Large Scale Central

R/C install finished...BUT

Electronics Power and Sound
#1

I finished the installation of an R/C system scavenged from a model helicopter (4 channel now 2ch, 72.4 mHz) on an Accucraft Forney live steam locomotive. The linkages all work fine, the servos work well but the TX/RX works erratically.

During the installation, I constantly tested everything for fit and operation. Once I had everything seeming to operate smoothly, I replaced the bunker and fired up the boiler to preform a static test run.

For the first few seconds, everything ran fine, then I lost control of the two servos. They jumped around as if possessed and would not respond to the controls. I originally wrapped the antenna around the bunker, careful not to cross the previous loop, but even after unwinding the antenna wire and extending the TX antenna the controls only worked sporadically.

I charged the battery (8.4 VDC 650 maH) checked the connections and removed the RX from the brass bunker next to the battery. Short of replacing the TX/RX with new units (2.4 GHz) I am stumped for a fix to this problem.

Any suggestions?

#2

Being a BIG R/C aircraft guy I have run into this a few times over the years. At least if a train acts up it likely won’t crash into someone!

Start by removing all but one servo from the receiver…Move the servo lead from channel to channel and see if it reacts the same. Do this with each servo.

I had one of my planes act up like this just a week ago…Turned out to be one servo lost it’s “center”. Lucky it happened on the ground.

If all channels act the same with both servos then you have a problem with the trans or receiver…likely best to chuck the old technology and move to 2.4Ghz.

#3

Oh, are you running the receiver off 8.4 VDC direct??? If so you likely fried it. Most R/C systems run on 4.8 to 6 VDC.

Edit: By “fried it” I meant possible damage to the servos or the receiver. Swap out both to see which is possibly affected.

#4

Unless you have a BEC fitted 8.4 volts will do damage.

#5

I really think going to 2.4 is the way to go. I “kludged” a similar set up using an old car radio but it was at best a work-around. The newer 2.4 systems are just so cheap these days.

#6

I used the same setup as was in the heli, battery plugged into the rx, the servos plugged into the rx. The difference is I rewired the potentiometers in the tx to control two servos instead of two servos and two motors.

Thanks Mark I will test the “one servo at a time” troubleshoot. I do have the j-bar servo failing to center itself 100% of the time, but even when I hold the j-bar forward and apply throttle it will act up.

I am STILL at a loss for the reason for the change in frequency (74mHz to 2.4 GHz). I am not concerned about transmitting 500 meters away, besides the longer 4 meter wave-length should carry farther than the 13cm anyway. FCC regulates interference so that should not be a problem. What am I missing here?

#7
David Hill said:
What am I missing here?
The big issue is ground plane interference. 27 and 72 bands lose a TON of their range if your track is on/near the ground. 2.4 doesnt seem to suffer from the same problem.
#8
Bob McCown said:
David Hill said:
What am I missing here?
The big issue is ground plane interference. 27 and 72 bands lose a TON of their range if your track is on/near the ground. 2.4 doesnt seem to suffer from the same problem.
Ahhaa! I could add some radials, right? :-)
#9

P.S. Will my existing servos plug into the 2.4 GHz stuff? What should I look for in a TX/RX?

I found this unit: http://www.hobbyking.com/hobbyking/store/_16239__HobbyKing_HK6DF_2_4Ghz_FHSS_6Ch_Tx_Rx_Mode_2.html

#10

Your servos will plug in just fine.
Even the low cost (Under US$50) 2.4 GHz systems have 6 channels. Choose a brand that also supplies extra receivers.
If you intend having more than one live steam model, a model memory system could be desirable. This is where an in the TX computer can be programmed for settings appropriate to different models.

There is no way adding various suppression techniques to RFI will cure on the ground “glitching” and “twitching” of servos.
That is one of the reasons why 2.4 GHz was invented.

#11

Thanks Tony! I didn’t consider the added RX for additional installations. One unit I looked at online, the TX and the RX only work with each other but it has a “bind plug” I suppose to lock in the settings. (??)

#12

Most, if not all, 2.4 Ghz R/C systems are proprietary. In that, RX’s will only work with the same brand.
Conversely, with most 2.4 GHz R/C systems, virtually every same brand RX can be bound to any TX via use of the binding plug or binding pushbutton on the RX.
That means you can have as many RX’s bound to one TX as you wish.
One brand that does not do that is Hobby King (and their myriad of re branded same systems). To make matters even more complicated with HK, they have different versions of the same basic systems.
I particularly like the Planet brand. Any RX they make will work with any of the TX’s. However, as far as I know Planet brand is not yet available in the USA. Planet may supply a re branded system in the USA, but, I have not been able to locate such systems.

Once upon a time any same frequency R/C system RX would work with any other brand of TX. Not any more. They are now all proprietary. Except of course for the servos. With the possibility of one or two exceptions, any brand of standard servos will all work with any brand of RX.

#13

Hey Tony - The Planet is now available in the USA.

http://www.hobby-lobby.com/planet_5_radio_2.4ghz_transmitter_1034249_prd1.htm?pSearchQueryId=1723867

#14

Thanks Del.

I was wondering how long it would take the USA market to latch on to such a great piece of gear.
The only criticism I have of the way Planet does binding is that you have to actually be able to touch the RX to bind it. That means binding “in situ” is a little more difficult than say Spektrum is. With SPEKTRUM (and Hobby King) you can add an externally mounted switch on a lead and bind SPEKTRUM RX’s without gaining access to the RX.
However the actual binding process of Planet is certainly one hand only.
Here we have a good range of different RX’s and soon will have the new 7 channel TX already available in the UK.

#15

I saw no 2 ch servo controller RX in your product list for my application though, only ESC and sound. I noticed the Planet TX. I may take your suggestion for one of those systems.

#16

Well, it seems I forgot all about Mr. Faraday and his electro-magnetism discovery. Once I removed the tape and separated the two servo cables, all works fine. DUH?!

#17

David, Here was here in Australia. Not here in my business. I do sell a variety of 2.4 GHz R/C systems for Australian customers only. It would not be economical for USA customers to buy RX’s from me.
I doubt you will find 2.4 Ghz 2 ch RX’s, you can probably only get 3 ch RX’s. They are so small nowadays most users select 5 or 6 ch RX’s as they are usually the least expensive.

#18
David Hill said:
For the first few seconds, everything ran fine, then I lost control of the two servos. They jumped around as if possessed and would not respond to the controls. I originally wrapped the antenna around the bunker, careful not to cross the previous loop, but even after unwinding the antenna wire and extending the TX antenna the controls only worked sporadically.

Any suggestions?


David,

A bit late, but you might be interested to hear that the guys at my r/c store told me knowingly about ‘metal-to-metal’ interference. Apparently, if you have two bits of metal loosely banging together (like a loco-tender link, or a trailing truck, or even an axle in a brass axle bearing,) then you get serious ‘glitching’ on a standard 27 or 75mhz rig. They get around it in planes and cars by extensive use of nylon bushings, rods, clevis and even nylon bolts/nuts.

The 2.4Ghz stuff is digitally coded with an address in each message, plus a checksum. [I actually think it is WiFi chips repurposed for us.] The rcvr ignores a message that isn’t correct, and the tx keeps trying until you tell it to stop by taking your finger off the knob/stick.