Vac-U-Tug recovery boat build

[Make-a-Wake]

I was wondering about the cell count you would use, I was hoping i wasnt gonna read you were using 6s or something crazy. 2s and that motor will give you great runtime and good low speed torque and allow you to use a decent size prop with some bite. Glad the 1500 grit worked out.

[alanr77]

I am using 2 5000mah turnigy nanotech 2s batteries wired in parallel for 2s 10,000 mah.

[alanr77]

With the 950kv motor it should spin around 7k unloaded. The 50mm 4 blade prop is rated to 7000 rpm. Loaded speed should be in the 5-6k range at full throttle. The way this boat is set up, I shouldn't need to go past 1/2 throttle when just running around. I want the high reserve for towing operations.

[Make-a-Wake]

I retrospect a 700 brushed would probably have been better since a brushless ESC especially doesnt like tooling around at half throttle and having to manage the voltage at mid throttle. Hopefully with only 2s2p it wont be an issue with your brushless setup..............you may consider a smaller prop to be able to throttle up more.

[alanr77]

MaW: a brushed 700 would be going in the opposite direction from where I want to go. An underlying theme for this build was to update the running gear to something from this decade. I guess I forgot to list that as my intention in the first post. When researching the running gear for this boat, or any tug, all I could find were posts from people telling the builders to pull motors out of hairdryers and such. It was insinuated and sometimes flat out written that "brushed motors have no place in scale builds". Now, being just below mid life, I was around when brushed motors were all we had and at the time the only choice. However, now, we have much better technology and the days of the brushed motor are coming to an end. I can't really think of any benefit a brushed motor has over a brushless motor. I have 14 planes and 6 helicopters all running brushless setups from 2s to 6s. I rarely run any of them at full throttle other than during take off. I have never had any issues with my esc's handling this over the past 6 years. I thought about the reasoning for your caution and at first came up with the lower loading of my airplanes spinning smaller props, but I could not logically apply that theory to my helicopters, which spin large diameter blades and drive belt tails. If I am missing something here let me know. Beyond all of this, I feel that in a lot of ways older, experienced modelers are holding onto their brushed motors like people in the 80's did with VHS tapes. So instead of following the masses I'm going to show it can be done- because eventually we will run out of hairdryers to steal motors out of....:] By the way, please don't take this as a defensive backlash at your post- no harm intended, I really appreciate your input and advice, besides, I think there may be 2 people watching this and I don't want to lose my only audience.

So, being that to me these are toys that I play with when I am unable or don't feel like working on my full size toys, I like to experiment with them. When all is said and done I will have less money in this tug than it costs me to buy a gallon of bottom paint for the big boat. So if I burn up some stuff, so be it. [mind you, I will not play this game with the FE build as the electronics are going to set me back a few grand]

Having said all this, lets troubleshoot my logic when I chose the components of this build;

Stock motor specs:

Specifications:
Dimensions : Ø 27.5 X 38.0 mm
Shaft Diameter : Ø 2.305 mm
Input Voltage : 24.0 V DC
No Load Speed : 22000 rpm
No Load Current : 0.20 A
Nominal Speed : 18500 rpm
Nominal Torque : 10.00 mNm
Nominal Current : 1.20 A
Stall Torque : 60.00 mNm
Stall Current : 6.00 A
Maximum Output Power : 35.00 W
Maximum Efficiency : 70 %
Torque at Maximum Efficiency : 10.00 mNm
Speed at Maximum Efficiency : 18500 rpm
Life (typical) : 150 hr
Weight : 65 g
Operation Temperature : -10 to 55 °C

Upgraded brushless motor specs:

Spec.
Battery: 2~4 Cell /7.4~14.8V
RPM: 950kv
Max current: 23.2A
No load current: 1A
Max power: 243W
Internal resistance: 0.070 ohm
Weight: 70g (including connectors)
Diameter of shaft: 4mm
Dimensions: 28x36m
Prop size: 7.4V/12x6 14.8V/9x6
Max thrust: 850g
Storage Temperature : -20 to 80 °C
Electrical Connection : terminals

I will be running a 30 amp esc with this motor- forced water cooling on the motor mount and esc. Goal is to spin a 50 mm 4 blade prop that will push the boat to hull speed at less than 1/2 throttle. I purchased this motor after spending hours comparing the specs of countless motors. the goal was to increase the efficiency and triple the watts without increasing the rated rpm. I think I have come close to this. Do you not agree? Give me some insight to what I have missed. Thanks for the replies. Alan

[Make-a-Wake]

I hear ya loud and clear, my "insight" is that brushless ESC's dont like being powered at half throttle, they hate it and will overheat having to manage the current, ripple currents can result and then the ESC can fry, that's the only part of the setup that worries me. Keep on building!!

[jj2003]

I'm dropping in on this one alanr77......so now you have an audience of 3...hehehe! Nice build process :)

[marko500]

Oh I think there's more then 3 watching this thread. I've been following it too. Very nice build so far. I have a Vac-U-Tow that we use for rescues, works great.

[alanr77]

Good afternoon, ok, after letting the motor mount dry overnight, the next step is to start placing the components into the hull liner. Now, the instructions only call for the rudder servo to be mounted. There are tiny dimples already in place to guide your drill bit when installing the rudder servo. I found that the hole and dimples match the mounting tabs of a Futaba S3004 standard servo perfectly and mounting it was easy. However, I am installing two additional servos and switches. The first will use channel 5 and turn on the lights. The second using channel 6 will turn on the water pump and radar dome. If you remember, I am using a micro water pump to force cool the components. The hull will not move fast enough to draw water on it's own. The radar dome will spin when the pump is on to tell me it is running. The light switch will control navigation lights, deck lights and two spotlights.

First, I marked the location of the mounting holes for the tray within the hull liner
marktrayholes1.jpg

Next I drilled the holes with a hand drill
drilltrayhole2.jpg

I had to move the entire tray forward from the stock location because the large servo hit the motor tray. Small oversight when I designed the motor tray.
fwdtryservo3.jpg

I played around with the direction that the servo would face. I had to ensure that the rudder control arm would clear the motor mount
dryftservodirection4.jpg

Then I started placing all the components where I thought they should be. This is going to require some ingenuity
dryfitcompon5.jpg

[alanr77]

Lots of parts. This hull is looking small....the main receiver is going to be below decks, the satellite receiver will be on the bridge with it's antenna attached to the simulated VHF antenna
wherefit6.jpg

I marked the location of the two micro servo's and switches. They were cut out with a Dremel and a razor blade. Not pretty but functional and will be unseen
marklocation7.jpg

I had to offset the servo's slightly to accommodate the curve of the hull. I am not sure how all of this will fit so I want to leave myself options later
offsettoclrhull8.jpg

After everything was cut out, I placed reinforcement strips of epoxy saturated balsa under the screw holes
reinforcescrewhole9.jpg

When screwed down you can see the offset. May not be necessary but it's better to do it now
offsetswitch10.jpg

[alanr77]

After everything was secured, I dry fit the component tray again to make sure everything fit so far
dryfittray11.jpg

I had to tweak the servos a bit to clear the hull liner. There are so many pieces going into this hull that the placement of components has to be well thought out in advance.
tweakservi12.jpg

Next I drilled the holes in the switches for the rod that will connect to the two micro servo's
switchhole13.jpg

Then I trimmed the bottom of the screws. No need to have extra sharp bits sticking out. This hull will have a mess of wires and water tubes running around so I'm trying to prevent issues later
trimscrew14.jpg

After putting it all together, I went to center the servo's and found out my old GWS servo was shot. As you can see, I am reusing many parts that I have laying around, such as screws and servo's. Luckily I have packs of micro servo's left over from other builds so I installed a towerpro micro servo in place of the GWS servo. It's a little taller but shouldn't cause an issue
centerservo15.jpg

Also while doing this I found that my transmitter was not using channel 5 at all and channel 6 using both the right stick and switch a. Unfortunately, the cheap ExceedRC Tx I had laying around can only be programmed via laptop and programming cable. Thats enough work for today though and I will tackle that tomorrow.

[Make-a-Wake]

You gonna use the Lipo to power the pump as well?

Why 2 servo's............didnt see it if you explained.

[ray schrauwen]

Are you adding any ballast?

[alanr77]

MaW; three servos are being used. The large Futaba servo is for the rudder. The two micro servos will be used to actuate small switches controlling 1) all lights, 2) water pump and radar dome motor. The two lipos in parallel will power everything. This tug is designed to run on a 1200 mah nicad pack so 10,000 mah of lipo power should give good run times even with all systems operating. I will most likely get bored before running the battery down.

RayS; the instructions call for ballast, however, I am adding lots of weight in running gear and accessories. The ballast is supposed to be glued in between the inner and outer hull. Once I have all the components installed I will put it in the bathtub to check the water line and add ballast as needed. Then I will attach the liner to the outer hull.

[Make-a-Wake]

I think 10,000 mah is plenty of ballast lol