Ultra slow control

hollybeau
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Ultra slow control

Postby hollybeau » Sun Jun 19, 2022 6:38 pm

I am now onto my fourth loco using radio control (three in 00 for my local club, one for myself in S4) so although I am no expert I am becoming familiar with the method of operation and control. To date it has met if not exceeded my hopes and expectations. However, there is one element that concerns me and is not as good as "normal" - DC/DCC - operation and that concerns the ability to control locos very slowly. With my DCC-powered locos I can easily set them to run at such a crawl that they can hardly be seen to move: I have yet to achieve anything like that with radio control. This could be me of course not using/sourcing the correct components or it may be a weakness in the system. My current loco, a Midland Johnson 1134 Saddle tank uses a 6 volt motor (from the usual sources in China) mated to a High Level gearbox with a ratio of 1:60. The radio components consist of a Micron Rx 41D receiver and a Tx22 transmitter (made up from a kit). The gearbox ratio is the highest I can go for so I could not make it run slower by that route. To my mind the transmitter, being a simple centre off type with forwards and reverse to either side lacks delicate "feel" and may be the weak link but I am not aware of any better alternative - unless someone on here knows better of course.
I hope none of the above puts anyone off from having a dabble in radio control as I think it is the future. However, any tips or comments on how to achieve slower running would be gratefully received.

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jon price
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Re: Ultra slow control

Postby jon price » Sun Jun 19, 2022 8:52 pm

I suppose one response to this is that as far as I am aware the prototype rarely, if ever, ran so slow that it could barely be seen to move.
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JFS
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Re: Ultra slow control

Postby JFS » Sun Jun 19, 2022 9:37 pm

jon price wrote:I suppose one response to this is that as far as I am aware the prototype rarely, if ever, ran so slow that it could barely be seen to move.


Perhaps you miss an important point: a loco which cannot run infinitely slowly must, perforce, start with a jerk since it can only start at the minimum speed of which it is capable of running. By contrast, one which can do so will always start imperceptably.

Putting that another way, EVERY prototype loco runs "so slow that it could barely be seen to move" if only as it moves off from rest.

Unfortunately, I can't offer any specific help with the issue, but I feel sure that the problem with the RC equipment is due to its lack of fine resolution by contrast with a DCC system. But there have, over the years been a number of Trade solutions which have come and (mostly) gone so this issue must have been tackled by others.
Also, the latest Decoder chips incorporate feedback and this is an important element in maintaining constant speeds regardless of changeable motor loads which will not be present in the RC system.

Best Wishes,

davebradwell
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Re: Ultra slow control

Postby davebradwell » Sun Jun 19, 2022 10:06 pm

Yes, the RC devices that have been referenced here on the forum have used a fairly basic from of motor control which uses a variable pulse width. The better dcc decoders use sophisticated feedback systems which include a whole range of tweaks to get round any resonances which can plague any pulsed system. The RC systems will improve, of course, to follow demand but meanwhile it's back to high gear ratios, flywheels and all the other dodges used before we had such decoders.

DaveB

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nigelcliffe
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Re: Ultra slow control

Postby nigelcliffe » Mon Jun 20, 2022 7:18 am

I assume you've been through the (limited) range of settings for the PWM within the radio receivers ? Those do alter the motor control, though there's only a handful of options available.


Nigel

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zebedeesknees
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Re: Ultra slow control

Postby zebedeesknees » Mon Jun 20, 2022 11:13 am

nigelcliffe wrote:I assume you've been through the (limited) range of settings for the PWM within the radio receivers ? Those do alter the motor control, though there's only a handful of options available.


Nigel


On the Micron site it shows options for 'centre off' or 'full range' for the control knob on your Tx. The latter option uses the Channel 3 switch for reversing. There is also the option of altering the pwm to 12, 60,130, or 300Hz from the 700Hz that comes as standard. The 12 may be a bit low, but ideal for diesel models!
Personally, I prefer centre off so have never tried to alter my Txs, but would recommend programming the Rx to 130Hz if your motor is coreless, or 60Hz for an iron cored type.
Admittedly, programming the receivers looks daunting, so I invested in a Prog1 while they were available, but reading the MERG digest daily, most other electrickery on model railways appears no easier. Must be me'age...

Ted.
(A purists' purist)

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zebedeesknees
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Re: Ultra slow control

Postby zebedeesknees » Mon Jun 20, 2022 12:52 pm

More thoughts...

Bryan, you say that the motor is Chinese and 6 volt - some of those are very high revving. But you don't mention the power supply. I assumed that you are using a 1S (3.7v nom.) battery, but is that correct? If the volts to the Rx are higher than 5, then that might be an issue.

Another point - lowering the pwm, contrary to some opinions I have seen rercently, has the advantage of reducing initial 'stiction' so reducing any tendency of the loco to rush off at a faster speed than it will slow down to after starting. And also, it increases the torque from the motor at low speeds so that more haulage is available at lower speed setting on the control knob.

There is a danger though, that prolonged use of a low pwm at the haulage limit may cause some heating of the motor, depending on the supply voltage, but one's olfactory senses should warn in time!

Ted.
(A purists' purist)

hollybeau
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Re: Ultra slow control

Postby hollybeau » Mon Jun 20, 2022 5:32 pm

My thanks for all these replies and particularly to Nigel and Ted for making me aware of the ability to change the pwm frequency. That said, looking at the Micron and Deltang web sites the instructions on how to do this looks daunting to say the least.
Unless I pluck up the courage I think that when the opportunity arises I will swop out the one I have for use in the club's next loco (they don't mind semi jack rabbit starts) and buy myself a receiver that comes pre-programmed to the lower frequencies suggested by Ted.(This seems possible according to the options available). The transmitter I am using is on loan from the club so when I get my own (probably another kit build) I will get the "low-off" variant with separate direction switch which should give greater range and thus more control of speed.
The battery by the way is a 1S (3.7 volt) so is well below the notional "top-speed" of the 6v. motor. When set to maximum on the transmitter the loco moves a little faster in scale speed than I suspect the prototype was capable of but not unacceptably so - suggesting that the gearing ratios aren't too far out.

Thanks again.

Bryan

nigelcliffe
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Re: Ultra slow control

Postby nigelcliffe » Mon Jun 20, 2022 6:35 pm

hollybeau wrote:My thanks for all these replies and particularly to Nigel and Ted for making me aware of the ability to change the pwm frequency. That said, looking at the Micron and Deltang web sites the instructions on how to do this looks daunting to say the least.


The instructions do look horrible, but patient working out of how they relate to your transmitter means they make sense.
One needs to know which button/lever combination have to be pressed as the receiver is powered on to put the receiver into programming mode.
And which lever/knob causes the programming to advance either in levels, or changing values, or the save/exit.

Then, its just tedious - several level shifts to get to the appropriate level for the PWM setting, counting the various flashes on the receiver LED to indicate what is going on. Then cycle through the different PWM options, and exit.

Knowing how to exit if you are lost is important.


I found I had to write it down very carefully for the first few goes. Then it became OK just following the Micron instruction sheet.


- Nigel

hollybeau
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Re: Ultra slow control

Postby hollybeau » Sun Jun 26, 2022 6:31 pm

I was encouraged by Nigel to have a go but still did not feel confident enough in the exact steps to take as the Deltang instructions are not easy to understand - in my non- electronic brain at least. I therefore asked Andy at Micron for help. I have always found him very helpful in the past but this time he has surpassed himself. He has agreed that I may post his response which is as follows:

Lowering the PWM frequency can be done with a Tx22 but does require a bit of playing with the controls. I set the default PWM to 700Hz as that was what many customers were requesting and, in my experience, gives a smoother motor response. But I can understand the need for a bit more 'grunt' at the lower end so long as it isn't used too much which would overheat the motor (and the ESC chip).

The following is a description of how to program the Rx41 for 130Hz PWM. It will seem daunting if you have never programmed a receiver, but is the full detail. With practice, it will seem simple! If you don't feel up to the task, you can send the receiver to me and I will do the programming. A Prog3 does make it easier but at the cost of £22.

Rx4x receivers can only be put into programming mode using the 'ch2/ch4 method. This requires R/C channels 2 and 4 to be at high or low values when the receiver is switched on. Ch2 is the Selecta switch but Tx22 has no ch4 control. The Inertia control can be reconfigured to operate ch4; the way that this is done is to:
- switch the Tx on and wait 90 seconds without touching a control
- press and hold down the bind button
- after 20 seconds, the LED will go out for 2 seconds and then come on
- release the bind button when the LED has come back on
- switch the tx off

The Inertia control now operates R/C ch4.

To get the Rx41 into programming mode:
- place the Selecta switch at position 12
- place the Inertia knob at max
- switch the Tx on
- switch the Rx on
- after a short delay, the Rx LED will flash fast
- move the Selecta switch to position 6
- centre the Inertia knob
- the Rx LED will flash once, pause and repeat - this is called a 1-flash

The Rx is now in programming mode and displaying value 1 for the 1st programming level.

To set 130Hz PWM, the program sequence 4,2,2,1,3 is entered. Each digit in the sequence is the value for a programming level - thus there are 5 levels to set the PWM. The value at any level is shown by the flash count - e.g. 4- flash = value 4 (4-flash is a sequence of 4 flashes a pause and repeat). You can find the full programming detail on the Deltang web page http://www.deltang.co.uk/rx41d-v520-p.htm.

To increase the value: press the Tx toggle switch down and release. If the initial value of a level is greater than what you want, you need to toggle down until the value gets to the max and then returns to 1.

To accept a level value and step on to the next level: press the Tx toggle switch up and release. When you reach the last level for a program sequence, the Rx returns to receive mode and LED will light continuously.

Where down = reverse and up = forward for Tx22 configured for low-off throttle.

So, to get to 4-flash for the 1st level value, you need to press the toggle down and release 3 times. The LED will then show 4-flash.

Toggle up to accept the 4 and go to level 2. The initial value for level 2 is 1-flash so you need to toggle down once to get to 2-flash.

Toggle up to accept the 2 and go to level 3. The initial value for level 3 is 2-flash (LED2 enabled) so toggle up to accept and step on to level 4.

The initial value for level 4 is 1 (P1) so toggle up to accept and step on to level 5.

Level is set to 700Hz so the initial flash value is 5. Toggle down 3 times to wrap around to 3-flash. Toggle up to accept and that is the end so the LED lights continuously.

In short form the process is:
- get the Rx into program mode
- toggle down 3 times = 4-flash at level 1
- toggle up = 1-flash at level 2
- toggle down = 2 flash at level 2
- toggle up = 2-flash at level 3
- toggle up = 1-flash at level 4
- toggle up = 5-flash at level 5
- toggle down 3 times = 3-flash at level 5
- toggle up
- done

The Tx22 Inertia knob can be returned to controlling inertia by repeating the steps at the beginning - i.e Tx on, wait 90 seconds, press and hold button until LED goes off, release bind button when LED comes back on.


After reading this through several times and having a few false starts where I lost my place (and found that it is easy to start again simply by turning off the receiver) I am happy to report that I have successfully reprogrammed the receiver. It now controls the motor much better, allowing for proper slow starts. The top speed does not seem to have been affected.
Buoyed by this success I am now inclined to build another transmitter but this time with a "low off" start (and direction being by a separate toggle switch). This should in theory at least give a wider range on the "pot" and thus even more control. Not quite the 128 steps in DCC but getting nearer. Andy has already sent me the "code" to allow the receiver to be reprogrammed to be used in this way.

I hope Andy's advice is helpful to others who may be floundering as I was.

Bryan

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zebedeesknees
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Re: Ultra slow control

Postby zebedeesknees » Tue Jun 28, 2022 3:48 pm

hollybeau wrote:I was encouraged by Nigel to have a go but still did not feel confident enough in the exact steps to take as the Deltang instructions are not easy to understand - in my non- electronic brain at least. I therefore asked Andy at Micron for help. I have always found him very helpful in the past but this time he has surpassed himself. He has agreed that I may post his response which is as follows:

(Snipped, that lot hurt!)
I too have always found Andy at Micron most helpful, as was David Theunissen before he passed the marketing over to Andy.

After reading this through several times and having a few false starts where I lost my place (and found that it is easy to start again simply by turning off the receiver) I am happy to report that I have successfully reprogrammed the receiver.


That was beyond me, and probably still is! Excellent achievement Bryan. I looked at the instructions, bottled it and bought a Prog, in my case the Prog1 which is no longer available. Even that was fraught, with warnings about damage from incorrect connections, so I designed a stripboard circuit to make the selections easier and safer.

The buttons in the row switch each relative 'level' in programming, while the toggle switch lower left selects 'up' or 'down' in the count sent to that level. After setting those, the button on the side of the Tx pcb is pressed to lock the settings into the Tx. This board is then powered off. (I have since added an on/off switch to the board to save unplugging and replugging the power) The Rx is then powered, and when it goes into 'fast flash'/receive mode, the board is repowered with the Tx button held down, and the settings are transferred to the Rx. Both flash a 'thank you'! An advantage here is that the settings are retained in the Prog Tx, so if more Rxs require the same setting, that can be done very quickly.
Learning all that didn't come easy...

DSCF0071.JPG


And here is the underside should anyone wish to study/copy it.

DSCF0072.JPG


It now controls the motor much better, allowing for proper slow starts. The top speed does not seem to have been affected.

From my running at 12Hz the diesel simulating growl from the motor seems to disappear at around half max speed. This might be the motor back emf, or possibly the Rx smoothes the pwm at that level. I did ask David T. if it would be possible for the pwm frequency to increase with applied voltage for my diesel models, but I think he may not have felt the effort to be worthwhile.
Btw, I find with my centre off preference, that slow starts are more reliable if the inertia knob is set to around 30%.


Buoyed by this success I am now inclined to build another transmitter but this time with a "low off" start (and direction being by a separate toggle switch). This should in theory at least give a wider range on the "pot" and thus even more control. Not quite the 128 steps in DCC but getting nearer. Andy has already sent me the "code" to allow the receiver to be reprogrammed to be used in this way.

I hope Andy's advice is helpful to others who may be floundering as I was.

Bryan


Reading your post has certainly helped me to follow some of the logic of the programming, thank you Bryan.

Ted.
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