Formula For Calculating Speed (Revisited)

[siberianhusky]

SpeedCalc.exe
LOL I got bored having coffee. This works with vista, not sure about any other flavours.
Anything else?

[Mel279]

how to calculate speed for twin-drive cat?

[siberianhusky]

update that clarifies the pitch to be input

[sailr]

Cool! Works great! Thanks!

[6sHyper]

update that clarifies the pitch to be input

geez not to shabby, its fairly close to my 3 boats i currently have setup and the gps i'm getting out of them, thanks

[Eodman]

Hey Mel, I asked the same question in the original post and If I remember right(which at my age ... well) there is an addition to the equation. I can't get the link to open for the old post so not sure! I wanted to know because of my twin jolly!

[siberianhusky]

Let me know and I'll try to add twin calculations, might also work on adding a section where you can enter a custom number for the hull slip factor.
Things like this are pretty easy to whip up in VB. There is only about 8 lines of actual code in this app as it sits.

[PDR447]

any chance of making it java or something so that it would be an OS independent app?

[CornelP]

Thanks SweetAccord for the link on FE Calculator. For some reason I can't enter new data for Neu motors and Castle ESC... I'll see if I can come up with something.
.

Under Program Files/Fast Electric Boat Calculator you will find a text file called fecalc. Edit that according to the instructions. I'll take a look in my office pc, I might have the Feigao motors and some Turnigy batteries added...


Edit: I attach the file, I had it at home. It was edited by many OSE members in different versions. I just brought them together and added a couple.

[siberianhusky]

LOL I haven't coded in Java in about 15 years. All I really know is PicMicro assembler. That was just something I whipped up in about 5 minutes,I learned VB so I could create a front end to control micro controllers from a PC.
I've been back into stonework for a long time now, I make more money as a stone mason and have more fun doing it! I hated working inside.

[Mel279]

Hey Mel, I asked the same question in the original post and If I remember right(which at my age ... well) there is an addition to the equation. I can't get the link to open for the old post so not sure! I wanted to know because of my twin jolly!

thats ok, someone will get it for me..I hope

[10gauge]

Mel and Eodman:

how to calculate speed for twin-drive cat?

And yes, Eodman, I remember you asking about twin drives 3 years ago, when I first introduced the formula. The link to my first threads are listed in the beginning of my post.

I will try to answer the question intuitively as possible. I don't think there's a linear increase in speed with twin drives over single drive. Sure, on a twin the initial acceleration is faster than a single, but the terminal speed is hindered to a greater extent by dividing power between 2 smaller motors, smaller props, extra drag, and extra weight.

Are the LiPo packs being shared among 2 motors, or does each motor have its own power pack?... If you have a shared power source for each motor, and after factoring in the offsets, the increase in speed for a twin is on the order of 19%. Formula for Twin vs Single - for identical motors and props in both setups, the comparative equation for a twin cat is: (hypothetical)

mph (Twin-Cat) = [prop pitch] x [Prop dia(mm)] x [kV] x [LiPo V] / 31060


I stopped testing/formulating on twin drives because I quickly realized that there was no big increase in speed with twins to justify the extra investment. More than anything else, prop factor and power from LiPos are the 2 most important factors in performance. If I want better performance = Bigger motor + larger prop!

[Eodman]

Oh but the sight of them props setting on either side & the sound of twins when at speed are worth it to me!

I think it has to do with my early formative years! We had a cabin on a lake in upstate NY and a family had handbuilt a Cat & mounted twin Merc 65 horsepower outboards on it! Now back then Mercs were all the rage & outboards were barely touch 90 horsepower so this thing was just the Cats' Meow. Fast as snot too!

Sadly it was lost in a fire over winter a few years back! But twins are in!

[bbill1]

How are you guys coming up with your prop pitches? The pitch on a raw x447 is 2.59. Yet in the example below from post #1, it is listed as 1.4.

EXAMPLES. Comparison of GPS and calculated speeds:
Setup 1: Lehner 2250/11, 8S, x447, claimed speed 60mph
(1.4 x 47 x 1076 x 29.6) / 36970 = 57mph calculated speed

I've been into nitro for quite awhile and have never come across any other numbers for pitch other than what would be listed on a prop chart. (in inches and are 2+ inches of pitch for any props I have ever used.)

[siberianhusky]

1.4 x 47 = 65.8mm = 2.59"
what don't you understand?
Octura props have always been numbered this way, makes it super easy to figure out what you have.