---RC PiNYoT---

Leopard 4082 1600kv
Turnigy 180 marine esc
6s lipo 5000maH 35C
Octura x445

I am planning to put them on 36" Atlas van Lines U1 hydro that I will be converting to electric. Also, will I get 40mph with this setup? Thanks.

785boats

I think 40,000revs is a bit much for that set up & boat. The Amps will be way up there
In my opinion a 4082 1250kv motor on 6s with that ESC would be better.
If you are buying props get the M445. But I think you would do better with a lifting prop like an ABC H-5 or H-7 as a starting point. You should hit the 50's with that
[link]http://www.offshoreelectrics.com/products.php?cat=ABC+H+Series+Propellers[/link]
Cheers.
Paul.

ryan_t888

Did you receive my PM reply? On my end it says it has been deleted.

madnesss

I just built a HK Genisis with
Leopard 4082 1500kv
Seaking 180 esc
x445
running on 3s 50c 5000 x2 series for 6s
If my calculations are correct, I am aiming for 50-55mph, closer to 53 though.
It's a pretty common settup, Offshore makes this in a plug and play drop in for any boat.

Von Ohain

I believe his revs will be more like 23000 rpm.
33000 sounds like unloaded rpms, that number will never be achieved in real life with a loaded motor.
How 40000 rpm came up, I have no idea.

The formula is

6 (cells) * 3,7 (Volts per cell) * 1500 (Kv. rpm per volt) * 0,7 (constant to account for voltage drop etc) = 23310 rpm

ryan_t888

Values everyone goes by is unloaded RPM to determine the feasibility of a setup. It's recommended by many to use nominal voltage. However, some people like to consider peak charge voltage. This typically leads to a more conservative setup which is HIGHLY desired in a public based forum. That's where 40 000 comes from. People who use it understand it's not a loaded value.

Von Ohain

If thats the case then it sounds to me like this whole "stick to 30 000 rpm" rule is just nonsense.
I'm running 2200Kv 3674 Leopard on 6cells, and it works fine. Batteries get hot, but no real trouble.
I set up a boat for my friend with 1650kv 3674 Leopard just to be on the safe side, and it doesn't even get warm to the touch.
Thats definetly what Iwould concider a conservative setup.
If 1500Kv 6S is "HOT", then conservative is a Nikko boat. We don't want Nikko boats?
Thats just my opinion anyway.
I use loaded RPMs, fairytale-numbers is no good in real life anyway.

ryan_t888

Why do I and others get this very overwhelming feeling of "it's my way, or the highway" with some of your replies?
Why am I able to respect the method that works for others even though it's not the one I use?

Any RPM calculation whether it's unloaded or loaded is essentially a fairy-tale value in that case. I've been sent data for help in development of setups pulling loaded RPM nearly equal to unloaded RPM.(from nominal voltage) Yes, it can happen. These setups throw my calculator so far off as it assumes every setup has the same "constant."

There is more to a conservative setup than just RPM. Some of the older hydro's depending on how they were built, were quite heavy and do require a larger prop to push them effectively. The nitro engine that ran in one of these would use a prop that is quite larger than the 45mm in the original post. There are plenty of guys running in the 26 000 unloaded RPM region who have very "hot" setups capable of demanding power.

Making the right selection is not an easy task.

Von Ohain

Sure there is individual differences from boat to boat, but I thought the accepted rule of thumb was 30 000 rpm.
Both 40 000 and 23 000 is pretty far off, and when people can achieve both these rpm estimates with exactly the same setup, then it might be time to take a look at the way we estimate these numbers?
An estimation is an estimation and not dead exact, I dont claim it to be ether. But its a lot better to have an estimate, than nothing.
Only trial and error can get you to a very optimal setup for that specific boat, but having a clue of where to begin is nice.

Snowride

Sounds good to me and falls into the acceptable area in motor kv/cell quantity. http://forums.offshoreelectrics.com/...5&d=1302274810

---RC PiNYoT---

Hi Ryan. Sorry I didn't get your PM reply. Must be something wrong with my settings.

---RC PiNYoT---

Thank you guys for all the helpful info.
Ryan I just sent you another pm.

ryan_t888

You have your settings set to reject my PM's.

785boats

Sorry guys. I must explain.
Firstly the initial post stated 1600kv not 1500.
The 40,000 revs came from a fully charged pack voltage of 25V x 1600 kv = 40,000 revs. A parallel pack set up on this will have very little voltage drop initially & the motor will try to spin up to these revs at the start of a run.
The nominal voltage of 22V x 1600kv will yield 35000revs. Yes they are both unloaded revs.

Von Ohain.
Could you explain your use of a 0.7 factor for volt drop when you are already using the nominal voltage of 3.7V/cell in your calcs. I don't quite understand that.

Cheers.
Paul.

madnesss

785, there's thousands of setups out there that work for some and not for others,.

offshore electricssells your setup as a kit so it should work fine for you, just keep and eye on your temps as you try different props,

	Product ID: ose-4082-combo Leopard 4082 & SeaKing 180 Combo
	<form id="ectform10" method="post" action="cart.php" style="padding-bottom: 0px; margin: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px" name="tForm10"> <input type="hidden" name="id" value="ose-4082-combo" /> <input type="hidden" name="mode" value="add" /> <input id="qnt10x" type="hidden" name="quant" /> This is a rti (ready to install) Motor and Esc combo by OffshoreElectrics. This plug and play power system is meant for a boat that requires 2000 watts of power in the 4-6 pound area. We have done all the hard work, soldering and installing the parts for top performance. We offer this in5 kv's packages. 1600Kv for 4s to 6s Lipo* Killer setup for Traxxas Spartan System Includes: Leopard 4082 Motor. SeaKing 180 Esc with ESC Bank. Leopard 4050 or 4068 Water Jacket. Ose 5.5mm bullet connectors on the battery and an 5.5mm extra set for your batteries. All connectors and water jacket installed. All included items are in the picture. Requires: Lipo packs, with 50c or greater rating. You to solder the included connectors to your packs. Silicon tubing and water pickup/exit. 4082 combo kv: <input class="prodoption" type="radio" style="vertical-align: middle" name="optn10x0" value="829" />1250kv special order (2) <input class="prodoption" type="radio" style="vertical-align: middle" name="optn10x0" value="830" />1600kv (0) <input class="prodoption" type="radio" style="vertical-align: middle" name="optn10x0" value="831" />1800kv (0) <input class="prodoption" type="radio" style="vertical-align: middle" name="optn10x0" value="843" />2000kv (1) <input class="prodoption" type="radio" style="vertical-align: middle" name="optn10x0" value="847" />2200kv (2) Pick jacket size?: <input class="prodoption" type="radio" style="vertical-align: middle" name="optn10x1" value="803" />Leo 4050 jacket (43) <input class="prodoption" type="radio" style="vertical-align: middle" name="optn10x1" value="804" />Leo 4070 Jacket(40mm dia x 70mm long) (20) </form>
	Price: $249.99	<input alt="Quantity" maxlength="5" size="2" name="w10quant" value="1" type="text" />
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Von Ohain

The 0.7 factor is a simplification of a lot of factors which will reduce the actual RPM number from the theoretical RPM number.
The battery voltage will drop under heavy amp draws. No battery will sustain neither nominal voltage (3.7v per cell) nor top charge voltage (4,2v per cell) under heavy amp draws.
Further, there is ohmic resistivity in the battery wires which will cause voltage drop before the ESC, and both the motor itself and the wires between motor and ESC will cause both ohmic resistivity and reactive impedance to cause even further voltage drop.

So the 0.7 constant is a factor and a (gross) simplification to take these voltage drops into account.
More detailed data would be desirable, I agree, but since detailed data sheets for motors is few and far in between, and rpm/torque characteristics for R/C marine propellers is nonexistent, I'm afraid that doing this calculation "by the book" is impossible.
So the 0.7 factor is the second best thing, estimate real rpms.

785boats

Thanks for your explanation. I'm an industrial electrician by trade & understand voltage drop,resistance, amploads etc. It's just that the way I read your calcs you were de rating 3.7v by a factor of 0.7 which looked like you were expecting the cells to be running at 2.59V under load.
But a good battery set up will only drop about 0.5-0.7v under load. That's what gives the nominal voltage rating of 3.7V from the fully charged 4.2v rating.
I think you will find that under load a 1500kv motor on 6s will be spinning a lot faster than the 23310rpm in your calcs. Especially with that 4082 4 pole motor in a Hydro spinning a 445 prop as the OP was asking about in the first post.

Ryan.
Any chance you could do a calculation of amp draw on that set up with your calcs engine? Just out of interest. But remember, the OP was asking about the 1600kv motor.
Cheers.

Paul.

Von Ohain

Further you must remember that these motors is DC motors (BLDC - BrushLess Direct Current), and the motor-ESC unit both behaves as, and is treated in calculations as, a brushed DC motor.
And as you probably know with DC motors, they do drop RPMs under load, even if supplied voltage remain constant.
So does the brushless motors of our hobby. This 0.7 factor also accounts for that.


DC Motor? How?

http://en.wikipedia.org/wiki/BLDC
The way the operation an ESC works is electrically similar to that of a mechanical commutator.
Allthough the mechanical similarity of a BLDC and a PMSM (Permanent Magnet Synchronous Machine) makes confusion easy, the difference lies in how they are driven.
A BLDC Has a constant timing angle, just like a DC motor, which all the difference arises in.
In a BLDC, the motor decides what RPM to run at, and the ESC just follows suit by comutating when the timing angle is correct. Exactly like the commutator of a DC motor.
So, BLDC: Constant timing angle, RPM varies with load.

A PMSM is locked by the frequency of the grid its connected to, and the motor has no influence whatsoever on what rpm itself is running at.
It does not have an exact timing angle, and the grid (or frequency converter) reads no back-emf from the motor whatsoever to adjust supplied power. Unlike BLDC.
So, PMSM: Constant RPM, timing angle varies with load.

Thats the difference, allthough mechanically identical to a 3 phase AC machine, it is not because it must be seen together with the unit that drives it.
If its coupled to a ESC, it is a brushless DC motor, and behaves like a brushless DC motor which WILL drop rpm under load, even if supplied voltage is constant.
If you couple it to a frequency converter, then it becomes a different story altogether. Then it is an AC motor.

ryan_t888

Hey Paul,

I don't currently have something that will pull this kind of data. However, with everything that I have so far it will be something I will be looking in to for the future.

Ryan