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Thread: Dumb Idea: So like... what about jumpjets?

  1. #11
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    Re: Dumb Idea: So like... what about jumpjets?

    Quote Originally Posted by ArduTank View Post
    Surprised no-one has tried low volume water-cooling for their servo MOSFETs. Wouldn't take much flow/tubing diameter.
    If I understand correctly, the AX-12 mosfets are awkwardly located under a folded over capacitor, and the clearance space inside the servo is pretty minimal. I guess if you have R-Team style heat sinks poking out, you could water cool those, but that would probably be overkill. I also saw someone on the forums has a phantomX hexapod with little pc fans on the servos. Not sure how effective that is.

    A simple cheap cooling option with low risk of damaging servos is something we've been thinking a bit about lately. Seems like the folded metal things R-Team uses are the most reasonable option (if you have sheet metal tools and can risk breaking a couple servos).

    Speaking of which, any chance the dimensions for those heat sinks are available somewhere? Might actually have the resources to pull that off now.

  2. #12

    Re: Dumb Idea: So like... what about jumpjets?

    I recall R-team actually posting a print of the heat sink.
    I looked at it, even built a possible die for the thing in Fusion, but then decided that torsion springs was a better option for me.
    I know this isn't the most convenient format (just screen shots from Fusion) but hopefully it's better than nothing!



  3. #13
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    Re: Dumb Idea: So like... what about jumpjets?

    Quote Originally Posted by jwatte View Post
    I recall R-team actually posting a print of the heat sink.
    I looked at it, even built a possible die for the thing in Fusion, but then decided that torsion springs was a better option for me.
    I know this isn't the most convenient format (just screen shots from Fusion) but hopefully it's better than nothing!
    Awesome. Thanks!
    I really also should look into springs. It makes a lot of sense.

  4. #14
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    Re: Dumb Idea: So like... what about jumpjets?

    I got an assortment of different springs and tried them. Picked the spring that in all 4 knees had the lower middle servo current draw. The spring took the static body weight off the middle servo. Initially I used a regular spring in compression. It mostly self centered. Next year I replaced it with a barrel spring. The barrel spring always self centers. Picked the barrel spring up at Ace Hardware. Ace has a large assortment of springs. McMaster-Carr has a larger selection. I stole the knee spring idea from Eric's Tychus biped in 2012 Robogames. His robot spring configuration was different than my implementation but same basic idea.

    My servos are all heat sunk. The middle servo got really hot without the heatsinking, to the point of failure if I moved fast with a load. Had to replace the two 8 pin SOIC dual MOSFETs in the servo. After heatsinking it never failed and only got warm. With the spring it doesn't even get very warm and my current draw is lower so I could go a faster with a smaller battery. I used 25 mils thick aluminum to make the heat sinks.

    To cut the plastic AX-12 servo I draw a horizontal line on 3 sides of the servo for where I want to cut the plastic. I then take light colored tape and adhere it to the plastic at the edge of the horizontal line I drew. Now I have a visible guide of how far down to cut the plastic. I then mark the vertical lines to the tape. I use a dremel tool to gently cut the vertical lines and clear away some of the material. I trim the remaining plastic out with a razer blade. This is very repeatable. I also unscrew the circuit card and lift it out 90 degrees. I de-solder the 47uF aluminum electrolytic capacitor and take it out. I replace it with a new capacitor with longer leads. I bend the leads 90 degrees and put it in the two pad holes. I place a 25 mil small piece of aluminum on the two 8 pin SOIC MOSFET packages and lower the capacitor until it rests on the aluminum. I then solder the two leads in place. I think this technique allows the heatsink with the thermal grease to rest flatter on both dual MOSFET packages and get more heat out. I noticed that on some of the AX12s, the factory gap between the cap and MOSFETs varies and therefore causes the heatsink surface to tilt up and not contact the further out MOSFET package. Replacing the capacitor fixes this and allows the heatsink to always rest flat on both packages. I've done this probably 24 times now and have never damaged an AX-12 so I wouldn't not do it for concern over damaging one. I attached an AX12 schematic.
    Attached Files Attached Files

  5. #15
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    Re: Dumb Idea: So like... what about jumpjets?

    The small hole in the heatsink drawing is to allow the AX-12 servo LED to show through. The larger hole is for clearance of servo hardware. The AX-18A is very similar. Only difference is the LED hole needs to move closer to the middle and no large hole is required for clearance.

  6. #16
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    Re: Dumb Idea: So like... what about jumpjets?

    Wow. Thanks for all the details. Those are good things to know ahead of time rather than finding out along the way.

  7. #17
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    Re: Dumb Idea: So like... what about jumpjets?

    Quote Originally Posted by byi View Post
    Yea... I'm pretty bummed, but one guy had to drop out this spring, exams are killing me right now, and then we all have issues travelling. Just wasn't going to happen this time. We'll be ready for whatever event happens next (if Tucson happens again or maybe possibly I've heard rumors of NY Maker Faire?). If there isn't anything running before May next year, at least we'll have had time to scrimmage with Columbia.
    Sounds like we are going to try to have a NY Maker Faire event this year. I'm not running it.. James from West Point (formerly from Columbia) is organizing it and I'll help out as needed.

    Probably won't be quite a big as the Bay Area Maker Faire. I think he is also talking about having some sort of a "Tank" event as well, which will have a lower entry bar than a full fledged Mech.

  8. #18

    Re: Dumb Idea: So like... what about jumpjets?

    I bet the three "editor's choice" ribbons for Bay Area Maker Faire may help open the door for NYMF :-D

  9. #19
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    Re: Dumb Idea: So like... what about jumpjets?

    Quote Originally Posted by jwatte View Post
    I bet the three "editor's choice" ribbons for Bay Area Maker Faire may help open the door for NYMF :-D
    Ya.. when we received them I didn't know what they meant (being new to Maker Faire), but figured it was a good thing.

    Looking at 2018 Bay Area's editors choice awards, quite a few received a single ribbon, a few received two ribbons, and very very few received three or more. Guess we did OK. We did get quite a bit of attention. Guess it helps that we were "new" to Maker Faire. I assume a lot the exhibits are there every year so get old after a while.

  10. #20
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    Re: Dumb Idea: So like... what about jumpjets?

    Quote Originally Posted by GhengisDhon View Post
    Sounds like we are going to try to have a NY Maker Faire event this year. I'm not running it.. James from West Point (formerly from Columbia) is organizing it and I'll help out as needed.

    Probably won't be quite a big as the Bay Area Maker Faire. I think he is also talking about having some sort of a "Tank" event as well, which will have a lower entry bar than a full fledged Mech.

    That's great to hear! That will certainly put some pressure on the team here to stay on schedule this summer.

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