I acquired a 72M 4 channel R/C helicopter with transmitter, batteries, receiver, etc.
Can this type of electronics be adapted to power and run trains?
In theory, yes.
In practice, no.
72 MHz is illegal for ground use. Plus it is very susceptible to RFI.
Only 2.4 GHz stuff is reliable enough not to have to muck around suppressing motor “noise” to let the R/C work properly.
You will need an ESC that can handle somewhere between 12-24 volts to actually run the locos.
Trying to use cheap R/C stuff hacked out of cars, etc is kind of what got me into the business of making battery powered control systems dedicated for use with trains. Yes, the hack may work, but what you end up with is usually less than desirable. Buying equipment designed for use with trains, will result in much more satisfaction in the long run.
If the helio transmitter accepts a 2.4 GhZ crystal would it be useful for train use?
A 4 channel 72 MHz system cannot usually be converted to 2.4 GHz simply by changing crystals.
They are totally different.
Okay, thanks Tony and Del. Here I thought I made a big score. Even the batteries are only 5 AA size. I will likely settle for getting it flight worthy again.
…and to rub it in, you can buy a really good quality 5 channel 2.4 GHz TX and RX for less than US$50 delivered to your door. Extra RX’s are around US$15 each. 
TonyWalsham said:Rubbing a little salt to the wound, eh? I did get the helio in trade for a little bit of electrician work, so even as a toy, I am happy.
.....and to rub it in, you can buy a really good quality 5 channel 2.4 GHz TX and RX for less than US$50 delivered to your door. Extra RX's are around US$15 each. ;)
I honestly do not understand why the 72 meter frequency could not be used. Where I may have a problem is with the motor control not having sufficient mA rating for the loco motor. I dunno??
The cost of the RX/TX are inexpensive enough. What about the batteries?
A. 72 MHz is an air frequency and it is illegal to use it for ground control models.
B. 72 MHz is very susceptible to RFI which will cause the dreaded “glitches” and end up destroying loco gear boxes.
C. Whilst the supplied ESC in the Heli may be able to handle the amps needed, it cannot handle the higher voltage for powering Large Scale locos.
As well as the Tx and Rx you will need an ESC to actually control the speed/direction and any sound triggers plus the actual batteries to power the loco. What is best for your situation depends on the particular loco and what you want to do with it.
To add to Tony’s reply my standard answer to folks at the hobby shop who wanted to do what you propose was that they could imagine them selves runnign their relatively slow adn safe ground model ona na aircraft frequency with someone else running a several thousand dollar highly detailed and FAST model airplane and when you switched on your radio to ahve it crash. Oh that’s not so bad they’d say. Ok I’d add in, what if it crashed into your house full of nitro fuel? Burned it down with your family in it? How would you feel then? Ok the likely hood of it causing a catastrophic fire is slim but…it got the point across to the customers at the hobby shop who were…“un-educated”. David I KNOW you know better.
Chas
I guess I should learn how to fly the helio and leave the trains on track power for now. sigh
And heli flying is another ball o wax…what kind of heli did you get?
It is a small model Excel Falcon 40, 4 channel single rotary wing with separate tail rotor motor. I had it hovering once, but I don’t know if something is not right with it or the operator. I try to trim it according to the OM but …
I’ll next practice the “scooting” method before I attempt tail in flight.