Boldly Going Where No Man Has Gone Before. RC Nano-Hydro

[Jerryemartin1958]

Are these the model kits that were sold at the unlimited races back in the 80s. I bought one of the miss bardahl

[Dr. Jet]

Are these the model kits that were sold at the unlimited races back in the 80s. I bought one of the miss bardahl

I believe that is the case. I too have the Miss Bardahl. Speaking of which, it finally arrived (Thanks again Jim! ). Man, is it TINY!! One of the valve covers was missing, but that's no big deal, I'll just make new ones from balsa. I think they'll look better in balsa anyway.

The quality of the molding is actually quite good. Rather than being pulled over a male mold, it was pulled INTO a female mold.

I'm going to do a lot of thinking and sketches before I start gluing anything. My basic concepts were good. The strut will work as built; I need to shorten the tang and the bracket, but that's just a few seconds on the sander; and I may shorten the length of the strut itself as well. The servo will just barely fit, but it will work. The battery may be a bit too big to fit through the hatch. I may drop down to 300mah and save 10 grams in the process.

I have some super-thin CF sheet. I may make a new transom doubler piece from it, then I can fill the indentation in the bottom of the hull for the prop with a thick Cab-O-Sil and epoxy mix. Some of this will be ground out to mount the strut through the transom, so it will make the fill a structural member.

The kit had hefty doublers in the engine and aft cowl to attach Velcro to the parts. I'm going to eliminate these and do the deck hatch as indicated in the sketch above. This will either be an overall weight savings or a wash. I plan to make the "shoebox" lip on the deck as small as possible (1/16"+) to shave a few grams and trim the hull bottom a bit more to the scored line on it (another gram or so).

The kit also had the batteries in the aft cowl and a big heavy slider switch under the engine. Eliminating the switch will save quite a few grams and relocating the motor and batteries will greatly help the balance.

All in all, this will be a challenging project, bit I think I can do it at nearly the same weight as the "stock" boats. A better balance and the ability to fine tune things may make a winner.

Photos when the sun comes up.......

[NativePaul]

Do you have scales good enough to weigh the hull, doublers, and the switch?

How wide is it?

I look forward to photos of the bottom, do you think the bottom is usable? How deep are the sponsons below the floor?

[Dr. Jet]

Do you have scales good enough to weigh the hull, doublers, and the switch?

Yes I do. Good to 0.01 grams. Here are the weights thus far (in grams). Realize, I will be trimming some of the parts, eliminating others, and adding some as the build progresses. I'll keep a running total of the various weights and report them here.

Deck - 12.78
Hull - 11.91
Cowl - 1.74
Motor - 1.20
Valve cover - 0.38 x 2
Motor doubler - 0.74 (Eliminate)
Cowl doubler - 1.75 (Eliminate)
Fin - 0.99
Switch - 1.71 (Eliminate)
Servo - 1.98
Strut and Bracket - 1.59
Prop - 0.12
Motor - 14.5 (per Mfgr)
ESC - 6 (per Mfgr)
Battery - 16 (per Mfgr)

Weights of "stock" gear as provided by Native Paul

Motor - 18
Battery - 23

Unknown "stock" weights

Driveshaft and Stuffing Tube
Coupler
Rudder
Wires
Velcro

I am already under stock weights with the motor/battery ESC by 3-1/2 grams. I should have a lighter driveline, I'll definitely have a lighter rudder, and with the trimming (2 grams??) and eliminating (another 5 grams??) of parts, I should be able to be at or below the stock weight of the uncontrolled model.

How wide is it?

3-1/2 "

How deep are the sponsons below the floor?

About 1/4" Should be adequate at this scale.

[Dr. Jet]

Better Bottom Photos

I've been thinking about removing the "bumps" on the bottom, but at this point I think I will leave it alone. I'm going to fill the depression for the prop, and may put some full-length air traps on it.

[Dr. Jet]

So I thought I'd do a little test and sand the motor down to where it didn't look like it was sitting on top of the hull, i.e. a more "scale" appearance. The result? 0.58 grams which is less than half the weight of the "tall" motor (1.20 grams) and it looks a lot better.

Half a gram here, half a gram there, it will add up.

[Dr. Jet]

I had some free time so I trimmed the deck a bit more and opened the hole below the aft cowl. New weight: 10.89 grams or 1.89 gram reduction.

Did some sanding on the hull bottom. 11.41 grams. 0.50 gram reduction.
Sanded the cowl. 1.49 grams. 0.25 gram reduction.

That's 3.26 grams sanded off just today. Add in the parts eliminated (4.2 grams) and that's 7.46 grams shaved off.



Looking at the numbers, the stock boats are somewhere around 75 grams, excluding wires, driveshaft, stuffing tube, Velcro and paint. That will be my goal weight.

[Dr. Jet]

I made the transom doubler this morning. 0.21 grams. A good portion of this will be removed when I create the hole for the strut and rudder brackets. Photos to follow.

[Dr. Jet]

With the transom doubler in place (glue is cooking off), I could trim the strut and strut bracket. New weight: 1.59 grams, or 0.75 grams less than before.

[Dr. Jet]

I made a rudder and rudder bracket. 0.75 grams. It has to be 1/4 the weight of the stock fixed rudder.

[Dr. Jet]

Strut mounted

I got the strut mounted. I cut a square hole in the transom, then tacked the strut bracket in place with some CA. After that, I filled the "venturi" with a real dry mix of epoxy and Cab-O-Sil. The screw holding the strut in place is from an eyeglass repair kit.

Total weight of hull bottom w/ strut: 13.86 grams

[Dr. Jet]

Back to this project for a moment. I am somewhat in an impass as I need the motor to do a weight and balance and establish the locations of the various parts. I ordered the motor from HK on December 18 and this is what tracking says:

Dec 22, 2017
02:47 pm
The item is lodged to airport warehouse in originating country PostNL

Dec 26, 2017
02:09 pm
The item has left the originating country PostNL International

Dec 27, 2017
01:50 am
The item is ready for shipment PostNL International



12/26 The item has left the originating country; 12/27 The item is ready for shipment?

USPS has no info on this package.

Maybe I'll make the motor coupler today.

https://www.youtube.com/watch?v=zjU8L6go1VA

[Dr. Jet]

Motor Coupler

The motor coupler may be the most complex single component of this entire build because of the precision required and the smallness of the part.

I have some 3/8 aluminum hex stock that will be the basis for this part. I'll turn it down just a little bit to establish a good edge, but still leave enough flat to make it easy to drill for the set screws. Then, I'll move the work to the mill to establish the exact vertical center and drill and tap the holes for the set screws. Then, it will be back to the lathe to drill a 1.2mm hole the full depth, followed by the 1.5mm reamer, then the 1/16" reamer to the precise depth. Next, I'll turn it down to 3/16" diameter, add the taper at the output end, then finally do the reduction at the motor end and cut the piece off.

I don't have digital readouts on either of my machines, so I have to use dial indicators with magnetic bases to determine travel amounts as I really don't trust the feed indicators due to backlash.

[Dr. Jet]

Coupler done!

I measured the length of my setscrews and decided to make the outer diameter of the coupler 0.250"; otherwise it's all per my sketch. 1.28 grams with 4 SS setscrews.

[Dr. Jet]

Weight Update

According to the information I have available, the stock boats are somewhere around 75 grams, excluding wires, driveshaft, stuffing tube, Velcro and paint. I have contacted Chris Casper and he is sending me information on the power system and I can extrapolate the all-up weight of the free-running boat from the information provided.

My current weight total is 67.45 grams. I will be removing some wires from the ESC and soldering the motor wires directly to the board and probably eliminating the shrink-tube wrap on it as well for some savings. I have yet to settle on a receiver, but that should be in the 5 gram range. My driveshaft should be considerably lighter as it will be primarily 1/32 wire. I may also use 1/32 wire for the rudder pushrod with some brass tubing sleeves to make a water-tight seal.

All in all, I'm confident that this will be at or under the weight of the free-runners, will be better balanced, and should have a better power-to-weight ratio.

It just might work....