S.R.M (Super Range Mod)

[ph2t]

Hey everyone. Like most of you who own Microsizers I’m sick of the crappy range these things get. So I thought I’d try a few things out to improve this. First thing I tried was the telescopic antenna mod. No luck, range was still crap. I looked for the infamous “cripple capacitor”, didn’t find one (to be honest I didn’t look too hard).

Sooooo, I thought I’d do what I do best and is mod the beast!.
After a fair bit of research I found that you could isolate the power to the TX2 chip on the controller whilst upping the power to the RF amp to increase range. For added functionality I isolated the charging circuit as well back down to 3 volts so I wouldn’t blow my nice new RX-7 Microsizer.

From the datasheet for the TX2/RX2 chipset the maximum voltage that the chip in the transmitter can handle is 5V. So I isolated this using a 78L05 (L for low power) voltage regulator to stop it from blowing up when putting 9V to it!

This is all theory at the moment. I hope to build this on the weekend so I will provide pics and posibly video to backup my findings.

For now though here is my circuit which is the original TOMY circuit modified as explained above.

Cheers,

ph2t.

Edited by – ph2t on 10 April 2003 13:48:49

[micro_Amps]

Ph2t, I have tried essentially the same thing with average results. Let us know how you go tho.
I was running the Tx chip on 3v and the RF tx cct on 6v with no obvious change to range…go figure!
The biggest changes to range I have found is removing the cripple cap on the Rx pcb, changing the Rx aerial for a fine piano wire about 125mm long and retuning the vari-inductor on the car pcb. This got me about about 8 meters indoors and about 20 outdoors on a 27Mhz single speed twin cell bit. Also I noticed that holding the car up off the groud increases range by heaps. Not that it means anything for car enthusiasts but if you were to put the R/C gear into a plane the range is potentially 50+ meters.
Running the chip on 5V may produce a higher output signal if the output codes are switched from 0v to Vcc. I’d be interested to see your results.
uA 🙂

[SurfmyStrat]

u should write a book, how to mod your Tomy for dummies, written and copywrited by ph2t. (can i get a free copy?)

27 MHz Mitsubishi
other cars in parts

[ekwj]

LoL.. a copy for me too

The sky is the limit! |ekR34| http://www.ekr34.tk

[ph2t]

Well, I’ve done the mod and didn’t get the best results. Before the mod my RX7 MS got a crapy 3-4m range. Now I get about 8m, which is not bad but not what I was expecting.:evil:

See the pic below for the mod. I had to remove pin 9 on the TX chip from the pcb to be able to isolate the power from the rest of the board. This was a bit dodgy but it worked.

Here is a (fuzzy) closeup of the mod. I haven’t implemented the charger side of the circuit just the reduced 5V rail to the TX chip. I think I blew the Zener diode, during testing it wasn’t dropping the voltage by 6V as it was meant to.

Whilst I was at it I removed the stock antenna and replaced it with some fine enamled wire that was spiraled twice over. This added about 2 meters to the range. The wire in the pic is moving when I took the photos so it looks like two wires instead of one.:)

Back to the drawing board…………..

ph2t.

Edited by – Shypo on 15 April 2003 22:53:56

[Efarel]

Hi Ph2t,
greetings from Italy !

Speaking about your experiment let me give another point of view…

You are disappointed about your results because you are trying to obtain max range.

BUT I race on my track only so I don’t need extreme range… a stronger signal up to 5 meters means less interference and a more responsive car.

I made some experiment with 4,5 and 6 volts and I can assure you that interference are drastically reduced and cars are smoother !

So, another time, GO ON !!!
I think it is time to set up a little web site with your precious works, ideas and work in progress !

Another point of view… with this mod I can use my normal NiCd 1/10 7,2V battery pack to power my controllers, I don’t need a lot of AAA batteries but a single 7,2V racing pack, one pack one quick charge and no more battery problems !

GO !:smiley2:

Ciao
Efarel

[ph2t]

Hey Efarel, you make some good points, but I still wanna get as much as I can out of this as possible.:)

Hey Micro, where is the cripple cap on the RX board? This news to me?:shock:

ph2t.

[micro_Amps]

Yeh there is. Alot has been written about it, I think QFM has a fairly straight forward instruction to remove it. It is an smt cap and doesnt always make a huge difference. If you remove it be sure to retune the vari-inductance to get maximum effect.
:)uA

Edited by – Shypo on 15 April 2003 22:52:20

[micro_Amps]

Hey ph2t, I have a theory that the range increase you experienced was only because of the Vcc increase (from 3v to 5v) on the chip, and not due to the Vcc increase on the Rf cct. Any chance you can test this while you have a test rig going. I’m strung a bit for time, its either forums or play or electronics, and at the moment its forums.
:)uA

[ph2t]

So far I’m at 9 meters (27ft) without re-tuning the variable inductor. I will do this tomorrow. I’ve managed to put everything back into the MS controller (quite happy with myself):D:D
The batt compartment doesn’t fit the 9v batt very well even after getting rid of excess plastic.
At least with this setup I could charge a daul batt combo without too much difficulty. I’ve lost the timer function though, it was too tricky to isolate the charger circuit from the rest of the circuit because the PCB I have is newer than the schematic I’ve based my design on. EG: The timer circuit uses a LM293 Comparator chip, whilst the original schematic uses a transistor based timer instead. (Thanks for the heads up on that one uA:))

ph2t.

[ph2t]

uA, I was writing my previous response as you posted yours, so I missed that in my reply.

I will test this for you no sweats. Gotta crash now though, got an early start tomorrow.

Cheers,

ph2t.

[ph2t]

Quote:

Back to the drawing board…………..

ph2t.

Edited by – Shypo on 15 April 2003 22:53:56

I wonder what Shypo edited in my post?:question:

[z-beam]

“with great power comes great responsibility”

[ph2t]

Micro, put the Vcc to the TX chip back down to 3V. No difference. Range is still the same.
I also removed the crip cap from the Car’s PCB and got an extra meter.

So I’m now at 9 meters……….

Gotta get me a better telescopic antenna to put on the controller, the telescopic I’ve got i ripped from one of the clones.

Does anyone know where I can buy these from? (too lazy at tha ‘mo to check my usual haunts…:smiley16:)

ph2t.

[ph2t]

I found this circuit on the net.

This is an RF power amplifier that can be built out of stock parts. I”ll need to do some calculations on the LC networks to confirm the operating freq of this amp. I believe it’s set around the 27MHz range since I got this from a microflight site. Here is the site with more info here.

Ph2t.

[micro_Amps]

OK so the TX2C vcc makes no diference, now we know for sure, thanks for doing that.

I think the guys at Bitchargoz have the aerials, see the for sale section for their address

Re the rf amp cct, can you sub the values in from the BCG Tx. The cct is close to the one that exists in the controller in the first place.
uA

[Efarel]

Ciao !

ok you demonstated that Vcc adds no meters to our beloved Tx, but do a higher Vcc produce a stronger signal ?

Thank you
Efarel

[ph2t]

Yes it *should* but I think you need to re-tune the coupling capacitor and inductor that connects to the ariel.

ph2t.

[Prabbit]

ph2, I’ve added a frequency amplifier to my controller similar to the second schematic you have posted here. It seemed to help a little but not much. Is was a lot of work for little results. I noticed it seemed to make other bits in the area on different freqs jump a little bit. The best mod I’ve done for range is remove the cripple cap, add a cat5 aerial on the car and a long telescoping aerial on the controller.

I’m at 34 feet (11 meters)
-Peter

[Prabbit]

Oh, yeah. I also noticed a longer range once I did the dual cell mod on the car.

-Peter

[micro_Amps]

That is actually the biggest difference I have noticed. My dual cell with a piano wire whip aerial has the longest range of all my bits.
I suppose I need to maesure it properly.
uA

[Author]

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