The Evil Doctor's Next Project

[Dr. Jet]

Well this project took a back seat to the MPR and the Short Circuit for quite some time. With the Short Circuit nearing completion, this one will be coming back on the the bench.

It's now the summer flying season , so building time will be greatly reduced, but I promise this one will be next in the water.

[Dr. Jet]

Well, here we are, almost a year to the day since my last post here. With the recent completion of the 16" Cat, this project will finally move up to the forefront. I did put a larger motor in the Atlas prototype and hope to have some vids of that the next time out. The scale Atlas will probably get finished painting in this time period as well and may get a motor swap if I like the performance of the new one in the prototype.

[Dr. Jet]

I epoxied the sponson pieces together using a gluing/alignment fixture I made. I drilled 5mm holes with the exact spacing of the booms in a sheet of 3/4" aluminum that was slightly larger than the outline of the sponson. Then I put 5mm pins in the holes and built a "Sponson Sandwich" over these alignment pins. I started with a sheet of wax paper, then the outer 1/64" ply skin, then the two 1/4" balsa sponson innards, then the other outer skin, then another sheet of wax paper, and finally a second sheet of 3/4" aluminum drilled to fit the 5mm alignment pins. This whole sandwich went into a bench vise and I pulled the alignment pins out before the epoxy started to set (I didn't want to risk gluing them to the sponsons). It would have been really easy to crush the sponson in the vice, so I only used enough pressure to guarantee that there were no voids in the gluing surfaces.

Photos of the finished sponsons to follow when the epoxy cures.

[Dr. Jet]

The bare sponsons came out really light, about 8 grams each.

[NativePaul]

Wow, that is great! I didnt think that would be possible with wood, even with ride plates and sealant yet to add, I think they will end up being half the weight of my kevlar molded ones.

Please carry on weighing everything as you go, I find it really interesting.

[Dr. Jet]

I used 1/4" contest-grade balsa for the "innards" of the sponsons which really kept the weight down. The insides of the sponsons are already coated with a light layer of epoxy, so not much more will be added with the exterior sealant. I will weigh the tub once it is completed and report the data here.

[Dr. Jet]

This rigger project has been on hold for a while due to some guitars I needed to work on, and now the Chinese Bat-Eating Flu scare has all the nitrile/latex gloves at Harbor Freight purchased by hoarders. Gotta have gloves if you're going to play with epoxy.

In the interim, I have a new First-World dilemma: As I was digging through all my spare parts, I stumbled upon a perfectly good Neu 1112/1.5D. This motor is a BEAST in a 2950-class housing, and dripping with higher efficiency than most similar-sized motors. The motor's diminutive size means it's suitable for hulls in the 450mm ~ 500mm range.

I'd like to find a suitable hull to build around this motor, but with a Kv of almost 5000 rpm/V, I'm somewhat limited. I could make a super lightweight gearbox and put it in a larger hull and try to take advantage of lighter weight over similar hulls with bigger power systems.

Anybody have any suggestions what to do with this motor (no, I'm not going to sell it )?

[NativePaul]

That motor is enough to make a Mono1 or Hydro1 (lightweight, efficient 650mm ish, self righting) hull go well on 2s. Spirit of Ukraine or Falcon from Offshore Maniac, Exe2.5 from Ecomaster, Phoenix from RC-sails, Scord 3 or 5 from Tenshock, Arcas from ETTI.

It sounds like you are not after a build, so I wont suggest beefing up the other one of these you have, and putting it in there on 3s for a SAWs setup. (Sorry but with this Covid crisis I have lost my job, and am no longer in a financial position to buy the other one off you.)

[Dr. Jet]

Hello NP,

Sorry to hear about your gig in all this Covid nonsense. I was hoping you would chime in on this subject; you always seem to have your finger on the pulse of what's new and cool in the European Mini-Market. You are correct; I'm not looking for a wood build, rather a complete composite hull. I doubt any of the 1/20 scale hydros I've done thus far would hold up to this motor, they're too lightly constructed and are more about looks than all-out speed.

While a dedicated SAW boat might be fun, it may not be the most practical application for my purposes. Besides, where would I find a prop small enough to run a 5000 rpm/V motor on 3S without letting all the smoke out? I'd like to put it in a sport scale hydro, but I don't see any appropriate hulls in the 500 mm range. Everything seems to be 450 mm or less, or 600 mm and greater. My second choice would be a cat, but again, it seems that all the hulls are either too big or just too small. The MHZ Micro Iceberg might work, but my prior experience with this hull is it doesn't corner very well when fitted with a lot of power. My next choice would be a mono, and here it seems like the selection of suitable hulls is much greater. My last choice would be a 'rigger. Yes, I would build one and the NeuMotor would make it a go like stink, no doubt.

Remember, I am not constrained by any rules for "class" racing. I don't have minimums or maximums to limit things, just my imagination, my budget, and my ultimate goals. In this case, my goal would be for something that goes around in circles really fast.

I'd like to follow-up on the suggestions you have made. Can you provide some links?

[NativePaul]

X432 would be fine for sure and probably more, I've run a 4800kv 28x36 Mega 16/15/2 which is smaller and I don't rate quite as highly as an old Neu on detongued x435 and X632 for a fun 6 laps at a time, and a very cut up 32mm V935 for SAWs runs in a Mini Hydro with a castle 50A ESC.

I know you don't race, but as I am a racer 90+% of the FE boats I see are race boats, and 90+% of the non race boats I see are disappointing RTRs, so even though you don't need a race boat they will always be most of my suggestions.

Most of the cats I have seen in this size range I've made myself, if I wanted to buy one that would turn well it would be the Dr Psyko Flatcat, which I think is in the right size range, but I last saw one 5 years ago and I haven't seen many, so check before buying, and don't consider it if running in rough water is important to you, it is fast and good handling , but very much a calm water boat with low deadrise, tunnel depth, and freeboard.

Tenshock Scord 5

Etti Arcas rigger, they have squished the photo though as they often do with their thumnails so to see what it looks like you will have to to the Hydro1 section and view the sponsons and tub separately.

Ecomaster Exe 2.5

"Offshore maniac" in Ukraine make the Spirit of Ukraine, Stinger and Harpoon monos, Falcon and Hydron riggers in this size range, and "RC-Sails" in Romania make the Phoenix Rigger in this size range, they are proper cottage industrys, both make great boats, but neither have a website, I don't think you can link to a facebook page which is the best way to find them, but if you are on facebook look up those names, or if not, I can PM you an email address.

[Dr. Jet]

Hmmm... FE Calc says that X432/motor/'rigger hull combo would draw somewhere in the neighborhood of 65 amps. Certainly doable, but run times would be limited. A tiny bit more pitch and a bit less diameter is even better in terms of current draw and projected speed. A Y531 looks pretty good, but they are only available in plastic. A de-tongued and slightly reduced X432 may be the ticket. Maybe even an X434 reduced to 30~31mm??

Anyhow, your response was exactly what I needed/hoped to learn and I will certainly follow-up on your suggestions.

[NativePaul]

I have not used FE calc, can you link to it for me please? Do you input the boat size and weight? My guess is that it isn't scaling to mini sized boats properly.

In case there was any confusion I was only suggesting 3s for a mini size boat, with limited runtime. For all the boats I linked, I would use 2s without doubt, a 2s 5000mAh pack x435 (Hydro) or low area CNC 436 (mono) should net you somewhere around 5 minutes runtime.

I will embed a video of my mini hydro, a JAE Minisprint weighing aprox 560g running the setup mentiond above on a detongued X435, the average amp draw under power was 40A with a peaks in the low 70s, your KV is a little higher but your I would be surprised if it was more than much more than 50A average with the same prop. An x432 wont be pulling an average 65A in a mini rigger, that is for sure, my guesstimate would be about half that. I was pulling aprox 120 mAh per lap so could have run for 12 laps easily but not wanting to overheat my 2836 motor or uncooled ESC went for a USA race boat style 6 laps to limit run time and heat build up, I wouldn't recommend a 2200mAh battery and emptying it, but if you limit your runtime to about a minute it should be fine.

[Dr. Jet]

The version of FE Calc I have is quite old and has its limitations, but when I input modern motor constants and propeller data it does a pretty fair job of predicting current draws. It is merely a simple spreadsheet program. It does not take into account things like reducing the load on a prop by removing tongues, back-cutting and other tricks, so if anything it tends to estimate high. It also has no idea what a twin motor cat is...

[Dr. Jet]

While I'm on the topic of NeuMotors, I'd like to add that I have been friends with Steve Neu for nearly 50 years, and as such, I have an "inside track" when it comes to ordering and buying NeuMotors. Because of this, I have a few of the smaller NeuMotors languishing in my collection. At this very moment, I am in the painting/blueprinting phase of another Neu-powered Micro project that I have not revealed until now. What it is will remain secret, but as a teaser, I'll say this: I'm debating on the final paint scheme. I could do yet another "Short Circuit" theme, another "Auric Enterprises" theme, or the stock "semi-scale" theme, although I'm leaning towards the Auric theme as of today.

Stay tuned.....

[Dr. Jet]

Another languishing project I have that is now seaworthy is my Vortex. This was one of the first Vortex hulls that had a turbine style hatch, but my hatch warped into something resembling a pretzel. I made a replacement hatch from a sheet of basswood and a streamlined bubble from a BBY micro hydro. The hull is stiff as a board now with CF floor reinforcement and expanding polyurethane foam against Depron stringers in the sponsons, nose, and aft non-trips to make all of those into one solid structure Power is a Neu 1107/2Y turning a cut-down CNC 1832/3 on a 2.25AH 2S.

[eXoNerated]

...

[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]

......

[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.