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View Full Version : [Question(s)] Anyone made a servo heat sink?



Slugman
05-29-2012, 05:10 PM
A number of recent posts have mentioned the overheating of servos & their limited ability to lose heat. Instead of hi-jacking their threads I thought I better ask seperately.

Has anyone made a heat-sink for a Bioloid servo, or any other type of servo for that matter?
It obviously requires the butchering of the servo itself.

Without looking into it too much since I don't know the maths for it, I was thinking that it would have to be a smallish block of fins projecting out of the side of the servo case. The Bioloid frames would get in the way if it was more than 2mm out from the servo case, which limits it a fair bit. I'm looking at the heat loss vs extra weight here, & assuming the heat sink seals off against the servo case to protect the internal components. Weight should only be about 2-3 grams per servo, so would it be worth it for those couple of servos we have that always seem to overheat?

It shouldn't be too hard to make, so I thought someone here might have already done it.

tician
05-29-2012, 06:46 PM
I could swear I have seen servos modded with heatsinks, but I can't recall where.

Looking at how the motor is mounted in an AX-12+, you might be able to cut out part of the rectangular protrusion from the bottom side and attach a heatsink directly to the motor can without compromising the structural integrity of the servo or motor mount. All the better if part of the heatsink is an aluminum frame attached to that end to ensure structural integrity and motor mounting stability. I'm envisioning an aluminum version of the F3 frame attached to a block of aluminum fitting into a hole (~3/8" x ~1/2") in the bottom with an internally rounded side to contact the motor can (use ceramic thermal adhesive to connect the heatsink to ensure the motor can will not spin in place and damage the servo). Just having a hole in the plastic to keep part of the motor can exposed might offer an improvement since plastic is not a very good thermal conductor (though keeping it open would increase the risk of debris damaging the internals).

Slugman
05-29-2012, 07:48 PM
Hmmm, F3..... Which one is that again?:confused:
If I'm reading your post correctly, then that's how I envisaged making the heat sink - I could make the aluminium contact the motor easily enough with paste, then stick a flat heat sink to it so it seals the case & projects out a bit. It's probably only a few hours work, just not sure if there's any point. Although.... the more I think about it, the more I think it could make a difference for those critical servos. Not suitable for all of them, just the ones that are at their limit. Your comment about the lack of heat transfer through plastic is a very good point. Much better to get that heat out in the breeze where it can dissipate.

I.E. Get a rectangular block of ally, drill a hole the diam of the motor can, cut it in half with a 1mm grinder blade, then grind the flat sides down to fit the hole in the servo case, & fit a sink to the outside flat part. Glue to can with heat paste. Done.

OK, looks like I might have to pull those two servos apart & have a good look inside to work out the best way to orient the sink.

Out of interest, by "from the bottom side" do you mean the short end of the servo opp the horn end? It would be great if I could get the heat sink there, as it would be the best place (for me). I could probably get the sink to project 10mm out at that end.

tician
05-29-2012, 08:48 PM
If you take off the face plate that the four long screws screw into (the circuit board side opposite the horn side), then you will see the motor touching the side that I refer to as the bottom (little rectangular protrusion between the face plates with four spots to insert nuts). The protrusion is there simply because the motor extends slightly beyond the rest of the case at that side. Beware though that not all of the protrusion is safe to cut into as the 1/4~1/3 closest to the gear train side is to support/secure the motor and separate the electronics from the gear train and its grease.

F3 frame. (http://www.trossenrobotics.com/store/p/6181-Bioloid-Frame-F3.aspx)

Slugman
05-29-2012, 10:41 PM
OK, thanks. I just had a look at my sketchup drawing of my robot, & putting the sink there is a bit of a problem for me for both the ankles & hips - Would need to make a longer version of the F6 frames to hold the pair of servos together. Luckily I don't use the F5 frames, since I use my hinge & lever version for both hips & ankles. I would just have to re-do the hinge a bit wider. I've been meaning to get them made properly (Laser cut) but the prototypes are still on there at the moment, so it's no big deal to change them.

I'll still take the servo apart to have a look though, as from my sketchup pic it looks like I might be able to make an L-shape to get the heat sink to the small end opp the horn. Not as direct for heat transfer, but if it's made from aluminium it should be OK. The L-shape looks like it could be up to 1-2mm thick between the servos without having to make the F6 frames longer, depending on how much the motor sticks out.

Thanks again! :happy: