Props


#1

I have been using 3 bladed Dumans 3 inch brass props but decided to try the props recommended by the group. Yesterday I "flew" the OpenROV on the brass props and then changed to the Graupner 65 mm props. There was a big difference in performance to the positive. It is easy to change them at the dive site as they are attached with 4-40 set screws. My neutral weight was off with the new props and I had trouble diving. The new props are lighter. I am going to stick with the Graupner plastic props and readjust my neutral weight.

Before I changed props I played with using keyboard "7" and "8" keys. These allow you to set the vertical speed of the motor so it stays on. I was able to adjust the speed to maintain depth and still drive around, this is very neat! I have played with this before but yesterday took the time to fine tune it watching my depth indicator.

Life is good!

1206-dumansbrassprops.jpg (266 KB) 1207-graupnerprop.jpg (263 KB) 1208-openrov241propsp2.jpg (245 KB)

#2

Hi John you seem to always come up with new ideas and I noticed the use of a insert sleeve and set screw on the plastic props. Did you remove the original insert and if so was it difficult to come out? Did you make your own sleeve or did you source them from a vendor? I really like the idea of the prop attaching directly to the shaft using a set screw rather than using an adapter. I have been looking for adapters but can only seem to find the flexible type to go from 3mm to 4mm and I am not sure how they would work. As you have found out the new props seem to work great.


#3

I drilled out the props using #14 drill (.1820 inch). On the plastic prop some sleeve was left and on the brass props just drill out the threads. I used a 4-40 by .5 inch round alum stand off for the center. I pressed it in using a vise. You then drill out the standoff to fit the motor shaft. I found the shaft to be around .1135-.1140 inch. I used a #32 drill (.1160 inch) for a nice slide fit. You don't want to fight with the props getting them on/off at the dive site. Last you drill out the side of the prop going through the standoff for a 4-40 set screw. I bought the set screws from McMaster Carr. Part number 92313A106 Type 316 SS Cup Point Set Screw 4- 40 Thread, 1/4" Long, packs of 25.

Building stuff for companies over the years I have ended up with collection of standoffs, so I just had them around the shop.

1209-standoff.jpg (96.1 KB)

#4

Hi John

Thanks for the great info I am going to check this out, did you have to tap the standoff for the set screw or just bore the hole and let the screw make it's own threads as you screw it in? Also did you have any issues getting the hole perfectly centered in the standoff so you don't get any wobble in the prop? PS That was a great call yesterday and I am looking forward to the new Cape and goodies such as the pressure sensor and navigation.


#5

I tapped it. 4-40 threads are pretty small and I would wreck the Allen screw if I self threaded it. I am probably a little off but I used small v-block to hold the round surface. The insert stuck out a little and I clamped to that. At the end I cut if off flush with the face of the prop. Now that I think about it a longer stand off would make that easier, more to grip. In my motor housings on the round side I have 2 holes that allow me to tighten the set screws with a long Allen wrench. I don't have to reach in from the front face. I had holes for this even when the motors were in the standard location because it was a pain to tighten the set screws.

I agree about the call and cannot wait to try the new electronics. I have several ideas for things to add.