An Unexpected Success

[Dr. Jet]

Oh Great.........



I spent a whole lot of time and effort researching and designing geardrives because I could no longer find a 2030 inrunner with the appropriate Kv. Well, in addition to designing all the stuff to make the gear drive assembly, I've also been searching for that elusive 2030 motor with a usable Kv all over the 'Net.

Lo and behold, and shortly after finishing up the design and placement of all the geardrive parts on a sheet of 1/16" ply, I stumbled upon a source of cheap, readily available 2030 motors with Kvs of 2900, 3100, 3300, 3600, 3900 and higher. Duh! (See: https://www.rcecho.com/Brushless-Mot...or/?sort=price)

Now what?? I'll still build the geardrive for Prototype #5 (because I can) and test it against the other motors I have selected. I still have foam cut for another hull, plus the styrene, laser-cut parts, drive shafts, rudders, servos and all the other assorted parts to build prototype #6. I will hold off on building #6 until I have more data on Prototypes #2 through #5. I've spent a lot of time making the hull on #5 smooth and shiny. #6 will be a quick-and-dirty test-bed and as such may look a bit "Ragged" when compared to the others. The hull shape (no non-trips, symmetric non-trips, or asymmetric non-trips) will be based on testing of the earlier prototypes.

After all that is completed and I have an optimized design based on real world testing of all the prototypes, I'll build the "FINAL ONE". That will give me a fleet of 6 single-steppers that all fit into a keyboard case for easy transport and storage.

Then I'll get back to other languishing projects.

[Dr. Jet]

Update........

I sent the CAD drawings to the laser guy this morning. I included several dozen geardrive/servo assemblies for the 1222 motor setup, a motor mount fix for the 1:20 Shovelnose kit (there was a dimensional bust in the original ), and motor mount plates that fit the 2030 inrunners. These motor mount plates are swap-able replacements for all the mounts I previously made that fit the little outrunners.

Now, no matter which power system works the best/is most readily available/is cheapest and most effective, I'll have parts on hand for many more single-steppers down the line.

[Dr. Jet]

For those considering gears......

As I stated above, the need for gears in FE is, for the most part, just a distant memory. Yet, there may come a time when gears are the best options, especially when dealing with these really little boats where motor choices are limited, or there are physical space limitations.

Over the years, I've collected a bunch of gears and geardrive assemblies; the latter mainly for aircraft applications. For the most part, you can find slot car and RC car gears that will work in the little single-stepper I'm presenting here or similar-sized applications. The Hughey gears were bullet-proof nylon with metal hubs and had a pitch (pitch ratio) of 32. They were quite large in comparison to what I'm using here. Slot cars most often use 48 pitch gears with the occasional 64 pitch. In all the gearbox photos I attached above, I used 64 pitch gears from slot car applications and from SDP/SI.

But that was then.... Now enter Metric Pitch gears. I am going to use 0.4 Module (the metric measurement standard instead of pitch) in this application; but here's what I discovered: 0.4M gears are REALLY CLOSE, but not exactly like 64 pitch gears. 0.5M (0.6M?? ) gears are REALLY CLOSE, but not exactly like 48 pitch gears. You could probably run a Metric/Imperial gear train for several minutes before you ground all the teeth off.

So take heed my friends; pay close attention to any gear set you plan to use; make certain your pitches are right.

[Dr. Jet]

Wow, all this time I've been working on the geardrive, I never realized how truly tiny it's going to be. On the computer, it fills the screen... It's going to be an order of magnitude smaller than the geardrives I posted earlier (and below). I made those drives from hand-shaped carbon fiber sheet and brass tube. The geardrive/motor mount/servo mount assembly I'm planning will be 1/16" plywood hardened with either thin CA or thinned L-285 epoxy. Thank goodness for laser-cutting, it would be insane to attempt to make all these tiny and intricate plywood parts by hand....

I never realized how tiny the motor is as well. It's the size of the last joint of my pinky finger. This may work to my advantage because I still fear having over-powered hulls that make better airplanes than boats. This may be in the right ballpark for a proper power system, and be several grams lighter.

On the other hand, it may be too small for the 350mm hull I'm building here. Depending on the results I get with the geardrive, I may adapt a new and even smaller hull design to work with it.

[Dr. Jet]

I've been thinking.... (Uh-oh... )... I'm designing a plywood structure to hold the motor, the servo, and the gearbox out of 1/16" plywood, and I'm asking myself:

Why?

Because plywood cuts easily with a CNC laser and can make some intricate and highly detailed parts.

How did you mount servos in really thin airplane wings back in the day?

I glued them into place.

Why not glue the servo in the hull?

Uh...... Water intrusion?

And where would the servo be in your wood contraption?

Uh..... Exactly the same place if I glued it in.

Your previous gearboxes had carbon fiber motor mounts, why not make your contraption from carbon fiber?

A laser won't cut carbon fiber very well and they're pretty tiny and intricate to make by hand.

A ball-bearing stuffing tube is the same size as the ball bearing support tube in your gearboxes. Why not just attach a carbon fiber motor mount to the stuffing tube like you did in the older gearboxes, and eliminate ALL the plywood contraption? The stuffing tube would become the main structural member holding the motor and the gears. The flexibility such a system would produce would make a complete drive unit that would fit into a number of different style hulls and provide a very low profile.

Uh.... I dunno... Maybe the weight of the motor would create a rotational load on the stuffing tube where it goes through the foam step.

Could you make an "Anti-rotational" support of some sort?

I suppose I could.

So why not just make a carbon fiber mount to go on the stuffing tube?

The parts are so small and intricate, it would be really hard to make by hand.

Can you CNC cut them?

Not with a laser, but a desktop CNC router might work.

Well, what are you waiting for?

Doing the research now....

[Dr. Jet]

Research Results

Hmmmm.... It looks like everybody has a pretty high minimum charge. Add to that shipping, raw materials, taxes and the cost per unit goes way up. And there's no way I'll ever use 120 of them. I can actually buy a (cheap and flimsy) desktop router for less than some outfit's minimum charge. Or..... I could buy a better quality desktop CNC router and have the ability to make more than just carbon fiber micro-gears.

Hmmmmm....

[NativePaul]

I glue all my servos in, bar one kit that came with a mount (which broke) I always have, and going forwards always will. You can't beat it for lightness, stiffness, reliability, cost, or ease.

I waterproof my servos before use, and if the hull or servo is experimental and I may need to be salvage or replace the servo, I glue the servo to a sheet of thin balsa and glue that to the hull, so the servo can be easily chiselled out, and the servo or hull can be sanded flat for a replacement servo/hull.

[Dr. Jet]

I did some tests with the styrene sheet bottom and hot melt glue. It holds the servo just fine, doesn't distort the styrene, and the servo can be removed with some work or running some monofilament fishing line through the glue joint with a sawing motion. I'm not too concerned if a servo gets wet and dies. I think I paid somewhere around a dollar or so each for them in quantities of 10.

So I may be seriously thinking about buying one of those desktop CNC routers to make cool carbon fiber geardrives.

[bhorowitz]

Just want to say, that I love following your threads.
Bob

[Dr. Jet]

Just want to say, that I love following your threads.
Bob

Thanks.....

I'm kinda using these threads in the Mini forums as a "Stream of Consciousness" thing. Almost like my own personal blog. I keep it limited to just this forum and for the most part focused on discussions about the minis. I'm sure Steve appreciates that.

Weather permitting, I'll try to get videos this Monday. I won't have any geared ones at that time though.

[Dr. Jet]

The Results??

Well, here are the results of my research and review: Having parts cut by a professional vendor is cost-prohibitive. It would be great to find a guy down the street with a CNC router that could do it. The best and easiest avenue is to buy my own router and fabricate my own parts. The problem with that approach is a quality machine also needs bits, hardware, software, space to set it up, learning curves to use it, and a whole bunch of other unforeseen things to make it work; suddenly, amortizing the investment is probably impossible.

So what to do? I'll make some of the plywood "Contraptions" as originally planned, but I will also cut some of the micro gear motor mounts that attach directly to the stuffing tube. To stiffen them up, I'll laminate some CF on one face of them, open the holes and slots with needle files, then, do the same thing to the other side. It will be the single strongest part of the boat, with maybe the exception of the stainless steel prop shaft.

Stay tuned.....

[Dr. Jet]

Packing up my stuff and heading to the pond. Let's hope the videos work out....

[Dr. Jet]

Good News, Bad News, Success, Failure......

It was smooth water on the lake!

Well, the first one I threw in the water for testing was Prototype #2 "Homie". Homie has the 3300Kv inrunner that started this whole single-step hydro endeavor when it seemed to work so well in that first hull even though it was so bulky.

I put Homie in the water, goosed the throttle, and promptly broke the driveline,thereby rendering it useless for further testing and sending a brand-new prop to the bottom of the lake.

I thought I'd go right to Prototype #4 next, seeing as it was the result of my more recent ideas. Thinking I may have excess power available, I ran the first bit at partial throttle. I found a throttle setting where it ran extremely well with a perfect attitude and was capable of nice, tight turns. It would tend to lean towards the outside of the turn and I think an angled turn fin would help that as it would want to dig the inside edge of the hull downward as opposed to lifting as it was with the straight fin on the hull (I just used the fin from the original prototype hull). So far so good. Now, it's time to open 'er up!

I wait until it is coming at me (so it's closer to shore and I don't have to go so far to retrieve it if something goes wrong) and hit the throttle.........

It all happened so fast, I don't recall the exact sequence. First, it hauled @$$, then there was some flying, some torque rolls, some swimming around underwater looking like a fish, and surfacing somewhat reminiscent of that submarine-based launch of a Trident missile that everyone has seen on TV at some time. I learned to drive it after a while and could do OK, but given the available power (and the urge to use it.. ), it was for the most part uncontrollable. It's own wake from an earlier lap was enough to launch it or send it in a emergency submarine dive depending on the magnitude and orientation of the wake and your speed.

I did manage to do some CG testing, and it was much better with the CG moved forward.

In my playing around with #4, I noticed it was real torque-sensitive. I might attribute that to the outrunner motor. All those big, heavy (relative) magnets spinning in a large (relative) radius IS going to have an impact.

All of this makes me think the little geared motor concept may actually be the ticket for this hull. I am currently using a 1000mah battery, and since I want to move the CG forward, I may go with a considerably smaller battery since the geared motor arrangement will draw less current (lower total Watts). This kills two birds with one stone: Improved CG and lower overall weight.

Oh yeah, the last bummer. There was no one there that could take videos...... Next time out I may have Prototype #5, the geared one, ready to go.

[Dr. Jet]

I'm eventually going to have the motor mounts for the geardrives laser-cut from 1/16" ply. Because the final part is so small and delicate, these wood mounts will need to be stiffened with CA, thin epoxy and/or thin layers of fiberglass or CF fabric. I made a motor mount for Prototype #5 out of CF plate and based on the dimensional drawings provided by the motor supplier. It was not easy.

[larryrose11]

A tiny motor mount for the gear setup. Nice work there. Adjustable I assume for different gears. No other reason to cut a slot like that.