is not a HD/Rotorworkz product. "

... now I'm confused ..... I mean, I know the heads are different but I assumed that they came from the same manufacturer .... guess I'm wrong then ?

[Rotorworkz]

So you are using the higher rotor hub and your flybar cage is made as a "V". What does this give you in cyclic without binding ?

Harald

Yes that Flybar carriage is a prototype it allows Extreme throws of Cyclic pitch with all pitch ranges for Pop or Lock style Flying

[Ticidytoc]

To get same flighttime with 4s , a 3700mAh is needed indeed. Weight is almost the same = 384gram
But with 6s don't forget the external batterypack / ubec .... another 50 grams ...... :-(

I will be using an external UBEC, 75A ESC, and a Futaba 601 gyro. So as you can see I am not to worried about weight. I think the heli will perform just fine with my selected gear on any of the 3 cell counts I listed.

[BobOD]

Nice analysis 666yeti666. I think 6s should prove to be a bit more efficient depending on the motor and gearing. It'll probably be some time before this is narrowed in on...if it ever does get there that is:)

So far, I like my 4s setup and am not in a big hurry to change. The benefit of using 2 of my trex450 packs is not a benefit for me...I'm 4s on my 450. I'd have to go 8s to be practical.

For me, it's not been a problem to share the packs. I just make sure they are fully charged before putting them in parallel. In fact, it's a tremendous benefit. I have four 4s2100 packs so I can fly the 450 practacaly non-stop. Cellpro 18C which I paid $62 each for...$248 and I have two packs for my HDX500 or four for my trex. :D

My HDX hovers at 400W and will regularly peak well over 1000W with this setup which is pretty respectable I think. HS is 2600 which, in my opinion, is all that's needed for full 3D...2700 max. Any more and the consumption is outpacing the benefit.

Anyway, even with the bigger gear, I think there will be higher kv motors which will still allow 4s. This could be a benefit. However, often overlooked is the efficiency of the gearing. Not that I think it would be enough to effect flight time that much but, rather, gear life. I've never had a gear for my trex450 that has held up half as well as the 94T in my HDX500. It's not 0.6 vs 0.5 module either...that's not enough to make the difference I see. I think it's tooth velocity. I predict the 140T gear will not hold up nearly as well. Not a reason not to try of course but worth some consideration.

[helidirect]

Bob,

Would you like to try the 130T or 140T main gear?

Steve

[BobOD]

Bob,

Would you like to try the 130T or 140T main gear?

Steve

I love trying all things. :D
Not sure what motor/bat/pinion I'd need though.

[helidirect]

Charley's using 12T pinion on Z20 1470 motor.

Steve

[jnngill]

That thing must be a rocket. Thats a ton of power for such a small heli.

[Ticidytoc]

Not sure what motor/bat/pinion I'd need though.

The Tonic-X Z20A 1700KV (http://www.helidirect.com/product_info.php?cPath=44&products_id=6011) on the 130T would need a 14T or 15T for the headspeeds you like. With the 140T gear I would use the 15T or a 16T, all of this assuming 4s.

[666yeti666]

I was wondering how did you came to a headspeed of 2600 with a pinion of 14T / 15T with 4 cells lipo and 130T maingear with a 1700kv motor ?
I've just done a quick calc. and came only to a max HS of about 2300 (3.5V/cell , 90% efficiency)
1700*4*3.5*14/130*0.9=2307

And 3.5V/cell is already quite high, I don't know if the cells of Bobod can sustain such high voltage under those loads otherwise it will be even lower ?
Or am I wrong ...... ?
I find it allways difficult to predict HS in theory, maybe you guys have more experience in practice.

For myself I was aiming on a headspeed of about 2200. I think I want to use the kora 15-12 with a kv of 920. Read some good stories about the kora motor, despite it's low weight.
So with a maingear of 94 and a pinion of 21, an efficiency of 90% and a governor set to 85% that would lead to : 920*4*3.5*21/94*0.9*0.85=2200 (gear ratio = 1 : 4.5)
I would use flightpower 4s evo 25 3700 which can easily hold an average of 3.5V/cell at a load of 5C to 10C (according the discharge curve of the 3700).
Would that be achievable in practice ?

With a 24T pinion that would give me a HS of about 2500 .

@Bobod: would 2200 be enough for mild aerobatics ?

[Ticidytoc]

In practice I have found using 3.7v/cell seems to come close enough when predicting RPM. This provided you are using quality LiPo packs. Of course this is not an exact science, and variables such as pack quality, equipment, and settings will cause your final results to vary. This is why I listed 2 pinions for each setup and with the 15T should be around 2542rpm.