RC sub workshop 28mm cnc kmb impeller on ebay! - RC Groups
Thread Tools
Jun 01, 2017, 11:32 AM
Registered User
Discussion

RC sub workshop 28mm cnc kmb impeller on ebay!


Anybody tried one these cnc 3 blade copper impeller from rcsubshop ?? I caved and bought one..

They are on ebay right now.
Sign up now
to remove ads between posts
Jun 01, 2017, 12:34 PM
Just Plane Nutts
AirDOGGe's Avatar
Link?
Jun 01, 2017, 01:51 PM
Registered User
unusual_rc's Avatar
I only know they have a copper 3D printed impeller available.

I have not read any feedback about it.
Since the Kehrer 28mm 2-blade "internal propeller" has a very large pitch, the 3 blade version seems to have less pitch.
But I can only guess since there is no data available yet.
Jun 01, 2017, 04:57 PM
Registered User
Kayaker's Avatar
They also sell it on ebay; http://www.ebay.com/itm/272436941720?rmvSB=true

I don't believe this impeller is made using a CNC and I think it is brass not copper. I would need to hold it in my hands to tell.
Last edited by Kayaker; Jun 01, 2017 at 06:04 PM.
Jun 02, 2017, 02:29 PM
Platinum Card Member
sundogz's Avatar
It is not 3D printed (does look similar), but made on a CNC machine. Probably brass, looks to be less pitch (better water pick up?) and needs some leading edge work to take that sharp corner off!

Looking forward to your testing it!
Jun 02, 2017, 06:28 PM
Registered User
Kayaker's Avatar
If you look closely at this next photo you can see the casting lines. I believe this is lost wax cast using a rubber mold to copy an original CNC impeller. It looks to me like they picked the pitch of the blades to match what can be used with a rubber mold. Blades can't overlap.

If I was a young guy looking for a job, putting these together would be an easy business to get into. Almost no capital outlay. Very little work pressing shafts into impellers if you are not doing the casting yourself. This type of casting is very easy. I made a lot of jewelry this way in the 1970's. I can cast about 50 of these in a day.

I would have to see one of these impellers to know if I am right.
Last edited by Kayaker; Jun 02, 2017 at 06:59 PM.
Jun 02, 2017, 07:16 PM
Platinum Card Member
sundogz's Avatar
Well that's entirely possible. I know I would have polished off the engraving lines before I made a cast of it! I'm looking forward to RainClod getting one to fondle and spin.
Jun 03, 2017, 12:21 PM
Registered User
unusual_rc's Avatar
I have seen earlier pictures, which were 3d printed.
They could have made a wax model from a 3D printed model for casting.
Anyway, it sure looks rough!

Still I like the concept of less pitch, which would enable higher rpm in theory.
Jun 12, 2017, 01:43 PM
Registered User
Looks like it should show up tomorrow... stoked I think
Jun 12, 2017, 02:42 PM
Registered User
Kayaker's Avatar
I also ordered one of these three blade impellers. I'm looking forward to seeing the differences between them. My expectations are that it will work better at staying hooked in bubbly water. The KMB jet drive is an axial flow drive. It works by moving a lot of water at very low pressure. I expect the down side to this much heavier impeller will be slower response to spin up.

Less pitch, higher RPM, smaller nozzle outlet is part of what makes a mixed flow put out more water velocity (but half the volume) making them faster at top speed, better for a lake. An axial pump like KMB has much better “hole shot”, more predictable steering and sucking air is less of a problem. This is better in rapids.

I have many hours on both types of pumps if someone needs more detail for design reasons. A mixed flow pump is designed for the engine it will be used with. This makes it more useful for gas engines and less useful for electric motors that have a very flat torque curve and can spin at high RPM.
Jun 12, 2017, 11:01 PM
Registered User


Ha it showed up today
Jun 13, 2017, 12:20 AM
Registered User
A little 200,400,2000 wet sand paper
And dremel with buffing compound later and

Jun 13, 2017, 07:18 AM
Registered User
Very clean and smooth.
Jun 13, 2017, 10:10 AM
Registered User
Quote:
Originally Posted by unusual_rc
I have seen earlier pictures, which were 3d printed.
They could have made a wax model from a 3D printed model for casting.
Anyway, it sure looks rough!

Still I like the concept of less pitch, which would enable higher rpm in theory.
From comparing side by side the metal one does not have less pitch. It simply has one more blade....
Last edited by RainClod; Jun 13, 2017 at 11:02 AM.


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Kmb 28mm cooling ... RainClod Jet Drive Boats 19 Jun 02, 2017 03:48 PM
Build Log Setting up a KMB scale 28mm Jet Drive with reverse Tollytime Dock Talk 47 Aug 22, 2016 10:48 AM
Discussion How much power can a KMB 28mm jet unit take? The_Angry_Saxon Racing Boats - Electric 18 Sep 17, 2015 01:41 PM
Discussion rc sub workshop r/cjunkie Submarines 0 Jun 18, 2014 10:50 PM
Help! Kmb 28mm? bmangdog_6 Racing Boats - Electric 8 Aug 05, 2012 07:24 PM