Sunday, January 19, 2020

Project Updates

Been keeping busy with all the little projects going on here.

Mounted a terminal strip in the Supro amp so I have some tie points for the new capacitors.


Next time you see the chassis I'll have it finished. I put the refurbished grill cloth back in the case, along with the new speaker and carrying handle, but didn't take any pix.....D'OH!

And I brought all the fiddly bits for my little "Senton" 4x4 truck down to the basement, put them all back where they belonged, and tested it for steering and throttle response while it was sitting on the test stand.


Next up for this little guy is to fit the GoPro mount, and wait for the geese to show up. Should be a real Hoot and a Holler!

I also gathered up the parts I had "in stock" for the "Limitless" Speed Run car. Here's the steering servo installed, and the radio being fitted-up.



And not wanting to spend $300 on a motor and Electronic Speed Controller ("ESC"), I found a new pull from another Arrma car on eBay, and picked it up for $100. I'm trying to keep the costs on this down, and this motor/ESC pair is plenty good enough for learning how to drive this thing. My fellow Arrm Forum members tell me this "beginner's setup" should be good for 80~85MPH with the stock gearing, and possibly good for ~100MPH with different gearing and some other tuning tweaks.



Electronics package mounted, along with the motor.


After I power the car up the first time and do the initial setup, I'll connect the servo arm, and do the final steering trim. 100MPH = 147 ft/sec, so you really have to have the steering dialed-in, and make some adjustments on the radio to calm it down some. At that speed, a slight twitch on the steering wheel can send you flying off course.


After I'm comfortable driving it in this configuration, I'll upgrade the ESC. The ESC I'm looking at is capable of passing much more current, while running cooler (less loss), and allows more adjustments, one of which is "Braking Strength". You should be able to lock up all four wheels at maximum braking effort (the little truck does this easily), and this ESC can't do that when the vehicle it's in is using the gearing required for high-speed running.

One of the things I have to learn more about are the speed controllers and motors. Way back when, in a different life, I used to design large "Variable Frequency" AC, three-phase motor controls, so I know three-phase power systems fairly well, but that was 40 years ago. One of the differences is that these little brushless DC motors use a permanent magnet rotor, whereas the big motors I used before are your typical three-phase "Squirrel Cage" motors that have aluminum or copper bars making up the rotor. The spinning magnetic field in the stator coils induces currents into the bars, and the rotor gets "dragged" around trying to follow the magnetic field. This causes the rotor to "slip", spinning at a lower speed than the magnetic field rotates at. The permanent magnet rotors don't do this, being pretty much locked into the same rotational speed as the magnetic field.

I've seen schematics of these ESC's on the web, so now I have to go round them up and study them. Time to brush-up on "4 Quadrant Control" again!

4 comments:

  1. Awwww....thanks, WSF!

    It's just something I've always been "good" at. I didn't have any kids my own age to play with in the neighborhood, so I always had my nose stuck in a book, or was down in the basement building model airplanes and cars, and then got interested in radio stuff.

    I guess when you learn things at an early age, they stick with you.

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  2. You always have the coolest projects!

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