I tried to laser cut hubs to fit the props to motor shafts as described in the assembly notes, but was not happy with the results. So I used some 5/16 alum. shaft and drilled a #32 hole (0.116 inch) hole thru the center of the shaft. I put the shaft in the lathe so it was easy to find the center of the shaft. I used a center drill to start the hole. I made the shafts 1.125 inches long and later cut them down to the width of the props. The props from HobbyKing were #OR001-01503/4847 replacement fan for 3inch/76.2mm EDF (7blade) and had a 5/16 dia. mounting hole. The motor shafts are around 0.1155 inches. So you need a hub to lock the two pieces together. I used a vise to push the alum. shaft into the prop hole and made it flush. I drilled a hole in the side of the prop and through the alum. hub, I just made, for a 4-40 set screw. I tapped the hole and finished the hole with a bottom tap. The screw is to lock the prop/hub to the motor shaft. I drilled the threaded hole to line up with the motor shaft hole.
I made add a hole in the prop guards to make it easier to get the props on/off the motor shafts. You have to angle a screw driver to get to the set screw.
This is great John - thanks! I'm going to add a link to this method on the wiki.
Also, please keep us posted on how you like the Hobbyking props. The ROV is in need of better prop design.
according to the users on hobbyking, this is the right propadapter for the edf fan in the BOM, this should probably be added to the BOM, seems like the acrylic cutouts dont work that well for everyone.
David: that is the main reason for need of new prop design?
the acrylic prop guards have an ID of 3 inches and the props are listed at 3 inches in dia. Then depending on how you glued the base together, there is a problem. I had to cut the props down so that everything would clear. I took off around .2 inches off the props. I kept checking to see the clearance, but did all 3 props the same.
Not the reason. There are a dozen ways to solve the adapter issue. The acrylic cutouts have worked sufficiently well for us, so we haven't spent that much time on solving it.
I was thinking in terms of efficiency. The blades we are using are just off-the-shelf hobby props made for air. I'm certain there's a more efficient design. I've been meaning to play around with OpenProp but just haven't had the time...
i was thinking of the efficiency aswell, the propadapter thing was just for information for the users that may struggle with the cutout adapters.
I also want to show you a really nice and informative test a user on the homebuiltrovs forum performed, and some links to the props he uses.
a perfect motor for the m4 props could be the hextronix DT700(kv) that has a M4 shaft allready, and would probably give a bit more torque compared to the 800Kv motor in the BOM.
HK also has them in 750 and 900kv rating.
Thanks for the links, Thomas!
I just ordered a bunch of the cornwall props to test out once I get back.
I already have one of the motors you linked to- it's a lot bigger then it looks in the photo. The diameter of the rotating cup is 40mm! It is nice that it has the right threaded shaft already... maybe I'll give it a second look!