I've got FETs in my SE!

Mostly dealing with electronics and pcbs and modifying them, all the things that make electrical-engineers tick and the rest of us cringe in fear.
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ph2t
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Post by ph2t »

Hey micro, here's some suggestions. I was leaning towards this in previous investigations in my h-bridge thread.

Since I don't have a zz se yet, you guys are gonna be my eyes 'n ears, lol.

Take the following measurements:

At the terminals on the pcb where the motor connects take some voltage readings for both terminals (-ve and +ve of the motor) releative to ground. Given h-bridge theory when there is no fwd or rev command both motor terminals should be at the same voltage potential. This means there's no current flowing across the motor, therefore no movement.

Next take some more voltage readings at each terminal for fwd and rev respectively. Do this measurement for full fwd and full rev. I say this so the duty cycle is 100% and not stuffing with the DMM readings.

So you should have the following results:

Terminal______"Motor +"_____"Motor -"

Idle__________value(v)______value(v)

Full fwd_______value(v)______value(v)

Full rev_______value(v)______value(v)


Where value(v) is the voltage on the respective motor terminal relative to ground.

If someone could take these values and post them I'd be appreciated. I beleive with these real world values one should be able to design a circuit that would be able to realy switch a fet on at the persribed 3V+.

ph2t.
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Post by micro_Amps »

I see where you are heading ph2t, but..........

I spent some time on it today, and I've cracked it. Got my ZZ SE clocking about 13 km/h (8.5 mph) it screams now and still has full proportional control in both speed and steering control. Yee Haaaaaa.
It loves high speed motors and tall gears, has no problems pushing the red gears (on carpet) which are the ones I am using for the 13kmh speeds.
Its kinda like a fet modded BCG but because its heavier (50% heavier thankyou very much) it accelerates slower and takes nice smooth corners at speed, just before it flips or spins out, (depending on tyre choice and skill level).
It is now the utimate micro r/c, fully propo, good speed, great control, love it.
Ive put some stuff on my website, I'll post more stuff here in the morning, its getting late here.
My work for today, is done.
:) uA
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Post by ph2t »

Wow! That's great news Micro. I hope you find it in the goodness of your heart to share this with us lamefolk..... :grin:

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Post by crazydave »

ph2t wrote:Wow! That's great news Micro. I hope you find it in the goodness of your heart to share this with us lamefolk..... :grin:

ph2t.
Ditto

...or maybe a hint at least. :-D
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Post by payaso »

crazydave wrote:
ph2t wrote:Wow! That's great news Micro. I hope you find it in the goodness of your heart to share this with us lamefolk..... :grin:

ph2t.
Ditto

...or maybe a hint at least. :-D



You might have to change your user name to saint, or hero on this one man... Great find.. I must have this done to my car.



silla :D
payaso...... :)

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Post by bdebde »

That is awesome micro_Amps! And I get to have the second one in the world! YEE HAW! I can't wait for it to get back from down under!
Scotty, beam me up.
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Post by ph2t »

bdebde wrote:That is awesome micro_Amps! And I get to have the second one in the world! YEE HAW! I can't wait for it to get back from down under!


lucky bastard! If you could bdebde, take some vid man of a zzse pre and post fet mod that would be cool to see the tangible differences....

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Post by bdebde »

ph2t wrote:
bdebde wrote:That is awesome micro_Amps! And I get to have the second one in the world! YEE HAW! I can't wait for it to get back from down under!


lucky bastard! If you could bdebde, take some vid man of a zzse pre and post fet mod that would be cool to see the tangible differences....

ph2t.


I will have to see if I can borrow a digital vid camera, I have no way to capture from my tape camera. It will be a week before it gets home (mr. scott, energize). I can't wait!
Scotty, beam me up.
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Post by ph2t »

bdebde wrote:
ph2t wrote:
bdebde wrote:That is awesome micro_Amps! And I get to have the second one in the world! YEE HAW! I can't wait for it to get back from down under!


lucky bastard! If you could bdebde, take some vid man of a zzse pre and post fet mod that would be cool to see the tangible differences....

ph2t.


I will have to see if I can borrow a digital vid camera, I have no way to capture from my tape camera. It will be a week before it gets home (mr. scott, energize). I can't wait!


lol, bloody treckie!

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Post by VooDooMafia »

ph2t wrote:Wow! That's great news Micro. I hope you find it in the goodness of your heart to share this with us lamefolk..... :grin:

ph2t.



Thats a silly question of course he will bro micro amps is as much a pimp as we are :)
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Post by micro_Amps »

Guys I am going to be doing the $20 for mods thing again, just like the previous time with the BCG and Gen1 ZZs and clones.
All the details will be on my website.
Cheers,
:) uA
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Post by ph2t »

Here's some readings I've taken from the motor terminals:

Image

When the car moves fwd @ full throttle is gets 1.5V across the motor, when in reverse it gets 1.38V, this is 0.12V less. That's why the car is faster in fwd than in rev.

The goal of the mosfet mod is to make the results like this:

Image

Notice now that over 2V is going to the motor, this will then get the zzse up to speeds similar to dual cell bits, well that's the plan anyway. :???:

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Post by ph2t »

Well, 3 weeks down the track and still no luck, argghhhh! This car is drving me fuckin nuts!!! I've tried several different theories all to no avail at the moment. The last thing I want to do is to add 10 extra components just to make the thing work, it just would't be feasible.

Anyways I was checking out bit-racer.de the other day and came across this post from the legendary Kraut Microsash.

http://549.rapidforum.com/topic=100383367398

In this thread he details how to fet mod a ZZSE. The method detailed is exactly similar to the alternate daulcell fet mod method. What I mean by this is that instead of using 4*IRLML2502 n-chan fets, you use 2 * IRLML6401 and 2 * IRLML2052 fets instead. This can be done because the voltage source is now 2.4V instead of 1.2V and the voltage difference between GND and Vcc is enough to turn the fets on. Anyways, enough of the ubergeek speak.

This picture shows the two NPN transistors being replaced with the IRLML2502 fets. They are the two at the bottom of the picture. This is the underside of the PCB:

Image

You then have the other side (topside) of the PCB replacing the two PNP transistors with the two IRLML6401 p-chan fets. They are on the left of this picture.

Image

From the broken translations I got from babelfish it appears that this mod increases acceleration noticebly. As to the top end speed increasing I don't know. Yet to try this.... I don't beleive this is the be-all-end-all mod for he ZZSE, I still think better performance can be obtained.

I'm gonna give this mod a try now and let you fellas know my results.

Cheers,

ph2t.
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Post by payaso »

The top side of my SE PCB was un-touched when I got it back from micro_Amps. Must be a different method..



silla :D
payaso...... :)

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Post by ph2t »

Yeah, I'm pretty sure about that. In my conversations with microamps the main problem he (and now I) was facing was the low (0.9V) turn on voltage going into the Gate pin on the fet. In the mod above, Microsash has done nothing to counter this issue. So I think what we have above is a mod that gives you marginally better performance than the stock transistors but not the full jump forward that micro's fet mod produces...

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People are mean to you because you're a fucking idiot.
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