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Thread: R-Team AX-12 Heat Sinking Method

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    R-Team AX-12 Heat Sinking Method

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    Just to be clear. Do this at your own risk and we take no liability for the outcome. R-Team does this to all our AX-12 Servos (60+ so far) and has had no issues.

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    Last edited by GhengisDhon; 4 Weeks Ago at 10:22 PM.

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    Re: R-Team AX-12 Heat Sinking Method

    Inner side: I used Rubberized coating thinking it would help with insulation from the electronics, regular spray paint works fine. Or don't spray paint at all and leave bare metal.

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    Last edited by GhengisDhon; 4 Weeks Ago at 10:27 PM.

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    Re: R-Team AX-12 Heat Sinking Method

    Spray paint the outer side.

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    Last edited by GhengisDhon; 4 Weeks Ago at 10:28 PM.

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    Re: R-Team AX-12 Heat Sinking Method

    Requires some trimming of the AX-12 Case where the heat sinks poke through.

    Also use thermal paste between the HS and motor driver chip.

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    Last edited by GhengisDhon; 4 Weeks Ago at 10:29 PM.

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    Re: R-Team AX-12 Heat Sinking Method

    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

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    Re: R-Team AX-12 Heat Sinking Method

    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.

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    Re: R-Team AX-12 Heat Sinking Method

    The previous two replies are cut and pastes from somewhere else. Sorry if the discussion starts out as out of nowhere.

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    Re: R-Team AX-12 Heat Sinking Method

    I recently did 3 more servos, so I have four on Numa2. My own finding was that a dremel is slower and not needed with the AX12 case. Instead, I used a trapezoidal razor blade. Scored lines for the material I wanted to remove, then did a few passes easily slicing plastic slivers away until I had enough clearance for the heatsink.

    I did the heatsink folding afterwards.

    Now I just need to do some more hacking to my arbotix commander so that I can get a readout of the temperatures from the robot for monitoring purposes... I might still go for springs as an enhancement for next year.

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    Re: R-Team AX-12 Heat Sinking Method

    Thanks for passing all of this along, guys. It's a huge help.

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