The Sub-Genius MOSFET mod

[SuperFly]

Wow. Hue35 and I successfully completed the MOSFET mod last night. Everything you've read about this mod being both very difficult and very rewarding are true.

Keep in mind that prior to February or so, neither of us had ever messed with PCBs, and our soldering experience consisted of fixing the jacks in a wah-wah pedal or something like that (I'm speaking for hue35 here, I'm sure he'll correct me if I'm wrong). We are both graphic designers for our day jobs, so electronic engineering does not come naturally. I only point this out because there are some obvious experts with this sort of thing (ph2t and microamps come to mind), and that's not us.

Anyway, we'll post some tips, techniques and info that will help all you non-solder monkeys through it. Watch this thread, coming soon.

[CaboWabo]

*patiently waiting* lol

sounds perfect - I think I might be in the same group as you and hue...

[crazydave]

Doing my first mosfet mod today.

I'm like Hue, but I've actually etched my own PCBs, and made a few distortion pedals. My only experience with these tiny boards is popping off the crip cap.

My biggest concern is the tiny size, so I'm going to practice swapping few transistors first.

[SuperFly]

OK. Here's the first of the general tips:

• MicroAmp's tutorial says it takes about 2 hours. This is true for the most part, but we needed an additional 2 hours for troubleshooting/fixing broken stuff.

• You need 4 mosfets to do the mod. The little tabs break off very easily, so order extras. Hue35 and I each used 6, I believe.

• You need a really good soldering iron with a very fine tip. I would also recommend the really fine soldering wire.

• Don't drink too much coffee, and get up and stretch after each milestone.

• Hue35 removed a couple of the mosfets while troubleshooting no reverse function. He ended up replacing some of the original transistors, and now has a car that has the mosfet boost only in the forward direction. Actually quite useful, considering one usually uses reverse for crash recovery, and you don't really want all that torque in reverse. Not to mention perhaps only needing 2 mosfets to do the mod. We're going to look into this.

• Here are some really helpful diagrams from the german tutorial…







• One last thing: it's not obvious from the turorials I found that you will be gluing the 2 mosfets on the back of the pcb on their backs with the tabs facing up. We used superglue, but wished we had a hot glue gun. The superglue was fine, though.

[lefftoe]

yo, check out the bit-racer.de mosfet guide that cartman did, the pics show you an easier way to do it

i know babelfish turns german to jabberubbish
but check it:
http://549.rapidforum.com/topic=101684609757

see the two fets that you glue to the backside, and how you just need to offset them..........less wires makes this mod easier to do.......

[crazydave]

I didn't get around to the mosfets, but I practiced switching transistors, trying to save the steering on a board to use as a subject for the mosfet mod.

Here's what I learned:

Since I wanted to reuse the transistors after I removed them, I had to be careful not to break it. I used a piece of stripped wire as soldering braid to remove as much solder as possible. Then I inserted the tip of the exacto knife under the transistor, and twisted very lightly. Touched the soldering iron to the tab on the side w/ just one tab, and it came undone, and the transistor came up slightly. I stuck my finger nail under the tab, and when I laid the tip of of the soldering iron across the two tabs, the transistor came right off.

Now to put it back on the burned board. At first I tried soldering tweezers, but the transistor kept moving in the tip. So I just held it in place with my thumbnal, and heted the one tab. Which held it in place, while I did the 2 on the other side.

Took me about 20min. to do, and since 2 of the mosfet are direct swaps for the transistors, that half the mod right there.

I was mostly intimidated by the size, but I'm feeling pretty confident now. Hopefully I should have m a mosfet modded car by tomorrow evening.

[crazydave]

I used a Cannonball PCB that I had replaced the steering transistors with Microsizer ones. I opted for the on the top of the PCB version.

I was really nervous, because I'm using Mosfets donated by Havok. He gave me one set to practice with, and I didn't want to blow it. So my hands were shaking like crazy. I got everything a little crooked because of that, but i made sure that everything connected good.

I had all the mosfetes soldered to the board, I had made the jump from Q6 to Q2, and I had attached my wire to Q3, I was getting ready make my final connection without a hitch when the tab broke off the mosfet. So luckily it was a reverse one, and one of the flipped ones, so I just popped the same transistor off my MS donor board, and saved myself the last jump, which besides my crooked placement, makes it look cleaner, and like Superfly said, you don't need all that speed in reverse.

I threw in Black Sabbath "The Ozzy Ozzborne Years", a 76 min. CD, I was done by the second to last track, and racing my car during the last rack. So it took me a little over an hour.

I friggin' screams too. Dual cell like, but way punchier, and maybe not as much top speed, but I was popping wheelies, and flipping my car, with a Cannonball 2.6. I've got a dual cell Cannonball on the same frequency. I'll make a comparison video.


Oh yeah and speed was improved in reverse, even though I only used the one mosfet.

[hue35]

I threw in Black Sabbath "The Ozzy Ozzborne Years"

Perfect.

Hey Dave, what version of the mod did you do?

[noxorc]

excellent SuperFly.

I still have my two sets...


just gotta find the time.... (anyone got any to spare)

[crazydave]

I threw in Black Sabbath "The Ozzy Ozzborne Years"

Perfect.

Hey Dave, what version of the mod did you do?

This one, that's posted above. I just looked at this diagram.

[hue35]

I'll have to draw a diagram that shows what my accident produced. I ended up with the increased power for fwd only but it only uses 2 mosfets. The diagram you used must be increasing power to the steering too... do you notice a difference?

[crazydave]

Yeah, that's like a full mosfet mod. I didn't do the steering mosfets, and I ended up not doing the position 3 mosfet, which is for reverse.

Video coming soon

[maximan]

an someone make a list of what each position is where the diagram and what each one does

[crazydave]

Here's The vid (it's in Quicktime format):

FET'ed

In the first half we see the mosfet car on the right take the dual cell car. The Cannonaball dual cell does kinda suck, but it's a fair comparison, because the mosfet'ed car used the same PCB, and motor.

In the second half I'm just screwing around pulling wheelies.

[crazydave]

Here ya go, maximan.