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Alfa V2

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Postby Warpatroller » Fri May 16, 2008 1:08 am

Hmm, that is a strange size for the WTC diameter 37mm (1 15/32"). I am going to guess maybe it is 1.5" even, and that must be the outside diameter. Is the inside diameter 1 3/8"?

That is going to be the exact outside and inside diameter of the WTC for my project.

I looked at the SWM page and that 300-sized motor appears to me to be 15/16" or the same diameter as a Quarter. Your old Mabuchi motor looks like a speed 250 size motor, which is what I am considering for my WTC. These 250 motors typically spin 9722 RPM @ 5V The SWM 300 motor claims to spin 5400 RPM @ 5V. Supposedly the lower RPM should be better for a boat or sub, and not need a reduction gear setup.

I was trying to find out the diameter to see if i'd have sufficient room to clear a pushrod both above and below the motor in my tube. I see you put a bend in your pushrods to get them closer together to be able to pass through your seals.

My project will be a small boat also, similar in size to yours. Thanks for the close up photo.
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Postby petn7 » Fri May 16, 2008 11:00 am

Warpatroller wrote:Hmm, that is a strange size for the WTC diameter 37mm (1 15/32"). I am going to guess maybe it is 1.5" even, and that must be the outside diameter. Is the inside diameter 1 3/8"?

That is going to be the exact outside and inside diameter of the WTC for my project.

I looked at the SWM page and that 300-sized motor appears to me to be 15/16" or the same diameter as a Quarter. Your old Mabuchi motor looks like a speed 250 size motor, which is what I am considering for my WTC. These 250 motors typically spin 9722 RPM @ 5V The SWM 300 motor claims to spin 5400 RPM @ 5V. Supposedly the lower RPM should be better for a boat or sub, and not need a reduction gear setup.

I was trying to find out the diameter to see if i'd have sufficient room to clear a pushrod both above and below the motor in my tube. I see you put a bend in your pushrods to get them closer together to be able to pass through your seals.

My project will be a small boat also, similar in size to yours. Thanks for the close up photo.


I gave mm dimensions since redboat wasn't from the US. The exact dimensions are OD: 1.5 inches; ID: 1 3/8 inches. McMaster part number: 8585K43.

As for my old Mabuchi motor, it was run wet, in direct drive. I used 5 cells with that motor, but now I'm using 6 cells. Also, these cells are much newer, so should produce better performance. Finally, the Alfa V2 is a lighter sub (I think), so overall, performance should be the same or slightly better. I'm still looking for a pool for sea trials.

Let me know if you have more questions.
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Postby petn7 » Fri May 16, 2008 11:35 am

More pics:



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Postby Warpatroller » Fri May 16, 2008 3:35 pm

That McMaster part number is the identical one I am planning to obtain.

Your old Mabuchi looks like it came out of one of the earlier Walmart subs. I have the Walmart Gator and I am pretty certain that it uses a small reduction gear setup (so it is not direct drive). The motor housing in the Gator is opaque, so I cannot see inside it to confirm this. At one time, I was going to transplant this motor/housing/gearbox setup into my project hull. But I would rather not disable the Walmart sub by doing so.

For battery power, I plan on using four AAA 1000mAh NiMH batteries for a combined pack of 4.8 Volts. My receiver is spec'd for 4.8V, the ESC can work off it, and so could this SWM motor. That SWM motor actually turns 4500 RPM @ 5V (I had incorrectly stated 5400 RPM in a prior post). I might consider trying 5 cells for 6 Volts if I find the running speed to be too slow at 4.8 Volts. I am wanting a flank speed that is equivalent to a normal walking pace.

Another option I have is to use a Mitsumi DVD tray actuator motor that I have lying around. It is the same diameter as a regular speed 300 motor, but only .5" long. It spins at 4933 RPM @ 5V (based on Mitsumi's online specs), very similar RPMs per volt as the "special" SWM motor. I'm guessing though that maybe the SWM motor develops more torque, since it is physically longer.

The two blue micro-servos your using, did you get them from Caswell? They look like they might be the ones shown on his site. Maybe you got your propshaft seal there as well?
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Postby petn7 » Fri May 16, 2008 7:33 pm

Warpatroller wrote:The two blue micro-servos your using, did you get them from Caswell? They look like they might be the ones shown on his site. Maybe you got your propshaft seal there as well?


The servos are Hitec HS-50s. I wanted to use HS-55s, but they didn't fit. The shaft and pushrod seals are from Caswell (1/8" and 1/16").
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Postby redboat219 » Fri May 16, 2008 9:53 pm

petn7

Have you talked to Caswell regarding the micro airpump leaking back when under pressure?

From your fourth and fifth pics it seems that you can extent your wtc up to over the ballast tank holes in the bow and just up to the red dash lines in the stern. Could give you 1/2 to 1 inch more space.

Forgot to ask you this earlier. How did you manage to squeeze your stern linkages in such a small area? Can you post pics of those as well.

Thanks.

Warpatroller,

Sure like to see what you're building there.
"Make it simple, make it strong-and make it work!" - Mikhail Mil
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Postby petn7 » Fri May 16, 2008 11:42 pm

redboat,

I have the space for a pitch leveler (or 8 cells), for sure, but I'd have to lengthen the WTC, and I don't want to do that right now as I would like to do some testing, first.

With regards to the stern linkages, I can't get any good pics. I tried taking some, but they didn't show up very well. It's pretty straightforward and logical, though. I didn't use any tricks in getting my linkages for the rudder and stern dive planes.

As for Caswell, I have not talked to him, nor do I intend to, since I don't think there's anything he could do. I don't think the pumps he sells are defective.
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Postby Warpatroller » Sat May 17, 2008 2:03 am

Pet,

I looked up the HS-50 and Tower Hobbies show them to be discontinued. When I compare the specs to the Caswell servo, they are almost identical..at least dimension wise.

HS-50
--------
L = .82", W = .44", H = .87" Torque = .6kg/cm
interestingly it also states "For 4-cell (4.8V) use only."

Caswell Micro Servo BT50
------------------------------
Size: .45" x .8" x .85" (doesn't identify the dimensions)
Torque: 1.6kg/cm @ 4.8V (seems like the torque is VERY high compared to the HS-50..) Cheap Chinese no-name brand has 2.66 times the torque of the Hitec unit?? I wonder if that is really true.. Anyway, it would appear the Caswell servos will fit inside a 1.5" WTC in the same way your HS-50s do.

Redboat,

When I actually have something to show, I will put it on here. I am still waiting for the hull to arrive... The hull is in the process of being laid down at Deutsche Werft AG. We can never seem to get these "Wunderwaffen" boats assembled in a timely manner! When the hull finally does arrive the internal components will need to be installed in the most adverse of conditions.. Hopefully the boat will sail before the war ends..:lol: I crack myself up sometimes.. Anyway, just doing preliminary planning for my own little WuWa project to gradually work on over the summer.
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Postby petn7 » Sat May 17, 2008 10:31 am

War,

Only the Futaba J connecter HS-50 servo has been discontinued...at least according to Tower Hobbies' website.

The HS-55 servos flat out, will NOT WORK in the McMaster tubing we both bought. Actually, they'll fit, but you may run into trouble with servo horns. The HS-50s are a pretty tight fit themselves. The Caswell servos, being slightly bigger may not fit. However, if they do fit, having that extra torque will be very useful.
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Postby Warpatroller » Mon May 19, 2008 5:29 pm

Pet,

Your right about the HS-50 availability. There are also the GWS Pico servos, which are even smaller than the HS-50. What I don't like about the HS-50 is the cost of those units, $22 each. Pico's are $14 each and Caswell's are $8.

By the way, have you had a chance to run your Alfa with the new SWM motor? If so, how does it perform in your boat?

Steve
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Postby petn7 » Mon May 19, 2008 5:43 pm

Warpatroller wrote:Pet,

Your right about the HS-50 availability. There are also the GWS Pico servos, which are even smaller than the HS-50. What I don't like about the HS-50 is the cost of those units, $22 each. Pico's are $14 each and Caswell's are $8.

By the way, have you had a chance to run your Alfa with the new SWM motor? If so, how does it perform in your boat?

Steve


I won't get a chance to run my Alfa V2 for another few weeks, I imagine. I have done some dry "tests," which I ran to determine endurance. The run time, out of the water, at 100% throttle is "greater than" 20 minutes. The actual in-water runtime will be longer or shorter for several reasons. But anyways, the motor is producing more thrust than the older Mabuchi motor. This might be because an extra cell, though. Also, it turns out I need this extra torque since the motor doesn't run perfectly freely in the WTC. There's a lot of friction (the motor is perfectly lined up with the propeller shaft), so that extra torque is useful. If I decide to lengthen the WTC, I'll try to reduce this binding.

Bottom line: I haven't used the motor in the water, but it does produce lots of torque. I'm 96.83955% sure I'll be happy with this motor. It may not be perfect, but I think I'll keep it.

P.S. I didn't really break in the motor. If it makes a difference, oh well.
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Postby Warpatroller » Mon May 19, 2008 5:50 pm

Why is the motor not running freely in the WTC? What is the source of the friction? Is it because of your fuel tubing shaft linkage?

What is the total voltage and mAh capacity of your battery pack?

I don't think an electric motor really needs to be "broken in", like an internal combustion engine does.
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Postby petn7 » Mon May 19, 2008 6:11 pm

Warpatroller wrote:Why is the motor not running freely in the WTC? What is the source of the friction? Is it because of your fuel tubing shaft linkage?

What is the total voltage and mAh capacity of your battery pack?

I don't think an electric motor really needs to be "broken in", like an internal combustion engine does.


Brushed motors (at least for R/C cars) need to be broken in. The brushes need to be properly seated on the commutator. However, motors like the SWM 300 sized motor may not care if they're broken in or not.

The motor isn't running freely because the motor is just slightly off center in the WTC and as you can see from the pics, the shaft coming out of the WTC is slightly off center as well. This produces more friction from the fuel tubing as you already pointed out. The binding/friction isn't bad, but it's definitely there. I don't care about inefficiency, but the motor does get pretty warm, but then again, the WTC will get some cooling from the water that it doesn't get when run dry.

I'm using 2/3AAA NiMH batteries with 400mah of capacity (6 of them in series for 7.2 nominal volts). I got the cells them from here:

http://www.cheapbatterypacks.com/?sid=1127144
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Postby petn7 » Tue Aug 05, 2008 8:46 am

Here's a run of my Alfa at the SubRegatta

http://www.youtube.com/watch?v=tjTPiVuIpMU
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Postby petn7 » Wed Aug 06, 2008 1:34 pm

Here are some pictures Brad took of my Alfa V2


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