FET stacks

[Dangerous Dave]

after much trawling thru old posts (hello again 2003!!) I have decided to attempt the basic single cell FET mod. One answer I didn’t get was what is a FET stack? I’m guessing it’s just parallelling more FETs for even lower resistance and more current capability.

Do you guys physically ‘stack’ the additional FETS on top of one another?

As a side note, does anyone have a spare set of front steering uprights? I damaged mine when removing the front axles, despite trying a couple of methods 🙁

[betty.k]

Dangerous Dave wrote:

what is a FET stack? I’m guessing it’s just parallelling more FETs for even lower resistance and more current capability.

correct.

Do you guys physically ‘stack’ the additional FETS on top of one another?

yup, then bend down the pins and solder them to the pin underneath:smiley14: :8ball:

[Dangerous Dave]

I have finally got the goods to dual cell my Bit…

Original Compact Char G R34
X Trek 3.4
FETs
Custom rims
(soon to be) Dual cells – 110mAh 1/4’s

also have cells to make my FETed ZZMT a tri/quad cell monster!! ya reckon it will handle 4 cells?????

[betty.k]

i’d save the dual cell for last, you’d be amazed at the difference the fets make and may be happy with it as a single cell.

for the mt 3 cells is plenty fun. :8ball:

[jamiekulhanek]

I am building a small 10 gram indoor plane (50cm wingspan) using an LXX perfection PCB. Does anybody have any leftover FETs they would like to sell?

Thanks

[Dangerous Dave]

ta bk – I actually did the FET mods ages ago to both the Bit and MT, and yeah, it makes a BIG difference.

So this arvo I wander out to the shed with my new cells, Dremel the chassis a little, bit of soldering and 10 mins later I have a dualled Bit. What will it do when I first nail it on the kitchen table??

WHEELSTAND half way across (1m), then flipped over backwards!!

Turns out it doesn’t wheelie straight either, cos the rear of the body has tailpipes on one side only – so will add a second set later.

I think the wheelies may be a problem when trying to drive any kind of circuit, so am going to chase down some taller gearing to tame it (tried 4.95:1, but they’re too big).

[leonli17]

hehe…nice to see people finding fun in BCGs again…i looked through my collection the other day, brough back alota memories 🙂

Dangerous Dave: what u need is a booster PCB, it’ll stop the wheelies in most cases.

[betty.k]

nice lookin’ sled you got there dave;) :8ball:

[Dangerous Dave]

ta fellas

yeah I have only just realised there are ‘2 speed’ PCB’s around. What type of car do I need to buy to get a booster?

Re Jamiek’s FET question – RS Components have got the tiny IRLM2502’s and others, just order online and do a local pickup if there’s a store close by.

Or maybe Aaron, microamps, ph2t etc have bulk quantities?

[jamiekulhanek]

Dave, I was hoping somebody here might have some leftovers, specifically the names you just reeled off.

Booster gear seems to be a like hen’s teeth these days, sadly. Wasn’t long ago when they cost virtually nothing to buy, now everybody wants the again.

[Dangerous Dave]

aww I only got about 4 FETs left, but they are reserved for my ZZSE 🙁

Has anyone here done the DC mod to a ZZSE?? was it worth it?

[jamiekulhanek]

Dangerous Dave wrote:

aww I only got about 4 FETs left, but they are reserved for my ZZSE 🙁

Has anyone here done the DC mod to a ZZSE?? was it worth it?

ZZSE’s come DC’d from the factory, I think the only way of getting higher voltage is with Li-Po’s.

[Dangerous Dave]

sorry, shoulda been more clear..

meant the Duty Cycle mod (changing the PWM output on the throttle).

[leonli17]

I saw teh Duty Cycle Mod on pimp. i found the chip needed on the net, but i don’t know how the pins are connected on the board.
This mod would be good. SO anyone done it?

[betty.k]

don’t think any locals have it but what i’ve read from others who have is that it’s the best mod you can do to increase power.
it requires more than just soldering though, there’s some pic programming involved too. :8ball:
http://members.cox.net/codesuidae/DCMod.html

[jamiekulhanek]

Hmmm

I bit the bullet and ordered 10 2502’s from RS, at around $2.80 each once posted I thought it was a complete jib.

Anyway, I did the FET mod on a practically brand new working BIT chassis, cycled the NiCd on my charger and charged it up to a healthy 54mAh.

I removed the stock FETs, cleaned and tinned the pads, then proceeded to mount the new 2502’s.

At no time did I apply heat for more than 1.5 seconds, and after every joint I waited 5-10 seconds to allow any heat to dissipate. I then went over every joint so I knew there wasn’t a chance of a dry joint.

I put her back together, and…nothing. I changed the motor to a 1.6 (from 3.0) and all I could get was the motor ticking over slowly, slightly faster in reverse.

Thinking I must have applied to much heat to the FETs, I removed them and put on a fresh pair of 2502’s taking more care than before.

And again, the exact same problem.

What in the name of blue f*ck is going on!!! LOL

[Dangerous Dave]

should be 4 transistors to remove, and 4 2502’s put in, however with a single cell Bit, 2 of them are mounted remotely (on the underside or similar)with jumper wiring to them.

If this is what you have already done, then all ya can do is make sure all joints are good, and nothing is shorting anywhere.. check the ground wires too.

I’ve only done 2 FET mods – so I aint no expert… maybe someone else has some tips?

Good luck – it’s worth it!!!!!

[jamiekulhanek]

Obviously i’ve done something wrong then, I just replaced the 2 motor drive FETs with 2502’s. I can’t find a tutorial anywhere on what to do, and it’s been so long since i’ve actually been involved in electronics that I couldn’t figure it out on my own.

Can i get some help please?

Thanks

[betty.k]

i still have this old pic of the “flipped” method (neater in my opinion) and the normal method. “draht” means jumper wire;) :8ball:

[jamiekulhanek]

Well i did it exact to the pics, and it didnt work, i’m presuming flip means flip the FET over and bend the legs down? Cause that’s what I did.

Jesus i hope I didnt just fry $12 worth of FETs…

Regarding the flipped FETs, the leg that is attached to the jumper wire, i’m guessing that is NOT soldered to the pcb yeah? Think this might be my problemo.

[jamiekulhanek]

Well, those pads were the problemo, so I changed them and now have a screaming single cell machine. Can’t wait for my Lipo to arrive!

Next FET mod… I received a booster BCG (LXX Perfection) from betty.k which was dual celled and had a BIFF turbo. It was a wickedly fast little truck (hummer body, jacked up with a rear spring monoshock and H plate, front springs and patented betty.k lego wheels. This thing even had front and rear lights that were controlled by the 3rd channel!
Anyway I left it on charge and it killed the batteries, so I salvaged what I could.

I am putting this PCB in a project plane I’m building, because I thought the 2 speed would give a nice “cruise/climb” control. The biff weighed in at 0.65g which was just too heavy so it had to go, the DC-DC circuit (diode, electrolytic cap, IC, Inductor) was also removed to save weight as on anything over 2.5v it’s not needed.

Anyway, just wondering if anybody has FET modded a booster, and how it went.

[betty.k]

jamiekulhanek wrote:

Regarding the flipped FETs, the leg that is attached to the jumper wire, i’m guessing that is NOT soldered to the pcb yeah? Think this might be my problemo.
correct, there’s ya problem! :8ball:

[Author]

Posts