Monday, January 10, 2011

Hot n Cold

By now I will be back at Tech. By now I should be starting to go to class. Instead I've been holed up in my residence because GT has shut down due to a flurry of snowfall last evening. It is pretty cold outside, but alas there is work to do: Cake's drive escs are getting too hot!

Seth at the Robot Marketplace recently informed me of a new set of KW motors for the B-series gearmotors. These guys pull more current, but are spec'd at 937 rpms at 12V or so. That is ~300 rpms over the old motors which will work great for my 1.5" drive wheels.

But if you ask me, it still feels slow compared to DDT. So lets take the motor mods a step further.

Tower Hobbies sells paired motors for direct drive foamies. 180 sized, high rpm, high current, and the correct shaft diameter. More importantly, they were on sale for a bulk buy!

The operation was a simple motor switch since the mounting patterns were the same.



Here the motors are installed with the B16 gearboxes. Ignore the new escs for the time being.
Months ago, I also purchased two scorpion mini escs to replace the damaged scorpion HX dual esc. You may recall, I had some SMT components fall off the board and while it has served me well my distrust is well placed. The two scorpion minis side by side fit perfectly horizontal in the electronics bay and open up much more room for the wires and plugs from the drum.



I applied a light application of glue on the edges to hold the two boards together, so that I could use breadboard jumper wires to bridge the main esc terminals like P0W3R busses.



Note how there are two plugs on the esc. One plug is actually for battery, but the other connects the the drum esc. Having the same connect with the same polarity makes for stupid proofing.

The real problem was that the new motors drew more current than the escs could handle. Evaluating my options, I felt that adding heatsinks was a far easier solution than disabling current limiting or upgrading the FETs. I cut some blocks of 1/8" thick copper bar (back when copper was not ass expensive) and tapped some 4-40 threads to facilitate mounting to the FETs.




A light application of silicon based heatsinking compound helps heat transfer between the materials. I also made a note to sand and polish the mating surfaces. Oxidation on the bar left lots of non-conduction crud on the outside.




Finally mounted we discover the robot to be significantly quicker, with extended runtime. I can achieve approximate 3 minutes of vigorous driving before the escs overtemp. This is acceptable.

Here is everything installed in the robot. The first picture of this post shows an unexpected benefit of adding the heatsinks. The board material fits right in between the header pins and the capacitor in my AR6110 receiver for optimal space savings!


3 comments:

  1. Hi, I think I saw you at the InVenture Prize competition. What was your project?

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  2. hi anonymous. Some friends and I entered with the "Glide Board". I don't quite have any images or footage, but perhaps we will in good time.

    Out of curiosity, who is this?

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  3. My name is robert and i was also competing in the inventure prize. I plan to use the Invention Studio to build my prototype, so maybe ill see you around.

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