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ZB-1, ZB-2: Scratch Build Cylinder design for limited Production by Zero Bubble.

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  • #91
    Hello all,


    Its been a couple of weeks now and I have been simply testing the ZB-1 for water tightness and so far I haven't had any leaks. This is really good as It has mainly helped me ascertain just how tight the seal of the U cup seal lip should be over the shaft. You want a good grip but not too much friction. I think that I may have the balance just right.

    For a while I have been looking at the photos David has put up showing his twin shaft single motor end cap and this has made me want to produce one myself. Having a design like this has a couple of advantages. You only have one shaft to seal theoretically, but also won't have to worry about possible inconsistencies in speed between two motors. It also should be a little cheaper as there is only one motor.

    So I started once again by taking a block of Renshape and making sure my lathe had its way with it. Tightening a bolt through the center of it I could then affix it to the lather and start bringing it down to round and slightly oversize. Once I did this I had to get some gears organised. I also had to work out what I was doing the drive from the motor. I have decided to run the motor from below and have it engage with the right side gear. The right gear then engages with the left at the center of the end cap.


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    These nylon gears are hard and will be ideal. They feature a thicker section on top of main gear. This will be useful for drilling and fitting a locking pin through the stainless steel shaft later on.
    The next step was to locate the precise position of the rear of the shafts where they mount into the front surface of the end cap. They will sit in two flanges shallow 4mm Oil lite bushes. These supports hold the stainless shafts nicely.

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    You can see that the motor has also been fitted in the back and engages with the lower underside of the right hand gear. The motor in the back of the unit is in a tight position and placing it up to one side has been the only real and practical position to locate the motor that I have found.

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    The 4 mm flanged Oil lite bushes are clearly visible here. As with all my end caps the Renshape prototypes are oversize and will be then machined to reduce them to fit individual Polycarb tubes. The motor has a deep recess in the back. This is so that the small pinion gear that I use has enough distance to engage its teeth with the right gear that it sits right next to. Theis also allows a reasonably short 2.6mm hex bolt to screw the motor down inside the end cap and make it really secure.

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    David H



    Comment


    • #92
      Hello all,

      Now that I have worked out and fitted the location of the shafts, the interplay between the right side gear and the pinion of the motor I am now in position to create the outer housing and recess for the gears. This will be cut from a flat 5-6 mm sheet of Renshape that was cut off from an end cap that I had previously machined up on the lathe and was oversize. To do this I took the disc that was round and with a compass worked out the outlines of the gears and the pinion integrated. The Drilled out these gears and sanded along the inside.

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      The master end cap to the right has the holes drilled into it for the recesses of the flanged Oil-lite bush. The one on the right comes very close to the motor mounting area. I have less that a mm clearance between the recess for the edge of the motor rim and the back of the bush.

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      First radius drilled out. The hole in the center is the bolt hole that supports the piece on the lathe when initially turning up the end cap. It actually makes a really
      good alignment reference point between the two pieces.



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      The two arcs cut out for the gears nicely meshed. The blue outline in the outer outline of the raised housing. I have yet to drill the location for the pinion drive coming off the motor.
      This outer housing needs to be wide enough to enclose the gears, provide enough surface area to have a good bed of silicon laid down and provide enough width for two securing bolts to go through to
      secure the upper outer housing that will fit over and enclose the whole unit and act as the base for the seals.

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      Sanding inside the Motor recess I have always found to be tricky. I have to contort sandpaper, Harry Houdini style.. I have marked out the circle to cut for the pinion and also a recess to fit the motor mount
      2.6 mm bolt.

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      The top of the housing needs to have enough room to fit the push rod glands that I have developed. There is tight space between the underside inner flange of the end cap and the top of the outer housing. The holes for the glands will cut into the curved sides of the raised housing to some degree. This will make sense later.

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      Without the gears you can see the arrangement of the oil-lite bushes, the motor mount bolts and the pinion. The left bolt sits lower and deeper into the motor than the right one. This is because of the placement of the motor holes. Access is important if you need to get a motor off.


      David H

      Comment


      • #93
        Hello all,

        Once the profile of the raised housing has been finalized I traced it onto a piece of paper as I would need it later when I needed to create the block of Renshape that I would eventually carve the outer gear housing out of. Once this was done and some light sanding to make sure that the thickness and width of this housing was constant and how I wanted it, it would be time to use it as a template for the outer housing. this means that I wouldn't be gluing it to the end cap for a while

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        Here you see the raised hosing in position with the oil lite flanged bushes in place. The half arcs are cut in the top of the outer housing and then follow through with full holes for the pushrod seals in the end cap proper.

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        I have drilled the holes that will accommodate the bolts for the outer housing to clamp down and hold the entire unit together. Push rod seal holes are placed above the housing. The need to protrude halfway through the edge of the raised housing as the space is rather tight. One of the first things that I do with the new outer block of Renshape is to drill the holes through it in the corresponding location to the same holes in the raised housing.This gives you a good registration for the two parts to align up and make sure that all the gears and shafts do too.

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        The main outer housing has been roughly cut to size and will now get lots of sanding.

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        Here you can see the rough shape of the outer housing. Starts off as a solid boxy block and like the outer housing for the ZB-1 will be given a more curvy look. I envisage that it will look a bit like two ZB-1 housings next to each other and merged somewhat. The push rod gland holes are distinctive.

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        Here you can see the gears meshing together on the backside of the outer housing. I will soon be getting a forstner bit and drilling out the circle recesses for the gears to fit into. I aim for about 2 mm clearance on either side of the gears. The biggest challenge will be getting the shaft holes on the outer housing to line up precisely with those on the face of the end cap. You do not want any deviation from perfectly perpendicular to the end cap face.

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        More next week...


        David H

        Comment


        • #94
          So glad to see you not giving into the robots, David. You got two good hands, use 'em!
          "... well, that takes care of Jorgenson's theory!"

          Comment


          • #95
            Thanks David, especially with the shaft Bizzo.

            This week is really about carving out recesses for gears and making everything fit. The gears that I am using are Nylon ones. Nylon is a good had plastic and these gears mesh well. As can be seen from the last photo I have to drill the two holes for the main shafts to extend out of the outer housing. These will need to line up precisely with the recesses already in place with the shallow flanged Oil-lite bushings that effectively act as the backstop for the shafts as they sit against the front surface of the end cap.

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            After spending some time marking out and making sure that these two holes are precisely aligned, if not they would either diverge or converge the shafts and then gears would mesh at an uneven angle and the sides of the Oil lite bushed would wear, not good. One right they were drilled and the shafts installed and checked for accuracy and alignment once again.

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            These shaft holes need to also allow the bolt holes to align up for the bolts that attach the outer housing to the end cap. Once this is all aligned and ready I will be able to glue down the raised section on the base. Need to make sure that anything needing doing before that occurs is done. The outer housing requires a shallow recess for the gears to be drilled with a forstner bit. the main recess for the gears is in the base. I am partially recessing the flanged bearing as it runs through the holes in the outside surface off the outer housing as this will help give clearance to the gears and make sure that they are un-impeeded. The flanges will sit flat on the inside surface.

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            I can start carving away at the curved surfaces of the front. Like the ZB-1, this design will feature a curved set of housings that will culminate in a flat round area for the main seal. The seal design that I use on both the ZB-1 and ZB-2 will be universal. Why re-design the seal? The circular sections on the outside are for the seals and won't be touched with the exception of a light sanding.

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            I have been going at the Renshape with a rasp to take down the material quickly. Smoother files and smooth sandpaper. The hole in the middle straddling the two arcs is from the hole that was originally used to bolts down the disc to the lathe. This hole will eventually be covered over with filler. Need to also make sure that the holes and through shaft channels line up for the push rod seals to insert.

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            I have dremell-ed out a section for the pinion gear so that it doesn't rub against the back face of the outer housing. To make is easier to allow the nuts that screw onto the holding shafts to be secured tightly I have created arc'ed recesses along the flat section for the bold hole where it fits snugly between the two rounded housing sections. You can just see this on the lower housing as well. Enough to get narrow pliers in to tighten any way.

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            Sanded down to nearly a smooth surface and then lots of checking as I sand down the last couple or milli-metres and get symmetrical Yay! One push-rod seal is in place. I am about to glue down the base and then create a flange around the outside of the raised section. It will be important that this doesn't interfere with the seal holes. This thing is shaping up to be cool in a boxy and industrial kinda way.


            David H

            Comment


            • #96
              Hello all,

              It's been a busy week assembling the Prototype ZB-2 unit that I will use to do some final testing. Fitting components and making sure that everything is accessible and functional. It has thrown up a couple of surprises.

              From here it is really about sanding and getting the surfaces smooth and symmetrical. I sanded a smooth curve right up to the arc that shows the outer boundary of the Seal housing. I also did a lot of sanding around the recess sections for the two bolt holes and also made sure that the diameter of the holes and pass throughs for the push rod seals were consistent.

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              The 6 mm shafts have yet to be turned down to the 4mm that will be used. It also needs to be 4mm to pass through the oil lite, and the seal I have developed for all the cylinders. I now think that maybe I should have gone with 6mm. Less machining, a little more consistency of diametre with me needing to machine less of it and a more sturdy shaft arrangement. I can always go back and redesign a 6mm seal assembly. One day...

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              The Prototype ZB-1/2 with the ZB-1 single shaft unit tooled up and the first cast urethane sample out of the molds and ready to fit, install and test, test, test...
              I have also test fitted a seal to the hole and through channels on the prototype. You can also see the marking for me to dremel out access area either side of the
              top securing bolt. I have for spacing used the prototype seal outer housings to make sure that the circle perimeters that I put in place for the curved are to transition to flat, make sense and weren't overstepped or unrealistic.

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              This shot shows the need for an absolutely flat and level surface on both the raised section and the outer housing so that when the are seated tight against each other with the aid of silicon, produce a really good solid and airtight enclosure. I have have been thinking about whether to place a raised rim on the bottom surface with a corresponding valley profile on the underside of the outer housing to help with the silicon and avoid having an absolutely flat surface to have to seal. Thoughts anyone?

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              Damn those 6 mm shafts look good, and solid...


              David H

              Comment


              • #97
                Hello all,


                I have taken a step back from working on the twin shaft single motor. at this stage I haven't advanced it too much further as i deal with a popularity spike with the Delta. Whilst getting Delta hulls made and parts cast I have turned my attention to some parts that will fit inside the cylinder. For many years I have been using the pinch line system that was originally developed I believe for the "Sheerline' range of kits. Now I believe taken over by Becks model marine.

                The pinch valve is by comparison to alot of other systems, really crude. It involves a rotating Servo arm that pinches a nitro tube shut. It is easy to fix and reliable. It had little change of leaking, you just have to be sure that the pinch is complete. The design of my system utilizes this and as a result have decided to develop parts that will make this set up easier and simpler for people who may wish to build the cylinder along the same lines as I have.

                I have designed three parts to aid this. A bracket to hold the pinch line that is simply a nitro tube, a bracket to mount the micro switch and a small roller that can be attached to the arm of the servo that rotates as it moves past the line. I create these parts initially out of Renshape and spend some time making sure that they integrate properly where needed.


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                This design features a curved wall section that makes the area to be pinched push out towards the roller at maximum extension whilst not allowing the end bracket to impeed the roller arm. ( this was something that has always been a problem with this set up.)

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                The brackets have been designed so that the nitro tube is pulled to thin its diameter down as it is pushed down and then slots into the gap between the wall and the two brackets.The
                Nitro line will then take a 90 degree turn and be pulled forward as it comes out of the end cap wall then goes back into the end cap wall on the other side of the end cap.


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                Lots of sanding and smoothing and then working out where and how it will fit on the forward tray. Here you can see how the bracket presses up against the side of the servo and the roller arm is pretty much at
                the apex point of the pinch. I have decided that the bracket will be secured with 2 4mm bolts with the nuts embedded underneath in small channels.

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                The front tray is quite small. initially I went with an aluminium one however have decided since then to use a 3mm polycarb one.

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                Will give details on the other components next week.

                David H

                Comment


                • #98
                  Kinda reminds me of the roller clamps we use on I.V. lines.
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                  Make it simple, make strong, make it work!

                  Comment


                  • #99
                    Another way to do it is:
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                    Attached Files
                    If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

                    Comment


                    • Thanks Trout and Redboat,

                      Yes, similar technology. I have used this set up for nearly twenty years and although crude it is reliable and works. It is also ideal for the designs I'm developing for a complete beginner who wants a system they can get their head around and be able to fix any problem that arises. It just needs a bit of fine tuning on the part of the operator.

                      Getting back to the bracket which is the main part of the ballast tank mechanism I decided in stead of making closed loop retainers at either end to hold the nitro line down I would simply back curved hook type extensions with an inner surface curve to hold but not press and crease into the nitro line. It was also important that the line could do an abrupt 90 degree bend as it does along the left side before heading back out the through the front end cap.

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                      After I got the shape to where I liked it I gave it some primer and continued sanding and smoothing. On the bottom I decided to use a 4mm stainless bolt that was quite short. I would mold the nut into the casting by placing a bolt with the nut in place and pour the resin over the top. I decided to reduce the amount of material that would go into each casting by hollowing out the underside a little and making a round section that encloses the bolt hole and the embedded nut.

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                      Once the part is right it ready to create the mold. I decided to go with the part oriented vertically to the mold plane and not the usual parallel. This is how I often do the parts that are round, usually for end caps and the like. I carved out the piece of MDF and gave the mounting of the bracket a slight angle or tilt so that the bubbles will want to run to the top and and not stagnate halfway along a ridge.

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                      The 4mm bolts are inserted to create the bolt cavity and the nuts will be placed on the bolt in the area that is taken up by the round section that holds the bolt.
                      The play-Doh around the base keeps any silicon from getting under the part.

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                      These molds are easier to re-create than the usual ones that I usually create. I don't need to create the pouring channel and the air vents. That will come later. Here it's just PVC pipe and some silicon at the base. The register holes were pre-drilled.

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                      Once the silicon poured the mold could be pulled apart and then repeat the process however with the addition of the pouring channel and air vents. Here the part is placed in the mold that has just recently been pulled. I take a knife and trim off the fine extra material that has created a small thin film around the edge.

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                      With the tilt of the part I then add the pouring funnel at the highest point of the upper level. I will then make an air vent out of thin plastic milk bottle with a curve to catch the bubble and make it ride up to the top and out. This vent will run along the ridge and at the tops of the brackets so that bubbles do not accumulate there.

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                      The Balsa is the pouring channel with the widest part set to the approximate height of the silicon once poured.

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                      David h

                      Comment

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