Number cells/Motor Kv/Prop Size/Hull Size

[sunsation288]

Just one word , THANKS , for share all your knowledge guy , its realy appreciated....
Regards
Christian

[ReddyWatts]

Sunsation - thanks, but can't take full credit for this. Got the idea for a condensed spreadsheet while reading on another forum.

[ReddyWatts]

Sdart - You can use it either way. It is your preference, two 3S or one 6S. Whatever will work best in your hull or charger.
Eyekandy - Neither and I think that BEC is a user preference.
Ghost - I agree, but it is something they would have to keep updated since FE is a fast changing hobby. I am going to look into the amp ranges for the spreadsheet. Steven is supposed to be working on a forum spreadsheet we can enter our setups, to share with everyone.

[DISAR]

Nice work! In my opinion, these are general guidelines and one thing that is missing is estimated speed. For example for a 36" hull what is the speed with 8s, 1350 kv and 45 mm prop? Is it the same with the 800 kv and 55m prop?

Another think to mention is that I have a 36" mono running on 4s, 1700 kv, 45 mm prop, 100a ESC and runs around 35 mph.

[Steven Vaccaro]

Nice job.

[ReddyWatts]

Steven, thanks.

Disar, I will look into adding the general speeds to be expected from the different setups.

Ed, updated the spreadsheet with ESC amp ratings.

[DISAR]

Hi again,

Based on your values I prepared an Excel sheet as attached. This is for the 26-32" hulls but can be used for any of the sizes. Just insert the values in the blue boxes according to your values and it gives the required propeller according to the actual Kv and cells fitted on the boat.
This spreadsheet may be very simple and unuseful but I prepared it to see where I am standing and decided to post it.
Thanks for your valuable info.

[DISAR]

Let me correct previous spreadsheet , has one mistake in the chart view. This is the correct one.

[ReddyWatts]

Disar, can you explain more details on how to use the spreadsheat? Maybe give some examples.

[DISAR]

From the values you gave, for a specific hull size and specific lipo cells, a line is drawn (as in the chart) connecting point1* to point2**. Then somebody can insert his values( lipo cells and motor KV hence RPM) and find out what propeller diameter is needed. In other words, once the line is drawn (from your posted values) then you enter with the actual RPM and it gives you the prop.diameter (the method used is called linear interpolation in maths).

*point1: high Kv with small prop.diameter
**point 2: low Kv with large prop.diameter

For example for the 26-32" hull, you enter the following values:
In cell (a): Hull size (26-32)
In cell (b): Number of lipo cells (6)
In cell (c): High Kv (1800)
In cell (d): Low Kv (1100)
Cell (e) : Do not enter anything. Calculates RPM for the 1800 Kv
Cell (f) : Do not enter anything. Calculates RPM for the 1100 Kv
Cell (g): Small prop Diam (40)
Cell (h): Large prop Diam (52)
Cell (i): Enter Kv of your motor installed or to be bought (2900 for example)
Cell (j): Enter lipo cells that you use (3 for example)
Cell (k): Do not enter anything: Calculates actual RPM of your boat
Cell (l): Calculates propeller diam required (46mm for example)

According to the spreadsheet, I also prepared the following equations which for each boat hull size give you the propeller diameter according to your posted values:

17-27" : Prop Diam = -0.0006*RPM+53.913
20-27" : Prop Diam = -0.0006*RPM+59.5
24-29" : Prop Diam = -0.0006*RPM+59.714
26-32" : Prop Diam = -0.0008*RPM+70.857
30-36" : Prop Diam = -0.0006*RPM=69.545

The setups seem to be very high specs I would say racing giving high speeds I suppose.
I tried also with Eyekandyboats values and for my boats I got same results as my boat tests, using the 24-34" hull size with 4 cells Lipo values. The speeds for a 32" (2900 kv, 3s, 42mm) cat and 36" mono(1853kv, 4s, 45mm) are about 35-40 mph.

Thanks

[ReddyWatts]

Disar, thanks.

[ED66677]

that's really nice!
Has to be part of the holly FEB bible!

[DISAR]

A final comment is that I used the program with your posted values for the 24-29" hulls with 4s, for my boats and setups and the results are right on target.

32" cat (2900 Kv, 3s, 42 mm)
36" mono (1853 kV, 4s, 45 mm OR 1700 Kv, 4s, 45mm)

I have no experience with 6s and upwards setups and I cannot make any comments.

[DISAR]

Hi again,

Based on all the above I prepared the attached Excel file for calculating the prop diameter for each hull type and giving the setups. There are two sheets in the file one with the ReddyWatts values and one with the Eyekandyboats values.
The layout is:

17-24" Hulls, 2 cell Lipos
5500-3200 Kv
Please enter KV & number of Lipos
Motor KV 3200 ------------Here you enter the motor Kv
Lipo Cells Number 2 ------Here you enter to Lipo cells number

The required propeller diameter is
Prop Required 40 ----- Calculates prop diameter

[ReddyWatts]

Thanks again Disar

Remember, there are to many variables for this data to fit all the different hull and motor loads. Many setups will fall outside this general information spreadsheet.

This was mainly to show a structure of setups so you will see the "Big Picture" for a better understanding of FE.

Always start testing with a small prop and work up to your desired amp readings!


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