I then considered the weight distribution between front and back. The chimney and boiler with the balloon stack, and the batteries in the boiler weighed 230g. The cab is more or less over the wheels, so the only weight at the rear is the bunker and electronics therein. They only weigh 100g. So I had to add around100g of lead at the back. I checked the weight distribution by ensuring the loco balanced at roughly the centre like this..
- balancing.JPG (65.18 KiB) Viewed 4695 times
Now came the electronics.
For those of you not familiar with my method of RC, I’ll go into a bit of detail
I use Hobbyking 2.4 GHz controllers as made for model aircraft.
- Tx.JPG (180.34 KiB) Viewed 4695 times
You can see I have 3 different locos controllable from this one transmitter – and I have 10 transmitters!
I had a couple of 18650 LiIon cells reclaimed from an old laptop. I checked that 2 cells, with around 8V, gave a suitable speed. (see post 1)
The Hobbyking receiver and batteries are pushed into the boiler once the cab is lifted off.
- batt and Rx composite.jpg (378.91 KiB) Viewed 4695 times
There is a 3.7A solid state fuse (Polyswitch) mounted on the batteyr, to protect against short circuits. Charging is by connecting alligator clips to two ‘studs’ under the rear buffer beam.
The electronics is then pretty much all my own design.
I use a Hobbyking ESC for speed control and it just plugs into the ‘throttle’ output of the receiver. It has an in-built undervoltage detector to protect the LiIon batteries from over-discharge.
The rest of the electronics is based on a Picaxe programmable microcontroller – I know they are old technology, but I understand them and see no reason (yet) to learn about Arduino et al. The small picaxe 08M2 type has just 8 pins, runs off 3-5V and importantly has a white noise generator and PWM speed controller built in (but not used in this case).
Direction control is via a 5V coil, relay. I use the picaxe to decode the receiver pulse stream for the right Tx stick which I use for changing direction. It then picks up or drops out the reversing relay. The headlight control is also done here. (there is no rear light yet)
The same picaxe produces the steam chuff sounds. It takes the motor voltage as input to change the chuff rate. The chuff is just a white noise (generated by the picaxe) filtered and amplified by an LM386, 2W amplifier.
The chuff rate for a Heisler is still an unknown to me – I think the gearing is about 2:1 so it should chuff at 8 chuffs per wheel revolution I think. I’ll try and track down some videos.
And there is a sound to tell me if the Rx has lost the transmitter input too!
Unfortunately the are not enough pins on the Picaxe to let me have a whistle sound.
All this electronics is stuffed into the bunker – the wood load lifts off for access.
- electronics composite.jpg (1.11 MiB) Viewed 4695 times
The speaker is mounted in the bunker facing into the cab and is a tiny speaker made for laptops.
- speaker mounted.JPG (126.1 KiB) Viewed 4695 times
And the amazing thing is IT WORKED FIRST GO.
I just need to add a driver and fireman, and maybe a rear light, and the lettering/numbering and it will be done.