ph2t

[ph2t]

The bigger daul gang ones. Try a lower value I guess, pick, use your skillz man..:D

Centre the dual gang pot first, then adjust the trimmer pots till you get no signal for either fwd or rev. Then move the dual gang pot each way and see the results. Adjust the trimmers then as required.

[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]

Yeah it’s funny man, I got a similar response when I built it on veroboard. But on the bread board prototype it was OK. Try low values of the pots and see what that gives…. I haven’t changed any thing on the circuit. This is where I hit a brick wall as well. One day I’ll pull my finger out of my arse and continue with this mod……..

[ph2t]

Yeah it’s funny man, I got a similar response when I built it on veroboard. But on the bread board prototype it was OK. Try low values of the pots and see what that gives…. I haven’t changed any thing on the circuit. This is where I hit a brick wall as well. One day I’ll pull my finger out of my arse and continue with this mod……..

[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.

[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]

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.

[ph2t]

The Pro and Kings are marketed differnetly on the toyest website. What’s their torque like?

[ph2t]

The Pro and Kings are marketed differnetly on the toyest website. What’s their torque like?

[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.

[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

[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.

[ph2t]

That’s fer sure…..

[ph2t]

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

ph2t.

[ph2t]

See my video post above, I’ve just posted the movie in MPEG format…. I’m such a nice guy…..:approve:

[ph2t]

By Monday U.S time they *should* announce the winner.

[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]

It’s the blue thing with white stripes. It’s called a DIP switch. I believe each switch would turn on/off each crystal seperately.

[ph2t]

Micro, check you PM’s.:approve:

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