TRi-Rebel question with FOC - ugh the maths

[Hillslam]

Hi all,

Finishing up my parts list and want to make sure I did the math right.

I'm going to be using a Tri-Rebel BBW with a PC2 and plan on using the white die for the FOC.

So paired with a PC2 and 14650 7.4V li-ions, I'll wire the two blue dies in series, then take the white die off the FOC pad, thru the power extender with a 3.9ohm 5w resistor from the store here put on.

And then in hte PC's configs I'm leaving the LED current setting at 1000mA and the FOC strength setting at 1000 also. I admit I am confused as to the purpose of the FOC Strength setting on the RICE panel and PC config. The manual just describes this as "strength" from 0-511, but the new version of the configs go up to 1023? No idea whats that about?

So anyway, wanted to double check and run this by you all in the hopes I won't blow anything up, burn anything out, waste power or have a pathetically dim blade.

Thanks in advance. I know it seems a basic question, but my degree was in fluid flow not electrical

[TrypWyr]

And then in hte PC's configs I'm leaving the LED current setting at 1000mA and the FOC strength setting at 1000 also. I admit I am confused as to the purpose of the FOC Strength setting on the RICE panel and PC config. The manual just describes this as "strength" from 0-511, but the new version of the configs go up to 1023? No idea whats that about?

Huh.

Now that you mention it, I've never noticed that setting. Of course, I just wired up my first FoC saber and just ran with the default settings... (and I'm not using RICE on this saber) I will have to play with this one. I'd wager that this setting simply alters how much the FoC die "interferes" with the main LED (My term, for lack of anything better). Since the main power for the FoC die is hooked up via the PeX (7.4v), that's what I figured my resistor value from; works fine.

Good luck!

[Hillslam]

Ahhh, so its like how much the main die gets its power interupted? In order to bring out the FOC color more? That makes sense. Although the arbitrary seeming scale range is odd.

Anyhoo, I figure with the 3.9ohm 5w resistor in front of it on the 7.4v power the white die on the trirebel should be safe. I was thinking of being a little risky and dropping down to the 3.3ohm resistor since I didn't plan on having the FOC die ran alot, but that might be chancing. I'm not sure how resistant to over-voltage these dies are.

[erv]

hi there, Erv' here, I've been paged

You might have a look to the Nano Biscotte user's manual to learn about the "drive" which applies as well to CFv6 and PC2 FoC channels.

question #1 : 511 vs 1023. Chip changed between PCv1.6 and PC2.0, this is a consequence and it means overall more resolution but you're not directly concerned by that.

question #2 : how to use it. Rule of the thumb => leave it to the max, and calculate your resistor as you did above

question #3 : no, on PC at least, the FoC doesn't interfere with the main led, they have separate settings for the shimmer. The FoC drive (aka "strength") defines the max power of the FoC die when it's activated. You can adjust it in very special cases as explained in the NB user's manual (otherwise leave it to the max).

example of use :
- you calculate a resistor for sending 350 mA to your FoC die. You end with a 4.286875 ohm resistor that you can't find. If you put a 4.7 ohm, it will be dimmer. If you use a 3.9 ohm, you might send out too much current.
- in this case, you can decide to use the 3.9 ohm but you'll also adjust the drive to send out less... "drive" to the FoC die to compensate. 3.9/4.28<=> 91%. Use 91% of the drive, which is 1023 * 91 / 100 = 932. The PEx will act as a "digital resistor" that will compensate your physical power resistor.

check the details in the NB manual, but also, if you reach a very very low resistor (that you can't find at the store), overall below 0.5 ohm, you're darn close to be "direct drive" BUT going 0 ohm is dangerous. Compute the ratio as explained in the NB manual and adapt the drive to compensate no external resistor. This very case should not happen often unless you use 2 dice in series for the FoC, and the resulting forward voltage ends being VERY close to the batt voltage (hence super small resistor).

hope this helps
/excedrin
/advil

[Hillslam]

Thanks a ton Erv that was very helpful!

[erv]

you're very welcome. I'll add also something important (mentioned in the NB manual too) : NEVER lower the drive under 80% (820) as a(nother) rule of the thumb.