The Evil Doctor's Next Project

[eXoNerated]

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[Dr. Jet]

If anyone has a more advanced copy of FE Calc (or its modern equivalent) than I have, I would be interested in a copy as well. My current (really old) version uses Kv, Io, and Rm as the motor constants, plus the typical battery, ESC and propeller inputs. There is no input for number of motor poles (What is the relationship between Rm, Kt, and number of poles?? ) I am using really old battery and ESC numbers, but they're still close to modern numbers (in the big picture). Modern motor data is readily available, and since the propeller data is limited to pitch, diameter, and number of blades, virtually any propeller can be easily calculated and added to the inputs. All the empirical data is stored in a separate text file that is input into the spreadsheet when you run the program. To change a parameter, you modify the text file accordingly, then re-run the program.

[eXoNerated]

The Spuds FE boat calculator file is too large for the forum . Download it from this link https://www.rcgroups.com/forums/showpost.php?p=14935894

Regards
Hubert

[eXoNerated]

Ecalc torque finder is very useful as well. If you know the torque required for a job you can put the voltage an rpm values in and manipulate numbers for more predictive clarity. Here is a look at a NEU 1530 .5 D TL4 option at a crazy demand. Look at the efficiency , It craves the work but I dont think will last long at this power level and rpm.

[Dr. Jet]

[Dr. Jet]

I have decided to do the aforementioned Neu-powered Secret Project in the Auric Enterprises livery. I have something really special planned. Stay tuned.

I have another "unfinished" Neu-powered (1107/1.5Y/H) project on the shelves as well. I've run it countless times and it's stupid fast, but it is still in its bare white fiberglass hull form. This project is an MHZ Miss Madison and it will be the next one into the paint shop. I'll need to create a way to install the vertical fins so that I can remove them (I have a plan) and build the wing between them. I'll also need to find something that I can use for a convincing exhaust stack.

[eXoNerated]

Hi Doc,
What I did was redid each list will a full motor line . For instance on sheet may have all neu motors. Another sheet mght be scorpions , then Lehners dot dot dot. Id save the list with different name from the call up list and only point the program at the revised list buy currently re-naming it . I hope you unsderstand what im trying to say. You might just repopulate the entire motor list only the motors you find relevant.

For example I dont think you need to waste list space for 700BB's . What I really wish is we could get inside the calc and start to add things like blade area ratios and rake. We boaters need a place to submit data taken from logs appropriately headered then we can begin to trend things and allow empiracle data an influence. That would be very useful in my humble opinion. Please also take a look at the Ecalcs torque finder. If you have a target power level and rpm then you can find the torque needed fro that job. With the torque applet you put that number in for the torque your rpm and voltage and it generates the graph. It is a more directed way to find out how the motor will behave with your demand. If you need a link th that i have it. To me ecalc lke neumotor uses truly is the best calulator on the net.

Cant wait to see the smaller unlimited run. All you need for the conventional exhaust stack is a thin sheet of aluminium you just roll it. If it is a modern exhaust stack you are after u need an empty vegetable can ,shoestring, and a plastic solo cup. You make that odd loking modert stack from these pieces. For that size boat u may have to use a tomato paste can and find the smaller solo cups.

Regards,
Hubert

[Dr. Jet]

Hubert,

It looks like we are both using the same program (or version thereof) and I have several text files with different motors that I can run in the program. You are 100% on target with your idea of blade areas and rake being used in the program. For my purposes, I primarily want to make sure I don't over-amp a boat the first time I put it in the water, so my initial goal is prop selection for a given motor/battery combo rather than trying to select a motor based on prop/battery parameters.

[eXoNerated]

Have you see the formulas that would allow the application of BAR and rake... meaning have you see anywhere the correlations between those things and how they affect amp draw, speed, etc?

[Dr. Jet]

Have you see the formulas that would allow the application of BAR and rake... meaning have you see anywhere the correlations between those things and how they affect amp draw, speed, etc?

No, I haven't. BUT....... I would assume a lower blade area ratio = more rpm/less current. How much? I'd have to guess, but the differences would be of a small magnitude. In many respects the Blade Area Ratio in a propeller has similarities to the Aspect Ratio in a wing: The higher the Aspect Ratio, the lower the overall drag. Higher BAR (length/width) prop blades have less drag.

Rake? That has a real effect on the shape of the thrust cone and the lift it provides. Again, I would assume that any energy used in lifting the boat is energy not available to make it go forward and try to make an educated guess.

[eXoNerated]

Well the aspect ratio and bar are interelated but somewhat different. The 1918-50-10 for instance has an aspect ratio of 1.8 while the bar is 50. Typically higher aspect ratios P/D have higher lift coeeficients as well. The energy to lift the boat and push it foward are of the same family because in this case the props does both. Having a prop that lifts more than another allows a lower AOA in turn a lower strut angle. In a boat because of the physical orientation of the blades in relation to the water it's rather intuitive to say higher picthed props inherently have more lift.

There are 3 specific types of BAR. BAR simply is the area of a props ear divided by the full circle area based on its diameter. The 3 specific types are the Projected Area Ratio (PAR) the Developed Area Ratio (DAR) and the Expanded Area Ration (EAR) The aspect ratio is a cooeficient used in the calculation these. Bar is critical to the control of cavitation. Changes in it will effect a props efficiency and it's thrust making performance. The PAR or projected area ratio is the projected area of the outline projected on a flat surface below the prop when you look down on a prop. It will be the smallest bar number of the 3. The DAR or Developed Area Ratio is taken area from the outline of an untwisted blade detached from it's hub with the pitch set to 0. The EAR or Expanded Area Ration is the DAR all unwrapped on a flat surface with all its sections parallel. This is the mode used to examine the aerofoil properties of the blade. The DAR and EAR values should be close and they are used interchangeably dependent on what calculations are needed.

In other words If BAR has an effect on "thrust making performance" then it has an effect relating to increasing or decreasing the props slip.





Regards
Hubert

[Dr. Jet]

Wow! That's a lot of prop information. Maybe more than can be put into practical use for the micros simply due to the limited prop selection, BUT.......... that's useful to know when modding props (like when removing the tongues.)

[eXoNerated]

Hi Doc,
About the BAR disk area calculation. The papers dont say it but in my opinion it isnt an accurate measure unless you subtract the center of the circle areas IE the hub. It does nothing so why include it in the area of the disk calculation. For ur micro boat and its power levels you can fashion your own micro props. Someone in France is doing this and the results on his small riggers is outstanding!!!~

Thank you for your time and patience
Hubert

[eXoNerated]

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[Dr. Jet]

That's pretty cool. I actually have the tools necessary to build the prop making fixtures he's drawn up. It would open up a whole world of possibilities, but the effort required to do so would far outweigh the advantages. If I were doing a World Championship contender maybe, but since I'm really just a hobbyist, homemade props are just a bit much.