Dragon Shark - a new start

[IdefixRC]

Thanks for pointing this out. Did not dive deep enough into the forum yet to figure out that there was more
Hope the membership will go through soon (currently there are some paypal issues apparently - forum admin notified)

[subdude]

Please email me at emailJimButt@gmail.com and let me know what the issue is. I don't see any transactions on paypal from your email address.

[IdefixRC]

Please email me at emailJimButt@gmail.com and let me know what the issue is. I don't see any transactions on paypal from your email address.

Correct because Paypal does not even get to the step.....Complains about issues and diverts me back for both the one time and the annual subscription.
Will drop a mail to Jim.

[IdefixRC]

First 3D print test of printing the forward wtc cap was not very successful. While the part came out beautifully, the ABS shrinkage of around 1.3mm for the 104mm diameter was to much to keep the tolerance.
I will probably go the route of 3D printing all the interior bulkheads and trays (accounting for the ABS shrinkage by scaling the parts up) and make the caps and pistons with the lathe (feel much more confident with a solid piece of delrin )

[Guest]

Did you try and print it as a solid lump?

Or was the centre honeycombed to minimise material and heat build-up?

[IdefixRC]

Printed it with 15% infill to test it out. For a working part I would go for 100% else it will not be structural sound (compressed easily) and most likely not watertight.

[Guest]

If I was printing caps, I think I would be inclined to print them domed or hemispherical, that way they can be printed thin walled yet still be pressure resistant.

[IdefixRC]

The problem with thin wall is that the FDM process sometimes leaves small gaps between layers (especially around changes in shape - screw holes etc).
So it is not necessarily 100% water tight. In addition the areas around the mounting screws would need to be beefed up quite a bit in order to not compress when the caps are mounted.
But that does not mean that one should not try I will give it another shot once the O-rings have arrived.

Here is a picture of the quick and dirty cap I printed.

[IdefixRC]

While waiting for the Orings and the Delrin parts to arrive, a quick update on the proposed motor mount and seal.



Cut away drawing of the rear cap with the motor mount installed.
As my lathe is rather small I will have to make the endcap and the motor enclose out of 2 separate pieces. As the material I selected is delrin as other material is very hard to get here in small quantities and as delrin is very difficult to bond as far as I know, I will try and go for a press fit between motor enclosure and endcap. Other option would be to screw it on and incorporate a oring either in axial or radial fashion into the motor enclosure. Not sure yet how I will approach this.

Also I hope that the single Engel shaft seal combined with the ball bearing to stabilize the shaft is up to the task to keep water out of the enclosure.
Other option I was thinking is to simply mount the brushless motor outside - in the water - and run the 3 connectors though the endcap and therefore completely eliminating the motor enclosure and seal issue.....

[Guest]

Seems a complex way of doing things. All you need is a shaft seal, which can be press fitted into the endcap, and an extended shaft running from the motor. The motor itself can be attached to a sheet metal plate, and screwed directly to the endcap. As the motor should have ball races as standard, further bearings are unnecessary, you just require a small bush at the propeller end of the shaft.

[IdefixRC]

Thought so as well today. Above is an adaptation of the original Arkmodel way of doing it. Will turn the motor around, mount it on 4 standoffs and integrate the seal directly into the endcap.....need to remind myself to stick to KISS...... ;-)

[IdefixRC]

Ok, here we go. Final motor endcap design. This should make things much easier.
Time to start cutting......

[IdefixRC]

Front endcap done. Learned something today: if it goes on real tight without grease, try with grease first before making the slots deeper....... Had to switch to the backup 3.5mm CS oring from the original planned 3mm oring because of that. Also the acrylic tube had quite a big internal tolerance, 104 to 103.30mm ID.

Next stop. Rear cap.

[Guest]

Ok, here we go. Final motor endcap design. This should make things much easier.
Time to start cutting......

[ATTACH=CONFIG]3593[/ATTACH]

Still a bit over engineered. Several of the parts there could be dispensed with. Most small to medium brushless outrunners come with a 3mm or 4mm shaft. This is often a press fit in a machine aluminium case, sometimes with a small grubscrew for extra security. These can be removed, and a new longer shaft in stainless steel press fitted in. This removes the need for a coupling between the motor and shaft seal.

Second attach a simple flat plate to the motor, and make it oversize, so you can then screw the plate directly to the endcap with self tapping screws, eliminating the stand-offs. The shaft seal can be press fitted directly in a drilled or bored out hole, you don't need the extra machined part that screws in.

[IdefixRC]

Actually I ended up press fitting the seal into the cap without the bearing as I slipped and bored the hole just 0.1mm to big. Instead of a press fit it became a perfect fit but with nearly no compression and I had to go deeper to press it in properly.

The coupler and standoffs are required unfortunately as I already have the 5mm seal, 5mm stainless steel shaft and the motor with a 3.2mm shaft.

With this both endcaps are done now.
Waiting for the piston tank orings to arrive before I start working in that one (this will be the interesting bit.....)