|Sep 13, 2003, 10:50 PM|
I saw the Rondo for the first time and decided it was nifty...
Then I got sick and couldn't go out and fly. I needed something to do, so I designed a Rondo Ripoff!
As you can see, it is round... As you can also see, it is in development. I have etched a prototype and it is looking promesing.
I will have to wait untill I get my hands on some real live speciments of the chip I intend to use for it to actually fly anything, but I have been testing the firmware in a equivialent chip, although to large to fit on the PCB.
* Speed-controller with 8-bit PWM.
* Max 14A(theoretical), 10A max to be safe.
* 1A BEC
- Working and running smoooooooth!
Current focus / todo:
- Add more decoupling to improve noise-immunity
- Get ahold of a LM2940 voltage regulator in SOT-223 case to compare against the lousy LM340 I have to use now.
And, before anyone asks: NO I will NOT be adding a breake, nor will I be adding current-limiting. The FET is fairly cheap and will burn if one short out motor. This can be your protection.
As for breake, use this ESC for fun stuff like flying wings or other placed u can stick a speed 280/300 motor...
Oh, and for those wondering: I will be using the Microchip PIC 12F629 in this ESC. It is only 8 pins, has flash-memory and costs less than $2 in singles!
|Sep 15, 2003, 10:53 AM|
New RR300 layout is done!
I've upgraded my CAD program so that I can rotate parts in any angle! I think the new layout is better as it has better connections for the RX-wires. Also, I used a new function to create arched tracks along the outer-rim.
There is decoupling-capacitors on V+ near the connection to RX and the microcontroller. There is also one over the motor together with a emf-diode. There is also the usual 2 capacitors on the regulator. I did add another larger capacitor on the V+ rail close the the regulator. This should make the system a lot more immune to noise.
The previous version could run with a LM340 regulator all the way down to 5.1 volts with a speed 280. The new version should get lower and if you can get ahold of a LM2940 is SOT-223 package, this should reach noise-immunity down to 3.6v ! (Wich would mean I need to add a LVC in order not to kill your battery's if you are stupid.)
|Sep 15, 2003, 04:33 PM|
Here's the new pcb almost done. Only thing missing is the actual microcontroller. I will be getting that tomorrow and then I will go flying!
|Sep 15, 2003, 07:17 PM|
Do you have that mounted on the motor? Good idea.
Ever since I started seeing you work on these electronics I have wanted to learn also. I'll be getting a soldering iron (i think this is a good first step...) soon just for regular hobby needs. My highschool offers no courses on working with electronics like this, the robotics club is more about building the robot (they buy pre-made robot control electronic boards), and the "tech" class is more about pneumatics and stuff....
maybe i can get a course at the local college over the summer or buy a few books or something
|Sep 16, 2003, 10:44 PM|
Hey Kreature, you might want to add a hole to strain-relieve the negative battery wire, it looks like it could pull the copper right off the board, especially if it is in a pusher, where a crash would pull that connection away from the board.
|Sep 17, 2003, 12:29 AM|
Nice work. You are very close, but might I suggest one more detail that I feel will help the cause. I see you added as much copper fill as you could to your primary heat disipating components, namely the FET and the regulator. This is good. What concerns me is the height and mass of C4. The leads on these surface mount electrolytics won't take a lot of lateral G's, especially when mounted vertically...don't ask me how I know. It's one of those mechanical moment thinguses ME's know about...out of my range. If you would like to try some small tantalum brick types for C4 instead, PM me, I got many to spare.
Another trick for heatsinking prototype stuff is to use a doublesided board and leave as much copper on this otherwise unused side as possible. Copper tape can make a double-sided board in a pinch as well. Then simply attach copper braid to the tabs, wrap over, and solder to the other side. Remember though to watch the polarity of your tabs and planes from one side to the other side--no shorts allowed. A +5 Vdc regulator tab inadvertently conected to the drain or source of the driver FET would get ugly. In that case, you would need to separate the backside copper to connect both.
FWIW, Very nice work!
|Sep 17, 2003, 01:44 AM|
zagisrule! I have thought about that as well... I don't think a hole will do anything as I am using 0.8mm thick board.
The jolt would snap the board instead. M+ on the other hand is actually soldered to the motor tab so it should be safe
Stickman, I am testing different layouts and ideas. That capacitor was already replaced the same night as I etched that board.
I am now using 2 large tantalum at the regulator, 1 smaller cheramic at the V+/GND outputs to the tx (this also happens to be close to the microcontroller) and a 0.1 uF cheramic over the motor poles.
I have also split the return-path of the emf between the motor pins so that it now goes through the diode and cap and meets with the regulators large tantalum instead of joining up with the regulators feed pin before the caps. This should reduce the noise a bit too.
When it comes to heat, there is no real issue with the FET as it has sooooo low internal resistance it can easily handle 10-14 amps without a heatsink. The FET is a logical-level controllable HEX-FET with only 4.7 mOhm on reistance and a 0.6v threshold.
at 90% duty it does NOT even get luke warm running a speed 280 on 8 cells.
The regulator on the other hand leaves to be seen. I don't think there will be any issues but the regulator has both short circuit and temp protection and essentially can NOT be distroyed.
I have tested the circuit a good deal now and it can run a 8-cell battery down to about 5.1volts before the BOD kicks in and stops the controller. At this time there isn't really any power left anyway and if you didn't notice thrust dissappearing waaay earlier than that U deserve to crash.
The new layout isn't as pretty but looks like this:
I do have room for some small 0805 or smaller type capacitors very close to the vreg pinns and will probably add that.
Also, I will add another cheramic up by gnd/V+ pads, simply because there is room
|Sep 17, 2003, 02:14 AM|
Mind you, if it goes, so does the model anyway
|Sep 17, 2003, 05:18 PM|
I see, I have just had some experience with pads coming off and it really peeves me when it happens. I saw that the + lead is going straight to the motor tab, good strain relief and as little as possible resistance.
What MOSFET are you using? You could easily do a 400-480 controller with a TO-252 FET. Adding a brake is not all that hard either, it is just a P-chan MOSFET that pulls the negative motor wire to Vcc to short the motor. You just need to add a code segment driving inverting P-chan driver high on a no throttle
|Sep 17, 2003, 10:23 PM|
Looking good....a good single sided layout--low noise, etc-- is often challenging to achieve. It really would be nice to have the luxury of a full ground plane on the other side wouldn't it--on the other hand: boring!
I'm breathing easier now, now that the electrolytic went bye bye.
Could always try reducing the 0.1 uF across the motor terminals to 47 nF with an additional 10 to 1 nF in parallel with it--might filter the higher frequency noise better.
Thanks for sharing your efforts.
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|Homebrew Rondo!||KreAture||DIY Electronics||36||Jan 24, 2005 11:23 PM|
|Homebrew Rondo!||KreAture||DIY Electronics||35||Nov 12, 2004 05:29 AM|