The BitChar-g FET H-bridge mod.

[micro_Amps]

You may have seen or heard of this mod on the net, well I decided to try it and the results are awesome.
Using a very fine soldering iron I changed the bipolar transistors that make up the H-bridge that drives the BCG.
The 4 transistors were changed for 4 x N-channel mosfets (hexfets).
Why change them ?
The original transistors have a reasonably high resistance, this causes power to be restricted as it goes through the transistor to the motor. The transistors have a reisistance around 0.4 ohms and the mosfets have a resistance of maximum 0.045 ohms (one tenth !)
The result is a moderate speed gain, but a HUGE gain in power at the rear wheels.
The single speed chassis I did the mod on now leaves my dual cell for dead. The top speed of the dual cell is still higher but because the FET modded car is only a single cell it is so light that the speed off the line leaves the dual cell in its dust.
Also the FET modded car handles corners ten times better than the dual cell around corners, again because it is not carrying the extra cell.
Even with a 3.8 motor and the highest gear set it will still pop wheelies and scream accross carpet like it is running on floor boards.
Here’s how it was done.

This is the standard Rx pcb showing the transistors, we’ve all seen this one before. Crip cap is still in place under the yellow component.

The 4 transistors that make up the H-bridge were then removed, and because this was a brand new (Compactchar-g) chassis I took the opportunity to remove the cripple capacitor too.

Two of the removed transistors were NPN type and are pin compatible with the new SMD N-channel MOSFET, so they go in first. They look the same as the transistors that have been removed but they are different in function.
Thats them nearest the V+ and F solder terminals.

Because the other 2 FETs are not compatible with the circuit board layout they need to be stuck on the back of the pcb and wired into the circuit.
Here is where they are glued in position under the pcb.

The two pairs of FETs then need to be wired together to complete the H-bridge. This is done with the blue fly leads you can see running from the front of the board to the back. The spaces where the other two transistors were removed (the PNPs) remain vacant and are not used.

When its all done and put back together you cant even notice any changes.

This is a tricky mod and you need to be fairly good with a soldering iron and have steady hands. It took me about 2 hours.
Just to state again, this was not my idea, I got the info from here, its all layed out in their instructions.

This little car is now a rocket, but its a different kind of fast. A dual cell is fast, but they have trouble on corners because they are so heavy. This FET mod single cell can go flat out through turns with out losing traction, sliding or flipping. It will leave any dual cell in its tracks, with the exception of long straight runs where the dual may catch up as it has a higher top speed.
But to get a single cell up to 90% of the speed of a dual cell and heaps more power to burn on ONE cell, its an excellent mod.

I’d like to see a multi cell FET mod, a triple cell booster FET mod, and maybe even a triple cell booster multi-FET mod, but they are ideas for another day…..(soon)

:)uA

Edited by – micro_Amps on 23 May 2003 08:26:14

[ph2t]

Dude, well done on an excellent mod. Are the FET’s the same IRLML2502 type stated on the German page? Can I buy some of ’em off you?:D

ph2t.

[SurfmyStrat]

interesting, does it kill the battery faster??? also could there be a way to harness that extra energy that is wasted when resisted so it can be sent to some LED’s up front of the car??? would there be enough energy for that???

[GT-ahh]

dude put the fets in parrallel and it will have even faster acceleration! muhahah
nice work man, I removed my fets and jumpered them for a drag car (no reverse but o-so-fast) but I couldnt find a suitable replacement FET so thats as far as I got. What fet are you using? If my FET supplier has them in stock ill put some on my mini-z FET order.

[micro_Amps]

The FETS are the IRLML2502 from Conrad as stated in the German site. As it turns out I should have bought more FETs because now I am in the process of converting multi cell boosters and I want to do a parrallel FET mod too (thanks GT-ahh), but all that is starting to chew up my reserves of FETs quickly.
I may do another order if people are interested in me doing the mod for them on their car, I will consider that too.
Havent done run test times with it yet, but to a certain extent the runtime depends on the motor and how much current it draws. Had some good long runs (approx. 10-15 mins)with a 3.8, but I am using the 150mAH cells.

This mod gives you almost dual cell performance in a single cell car that can be charged on a standard charger. It is pretty much the ultimate mod that improves performance and doesnt require external changes, eg extra battery outside or an extra charger.

Its the best mod I’ve found yet.

:D:D:DuA

Edited by – micro_Amps on 23 May 2003 22:26:47

[GT-ahh]

one of my suppliers has them in Australia for 87c each…lmao

[jamiekulhanek]

so THATS why KIT racers are so fast…….
i cant wait to do this one.

[ph2t]

GT, who is your supplier? What’s the min order qty?

ph2t.

[GT-ahh]

the run time should be improved because the new FETs have a lower internal resistance.

[ph2t]

Actually GT, the runtime will decrease because the current drain will increase.

From ohms law. I=V/R, as R decreases I will increase.

ph2t.

[micro_Amps]

Yes this is true. Im not having any troubles with the 150mAH cells, but it may make a difference with a 50mAH cell. Just have to do 2 or 3 charges before running, if you didnt do that already.

Ph2t and GT-ahh, you have PMs.

:)uA

[TallduDe]

niccce mod!!

are you really going to offer to build them for people???

if so any idea how much it would cost????

great mod (again)

[micro_Amps]

Talldude, I may start a thread later offering to install MOSFETs into peoples cars just to see if there is any interest.
It wont cost that much,the FETs are cheap, and I dont mind doing the tiny soldering for people that are keen to enjoy these cars.
I guess $20 including postage back to the owner will do.(in Oz, more postage for OS).
I suppose if people were to send me a bare chassis and 20 bucks in a post pack I could mod it and send it straight back to them in the same packet. Turnaround would be a day or two.
But I need to see if there is any interest.

I just converted 3 of my boosters to FET driven. With a 3.8 motor on boost now they scream, AND handle well.

:)uA

[leonli17]

Just wonder will I able to get those MOSFET from electrical stores in Melbourne?

[leonli17]

And, if we do this mod on a dual battery mod. will the motor stand it? how about on a tri cell? If it will all work, then can anyone do both Dual Battery(internal) mod and the FET mod for me together?

[leonli17]

Can anyone buy a booster BCG with controller for me and put both dual battery and FET mod on it. Then give it to me? If u can, how much will the total cost.

[TallduDe]

well micro Amps i am interested in this mod and for 20 bucks, ill send u a car or 2 😀

hope it works out

cheers

[micro_Amps]

Quote:

Can anyone buy a booster BCG with controller for me and put both dual battery and FET mod on it. Then give it to me? If u can, how much will the total cost.

I did have some prices listed here but I have decided not to do dual cell mods. If you want a car dual cell modded then perhaps you could send it to JamieKulhanek and then to me for the FET mod.

Quote:

I’ll send u a car or 2 hope it works out

Talldude, I will start another thread on this soon for people that are interested. I will of course test them all before posting them back. I have left you a PM.

If there is enough interest, and people are serious about having it done, I will start doing some.
:)uA

Edited by – micro_Amps on 25 May 2003 17:39:15

[jamiekulhanek]

Leon Li I can do the Dual cell mod for you.
PM me

[micro_Amps]

I am already taking orders do this MOSFET mod for people if they want.
The first car is on the workbench right now.
I am starting a new thread under “BCG Discussion” for people to go to if they want to discuss getting this mod done and prices, its here Getting the BCG FET mod done

Technical discussion (mainly) in this thread, from here on.
If you have liked what you have seen, and would like me to do this mod for you, please go to the new thread and we can arrange things from there.
If you have a technical post about this mod, please continue to post in this thread.
:)uA

Edited by – micro_Amps on 26 May 2003 15:35:03

[ph2t]

Can’t wait for my S2000 to come back from Micro’s chop shop… lol!

[micro_Amps]

Ive got a dual cell booster chassis in the workshop at the moment for a FET mod.
And a dual FET, and a 3.6v(internal) booster on the drawing board as well.
:)uA

[ph2t]

You’re gonna have to invent a new type of tyre that will stick to the road enough. All this extra power with no where to grip, arghhh!:evil:

[micro_Amps]

I read somewhere that putting a thin coat of rubber cement (glue) on the rear tyres with your finger and letting it dry gives excellent traction. When it gets all dusty and dirty, you just peel it off and put a new layer on.
:)uA

[ph2t]

Micro, an interesting side note:

Traditionally, when the car reaches that stage that it won’t move any further you could lift the car up off the ground and it would continue on for a little while (with no load) before dying completely.

Now (post FET mod), that stage of the battery drain allows you to continue driving the car around on the floor. The increase in current gives the motor enough tourque to be able to move under normal load. Ive gotten an extra 30-45 seconds runtime due to the extra current at the end-of-life charge.

So the irony here is that whilst the theoretical runtime is decrease due to increased current drain on the batt, it is practically increased due to the extra current available in the last stages……

Cheers,

ph2t.

[micro_Amps]

Thats interesting, so that means when you ‘feel’ the car starting to go flat you still have enough power left to get back to you for a charge.
:)uA

[ph2t]

Very important if you like sittin on yer arse like myself, lol!

[ph2t]

Dudes, has anyone gotten their hands on the IRLML2502 datasheets? Been lookin’ everywhere…..

Cheers,

ph2t.

[GT-ahh]

Package Micro 3/ SOT-23
Circuit DISCRETE
Polarity N
VBRdss (V) 20
RDS(on) 2.7V (mohms) 80.0
RDS(on) 4.5V (mohms) 45.0
ID @ 25C (A) 4.2
Id @ 100C (A) 3.4
QG Typ 8.0
QGD Typ 1.7
Rth(JC) 100
Power Dissipation (W) 1.3

couldnt find the proper data sheet but I do have this info

[ph2t]

Thanks GT.

I found it HERE it’s made by International Rectifier.

I’m really interested in this mod and I’ve been dong a bit of investigating. I’ve found some other fets from On Semiconductor that have even lower R_DS values than the irlml2502.

One of them is NTMS7N03R2. It has an R_DS of 0.023. Half of the irlml2502. BUT it has a higher gate voltage meaning that the RX2 chip might not put out a high enough voltage to drive the fet.

I got some more info at home (still at #$%^& work!) which I’ll post later.

Has anyone checked out DC-DC converters? The one that comes on the RX pcb is pretty crap. It’s only rated at about 30mA, when I try to use this to power the H-bridge the whole thing dies. Some measurements I took later show that the RX pcb drains up to 170mA from the battery. This is no load, the car’s upside down on the table. At full load (motor stopped) the pcb drains up to 260mA. In idle mode standing still the car drains 5-6mA.

There’s some great possibilites here. With the right DC-DC Converter design you *should* be able to pump out 3.3V rated at 200mA+ driven off a single 1.2V battery. Now that would be a fast car, damn!

And……, oh yeah, you can order FREE SAMPLES from Onsemi.com.:shock:

More to come……

ph2t.

Edited by – ph2t on 06 June 2003 20:12:28

[jamiekulhanek]

Micro Amps….How did u do the 3.6v internal mod?
I used a small 3.6v battery from jaycar but it was a piece of crap.

[ph2t]

I’ve done some study and got together a schematic of the FET H-bridge.

The FETs are connected differently than the normal Transistor H-Bridge that’s stock in these cars. This is due to the fact that 4 N-channel FETs are used instead of 2 N-Chan and 2 P-Chan FETs.

Micro, could you please check this against your notes, I’d like to confirm accuracy. I’ve noticed that R14 & R15 are bypassed from the original circuit as well. You might want to put them back in because the V_GS(th) value is 1.2V for the FET you use. I read in other forums that the output is approx 3V from the RX2 chip, if you could check that it would be great. You might be saturating the FET unnecessarily.

I just got my NTMS7N03R2 fets from Onsemi.com. Gonna build it up tonight!

ph2t.

[ph2t]

I found this LINK for a FET mod for daul cells. Seems that they use a different type of FET. Comments Micro?

ph2t.

[micro_Amps]

Quote:

Micro Amps….How did u do the 3.6v internal mod?

Jamie, it was 3 x 1.2v cells standing upright in a dremmeled out chassis. It didnt handle real well as the center of gravity is too high. It is in peices again now being rebuilt with 1.2v 40mAH button cells. When its finished it should be 3.6v 80mAH, hopefully when fully charged it will last long enough to be worthwhile.

Ph2t, your circuit is spot on. I have left the resistors out of the circuit because it is more difficult to modify and include them. They are not in the NPN transistors circuit, the are in the PNPs circuit, and the PNP ‘on’ signal circuit is not used, so its not that easy to just leave them in circuit. They are not bypassed, the circuit is left open ended, and not used because the signal is the wrong polarity. The signal to turn both fets on comes from the NPN transistor circuit. If you wanted to drop the gate voltage you could include a couple of smt 220ohm (roughly?) resistors but I havent seen any detrimental effects of slightly saturating these fets in ‘on’ state. The gate current is minute.
Most of the clones gate voltage is around 0.7v , which falls perfectly inbetween the 0.6 to 1.2v range for the 2502 fet gate voltage. Its only the Tomy gear that has 3v from the voltage doubler/regulator.
(I’m not certain that 3v is actually seen at the gate of the fets on a modded Tomy car anyway, must check)
Regarding the link for the other fet mod. I have seen this before. The P channel fet they use has a higher Vds voltage and the car must be a dual cell to have a high enough voltage to run through the P fets. If a complementary 0.6v P channel fet existed that would make the mod a whole lot easier for a single cell mod, but as far as I know, that is not the case.
:)uA

[ph2t]

Quote:

If a complementary 0.6v P channel fet existed that would make the mod a whole lot easier for a single cell mod, but as far as I know, that is not the case.
:)uA

Sounds like a challange…..:smiley16:

ph2t.

[jamiekulhanek]

Quote:

Quote:

Micro Amps….How did u do the 3.6v internal mod?

Jamie, it was 3 x 1.2v cells standing upright in a dremmeled out chassis. It didnt handle real well as the center of gravity is too high. It is in peices again now being rebuilt with 1.2v 40mAH button cells. When its finished it should be 3.6v 80mAH, hopefully when fully charged it will last long enough to be worthwhile.

A serious note here, if you are using those small button cells that come from jaycar (the green heatshrnk ones) you will be serverely disappointed. These tiny cells have no hope of delivering enough current to the motor, and can only be slow charged or they leak. I know this from experience. I think your best bet is the DC-DC converter.

[micro_Amps]

Yeh, I was using those. Thanks Jamie, I might have to reconsider my choice. I might spend a bit more time looking for other options. I may even put a modded booster pcb into a tricell zipzap chassis. The longer wheel base will fit the 3 x 150mAH cells lying down.
:)uA

[micro_Amps]

Yeh, I was using those. Thanks Jamie, I might have to reconsider my choice. I might spend a bit more time looking for other options. I may even put a modded booster pcb into a tricell zipzap chassis. The longer wheel base will fit the 3 x 150mAH cells lying down.
:)uA

[ph2t]

I wanted to find a FET that had an even lower Rds value than the FET made popular by this mod. The IRLML2502 has a typical value of 0.045 Ohms. I found this FET NTMS7N03R2 with a typical value of 0.023 Ohms. Half the Rds of the normal FET used!!! Cool! (In a very sad freakazoid sorta way…).

The package these NTMS7N03R2 is different to the ones normally used. So different in fact I’m gonna have to make a new PCB for ’em.

The FET is that little black package, I put a steering knuckle next to it to give you guys an idea of its size. On the right is the prototype track layout for the PCB.

Cause I don’t have the tools I’m gonna have to draw the track work onto the virgin copper PCB using a special reistive pen.

Now I let it dry for a few minutes then I put the PCB in some etching solution (basically an acid). After about 7 minutes all the uncovered copper is eaten away and I’m left with this:

Now to solder those FETs on.

Putting the FET board on the car

Now that the FET PCB is ready I need to connect it to the car. The car I’ve chosen to mod is an Lxx booster, the auto modellista one. First I’ve ripped the old transistors out and circled the area where I need to connect the FETs to in yellow.

After connecting the steering wires to the transistor pads circled above I then connected the FET PCB to the power terminals on the car PCB and then I removed the wires to the motor from the car and attached them to the FET PCB.

So the power wires go to the FET board, the steering wires (from the transistor pads, not the actual fine steering wires!) go to the FET PCB, BUT the motor is wired straight to the FET PCB.

That’s it. The only bugger is making the custom PCB, but I guess I could get the parts to do this fabrication using the PC instead of hand drawing it…..

I will post video of my testing ’cause I want to see how my own version of ths mod performs against the original German one. Just quickly I put the Lxx car on a cushion on my couch which is on an angle of about 50-60 degress. In un-boosted mode the car stood still and didn’t roll back. In boosted mode the @#$%^ acutally climbed the bloody cushion. More tests to follow.

ph2t.

Edited by – ph2t on 14 June 2003 10:49:09

[ph2t]

I wanted to find a FET that had an even lower Rds value than the FET made popular by this mod. The IRLML2502 has a typical value of 0.045 Ohms. I found this FET NTMS7N03R2 with a typical value of 0.023 Ohms. Half the Rds of the normal FET used!!! Cool! (In a very sad freakazoid sorta way…).

The package these NTMS7N03R2 is different to the ones normally used. So different in fact I’m gonna have to make a new PCB for ’em.

The FET is that little black package, I put a steering knuckle next to it to give you guys an idea of its size. On the right is the prototype track layout for the PCB.

Cause I don’t have the tools I’m gonna have to draw the track work onto the virgin copper PCB using a special reistive pen.

Now I let it dry for a few minutes then I put the PCB in some etching solution (basically an acid). After about 7 minutes all the uncovered copper is eaten away and I’m left with this:

Now to solder those FETs on.

Putting the FET board on the car

Now that the FET PCB is ready I need to connect it to the car. The car I’ve chosen to mod is an Lxx booster, the auto modellista one. First I’ve ripped the old transistors out and circled the area where I need to connect the FETs to in yellow.

After connecting the steering wires to the transistor pads circled above I then connected the FET PCB to the power terminals on the car PCB and then I removed the wires to the motor from the car and attached them to the FET PCB.

So the power wires go to the FET board, the steering wires (from the transistor pads, not the actual fine steering wires!) go to the FET PCB, BUT the motor is wired straight to the FET PCB.

That’s it. The only bugger is making the custom PCB, but I guess I could get the parts to do this fabrication using the PC instead of hand drawing it…..

I will post video of my testing ’cause I want to see how my own version of ths mod performs against the original German one. Just quickly I put the Lxx car on a cushion on my couch which is on an angle of about 50-60 degress. In un-boosted mode the car stood still and didn’t roll back. In boosted mode the @#$%^ acutally climbed the bloody cushion. More tests to follow.

ph2t.

Edited by – ph2t on 14 June 2003 10:49:09

[GT-ahh]

good stuff but maybe you should look out for a dual n channel/p channel s08 package, then you’d only need 2 chips and this would reduce the size of the board by 50%

[GT-ahh]

good stuff but maybe you should look out for a dual n channel/p channel s08 package, then you’d only need 2 chips and this would reduce the size of the board by 50%

[ph2t]

Good idea GT, I’ll look into it… It’s all about getting the best Rds and Vgs(th) values though……

ph2t.

[ph2t]

Good idea GT, I’ll look into it… It’s all about getting the best Rds and Vgs(th) values though……

ph2t.

[micro_Amps]

Ph2t, let us know how the modded car compares. I’d be interested to see how the 1.6v gate threshold voltage goes as the battery starts to go flat. Most of the clones have only 0.7v available to the gate to turn the fet on, so unfortunately this fet wouldnt be compatible to mod most clones. Have you found your run time reduced at all because of the higher V_GS(th) on this fet?.
Also the 7N03R2 fets R_DS(on) stated max. is 28mOHM, the 2502 has a typical R_DS(on) of 35mOHM, so they are very close, probably too close to tell a difference, but I’d be interested to know how it handles. They can always be paralleled up to decrease the resistance even further.

I have rummaged through my notes and found a few more fets that are suitable, but not as easy to use because they may require extra components, or are not as small as the 2502, or more expensive some up to US$5 each.
They are……
PVN012 optoisolated SSR IC,
GF4410,
GF2304,
SI4410,
ZXMN2A01FTA
:)uA

[micro_Amps]

Ph2t, let us know how the modded car compares. I’d be interested to see how the 1.6v gate threshold voltage goes as the battery starts to go flat. Most of the clones have only 0.7v available to the gate to turn the fet on, so unfortunately this fet wouldnt be compatible to mod most clones. Have you found your run time reduced at all because of the higher V_GS(th) on this fet?.
Also the 7N03R2 fets R_DS(on) stated max. is 28mOHM, the 2502 has a typical R_DS(on) of 35mOHM, so they are very close, probably too close to tell a difference, but I’d be interested to know how it handles. They can always be paralleled up to decrease the resistance even further.

I have rummaged through my notes and found a few more fets that are suitable, but not as easy to use because they may require extra components, or are not as small as the 2502, or more expensive some up to US$5 each.
They are……
PVN012 optoisolated SSR IC,
GF4410,
GF2304,
SI4410,
ZXMN2A01FTA
:)uA

[GT-ahh]

oi ph2t dont those so8 packaged chips have two fets in each? How come ur using 4 of em?

[GT-ahh]

oi ph2t dont those so8 packaged chips have two fets in each? How come ur using 4 of em?

[ph2t]

Nah man, they only have one FET in each. The pins on the SO-8 package double/quad up for current flow.

See there is only one Gate pin.

Micro, when you measured the output voltage from the RX chip on these clones was that as an open circuit? If the measurment was taken in circuit you might find that it is 0.7 volts because that’s the potential of the P-N junction from Base to Emitter of the NPN transistor. The Lxx clone I had had no problems. I measured the output voltage as an open circuit at 1.3V.

ph2t.

[ph2t]

Nah man, they only have one FET in each. The pins on the SO-8 package double/quad up for current flow.

See there is only one Gate pin.

Micro, when you measured the output voltage from the RX chip on these clones was that as an open circuit? If the measurment was taken in circuit you might find that it is 0.7 volts because that’s the potential of the P-N junction from Base to Emitter of the NPN transistor. The Lxx clone I had had no problems. I measured the output voltage as an open circuit at 1.3V.

ph2t.

[micro_Amps]

Nah, it was in circuit at the time.:sad:

uA

Edited by – micro_Amps on 16 June 2003 22:36:09

[micro_Amps]

Nah, it was in circuit at the time.:sad:

uA

Edited by – micro_Amps on 16 June 2003 22:36:09

[ph2t]

Bugger, I might have to go back to the drawing boards then…. Idealy I’d like to be able to do this mod without having to remove the transistors BUT move the motor off the circuit on the RX board onto the seperate FET h-bridge board…. And also with a super low Rds value FET.

[ph2t]

Bugger, I might have to go back to the drawing boards then…. Idealy I’d like to be able to do this mod without having to remove the transistors BUT move the motor off the circuit on the RX board onto the seperate FET h-bridge board…. And also with a super low Rds value FET.

[ph2t]

Found some interesting articles about motor drive theory. Worth the read.

HERE

and

HERE

ph2t.

[ph2t]

Found some interesting articles about motor drive theory. Worth the read.

HERE

and

HERE

ph2t.

[jamiekulhanek]

Just a Q, how much can those fets handle?

[jamiekulhanek]

Just a Q, how much can those fets handle?

[ph2t]

Which FETS?

The datasheets of all the FETs Micro and I have used are linked in this thread…..

:smiley2:

ph2t.

Edited by – ph2t on 17 June 2003 11:06:25

[ph2t]

Which FETS?

The datasheets of all the FETs Micro and I have used are linked in this thread…..

:smiley2:

ph2t.

Edited by – ph2t on 17 June 2003 11:06:25

[ph2t]

Poppin wheelies with a 3.0, nice!:p

More video:

TOMY 2.2 Motor & softs.

Perfection 3.0 Motor & softs.

ph2t.

Edited by – ph2t on 18 June 2003 10:22:12

[jamiekulhanek]

NICE!

[ph2t]

Hey Micro, check this out.

If you apply 1-2V to the gate of the irlml2502 FET, you are getting about 0.045 Ohms resistance. If you apply about 4V to the gate you can get this resistance down to about 0.03 Ohms. That’s why I use the 5V DC converter in my design, to really “turn on” the FET. Whilst the FET is in circuit I suggest you take some voltage readings at the gate and see what you’re getting. Let me know.

Cheers,

ph2t.

[SurfmyStrat]

ooooooooo, wheelie… doesnt seem like it takes a lot of speed to do it either. Nice torque, ones i had a stock clone that popped wheelies, broke though

[ph2t]

If you’re just looking at the animated GIF then it plays back slower than the real thing. View the AVI’s, they show it at the correct speed.

ph2t.

[jamiekulhanek]

Interesting about using the 5 volt DC-DC converter, looks like your fets could handle quite a few amps before they self-destruct.

[ph2t]

Yeah, the truth is in the testing.

ph2t.

[micro_Amps]

I’ll take some readings ph2t, and I’ll post them here. The graph shows the fet running 4 amps tho, so I would imagine the actual resistance would be slightly lower because in this graph it would include additional thermal resistance. At 4A they would be running so hot you couldnt touch them.
Still, there’s almost no difference between 0.040 ohms and 0.030 ohms accross a fet. Certainly not a measurable one anyway. I would imagine the average solder joint has a similar resistance to this.
For all practical purposes, there is a dead short accros the fet when it is turned on, differentiating between +/- 10 milliohms is surely splitting hairs.
But I will get some gate voltages, and post them.
:)uA

[ph2t]

Quote:

…….is surely splitting hairs.
:)uA

But that’s half the fun mate!

[micro_Amps]

Is it just my computer, or has the wheelie vid (above) sped up in the last couple of hours/days?
:)uA

[ph2t]

Quote:

Is it just my computer, or has the wheelie vid (above) sped up in the last couple of hours/days?
:)uA

It’s those beers you’ve been drinking……:p

[micro_Amps]

hehehe, probably right.
I think it has something to do with my poor overworked computer having 10 explorer windows open at the same time. The vid runs quick when I only have the one window open.
:)uA

[TallduDe]

just wondering

i got a car with pull back rims on the rear axel the traction it has now is very good. it can cope with the huge amount of speed generated by this mod, would pullback rims on the front improve steering aswell or are the tires tooo sticky and all it will do will make the car flip????

any advice would be great i just want to know before i start chopping up the front rims on my BCG. :smiley2:

[ph2t]

I have floorboards at home and the more sticky the rear and front tyres are the better the handling. I’ve noticed that having med -> hard tyres on the front just causes a lot of over steer….

[micro_Amps]

Talldude the pullback wheel mod is a good one, it makes the car sit lower and handles well on a grippy surface. I find the tyres a little too hard for the fast cars though. The rears need to be sticky or the car slides out all the time. For the fronts, I use medium to hards, I find softs grip to much and the car flips. (Its horses for coarses though, see ph2ts post above) Depends on the surface you are driving on.
Do the front wheel mod, it makes the car lower and has a good look to it, dont forget the little extra bits you have to add on the front axel pins.
:)uA

[TallduDe]

guess i wont know to i try it aye :smiley2:

when i get around to doing the mod i will tell the results.

but the pullback rears work real well for my bit before on my tiles all the car use to do was spin out on full boost now it drive straight but with hard tires on the front it kinda has bigger turning circles.

i really have to try the front wheel mod if acar is lower it always handles better i say.

[Weapon]

if you guys dont mind me asking what site or what shop did u get these mosfets from?

[oldtamiyaphile]

The pullback wheel mod is going to be even better now that you’ll be able to get different compunds courtesy the SBCG.

[TallduDe]

diffrent compounds??????

are they avaible now???

and. what compounds????

[ph2t]

yeah otp, spill……

ph2t.

[jamiekulhanek]

Yeah i found the pullback mod to be a bit of a disappointment.

OTP what do you mean when u said

“The pullback wheel mod is going to be even better now that you’ll be able to get different compunds courtesy the SBCG.”

[Weapon]

hey just a question, do u think the pcb/motor will die if i did a tri-cell mosfet mod on a bit? im trying to make a bit drag and this mod will just be awesome 😀

[oldtamiyaphile]

The Pullback mod is great because it gets the car sitting a lot lower and gets rid of the monster truck look. It also make the car wider and less likely to flip. The latest Tomys already have pullback rims, and they look a lot better than the chrome eight spoke jellybeans.

It’s hard to imagine Tomy won’t release a new tyre set with different compounds (hard, med, soft) for the Super BCG, which so far has been the only drawback of the pullback rims.

Weapon , the faster the motor spins the faster it will wear out. Simply the price you pay for more fun. The PCB (even stock) is fine up to 4 cells/5v. Just so you know, such a set up should get you into 25km/h (~16mph) teritory 😯

[micro_Amps]

Weapon, yes the fet mod will easily handle a tricell mod. It is seriously fast.
A tricell fet mod hits over 28km/h :shock::shock::shock:
Yeh I know, crazy, but true. Hard to control but DAMN fast. I havent tried a 4 cell fet mod yet.
Motors last ok, so long as you dont run them for long runs on a running treadmill or the like, and you let them cool down after runs. They do tend to get hot.
:)uA

[jamiekulhanek]

I rekon a bit with smoke pouring out the back would look saweeet.

[leonli17]

Jamie. use the smoke fountains.. put one in the back and press forward.(don’t do it indoors)

Micro_Amps have u done a MOSFET on a clone yet? And where did u get those MOSFET from? in Melbourne? or on the internet?

[micro_Amps]

Yes leonli17, I have fet modded several different types of clones for people. Including, shen qui wes, precious, zipzaps, hummers, Lxx boosters, and of course MS pros, and Tomy standard & booster machine sets.I can do all of them now, I’ve worked out the circuits and can alter the mod to suit any differences on the pcbs. 100% success rate so far.
Once modded, all have the same amazing results.:approve:

The fets are available at many places, RS components (AU), Conrads (DE), Digikey (USA).
All of these places sell on the net too.
Hope this helps.
:)uA

Edited by – micro_Amps on 07 July 2003 16:56:42

[leonli17]

yeah it really helps micro_Amps. thankx…. Have u done one on a Bit Char-A? or the HSV RC car?

[leonli17]

one more thing what type of MOSFETs r they? like which model?

[micro_Amps]

Leinli17 the fets are stated in all the different threads around on the net they are IRLML2502s.
I havent done a Char-A yet but I’d like to, I read good things about them. They should perform well.
I have bought the Monaro, as well as the HRT holden, havent fet modded them yet, but they will be going real fast when I do….one day.

:)uA

[barto_85]

After several days of reading this topic and not understanding it a hell of a lot, I got my fet modded car back from micro_Amps. It is very quick, its wheels spin taking off and doesn’t reverse straight away because there is so much power. It also does great donuts. havn’t tried it on carpet or hill climbing but have been told it can do these. Definitely worth getting done.

Edited by – barto_85 on 11 July 2003 18:11:36

[oldtamiyaphile]

Char-A’s are also known as Leyu Precious, chances are you’ve done one of those.

[TallduDe]

ok i was impressed by the first lot of cars i sent off to micro so i sent off a couple more……….

second time around they are the bomb!

the lxx booster i sent him now flys. off boost it has alot of power now and on boost well it flys.

and the tomy BCG i sent him with his new and improved method of fixing fets on is now a killar machine.
it has almost tooo much power but hay thats y its so much fun.

even on a race track on half boost with a 2.2 motor both cars have enuff torque to climb any lttle hills or bridges.

now all my cars are even more fun to race around with :D:D

[Crom]

(I know this maybe a little late, but I’ve been away for a while)

Wow! uA you’re amazing! Even though you didn’t develop this mod yourself, kudos to you for being nice enough to offer it to all the rest of us without the skills to do it ourselves!

Keep up the great work uA!

[Admin]

ph2t,

I am trying to follow what you did with the NTMS7N03R2 chips, but it appears the site you hosted the images on no longer exists. Could you please re-post them or e-mail me the pics. I would very much appreciate it. I just got some of these chips in the mail today…

Thanks so much!

Quote:

I wanted to find a FET that had an even lower Rds value than the FET made popular by this mod. The IRLML2502 has a typical value of 0.045 Ohms. I found this FET NTMS7N03R2 with a typical value of 0.023 Ohms. Half the Rds of the normal FET used!!! Cool! (In a very sad freakazoid sorta way…).

The package these NTMS7N03R2 is different to the ones normally used. So different in fact I’m gonna have to make a new PCB for ’em.

The FET is that little black package, I put a steering knuckle next to it to give you guys an idea of its size. On the right is the prototype track layout for the PCB.

Cause I don’t have the tools I’m gonna have to draw the track work onto the virgin copper PCB using a special reistive pen.

Now I let it dry for a few minutes then I put the PCB in some etching solution (basically an acid). After about 7 minutes all the uncovered copper is eaten away and I’m left with this:

Now to solder those FETs on.

Putting the FET board on the car

Now that the FET PCB is ready I need to connect it to the car. The car I’ve chosen to mod is an Lxx booster, the auto modellista one. First I’ve ripped the old transistors out and circled the area where I need to connect the FETs to in yellow.

After connecting the steering wires to the transistor pads circled above I then connected the FET PCB to the power terminals on the car PCB and then I removed the wires to the motor from the car and attached them to the FET PCB.

So the power wires go to the FET board, the steering wires (from the transistor pads, not the actual fine steering wires!) go to the FET PCB, BUT the motor is wired straight to the FET PCB.

That’s it. The only bugger is making the custom PCB, but I guess I could get the parts to do this fabrication using the PC instead of hand drawing it…..

I will post video of my testing ’cause I want to see how my own version of ths mod performs against the original German one. Just quickly I put the Lxx car on a cushion on my couch which is on an angle of about 50-60 degress. In un-boosted mode the car stood still and didn’t roll back. In boosted mode the @#$%^ acutally climbed the bloody cushion. More tests to follow.

ph2t.

Edited by – ph2t on 14 June 2003 10:49:09

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