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Jul 19, 2017, 03:45 PM
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unusual_rc's Avatar
Mixed flow with a tapered hub and "flat" wear-ring means a progressive pitch! And that is not that easy to do. Luckily I already played with that idea in my CAD software
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Jul 19, 2017, 04:00 PM
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Kayaker's Avatar
I see you have a place in your design for an air seal on the drive shaft between the grease port and the impeller. Is it for an O ring type seal or one like this for submarines?
http://www.ebay.com/itm/RC-Submarine...item419e2cc9e7

I'll bet the guy that supply’s sub workshop with the three blade brass impellers would make 3 different sizes if he can sell a few. Soon after you release the files for a jet drive I expect to see Chinese copy’s for sale on eBay. This will give the impeller maker a good market.
Jul 19, 2017, 05:13 PM
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Quote:
Originally Posted by Kayaker
I see you have a place in your design for an air seal on the drive shaft between the grease port and the impeller. Is it for an O ring type seal or one like this for submarines?
http://www.ebay.com/itm/RC-Submarine...item419e2cc9e7

I'll bet the guy that supply’s sub workshop with the three blade brass impellers would make 3 different sizes if he can sell a few. Soon after you release the files for a jet drive I expect to see Chinese copy’s for sale on eBay. This will give the impeller maker a good market.

Yes, that is for a double lipped grease seal to keep the grease in it's place - no more having the grease leak/migrate out of the drive and having to re-grease it frequently. It of course doubles as an air seal to insure no air is sucked through the shaft bore. As far as a Chinese knockoff, anything is possible I suppose. Imitation is the sincerest form of flattery - but we'll know the truth!
Jul 19, 2017, 06:00 PM
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If you make the shaft bore in the impeller small enough to be a hammer-on fit on the shaft they tend to stay put. You can add a little glue/loctite as well during assembly to make sure it stays put.

I had a hull in the queue from Heli as well. Sent him a message somewhat recently to check if he's ok but haven't heard anything. He has dropped off the map like this before and come back after a long break, so hopefully it's nothing serious.

Looking forward to seeing the mixed flow progressive pitch impeller!
Jul 19, 2017, 06:02 PM
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Quote:
Originally Posted by unusual_rc
Now it is waiting for the first test results. I am really looking forward to see the drive work.

And I also see the urge for a 28-32mm version. I do not like scaling, but I can adjust the current 45mm design parametrically to make it work in a smaller scale.

Also a version like SicRC's drive can be made by making small changes to the inlet housing, and designing a separate pressure chamber/ring and a separate stator housing.

It is an open source design. So everything is possible!
Indeed! Now I just need to learn SolidWorks I guess.
Jul 19, 2017, 08:52 PM
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Trim


Even when oriented properly, there are a few niglets that will need trimming. One is the area behind the coupler. It makes a nice arch when printed, but at the very top it will nest a bit, so will need to be whittled back. Another is the loading ramp/wedge. This is a wide area that is unsupported, but for reasons unknown to me, actually does a good job of spanning that space. The first few 'pulls' will be loose and the corners will nest, but it's easily trimmed off with an exacto knife or what have you. This sharp edge doesn't need to be sharp to work properly, so take it back to solid material and clean it up. The last bugger is the front facing ledge (recess) that goes though the hull when installed. This edge is at the bottom printed upside-down unsupported so will nest nicely. But there will be solid plastic behind it when you carve it back to look like the sides. No problem.

You'd think a 6mm bearing would fit onto a 6mm shaft, but no. It needs a bit of clearance. Not much, but some. This is easily remedied by chucking the shaft into a drill and spinning it while squeezing it in some aluminum oxide sandpaper. Doesn't take much, so no need to get carried away. The bearings fit snugly in their pockets and mine needed persuading with a punch. The oil (grease) seal was tight, and you may need to lube it a bit when forcing it into place (hollow side towards the front).
Jul 19, 2017, 11:43 PM
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What program do you use to create/ edit design? I've started researching printers and gained a little knowledge on the way but I'm still lacking in the CAD department. It's been a few since my high school Cad class lol. Apps for tablets or do you need a pic?
Jul 20, 2017, 01:35 AM
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I use SolidWorks for this design. That is easy for me since I use it for over 18 years now.
But learning from scratch will take some time in order to model something like this.
It is the inlet channel and impeller, which require surface modelling skills. That is the most difficult part to master. The same applies if you want to design a hull with it.

Unfortunately I do not know any new program which will be easy to master AND has the tools to make something like this.

The original creators of SolidWorks stepped into OnShape, which is an in browser (cloud) 3D CAD program. And as far as I know it can be obtained for free.
Jul 20, 2017, 08:34 AM
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Printer for large drives


Quote:
Originally Posted by Kraigv
What program do you use to create/ edit design? I've started researching printers and gained a little knowledge on the way but I'm still lacking in the CAD department. It's been a few since my high school Cad class lol. Apps for tablets or do you need a pic?
I use 123D Design and Meshmixer because they are free and easy to use (intuitive). But they are limited in functions, and Autodesk has already sold 123D to another company so will not provide future support. But there are lots of good programs such as Fusion, Blender, Sketchup and one I'll be learning and using soon (moving on up) Solidworks. It is the program Michiel used to design this jet drive and while a bit complicated has a tutorial built in and is professional quality. You'll likely not need more in software.

On a different subject, I have considered Gearbest to have some of the best deals on printers, and while perusing for printers that can handle larger models I found this one that can print up to 300x300x400mm tall! which would be adequate for any jet drive and can easily handle the big 75mm drives that are being used in surfboards and such. I believe it is a kit and would need assembly, but the design is uncomplicated and looks to be easily built. And building one is a great way to familiarize yourself with the hobby. But if you don't need such a large one, and don't care to get involved with building one then the Mecreator2 might be the way to go. It will print up to 160mm/sq and so should handle up to this 45mm drive we've designed. It got good reviews on Amazon and is more plug-and-play.
Jul 21, 2017, 08:56 AM
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Quote:
Originally Posted by unusual_rc
Unfortunately I do not know any new program which will be easy to master AND has the tools to make something like this.
The original creators of SolidWorks stepped into OnShape, which is an in browser (cloud) 3D CAD program. And as far as I know it can be obtained for free.
Neither do I. You can find some that are easier to use, but they lack in the 'tools' department. And I find it very dismaying how many of them are going the 'cloud' route. Those are the 'easier to use' programs. When you read their often lengthy agreement, you have to give permission for them to use or share your drawings.Yes, someone can ultimately make $ off your ideas. I see this more and more.

Stay away from 'cloud' anything. If you believe your data is safe in the cloud (any cloud system) then you must be living in a cloud. Any 'agreement' with such a company will always include a disclaimer to protect them in the event their system is hacked and your personal information and data has been compromised. And it probably will be - it's just a matter of time.
Jul 21, 2017, 12:25 PM
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45mm Jet drive build - cont.


A 4mm Allen (grub) screw works nicely for the grease port. Just screw it carefully into the hole (best done with a hex driver) and it will make it's own threads . Continue until it is flush with the top of the drive so it won't interfere with servo placement.

It is difficult to bend 2.5mm stainless rod (M3) into a sharp 90 degree angle, so I designed the holes for the grill/guard so that they will fit flush if bent similar to those in the picture below. The placement is a bit changed from the original pics on page 122 as I printed a copy and soon afterwards discovered the holes went clean through the drive so I had to move that end to a 'deeper' location. Be sure you have the updated file (v20.1B). If you use threaded rod, break or cut it leaving a couple threads on the end, it will help give the epoxy something to grab onto making for a better bond. You'll probably have to open the holes in the ramp end a bit to fit them in fully - I used a similar sized hex driver which did the trick. Cut the rods to the length shown and insert the ramp ends fully, making sure the other ends will fit into their corresponding holes. Then apply a drop of two parts epoxy into the holes and insert the bent ends, pushing down until they are fully seated. Clamp in place until the epoxy cures. I used a nylon wire tie which worked well.

All I had in brass tubing was 1/8" and 1/4" which was a bit too small and large for the cooling nipple, so I disassembled an old telescopic antenna (which is chrome plated brass) to get a piece the right diameter. It may not be necessary, but I like to taper the end that goes into the stator housing so that it insures good water pickup, and then epoxy it in place so the intake side is flush.

The impeller shaft will need a flat on it for the grub screw to grab onto. Slide the impeller on the shaft leaving 5mm sticking out the back (to go into the 6x15x6 stator bearing). Mark it through the grub screw hole with a sharpie, then remove the impeller and make two more marks to widen it to 8mm or so. Then grind a small flat with a dremel and stone (my preferred method) or use the method of your choice.
Last edited by sundogz; Aug 02, 2017 at 07:59 PM. Reason: I used 2.5mm push rod, but 2mm would work
Jul 21, 2017, 02:05 PM
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unusual_rc's Avatar
It looks awesome!
Cannot wait to see the full installed assembly!
Jul 21, 2017, 03:16 PM
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I have a 40" Prather Offshore Deep V the first drive was slated to go in, but I remembered that was for the 55mm drive we started with (that was too big for me to print). So I've got a preowned Proboat Formula Fastech coming, it should be here in a week or less. It is scaled more appropriately for the drive at 27". And the Fastech has a nice flat spot on the bottom, so it will practically install itself.
Last edited by sundogz; Jul 26, 2017 at 08:53 AM. Reason: Prather, not Dumas
Jul 22, 2017, 02:30 PM
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unusual_rc's Avatar
What's the hull made out of?
ABS or glass?
Jul 22, 2017, 03:06 PM
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sundogz's Avatar
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Fiberglass. It has been discontinued, so is somewhat difficult to find anymore. Here's an ad from Proboat.


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