Sunday, May 13, 2007
Saturday, May 12, 2007
Course Correction
With the rack and pinion setup in place, I hooked up the control lines for a trial run. I was ready for the satisfaction of an easily flopping rudder. However, upon testing the setup a few observations were made: 1. the rack required a tremendous amount of linear force to move the rudder; 2. the open end of the rack housing allowed the rack to pull away from the pinion gear when force was applied. The similar setups I'd seen in the SCR showed full housings for both the rack and the pinion gear. And they used bellcranks and brass rod to transefer the force to move the rack. Now I know why. My configuration, though sound, would require some modification.
While I chased the new varaibles through my head, an old notion came back to me: why not try an extremely short control tab mounted on the shaft linked to a conventional pushrod? I'd done this in my 1/96 USS Thresher which has a pretty confined tail cone. It would be easy enough to knock together and would settle that particular idea for good -- one way or another.
A push and the rudder answers to starboard.
The next trick is to finish the upper rudder fin, pour a mold, and cast an new GRP piece. Then everything can be fine tuned to fit inside. However, at present everything is within design parameters and fully functional. Once I figure out the best way to post it I'll have a short video of everything in action.
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While I chased the new varaibles through my head, an old notion came back to me: why not try an extremely short control tab mounted on the shaft linked to a conventional pushrod? I'd done this in my 1/96 USS Thresher which has a pretty confined tail cone. It would be easy enough to knock together and would settle that particular idea for good -- one way or another.
After a few hours in the shop the end result was a new keyed upper rudder shaft with a small control tab. It's width was dictated by the upper rudder fin dimension. A brass shaft hooks into it via a z-bend and the wheel collar connects it to the nyrod pushrod. Talk about keeping it simple!
A pull on the nyrod control link inside the hull and the rudder answers to port.
A push and the rudder answers to starboard.
The next trick is to finish the upper rudder fin, pour a mold, and cast an new GRP piece. Then everything can be fine tuned to fit inside. However, at present everything is within design parameters and fully functional. Once I figure out the best way to post it I'll have a short video of everything in action.Saturday, May 05, 2007
Engage The Rack & Pinion!
Spent some time installing the nyrod and fabricating a linkage set for the rack. The nyrod is Sullivan Precision Rod, 91.4 cm diameter, with a carbon fiber 2-56 pushrod. I drilled a hole in the control deck upright and inserted a length of brass tube to stabilize it as it passes through the bulkhead. The final turn is rather sharp so this keeps it from angling upward. Brass rod was cut to length, threaded to 2-56, bent into a Z-bend and screwed into the end of the control rod.
A control linkage tab was cut from brass stock along with a spacer of the same thickness. Both were clamped in place on the end of the rack and soldered. The spacer gave the tab the proper height to engage the control rod. A hole was drilled in the tab to accept the Z-bend in the rod.
One side of the rack housing (a square piece of brass tube) was opened to allow the rack tab to travel inside it. Keeping as much length of the housing as possible prevents slop when the rack moves. At present the housing is set in place. Ultimately it will bolt to the deck.
A close shot of how the rack engages the pinion gear. The shaft is not quite finished but the gear will ride just proud of the deck. The pinion shaft serves as the pin which holds the rudder in place. Another tab will be installed to keep the shaft and the gear from working upward during operation. While holding the rack housing in place, the control rod works easily inside the boat, turning the pinion back and forth. I can almost see the rudder wagging!
The results are very satisfying. This is the first model engineering project of this complexity I've ever attempted and it's pretty cool when it comes together. So far, the only fabbed items I've purchased are the rack and pinion gear. Everything else was made from stock K&S brass items using basic hobby tools (Dremel, disc sander, files, solder). And it all fits within the footprint of the upper rudder piece!
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A control linkage tab was cut from brass stock along with a spacer of the same thickness. Both were clamped in place on the end of the rack and soldered. The spacer gave the tab the proper height to engage the control rod. A hole was drilled in the tab to accept the Z-bend in the rod.
One side of the rack housing (a square piece of brass tube) was opened to allow the rack tab to travel inside it. Keeping as much length of the housing as possible prevents slop when the rack moves. At present the housing is set in place. Ultimately it will bolt to the deck.
A close shot of how the rack engages the pinion gear. The shaft is not quite finished but the gear will ride just proud of the deck. The pinion shaft serves as the pin which holds the rudder in place. Another tab will be installed to keep the shaft and the gear from working upward during operation. While holding the rack housing in place, the control rod works easily inside the boat, turning the pinion back and forth. I can almost see the rudder wagging!
The results are very satisfying. This is the first model engineering project of this complexity I've ever attempted and it's pretty cool when it comes together. So far, the only fabbed items I've purchased are the rack and pinion gear. Everything else was made from stock K&S brass items using basic hobby tools (Dremel, disc sander, files, solder). And it all fits within the footprint of the upper rudder piece!Thursday, May 03, 2007
Quickly I Turned...
Did a check on the travel needed for the rack to turn the rudder. Was surprised to learn that the current setup only requires about 1/8" push-pull to turn the rudder 35 degrees port and starboard of center. Less than I was anticipating. Should help keep things simple as I get into hooking the linkage up and making the rack fit within the confines of the upper rudder.
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