ZipZap Monster MOSFET Mod (Work in progress......)

crazydave · Post by **crazydave** » Tue Nov 16, 2004 5:02 pm

codesuidae wrote:I also took some video of the MT with the mosfet mod in, I can post links if anyone wants to see.

Video is good. I wanna see video.

ph2t wrote:with the high speed motor and gear set, it will flip on the spot, lol.... it's soo like a 1:64 version of my madforce it's not funny.....

Yes it is.

That's crazy dude. When I first got mine I was thinking theres more than enough space to cram dual SE batteries in there, but now I'm thinking, if I just get my FETs working right, this thing will be too nutty.

betty.k · Post by **betty.k** » Wed Nov 17, 2004 5:04 am

it's true! we had to put the green motor in it so we could keep it on the ground!

Finks · Post by **Finks** » Wed Nov 17, 2004 10:23 am

ph2t wrote:

Holy crap this is sickness. Two masters of current giving one of the best how to's ever.... and yet ph2t can't put his wheels on the right way....

codesuidae · Post by **codesuidae** » Wed Nov 17, 2004 11:17 am

ph2t wrote: Have any of you guys noticed you get that high pitched buzzing sound and then the top speed goes to shit?

Yes, although I hadn't had a chance to track to down yet. I was guessing that excessive clearance from the pinion hub to shaft was causing it to wobble as it was unloaded.

Did the graphite treatment take care of it?

hue35 · Post by **hue35** » Wed Nov 17, 2004 12:03 pm

Finks wrote:Two masters of current giving one of the best how to's ever.... and yet ph2t can't put his wheels on the right way....

Who's to say that's the wrong way? I'd say he's got 'em mounted the "aggressive" way... they'll get more bite in that direction.

richh · Post by **richh** » Wed Nov 17, 2004 3:38 pm

ph2t wrote:more madness......

Have any of you guys noticed you get that high pitched buzzing sound and then the top speed goes to shit?

ph2t.

i've seen that with the higher rpm motors. on mine i've cured it with a couple of paper shims on the idler gear. i noticed that it starts to screech when the idler starts drifting away from the chassis (too much slop left to right). the shims just take up some of the slop. you can see them here.

betty.k · Post by **betty.k** » Wed Nov 17, 2004 4:23 pm

i found a lot of noise coming from the front hubs too. i've just been using graphite all over so it won't attract dirt.

codesuidae · Post by **codesuidae** » Wed Nov 17, 2004 5:04 pm

betty.k wrote:i found a lot of noise coming from the front hubs too. i've just been using graphite all over so it won't attract dirt.

And speaking of the front hubs, mine have lots of slop, the front wheels wiggle all over, even when the nuts are nice 'n tight. Seems like too much play in the bearings. Anybody have an easy fix for that?

I have no idea if fixing it would make a performance difference, but it would be more elegant

betty.k · Post by **betty.k** » Wed Nov 17, 2004 5:34 pm

hmmmm

brass eyelets?

codesuidae · Post by **codesuidae** » Thu Nov 18, 2004 1:18 am

Well, I had a nice post composed listing all the gate and source to drain voltages on my MT, with the motor both loaded and unloaded, then firefox took a dump and lost my post.

Now, since its after 1am, I'm not going to do it all again

The gates were all either 4.92, 4.71 or 0.0 volts. I believe it was Q8 4.71, Q7 4.92, Q6 4.92, Q5 4.71.

The most interesting info is that the pFETs drop up to 0.06v source to drain when the motor is drawing max current (stalled). I don't know how much current is being delivered to the motor under these conditions, so I don't know how much power is being lost there. With the 2.6ish volt battery, and another 0.02ish volts drop at the nFET, perhaps as much as 3% of the power available is being lost in the fets. I could be way off though, I dunno for sure.

crazydave · Post by **crazydave** » Thu Nov 18, 2004 9:22 pm

Ok, I finally got the FETs working right in my car. Had a sinus headache, couldn't think. I went with ph2t's version, just because I could comprehend it at a glance, and it sure did work.

Aint got no numbers, but it mowed over the pile of Hot Wheel cars pretty good with orange gears in it. I'm happy.

Thanks a ton, both you guys. I guarantee I never ever would have figured that out on my own.

ph2t · Post by **ph2t** » Thu Nov 18, 2004 9:26 pm

code is the bloke who served the goods, I just got a room full of monkey's to do the work...........eventually one of 'em figured it out!

enjoy dave, outside on the grass is soo easy now it's not funny!

ph2t.

HACHI-RYOKU · Post by **HACHI-RYOKU** » Fri Nov 19, 2004 6:12 am

I've been watching this ever since I noticed it. I was going to swap trannies out for like fets at first, but it's a good thing I read this first. Thanks everybody for all their hard work. I'm one of the ones who will definately appreciate this.

PH2T, did you take any voltage readings after you put the li-poly in?

crazydave · Post by **crazydave** » Fri Nov 19, 2004 8:16 am

Oh and I forgot to say, Codesuidae, I tried to get that # for the resistor, but my PCB is just as blurred as yours. I think it is a 19 though.

codesuidae · Post by **codesuidae** » Fri Nov 19, 2004 10:05 am

crazydave wrote:Oh and I forgot to say, Codesuidae, I tried to get that # for the resistor, but my PCB is just as blurred as yours. I think it is a 19 though.

Cool, thanks. I'll take another look at mine. As long as there aren't any other R19's on the board, that'll work.

I'm going to try to put in a circuit to tune down the torque on startup, make it a bit easier to run a fast motor on high traction surfaces without flipping over. That'll give me another chance to take a look at that label.