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Old Dec 21, 2002, 02:48 AM
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I pulled a 7805 out of an old commodore 64 and replaced the small one. I added the caps and now have 4.96 V on the output.
Range is still about 40 ft. I'll have to mess around with the antenna now. Do you think a half wave wrapped on a stick would work? My radio is 57MHz I think a half wave is 8.1 feet for that frequency.
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Old Dec 21, 2002, 10:35 AM
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Quote:
Do you think a half wave wrapped on a stick would work?
There is no need for 1/2 wave. A 1/4 wave whip will work just as well (4.1 feet). Do NOT wrap it on a stick or do anything else to reduce its physical length by coiling it up -- that defeats the purpose you are after.

With the 1/4 wave aerial and a change in the antenna inductor's (base load) value, you should get another 5-6dB of signal. That will only get you to about 80 feet or so after the dust settles.

I am trying to understand why your range is so short. Questions:

(1) On the stock model (no mods, fresh out of the box), what was the observed range of the car? If it was under 12 feet, I suspect a cripple cap is in the Tx. There is a chance that it is there and is not obvious.

(2) The Rx must be updated too. Have you done the Rx antenna length extension and coil adjustment as described on the web page? Are you sure you tweaked the coil for best stability?

RC-CAM
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Old Dec 21, 2002, 10:37 AM
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FYI folks,

I see that Tomy has been advertising the new Turbo feature (Rev C chip related). Look for the BitChar-G's that are called "Booster Machines."

RC-CAM
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Old Dec 21, 2002, 03:50 PM
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The stock distance was 25-30 feet.
I still have stock antenna on rx and tx.
I havent adjusted coils yet.
I will do so later and change the length of the antennae.
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Old Dec 21, 2002, 04:11 PM
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On a stock 3V powered Tx with a 25-30' range, the 9V battery modification should have resulted in a +10dB to +11dB RF power gain. That alone should have boosted range to about 100'.

Perhaps others will try the 9V mod and report what they get. Hopefully most clone cars will react with a more impressive range like I achieved.

RC-CAM
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Old Dec 21, 2002, 08:21 PM
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Mr.RC-cam,

Might want to try 50 MAH cells, 150s seem way to heavy for an n-20 controlled ship.

That might make it fly better, no?

Paul
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Old Dec 21, 2002, 10:36 PM
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Quote:
Might want to try 50 MAH cells, 150s seem way to heavy for an n-20 controlled ship.
Yes, lighter cells would be the right thing to do. All I had were some 150mAH NiCD's and 150NiMH's.

RC-CAM
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Old Dec 22, 2002, 04:20 AM
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the 150 nimh should be fine. I recently constructed a 120mah nimh pack and the 120mah nimh wieghed 3.3g each as opposed to the 50mah nicad which tipped the scales at 4g each. Using the nimh saved .7gram per cell.
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Old Dec 22, 2002, 04:25 AM
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BTW Robbie these micro cars are available for AU$15 at Cheap As Chips. Bargain!! Friday after Christmas (payday ) I'm going to grab a few.
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Old Dec 22, 2002, 05:51 AM
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That alone should have boosted range to about 100'.

oops!

I just went outside with a tape measure I was guestimating the 40 ft. It's actually 80 ft' measured with a tape measure. I was going by the size of the road and guessing from that and the size of the yard - where I tested was a diagonal accross the road and yard so it goes to show not to guess on diastance.

Thanks RC-CAM for a great mod.

PS I was talking to my old electronics instructor today and he
read out of the voltage regulator book that about 10 years ago
the lm7805 was modified so that capacitors are not needed.
That is if the regulator is less than 2 inches away from the power supply ripple filter. In our case there is no ripple because we are powering the tx with batteries instead of rectified filtered ac.
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Old Dec 22, 2002, 11:18 AM
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Quote:
It's actually 80 ft' measured with a tape measure.
That is great news.

Quote:
PS I was talking to my old electronics instructor today and he read out of the voltage regulator book that about 10 years ago the lm7805 was modified so that capacitors are not needed.
Besides the two caps use to improve ripple rejection, they also ensure device stability. When the Vreg is close to a low impedance source voltage you can eliminate the input cap. But NEVER should you skip the output decoupling cap. Reliable designs always include both.

RC-CAM
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Old Dec 22, 2002, 12:05 PM
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they also ensure device stability

cool

Since my 7805 came from a commodoore 64 I would need
the input cap anyways.

here are some pics of the modifications.

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Old Dec 22, 2002, 02:35 PM
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Change Frequencies

Dear Mr. RC-CAM,

You seem to have knowledge on the RX' fine tuning. On our last Indoor Meet, I sold 6 of the cars I bought at eBay, and maybe we soon have a real frequency problem...

I replaced a 40 MHz transmitter's crystal with a 33 MHz type and tried to tune the new signal in at the reciever's coil, unfortunately not with a suited tool, so I broke this ferrite core.

Before I do further Microsizer sacrifying : Would you say that it is in general possible to do this 7 MHz step with the RX coil ?

So long,

Patrick
Team Klaustrophobia
www.unisport.tu-bs.de/~modellflug
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Old Dec 22, 2002, 02:48 PM
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Quote:
Would you say that it is in general possible to do this 7-MHz step with the RX coil?
Probably not. Other component changes would normally be required.

And there is still a good chance that the 35Mhz Tx's would interfere with your 33Mhz Rx. These Rx's are SuperRegen designs -- they have poor RF selectivity. But, if you reduced Tx power you might be able to share the airwaves with the neighboring frequency.

Lastly, the car would probably be illegal to operate in just about every part of the world.

Regards,
Mr. RC-CAM
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Old Dec 22, 2002, 03:03 PM
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Other ways to change frequencies ?

This is nice to get answers *this* quick...

You said that one would have to change other parts. Is this a easier work or would I have to redesign a complete section ?

The 35 MHz car would be a great Idea, but I only have the 27 and 40 MHz ones...

About the legality point : I tried my transmitters with no bis modification and they have only some 40 metres range, so I don't care about haveing an illegal frequency. In addition to this : I am aiming for a sub-once plane that would only be flown indoors anyway.

So long,

Patrick
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