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  • He Who Shall Not Be Named
    replied
    You cast your bulkhead radial flange over-size to the biggest diameter stock you can find (a stated diameter is one thing, the tolerance the manufacturer employs is another). And you don't cut it down to size and incorporate the O-ring grooves till you identify the specific cylinder the bulkhead is going into.

    No getting around this, Lexan cylinder tolerances are so wide you just can't simply cast a one-size-fits-all complete bulkhead. Each bulkhead has to be lathe turned to fit.

    David

    Leave a comment:


  • Subculture
    replied
    Polyurethane resin typically has very low shrinkage, unlike polyester resins which have very high shrinkage. I would estimate no more than 1-5% depending on thickness, cure time, and whether you add any filler in the resin e.g. glass, carbon fibre etc.

    Leave a comment:


  • Davidh
    replied
    Thanks everyone,

    I did’nt know about those videos. Very good. I have made plenty of cylinders before and machined numerous endcaps. I just wasn’t sure about whether I needed to consider shrinkage of the polyurethane at all. I am casting these endcaps because I want to go into limited production to produce a cylinder that will integrate into my kits.

    Thanks once again.

    David H

    Zero Bubble model design.

    Leave a comment:


  • george
    replied
    Hello HWSNBN Sir
    Would you tell me from whom do you get your gears that you used with your brushed motors to make a Dual Drive System for the Revel Type 7 & 9 and the part numbers Sir.

    Thanks

    Leave a comment:


  • Subculture
    replied
    I machine my endcaps from sheet stock plastic (PVC, polycarbonate and acrylic/pmma all work well), or use aluminium for bayonet rings. I rarely make more than one of anything, so there is little logic in casting unless I need extra features within the endcap.


    However if I went this route I wouldn't cast a groove into endcaps. I would just make a simple blank without the groove, and machine that in later, also leave enough meat on the part to allow for inconsistencies in the inside tube diameter- which can vary greatly,-and machine the part down to fit. With regards to groove depth I tend to work between 10-15% of o-ring cross section, depending on how accurate the tube is. Technical literature will often specify up to 25% squish, well I personally find that is too much and you'll have a fine time trying to remove your caps. Bear in mind that o-rings can be used in systems running hundreds of pounds of pressure, whereas we might be dealing with half an atmosphere at most.

    I tend to use 3mm (1/8") o-rings for most cylinders, but for sizes below say 50mm (2") I drop down to 2mm or less. I use nitrile and silicone o-rings, the latter tend to be a little bit softer, and don't degrade in the sunshine. I find nitrile works just fine, it's stronger and is a bit cheaper. Avoid exotics like Viton, EPDM etc. Overkill and much more expensive.

    One thing worth noting, if you have the room to do it, making the outer edge of endcap a bit bigger than the cylinder diameter will provide a nice piece to grip when removing the cap. Adding a knurled finish on the same edge will further improve grip. I'd also keep the edge as thick as possible, as PU resin tends to be quite brittle unless reinforced with glass or carbon fibre. All quite easy to integrate into a rubber tool.

    Leave a comment:


  • trout
    replied
    Part 1 - https://www.youtube.com/watch?v=wixmu3MPhjo
    Part 2 - https://www.youtube.com/watch?v=hWcryehE7EU
    Part 3 - https://www.youtube.com/watch?v=lh5kNb7m_oQ

    Very fine work by Andy! Wish he would do more (nudge, nudge).

    Leave a comment:


  • Peter W
    replied
    Andy has some excellent videos on YouTube about how to size endcaps and Orings. Well worth a watch I will see if I can get a link.

    Peter

    https://youtu.be/hWcryehE7EU this is part 2 of 3....couldn't find part 1 but as mentioned an excellent watch. (pretty sure 1 is on there somewhere)
    Last edited by Peter W; 01-10-2020, 12:34 PM.

    Leave a comment:


  • Davidh
    replied
    Hello David,

    I have machined up some renshape endcaps. I am currently thinking about how tight the fit should be for the section ( with the o-rings) that fits inside the tube. Do you machine the diameter such that it is a tight friction fit or do you have a tiny gap / difference with the O- rings making up the difference and providing the press fit.
    I suppose another way of asking is how much depth do you create for the O-ring groove? Is the depth of the groove about equal to the radius of the O-ring? As I have mentioned to you, I intend on making my endcaps the way you do. What shrinkage factors if any should I consider? Would there be any with the urethane moulds. I haven’t encountered it with my appendage parts moulds...yet.

    Click image for larger version

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    I hope this makes sense..

    David H

    Leave a comment:


  • Subculture
    replied
    Model cars and trucks present probably the severest loads for esc's, as they're constantly slamming on the brakes and have widely varying loads on the motor when compared with aeroplanes and boats.

    Leave a comment:


  • trout
    replied
    The RC truck/car folks use a cap pack to deal with that.
    I am just beginning to play with brushless motors. So, this conversation is very relevant. Here is a YouTube on this topic of a capacitor on an ESC.
    https://www.youtube.com/watch?v=R3V0Uj0EnBo

    Here is a video on some basics about a cap pack. Now with one you can leave your ESC with the motor.
    https://www.youtube.com/watch?v=ie8P3ocN1io
    or make your own
    https://www.youtube.com/watch?v=5xl5iwunADs
    Last edited by trout; 01-08-2020, 11:55 AM.

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by Subculture View Post
    I would give a cautious, probably. The best people to consult about this would be Mtroniks. They might say fine, or possibly advise fitting an additional low esr cap across the leads.
    Thanks for your attention to this. We value your input very much. I'll contact the Tech's at MTroniks.

    David

    Leave a comment:


  • Subculture
    replied
    I would give a cautious, probably. The best people to consult about this would be Mtroniks. They might say fine, or possibly advise fitting an additional low esr cap across the leads.

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by Subculture View Post
    I think the wires got crossed. You should aim to keep the esc as close to the battery as you can, matters a lot less if the wires to the motor are longer.
    Good catch, Andy! You were clear, I read your comment wrong.

    So, that puts the battery, two servos, the BEC, and the ESC up forward. That's a lot of wires, in close proximity to one another, through a very tight conduit (three motors wires, two servo leads, power zip-cord, BEC output wires, and ESC lead).

    Yikes!

    I so much want to keep the ESC and BEC in the after dry space! That would mean a battery-to-ESC cable about 15" long. Can I get away with that, Andy?

    David

    Leave a comment:


  • Subculture
    replied
    I think the wires got crossed. You should aim to keep the esc as close to the battery as you can, matters a lot less if the wires to the motor are longer.

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by Subculture View Post
    I believe that is to soak up back emf when the controller is stopping/braking or reversing, which can be more potent on long cable runs from battery to esc. Helps the long term health of the controllers FET's/

    Always pays to keep those cables as short as you can. if you have to extend, it's better to add on to the motor cables.
    Timely input, Andy. Today I work out the arrangement of devices within the after dry space. Based on your observation I'll butt that ESC right next to the motor. Thanks.

    David

    Leave a comment:

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