Remote Controls 27MHz

[clarion]

The Little Duck has been given a second hand remote control car, which he is happy to play with as a car by itself, but we wondered if we might be able to replace the missing controls.  Is it possible to just buy any remote working on the same frequency, or does it need to be the same brand (seems to be a fairly anonymous Chinese brand)?

I know there are some R/Cers among our number, so any advice would be welcome.

[Kim]

At the end of the 80s, in accordance with parental "siblings must get matching presents in order to promote harmony and disappointment" policy, my brother and both I had 27MHz radio control cars.  These were actually an awesome present (any child of the 80s knows that "remote control" => disappointing wire), and I'm sure we'd have had good fun racing them, if it weren't for the fact that they responded to each other's controls, with the directions reversed.

Stands to reason that while the frequencies of such things are standardised by the relevant regulations, the encoding scheme is going to be fairly arbitrary.  I expect that the electronics are a lot more integrated than they were in the 80s, and there's more chance of them using the same an off the shelf radio chipset, but even if you tore down the car and were able to identify a corresponding transmitter chip, I'm not sure how that would map to tracking down a control unit.  If you could even buy one on its own.

(I'm assuming this is toy-grade stuff, rather than the sort of thing used by serious R/C enthusiasts, with modular receivers/servos/crystals and all that.)

[David Martin]

Typically they were 'forward straight, reverse and turn' very limited in terms of control. Good luck!

[Kim]

Typically they were 'forward straight, reverse and turn' very limited in terms of control. Good luck!

I'd forgotten about those.  How to make radio control disappointing.

[andytheflyer]

The Little Duck has been given a second hand remote control car, which he is happy to play with as a car by itself, but we wondered if we might be able to replace the missing controls.  Is it possible to just buy any remote working on the same frequency, or does it need to be the same brand (seems to be a fairly anonymous Chinese brand)?

I know there are some R/Cers among our number, so any advice would be welcome.

I'm not an RC car enthusiast, but I have flown RC aeroplanes for about 20 years.   AFAIK, there's little difference between RC for cars and RC for aeroplanes, other than that the aeroplanes may have more channels (all mine are 9 ch) and they work on different frequencies - by law.

A 27MHZ car transmitter should talk to any 27MHZ receiver - certainly the 35MHZ aircraft (i.e. helicopters and fixed wing) transmitters generally don't care which make of 35MHZ receiver they talk to - I use Futaba transmitters and a mixture of receivers.  There is a difference in receivers (certainly for aircraft) in that some are Pulse Code Modulation (PCM) and some are PPM (Pulse Position Modulation).  My Futaba transmitters are (digital) PCM, but they will talk to an analogue PPM receiver if set up properly.

Whatever you do, don't try to convert the car to 35 MHz - that's illegal. 27 Meg is for cars, and 35 Meg for aircraft.

If you don't know the make of the 27MHZ receiver in the car, take it along to a good model shop and they will almost certainly try it out with a 27MHZ tranny.  Presumably the car won't have more than 3 or 4 channels (steering, throttle, brakes maybe?) so a tranny will cost very little.  You could simply buy a cheap 27MHz tranny off EBay and try it - you might be lucky - but a good model shop may be better value in the end.

You may need crystals - within the 27 (and 35) meg band, there are individual channels - and the older kit uses a crystal to set the channel to be used between tranny and receiver.  If you buy a transmitter you need to know what channel the car's transmitter is set to.  Some RC kit actually sorts out its own channels (called multiplex) and does not use a crystal.  Again, the model shop will help you.   I fly £1000 models that rely on a £5 crystal - seems crazy in this digital world, but it was state of the art only 10 to 15 years ago - all the RC display model pilots did it that way, flying model jets worth £20k.  So, if you have a crystal receiver, you'll need to know what channel it's on.

The real cost is in the car batteries - if it's oldish, the batteries may be shot, as in they won't hold a charge.  They can easily be replaced, but batteries are not cheap, and you usually need at least a couple so you can use one and have the second charging.  That then means that you need a charger capable of fast charging - these tend to be fairly sophisticated and have software that maximises battery charge and life.  It can all get a bit expensive (which is why I didn't go down the environmentally-sensitive path a few years ago and convert to electric - I fly good old nitro!).  If you have LiPo (Lithium polymer) batteries in the car, you need to be very careful how these are charged - they are safe, but can be dangerous if mis-charged.  If it's a cheapish car the batteries will probably be NiCad or NiMH - and these are very safe.  The model shop will help you there.

But, if you can get to a good RC model shop I'd be surprised if you can't get it all working at not very much cost.  It then depends on how much you want to spend!  But be careful,  RC gets addictive - well aeroplanes certainly do......

[Kim]

I'm not an RC car enthusiast, but I have flown RC aeroplanes for about 20 years.   AFAIK, there's little difference between RC for cars and RC for aeroplanes, other than that the aeroplanes may have more channels (all mine are 9 ch) and they work on different frequencies - by law.

I'm assuming this is toy-grade stuff, rather than the sort of thing used by serious R/C enthusiasts, with modular receivers/servos/crystals and all that.

The difference, until quite recently, was that it was impossible to build an aircraft that was small and cheap enough not to have proper RC kit in it.  When its got a wingspan of a metre and a spinny blade of death (and optional finnicky combustion engine) on the front, and represents hours of loving work, you need proportional control and decent radio range.  A child's toy car that doesn't go fast enough to result in more than a stubbed toe can have simple forward/back left/right digital controls, and an operating range of 10 metres...


So, first question, is it a toy or a model?

[andytheflyer]

The difference, until quite recently, was that it was impossible to build an aircraft that was small and cheap enough not to have proper RC kit in it.  When its got a wingspan of a metre and a spinny blade of death (and optional finnicky combustion engine) on the front, and represents hours of loving work, you need proportional control and decent radio range.  A child's toy car that doesn't go fast enough to result in more than a stubbed toe can have simple forward/back left/right digital controls, and an operating range of 10 metres...

Finicky combustion engine?  You mean a proper engine - scale models need scale engines - lots of finely engineered aluminium and steel, lovingly put together, tuned and maintained.  Burning environmentally-disastrous  nitromethane, and chucking out horribly sticky burnt oil.  I suppose these modern bits of copper wire and ally, spinning quietly at high revs and running off rare earth elements plucked from some quarry in China, and charged from a solar panel somewhere on a sunny day have their place, but not in my scale twins!     But I'd have to agree with you: some days, I look wistfully at my club mates simply charging a battery and going flying, whilst I'm still trying to get the two engines to throttle up together.

And a wingspan of a metre - now that is a toy......!

Anyway, hopefully the OP will get Little Duck's car running.  And for Little Duck, the bug will bite and he/she will end up building his/her own scale models, and developing engineering and technical skills. And I wish he/she well.

[Kim]

My brother tried to get into RC aircraft at one point (mid 1990s).  He joined the local club and had a mostly-complete trainer plane with glow-plug engine and proper Futaba PCM radio kit and all that stuff (and ambitions for some more interesting models once he'd got a bit of practice).  But he lost interest (read: developed an overriding interest in MOTAS and alternative volatile substances) before it ever got off the ground, and in spite of having helped with much of the build, it was verboten for me to finish the job on general principle.  Bah!

Other than having used servos for a couple of roboticsy things, I'm completely out of touch with the field.


(Little Duck has just turned 4, hence my suspicions of the level of kit described in the OP.  He's got to start somewhere, of course...)

[TheLurker]

Veering wildly off-topic...

The difference, until quite recently, was that it was impossible to build an aircraft that was small and cheap enough not to have proper RC kit in it.  When its got a wingspan of a metre and a spinny blade of death (and optional finnicky combustion engine) on the front, and represents hours of loving work, you need proportional control and decent radio range.  A child's toy car that doesn't go fast enough to result in more than a stubbed toe can have simple forward/back left/right digital controls, and an operating range of 10 metres...

Naaah.  RC types were flying single channel RC with rubber driven escapements ("bang bang") until at least the early 1970s (which counts as recent-ish in my book) and probably for good few years after.  RC kit was horribly, horribly expensive, not like nowadays.   Only this morning I took (electronic) delivery of the plan for a 35" wingspan Aermacchi Lockheed Santa Maria; 0.8cc engine single channel with conquest escapement which was published in '68 and that's a conversion from a powered free flight model.  So you don't *need* this all this modern proportional RC nonsense to fly your metre wingspan aeroplane with spinny-deth attachment.     

If anyone else out there is interested in the Santa Maria plan send me a postal order for 3/6d and you can have a copy (JPG) , or just PM me and we can sort summat out.

[clarion]

A bit more inspection tells me that it is an MJX R/C, and I am pleased to see that company has a reasonable online presence.  The car is a Mercedes model (driver Schneider), copyright 2005.

The battery looks essentially like six AA batteries wrapped together, with a 7.2v output

[trekker12]

I have some experience racing R/C cars although it was more than 15 years ago.

Essentially Andytheflyer is right. Most reasonably advanced R/C cars should have a removable crystal (looked a bit like a car fuse) so that one can be changed for another. With six cars racing at any one time the risk of interfering frequencies was quite high so strict rules were put in place and you had a colour code so everyone knew what colours were in use on the track at that time.

27MHZ is the main frequency and you will have a range either side of that to allow users to operate different channels at once.

Other than that any controller will work with any car so long as you match the crystals.

The batteries used to be 7.2V Ni-cad batteries, they are/were in my day packs of six soldered and taped together with a standard plug that connected through a digital controller/receiver* velcroed into the car, which then diverted power to the motor and a steering servo. We would need about 4 battery packs for a race meeting (you would get away with two but it was easier with four). A 12V leisure battery (the type caravanners use) would power a battery charger and would be enough for a days racing.

Six AA batteries sounds a lot smaller than the packs of 7.2v NiCads we used to use so things seem to have changed - not surprisingly.

Races lasted 4 minutes and the car with the most laps was declared the winner so that gives an idea of battery life. You would have heats, semi finals and finals and there were a variety of classes.

I raced in the 'stock' motor class. There was then a faster (and more expensive) class for 'modified' motors - I never really worked out the difference except one was faster than the other. I could get 6-7 minutes from the batteries on stock but all racing was limited to four so the modifieds could get to the end of a race with the same battery packs.

You would then have a tool that essentially drained the battery back to zero so you could recharge it from there. NiCads are cheaper than Li-ion to buy but quite sensitive to abuse, recharging continuously without discharging each time would kill them quite quickly. In your case running the car in the garden until it's dead isn't a problem. At a race meeting as soon as you switched your car and controller off, someone else would be allocated your channel for the next race so you had to discharge the battery without running the car.

Although having written all that I go back to Kim's question, is it a toy or a model? Work firewalls prevent me from looking it up but I suspect it's not the model/racing type I refer to above.


*There was a more basic type that worked on an analogue controller and had two servos, one for power and one for steering but they were out of date when I was racing so I suspect no longer seen anywhere.

[Tim Hall]

Little Duck has just turned 4,

How did that happen? Where did that time go?

[Kim]

Little Duck has just turned 4,

How did that happen?

The usual way.  With CAKE.   

[Wombat]

27MHz is such old hat, and rather poor, that the only source of such things is likely to be cheapo toys.  It is liable to interference by just about anything, including in my case by a greenhouse in the garden.  I've done land based models for many years, and they evolved from 27MHz to 40 MHz FM, and now, like everything else in the universe, to 2.4GHz, which is many orders of magnitude better in every conceivable way. 

Old 27MHz transmitter and receivers did indeed have replaceable crystals, but I suspect the cheapo toys had Tx and Rx with a choice of two crystals built into their circuitry.  Typically you often got two cars with different frequencies, but if you were unlucky, they might have had the same one...

Hunting about the car boot or market stalls seems about the best hope to me, and be prepared to get the wrong frequency a time or two!

[DuncanM]

There are loads of 27MHz controllers on eBay, but they will be the type that are used with crystals (it's interesting how retro R/C cars are a thing now).  If your car doesn't have a crystal to control what specific frequency around 27MHz it uses, then finding the right controller is likely to be a pain.
Modern batteries cost the same in £ as they did when I was racing them 25 years ago, and have twice the capacity, so that's definitely a good thing. My nephew has a new 2.4GHz monster truck - I want to put it side-by-side with my old Manta Ray and see how well they compare.

[Jakob]

Almost everything today is 2.4ghz. Longer range stuff will be 433 or 900mhz.  I use 2.4ghz (frsky) on my fun planes/drones and 433mhz on my 'serious' UAVs.