Building a radio controlled (electric) traction engine

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Southern188
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Re: Building a radio controlled (electric) traction engine

Post by Southern188 » Mon Apr 30, 2018 9:39 am

I had a similar problem recently, the DFPlayer sound card I was playing with interfered with another 5 volt circuit (not the processor). I solved it as you with a schottky diode and capacitor. I also changed the layout to ensure the 0v and 5v lines of the offending device went directly to the regulator rather than being at the end of the power lines.

Servos are electrically noisy. I use the Tower Pro SG90 on my steam train and they produce 500mv of noise on the 5v line but the processor I use is 3 volt so is well protected by it's internal regulator.

You have a 0.1uF capacitor in your circuit diagram, ensure you have one as close to the processor power rails as possible.

Great to see someone else with an oscilloscope. My 1970s Telequipment D61a is still working well!

Michael

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Re: Building a radio controlled (electric) traction engine

Post by gregh » Mon Apr 30, 2018 11:55 am

Southern188 wrote:
Mon Apr 30, 2018 9:39 am
I had a similar problem recently, the DFPlayer sound card I was playing with interfered with another 5 volt circuit (not the processor). I solved it as you with a schottky diode and capacitor. I also changed the layout to ensure the 0v and 5v lines of the offending device went directly to the regulator rather than being at the end of the power lines.
Not quite sure what you're saying, but my servo has separate power wires direct from battery and the picaxe+Rx are fed along another pair

Servos are electrically noisy. I use the Tower Pro SG90 on my steam train and they produce 500mv of noise on the 5v line but the processor I use is 3 volt so is well protected by it's internal regulator.

You have a 0.1uF capacitor in your circuit diagram, ensure you have one as close to the processor power rails as possible.
Yep, It's right at the picaxe terminals

Great to see someone else with an oscilloscope. My 1970s Telequipment D61a is still working well!

Michael
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Re: Building a radio controlled (electric) traction engine

Post by gregh » Mon Apr 30, 2018 12:10 pm

tom_tom_go wrote:
Mon Apr 30, 2018 9:35 am
Surely there is a faulty component causing this?
Always a possibility, but since I have got rid of the problem (fingers crossed) with the mods I made, it seems less likely to be a component.
What component could it be? I've tried different picaxe. I've checked that other Rx of the same type cause the same modulation on the battery. I hope it's not the servo as it's glued in. And I'm happy that the battery doesn't have too much internal resistance. I might try and measure another servo's current just for future reference.

One thing I do wonder about is the picaxe - datasheet says it operates internally on 3.3V but has a regulator so can operate from 5V and it selects automatically. I just wonder what it does as the voltage dips. Does it have trouble as the voltage falls and its internal regulator dropout voltage comes into play and that causes a restart?

Anyhow, while it continues to work, I ain't touching it.
Greg from downunder.
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Re: Building a radio controlled (electric) traction engine

Post by tom_tom_go » Mon Apr 30, 2018 1:22 pm

I agree, if it ain't broke don't fix it but having myslef had all sorts of odd issues with budget servos in the past I reckon it's that.

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Re: Building a radio controlled (electric) traction engine

Post by gregh » Tue May 01, 2018 12:59 am

tom_tom_go wrote:
Mon Apr 30, 2018 1:22 pm
I agree, if it ain't broke don't fix it but having myslef had all sorts of odd issues with budget servos in the past I reckon it's that.
Just to try and convince myself, I took a similar 'cheap blue' servo and had a look at it's waveforms.

Fed from my bench supply, it caused a 250mV dip in the supply every time it moved ( in engine I had 400mV).
I put a 1 ohm resistor in series and measured it's voltage drop= amps, and it takes a spike of 500mA each movement, with no load on the servo. I had estimated 1A in the engine, assuming 0.4 ohms. So I tested the battery and found its internal resistance incl the polyswitch is 0.6 ohms. So the servo would cause a 300mV dip calc compared to my measured 400mV. These are all close enough for me to say that I don't think the servo is faulty.
It all goes down as experience - running a servo takes big current spikes that have never been a problem for me before as I have always used a regulator for the picaxe supply.
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Re: Building a radio controlled (electric) traction engine

Post by gregh » Sun May 06, 2018 12:34 am

I started this project hoping to be able to program the engine to run a sequence of movements, like driving down a street. But soon realised that complicated moves like driving a round corners would not work due to minor variables like leaves pushing it slightly off course.
Anyway I persevered, 'just to prove to myself that I could do it' - by that I mean the programming part.
So I just wrote a program to make it do a 3-point turn. Here's the video. It includes part of the original video showing it being driven around the streets of my layout.
https://youtu.be/EOo8xxAJctw
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Re: Building a radio controlled (electric) traction engine

Post by tom_tom_go » Sun May 06, 2018 9:20 am

You have cracked that Greg just a shame the road is not forgiving enough for you to run the program.

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Re: Building a radio controlled (electric) traction engine

Post by ge_rik » Sun May 06, 2018 11:44 am

Neatly done, Greg. Pity you can't program to allow for the vagaries of the terrain - unless of course, you get Google to sponsor you.... :roll:

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Re: Building a radio controlled (electric) traction engine

Post by IanC » Sun May 06, 2018 12:44 pm

That traction engine is brilliant. I can only envy your skills.

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Re: Building a radio controlled (electric) traction engine

Post by tom_tom_go » Sun May 06, 2018 1:02 pm

Can you not do something with 'Back EMF' as I use to program this when I did DCC in OO scale for gradients?

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Re: Building a radio controlled (electric) traction engine

Post by gregh » Mon May 07, 2018 12:20 am

tom_tom_go wrote:
Sun May 06, 2018 1:02 pm
Can you not do something with 'Back EMF' as I use to program this when I did DCC in OO scale for gradients?
All things may be possible - just how much work do want to do. I assume you mean using back EMF feedback for speed control. Speed variations are not the main issue. It's the direction. Even ignoring what happens if it hits a rock or leaf and is deviated, there is the 'initial conditions' problem. Say I started it off pointing just one degree off straight, on a straight road - then after 4m it has wandered 70mm across the road! I just didn't think this through before I started with the auto idea. :scratch:

BTW on back emf - I did install 'constant speed' control in a G scale loco but didn't like it! So I took it out of the program. I found that I like to have to apply power as I go uphill and reduce it as I go down.
Greg from downunder.
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Re: Building a radio controlled (electric) traction engine

Post by gregh » Mon May 07, 2018 12:21 am

ge_rik wrote:
Sun May 06, 2018 11:44 am
Neatly done, Greg. Pity you can't program to allow for the vagaries of the terrain - unless of course, you get Google to sponsor you.... :roll:
Rik
I can see the traction engine now - spinning cylinders and radar dishes on top. All steam powered of course.
driverless.jpg
The driver is retained for 'observational purposes'.
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Re: Building a radio controlled (electric) traction engine

Post by FWLR » Mon May 07, 2018 7:47 am

That’s a brilliant bit of programming Greg. Thought it was going to stop at the ruler though….. :thumbleft: :thumbleft:
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Re: Building a radio controlled (electric) traction engine

Post by gregh » Mon May 07, 2018 11:41 pm

FWLR wrote:
Mon May 07, 2018 7:47 am
That’s a brilliant bit of programming Greg. Thought it was going to stop at the ruler though….. :thumbleft: :thumbleft:
Thanks Rod. I put the rulers there to see if it actually returned parallel to where it started and how far over it moved. Didn't quite get back parallel - a little less time on the reversing turn required.
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Re: Building a radio controlled (electric) traction engine

Post by gregh » Wed May 09, 2018 10:50 am

This should be my final post!
I tried putting lap top speakers in the roof, fed from sound recording card. Sounded reasonable, till I ran the engine, then the motor/gear noise swamped it out. End of experiment.
But I did add a hurricane lamp so the driver can see his controls. But really it's so I can see that the power is turned on!
IMG_7929 s.jpg
FINIS
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