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Thread: Some love for the Money Pit

  1. #21
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    Re: Some love for the Money Pit

    As for connectors, maybe try PCI-Express card-edge connectors? I've been looking at them for future versions of quadnought to make quick changes easier, and they are less expensive than most pin headers.

    Duck tape should work pretty well as protection against shorting. Not very pretty, but very durable and should only be visible if the bot rolls over.
    Last edited by tician; 05-27-2017 at 05:33 PM.
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  2. #22

    Re: Some love for the Money Pit

    Yeah, I've been considering card-edge connectors, too! They're great for PCBs. Harder for wiring up existing pieces.
    Is there a good board-to-wire solution based on card-edge?

  3. #23

    Re: Some love for the Money Pit

    The yearly Fusion license renewal is free, as long as it's for hobby use or for companies that aren't making much money.

    I think they really do fear open source -- if the open source gets a foothold and becomes good enough, they will start losing customers from the paying tier. Better to make a great, easy-to-use tool, free, and keep charging the people who can afford it, so that those who are skilled but short on time will spend their time using their software, rather than building competing software.


    Separately: I heard about your PCB stack before, but the cycloidal gearbox doesn't ring a bell. Pictures needed!
    And I think someone could give Robotis a run for their money with a brushless servo with an ARM controller.
    Perhaps use CAN bus -- it's starting to really take off among the more serious drone people, and it's an obvious extension to the RS-485 option.

  4. #24
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    Re: Some love for the Money Pit

    There are a number of card-edge to ribbon cable connectors, but not sure any of them are for PCI-e. Just search digikey for card-edge connectors that use IDC termination.

    I would make a PCB (50mm x ~100mm to take advantage of V-cut arrays with Seeed) with multiple PCI-e one-lane or four-lane connectors to build a buss and regular pin headers on the short edges to extend the buss as necessary. After that, make some PCBs with the PCI-e cutout and multiple mounting holes to attach it to the delrin carrier plate, and breakout all the PCI-e contacts to 0.05" headers and/or 0.1" headers for cicoil cables and other stuff mounted on the delrin carrier plate. The connectors alone would not be enough to keep things secure, so have to add some small brackets to secure the delrin carrier plate to the rover's structure, or just shove some screws/pins into holes in the slot after sliding in the carrier.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
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  5. #25
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    Re: Some love for the Money Pit

    Quadnought is a stack of 50x100 PCBs for PRS and/or large rovers (~80V up to ~50A). Current design moved toward PCI-e 4X connectors instead of crap pin headers and gave up trying to squeeze everything into a certain existing mass-production enclosure. Also moved to a PCB filled with twenty 100V/330uF D12.5mm through-hole caps instead of a single more expensive and unwieldy chassis mount cap.

    The 30mm square stack is a revival of a previous desire to build a custom servo from small hobby BLDCs and inexpensive cycloidal gearboxes, and the layout was derived from an earlier 50x100 Teensy PCB with dual DRV84x2 motor drivers and a RFM69 to be stuffed in a combot (derived from an even older 50x50 Teensy + RFM69 PCB). Abandoned the 'stack of ponoko lasercut delrin plates and no bearings' design for the gearboxes quite a while ago because of cost and tolerances. Hope to get a prototype printed and assembled in the next few weeks. At 14V and 4A, the two stage box with 1306-3100Kv motor could potentially hit up to 120 [RPM] (no-load) and 45 [kg-cm]. Settled on 30mm square since it was about as small as I could make the Teensy clone and it could slide into a length of 1.5"x0.125" square aluminum tube with two end-caps held together by threaded rod, standoffs, and a couple screws.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
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  6. #26
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    Re: Some love for the Money Pit

    Are the drone kids using CAN-proper, or just CAN transceivers? I have both CAN-proper and two UARTs with CAN transceivers laid out on my Teensy-3.2 clone, but have now split the comm board off from the teensy board due to lack of space and with the side-effect of increasing flexibility/customization. CAN ICs tend to be same cost or less expensive than RS-485 transceivers, do not require a direction pin (CAN-proper requires you read what you write to check for collisions), and overall provide a more robust comm channel. I was also thinking about using LDVS transceivers for a little while since I'm using rather large packet sizes in an etherCAT-like comm system but with UARTs instead of ethernet.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
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  7. #27

    Re: Some love for the Money Pit

    [quote]twenty 100V/330uF D12.5mm through-hole caps[/quote

    There's a lot to be said for that! You probably get lower ESR because of the parallel ganging, and you also have some redundancy to failure.

    Are the drone kids using CAN-proper, or just CAN transceivers?
    As far as I understand it, CAN-proper.

    I got a couple of CAN transcievers to be able to play with it for a bit (it's a bus I know less about than I should.) The Teensys and the Jetson both have CAN built in, sans transcievers.

    If I were building my own carrier boards and motor drivers, I could easily go backplane+card-edge boards.
    As it is, I'm using RoboClaws, and the Jetson, and a Teensy, and I'd have to run pin header jumpers to some carrier board that I would then plug into a backplane, and that seems overly redundant.

    In other news, I broke a 3/8 carbide endmill yesterday, because I was trying to run 4 flute in aluminum, which is almost never actually a good idea. Should have known better, but I wanted to try again ... :-)
    Anyway, parts are starting to come out, mostly on spec.

    The 24mm hexes I made were too big for the 24mm hex inserts in the wheels I bought; I milled them down to 23.8mm and they were a snug fit. Unfortunately, the 15/64 hole I drilled for the 6mm motor axle didn't have as much runout as I had hoped (!) so I'm planning to ream that to size. I just need to figure out the most time saving work holding and locating setup (important for reaming!)

    Also, I don't have any tapping fluid/cutting oil (I use WD-40 when hand tapping) so I wonder if I can cheese it with flood coolant...

  8. #28
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    Re: Some love for the Money Pit

    Quote Originally Posted by jwatte View Post
    If I were building my own carrier boards and motor drivers, I could easily go backplane+card-edge boards.
    As it is, I'm using RoboClaws, and the Jetson, and a Teensy, and I'd have to run pin header jumpers to some carrier board that I would then plug into a backplane, and that seems overly redundant.
    How is that much different from using those big, expensive connectors you were already looking at? Either way, you have to hard-mount the connectors to the delrin carrier plates, then use some sort of wire to link those connectors to the various devices mounted on the delrin carrier plates. Card-edge would be much cheaper, much more flexible, and capable of handling significant power (1A per contact: 36 contacts on PCI-e 1X and 64 contacts on a PCI-e 4X).
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
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  9. #29

    Re: Some love for the Money Pit

    The expensive connectors would let me crimp wires from header pins to expensive connectors, and then crimp a separate harness between expensive connectors.

    Going through PCBs I'd have to go from header pins to board, then from board to card edge, then from mainboard to bus. Which probably uses expensive connectors, anyway! I'm not making a 24" flexible board that covers the entire 'bot :-)

    I haven't dismissed the idea, just thinking through plusses and minuses.

  10. #30
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    Re: Some love for the Money Pit

    PCI Express headers in 1X and 4X sizes can be <$0.80 in singles. You could easily fit 8 card-edge breakout PCBs with numerous mounting holes on a single 100x100 board with V-cuts. That gets you 80 breakout boards in a single order of 10 PCBs with ENIG finish from Seeed for <$60 shipped.

    e.g. 25mm x 50mm breakout with many more finger contacts than pin headers due to 1mm spacing of fingers; also mouse-bites for snapping the panelized board into final shape. PCI-e headers usually have staggered pins for 1mm pitch along the card while still having plenty of room for routing traces between consecutive pins.
    Click image for larger version. 

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    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

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