Puffin - Trial and error engineering

[Occupant]

Better view of power key on the WTC inside body, canopy removed

[Occupant]

got the updated drive assembled, wired into the tail section, connectors backshells potted in. worked on the power distribution a bit and all seems to be working. Note the RX shown is the wrong one, its a rs9x.


The power key cuts power pre current sensor and has a visual indicator that the system is powered.


power key will be accessible in front near nose under canopy.

[RCENGR]

That makes more sense. I knew the TD-R10 allowed assigning S-port to the PWM pins, but I could not find it for the TD-R6.

I may be wrong on the current sensor. I don't have one to test, but after watching a video on setting one up, it looks like the onboard electronics may be powered by the RX. So if it doesn't get powered by the high voltage lines it may not draw power until the RX is on.

[Occupant]

RCENGR - Channel 5 is a sport , had to move my ballast pump from channel 5 to 6. for all my current / thrust measurements have been using it successfully. On the main screen have configured with model battery voltage, current, mah consumption as widgets allowing to gage whats going on. Good catch on moving the telemetry past the power key to eliminate power draw, thanks! one more thing, correction that's the wrong rx I have a R9SX receiver

[RCENGR]

Also, the current sensor should be after the power key, otherwise it will be draining the battery all the time. I would guess that the current drain is very low and you would probably be fine as long as you disconnect the battery at the end of every day at the pond.

[RCENGR]

Have you verified that you can use channel 5 for telemetry? I tried on my X18 and a TD-R6 and couldn't make it work. I think you have to use the connector on the top of the RX.

[Occupant]

With inputs from Bob (current target) Subculture (too fast a motor) CoPilot (impeller sizing and design) now have a respectable 7a at Max thrust of about 2.5 lbs. A few simple changes, 360kv 4108 motor, 1.75 impeller, clear flow path - motor was in the path, stretched it forward out of low along with minimal clearance between impeller and tube. i can get 1 lb thrust at 2.5 A now. Moving on to wiring the system up vs just testing the drive anyone see anything wrong with the wiring scheme?

[Occupant]

In addition to trying to reinvent the jet pump have been fixing things didn't like in the last build. The fin servos used to slide into a keyway, had too much slop an a bit of movement. revised the interface to a t - slot, now nice and tight fit. In addition rotated the servos to get the servo horn and fin hor on the same plane. Finally revised the silicone potting down to a single pour vs top and bottom. In the process of doing the mold made a removable cap for one wall that used the servo sharft as a mount and block the silicone from encasing the top surface. i printed the cap out of TPU to get a little flex and have abit of compliance. think it turned out pretty well.

[Occupant]

Kind of like the jet ski other than the motor is attached to the rudder ball and moves as a unit pivoting about the vertical axis. spent the morning with google trying to figure out the impeller rudder ball paramaters. then spent the afternoon with Microsoft copilot doing the same. I'm finding that google is a lot more flattering with a lot less useful info while Microsoft will actually try and solv problems and do the math. playing the two agains each other like and believe the copilot info. changing a few things to try and optimize performance - thrust / amp. tore the cad model up a bit, changing to a 1.75" impeller, lengthening the et tube to move the motor out of the flow path and then just swept the 1.75 thru a radius and angle out the bottom - more streamlined. then aded feature to allow putting a flow restriction nozzle to help guage a taper at the end of the output see if it effects thrust / amp.

[Scott T]

"movement and just under two amps will pull the assembly to the surface and start sucking air thru it. need to put this into the boat, run it in the pool vs static testing to get a better feel."

I read the sucking air but did not register the part about not in the boat static testing.

This is looking cool.

[Occupant]

water is drawn in from the bottom

[Scott T]

Sounds like you have plenty of thrust. You might add an intake baffle to suction the water below the waterline.

[Occupant]

Im my big Alfa, I was drawing 1.2A at cruise speed and 8A at full throttle. The Seawolf by Thundertiger draws 13A ful-tilt. Current consumption increases exponentially with speed through the water. I run the FAS40 current/voltage sensor for live telemetry in my personal boats.

The 20A is at max rpm, not sure i'll ever need that kind of power, a lower KV motor might be the answer - have gone from a 1000kv to a 580kv for this iteration. Anyone have history of using a slower motor ( one that doesn't come from a place that starts with Ali....

Ran the tests again trying to hit each amp 1,2,3,etc... as Bob said it jumps exponentially at a point. Also did something different, using reverse note when current moves the drive. in this case just blow an amp starte to get movement and just under two amps will pull the assembly to the surface and start sucking air thru it. need to put this into the boat, run it in the pool vs static testing to get a better feel.

The rudder ball has vanes in it in addition to the fins in the front.

[Subculture]

You're going to need some very good batteries to supply 20A with consistency. Does the shroud have some vanes to counter torque roll from the prop, otherwise handling might be interesting.

[Occupant]

Another day, another design, print, test.. more reading and googling.

Using the feedback here have a rough idea of what to shoot for. So far a 2” prop with a 1.5” pitch has had the best results so far putting out about 1.5 lbs of thrust with about 12 amps.

FYI tried a 1.5” prop in a 2” tube with odd results, throttle up forward and it goes reverse off to the side, reverse did the same - goes in reverse to the side???

After a while googling - started getting help designing a prop only to be corrected that it should be an impeller for a jet drive. something it suggested thru questioning is to have the impeller OD as close to the jet tube ID as possible to minimize blow by. Two simple changes made a huge difference in performance. first increased the length of each blade to complete the circle from the end view - no open free space, (traditional props have about 50% open area) same pitch as above. Second printed the impeller at 2” and sanded the perimeter until it was a slip fit into the tube.

his two small changes made a huge difference. Thrust went to about 3.5 pounds (21 amps, max throttle) - not seen in the pic is its bending the yardstick. Taking a couple other points hit 1 lb at about 3 amps, and from that what appeared to be decent flow but less thrust at about an amp.