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Postby Warpatroller » Fri Mar 13, 2009 12:23 am

Joel,

I don't know to what extent the motor torque roll will effect roll on the hull versus torque roll caused by props biting into the water. I just know that a motor itself will generate some roll. For example, if you stick a disconnected, unloaded servo on a table and power it up and rotate it back n forth with your transmitter, the entire servo box body will jerk from side to side on the table.

I remember my old Dodge Challenger V8 engines would generate noticeable torque roll when you hit the throttle with the transmission in neutral. The whole engine would rise up on the driver side and compress on the passenger side. When loaded and taking off in a drag racing manner the engine would generate so much torque roll that it would brake the driver side motor mount with the air cleaner smacking the underside of the hood as the engine tried to rotate toward the passenger side. I subsequently chained down the engine to the driver side of the K-frame which eliminated the broken motor mount problem, but i'd get some engine vibration transferred to the unibody through the chain.

Haven't seen too many threads relating to contra-rotating props on subs so I find this very interesting. About 3 years ago I saw a SubTech Albacore with contra props very similar to yours, but I never saw the boat run in the water.. I can't remember whether it used a differential or two motors like yours though.

What are the diameters of your aft solid propshaft and your hollow forward propshaft? Are you going to secure the two props with set screws or will the shafts be threaded?

When your at the point to test the system out, please let me know if the boat rolls at all. Maybe it won't be a problem, but I'm interested to know if it is or not.

Steve
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Postby ManOwaR » Sun Mar 15, 2009 3:06 pm

Ok Steve,
I almost forgot about this, I was just about to start in on the gearbox mould and then it clicked. Here is the picture of my system broken down. The outer shaft is 1/4" and the inner is 1/8". About the torque roll, I've been informed by a very smart man, of who has experience in this very subject, that the torque incurred on the boat will be zero. He also says that any torque brought on by the motors will only happen when you have a change in velocity of the motors. I have a Hemi too, and the only time I feel any tug on the side of the frame is when I gun the gas, but that effect goes away when the speed is stabalized. I have to make some long dogbones that will go from the motor outputs to the gearbox inputs, but I think you will get the idea here:

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Hope this helps,
Joel
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Postby Polaris » Sun Mar 15, 2009 3:25 pm

ManOwaR wrote:
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Joel, that setup is just plain cool!
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Postby ManOwaR » Mon Mar 16, 2009 7:54 am

Thanks Stuart,
Hopefully it works as well too! I think it will though.

Joel
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Postby greenman407 » Sat Mar 21, 2009 5:45 pm

I think that it is just awesome!!! I would like to do that with my Albacore as it had contra props on one of its versions. Thanks for sharing that with us. Now Ive got to figure out how to make one for myself. :) My drive system only has one output so I would have to split the drive into two drives. That might be too much for my speed400 motor.
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Postby greenman407 » Sat Mar 21, 2009 8:50 pm

I recall that Dave Merriman did the same sort of thing on a Albacore because I recall seeing a cabal report on it. Your pictures show your progress very well
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Postby ManOwaR » Sat Mar 21, 2009 9:40 pm

Hi Mark,
Thanks very much. Albacore would be awesome to do with contra props because there are so many good pictures of the final stern configuration, and it doesn't hurt that it's sitting complete abouve ground for the whole world to see!.

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Here's the Jacks;
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A guy would would have a very good chance of getting his model perfect to scale. Dave did do that back in the day he has been extremely helpful to me on this build, he has been on a few canoe rides in his time! As for you speed 400 I would definitely say that it would be too small to drive two props, for my system it will come down to using two 500s or one 600.

Joel
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Moulds Part1

Postby ManOwaR » Sat Mar 21, 2009 9:42 pm

Moulds,
That would be the subject of this and upcoming build blogs. Most everyone here knows how to build moulds I would think, so most of what you are going to see is my attempts at improving on past mould designs, refining to increase the quality of the final moulds and going further in complexity in trying out multi part moulds and building mother moulds.

The first thing I do before even starting to build a mould is do final check over of the parts I want to duplicate for flaws or details I might have missed before. In this case I am glad I did this because I almost forgot to scribe the non-skid lines into the tops of my sail plains. I also give all the parts the finish that I want, in the case of the sail plains I wet sand up to 1500 grit and then do a French polish using Maguire’s auto polish and diaper cloth…I knew these kids I have were good for something! LOL

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This time for all my moulds I am attempting to give all large parts their own resin supply channel and vent. This drastically improves my reproduction success ratio to castings as will the locations of where the sprues will enter and leave the parts. Like I’ve said earlier, I need to improve my efficiency when casting, for material cost saving and just plain old time. Production isn’t any fun when your casts work only sometimes.
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This red clay is awesome to work with. It doesn’t shrink and doesn’t stick to anything (except my hands). If it’s too hard to work with because of being in cold garage, I simply apply heat using my heat gun, and because its oil based it softens right up, you can even melt it if you want. It’s expensive, but like anything else, expensive usually means it’s not crap.

Ready for the second side pour. For a release agent I use Vaseline thinned down with mineral spirits. I brush on the liquid in a thin coat, the mineral spirits evaporate and voila, no brush marks left like if plain old Vaseline is used. The mixture doesn’t affect the primer surface either; actually if you buff it into the surface of the part you get a super gloss finish…nice;
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Next up is the making of my three part sail mould

Ragards,
Joel
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Postby Warpatroller » Sat Mar 21, 2009 10:37 pm

One of our group members has a Sub-Tech Albacore that is outfitted with the Merriman made contra props. He scratch built a plastic geared box to generate the twin rotation from one motor. The pressure hull in the boat leaks and the motor currently installed in the boat probably does not have enough power to spin both props. We were just discussing this boat today and I don't think he has ever had it successfully running and in the water using the currently mounted contra prop set-up.. This is one of the boats in our group that would be nice to get seaworthy, so she can sail.
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Postby junglelord » Sat Mar 21, 2009 10:46 pm

Well there are always newbies and its great to see how to do casting and what materials for parting agents, molds, vent channels, sprue placement.
Excellent pics and thread, thanks. I love the contra rotating blades.
8)
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Postby Skip Asay » Sun Mar 22, 2009 1:14 am

When I built my first Phase IV Albacore, I used 2 of the motors I usually shipped with Albacores and made a gearbox to drive the props. I found that the gearbox ate up too much power so I pulled everything out and went with the same 2 motors but mounted outside the pressure hull (yes, they were sealed) and then drove each shaft independently courtesy of a toothed belt. It worked great!

The motors used were 385 sized motors but no, not Speed 400s which are too powerful in my opinion. The drive reduction ratio remained at 2 1/2:1 although I did have to use longer belts.

Skip Asay
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Postby greenman407 » Sun Mar 22, 2009 12:22 pm

Hi Skip. Would you happen to have any pictures of that set-up that you could post here? That would be cool! As far as the contra props are concerned , other than having a cool drive system that nobody else will have, I dont know that there would be any real tangible advantage to having one on my boat. My Albacore with the speed 400 motor is already so fast that you have to run to keep up with it. Contra props will also counteract torque but with my boat , being properly ballasted with enough lead weight and countered with foam, torque doesnt seem to be an issue unless I gun it ,which is not very scale like. I recall the first time that I installed the speed 400 in my boat, I didnt have enough lead weight in it and when I took off just a little too fast it went through the water spinning like a drill bit. That was fun. But from the standpoint of doing something really challenging the dual props are it ,in my opinion. :D
Last edited by greenman407 on Sun Mar 22, 2009 7:43 pm, edited 1 time in total.
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Postby Skip Asay » Sun Mar 22, 2009 5:04 pm

I finally managed to find some (very old) pics.

One thing I noticed when converting from Phase III (single prop) to Phase IV (dual props) was that the normally fantastic turning radius courtesy of the "X" tail increased some. Torque roll is non existent, too.

Skip Asay

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Postby greenman407 » Sun Mar 22, 2009 5:19 pm

Nice! How did you seal the motors and where did you purchase all the hardware(pulleys ,belts,gears,motors)?
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Postby ManOwaR » Sun Mar 22, 2009 7:33 pm

Skip,
Do you have any pictures of the prop setup?

Joel
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