Another PCB mod and Schematic - Page 2

Mattydiah · #16 10-24-2002, 05:27 PM

Hey, Dayfall, is there any chance you could provide an actual picture of the PCB with arrows pointing to the points that we should be jumpering?? This will help out alot for the people who dont know how to read electrical schematics.

Thanks!!

Dayfall · #17 10-25-2002, 10:10 AM

- This thread has a good diagram of two resistors you should jumper (or at least jumper or replace with smaller resistors, which did)
http://tinyrc.com/forums/showthread....threadid=1736.

I am posting a picture of my board with the other two resistors to jumper or replace. They are marked in red.

- The NPNs (before I took mine out) got within 0.35 volts of ground. Darlington NPNs might get you to 0.2 volts.

- I definatly noticed an increase in power when I jumpered the resistors. I got around 5 to 10% increse I think. When I put in the MosFETs I got around another 5 to 10% increase. My testing was motly how well it ran on carpet and what slope it could climb. Electronics wise, I went from about 0.85v to about 1.1v to the motor.

tinyrc · #18 10-26-2002, 03:46 PM

Promoted to Bit Science.

Dayfall · #19 10-30-2002, 12:54 PM

Try as I might, I can not increase the voltage to the high side of the motor. I bet the no reverse mod DOES work great. The voltage drop is still about 0.3v. I tried a darlington transistor and (DUH) that didn't work. Darlingtons need lots of voltage to thier bases. Mosfets didn't work much better. The only solution was to just short out the resistors like in the original post.

We simply need more voltage. A negative voltage generator perhaps?

Nightwing · #20 10-30-2002, 02:10 PM

There has got to be a difference between how a Bit driver and a ZZ. Wonder why unless the transistor are not getting the same level of signal to switch? Unknown.

Oh Did this particle diagram of the front end receiver of a ZZ. Its not complet and has not been check fully for errors. This is mostly from the "top" side of the board. May get a chance this weekend to finish up but need something to crack the black expoxy when I get to the IC side of things.

mbartell · #21 11-26-2002, 09:06 AM

I was wondering- could you jumper the resistors listed in this post, on a dual cell car, or would that fry the whole thing?
It seems that if done wrong, they will fry on a single cell.

DarthRacer · #22 11-26-2002, 12:04 PM

Just reading over this again since it has been bumped.

Won't shorting the resistors promote decreased transistor and MOSFET life? Aren't they there in part to limit current flow?

Or are these transistors designed to handle more current than what is actually being used?
I might actually be brave enough to try this.

Nightwing · #23 11-26-2002, 12:43 PM

You do not want to excede either base current ot gate current if a FET.

Around on this board is a diagram for the H-Bridge.

Dayfall · #24 12-02-2002, 10:35 AM

If you are using a duel batt mod then I don't think you should try shorting the resistors unless you really know what you are doing. In the duel battery case I would suggest using 4 mosfets if you really want to get serious.

Jumpering can not hurt mosfets, but can hurt transistors. I don't remember the current they drew, so hopefully someone will measure it and post the results. Since I am no longer using the upper two transistors, I can't say if their life would have been shortened.

DarthRacer · #25 12-02-2002, 10:50 AM

Thanks for the reply.

I have read in another thread here where someone is using 100ohm resistors to replace the 220's, then someone else took that farther and used SMD resistors from an old hard drive.
I think I'm going to try 100ohm SMD resistors.

DarthRacer · #26 12-02-2002, 11:01 AM

Here is the thread I was talking about where a few people are using 100 ohm resistors.

http://tinyrc.com/forums/showthread....&threadid=2703

Snoopy · #27 12-18-2002, 09:49 PM

Hi Dayfall,
can you please tell us what's the exact part number of the n-fets from Digikey you used?
I tried to find N-Channel 25v SOT-23 mosfets, but they seem to have none. (only 30V)

Dayfall · #28 12-23-2002, 10:48 AM

The part number is FDV303NCT-ND for $.55

I can't wait till I get a big enough order so I can get some SMD LEDs for some light mods.

Nightwing · #29 12-23-2002, 11:12 AM

Instead of trying to remove the little nightmares you could parallel another 220ohm across each one. This will drop the effective restance down to 110 if you parallel a 220 across it

If you uses a 190 will make it around 101 ohms.

For the math incliend, here are two different formulas.

1/(1/R1)+(1/R2)) = effective value

or if you have two resistors

(R1 * R2)/(R1 + R2) = Results

So something around 190ohm will give you 100.

Craig · #30 12-24-2002, 10:51 AM

I thought this might help in your quest for more speed etc. It's the full schematic for the receiver.

Enjoy,
Craig Falknor