Round the pole

[Andy Stephenson]

Posted by Robin Colbourne on 29/03/2020 02:24:11:

Andy, Thank you for posting your power supply circuit diagram. Three questions:

1. At risk of appearing totally thick! Do the hand controllers go in line on the motor outputs shown?

2. Can you use standard Scalextric hand controllers with this speed controller?

3. How do you vary the input voltage to suit differences in line length?

Robin,

I think you misunderstand, this IS the controller, you need a DC power supply to feed it. The power is applied to the rails, positive and zero(-ve) and the motor is connected to where it says motor o/p. The speed is controlled by the potentiometer labelled VR1 on the schematic.

No need to use any other controller as explained above

The input voltage needs to be enough to overcome the resistance of the lines so using a variable power supply is the best solution.

We have been using the same controllers since I made them 25 years ago and they are still going strong. They were built into small plastic project boxes with slider pots some with spring returns. We have had them on really long lines at the Model Engineering Exhibition and short lines at club meetings in a village hall. The power supply we use is one in yellow case with various output voltages, I'm not sure who made it. It looks like Harry Butler isn't selling RTP kit any longer so it may be necessary to get a laboratory style bench power supply for this application.

[Robin Colbourne]

Thanks Andy, That clears things up. I was looking for a something variable but missed VR1. I'm more mechanical than electronic!

Phil at the RTP Hut does some variable voltage transformers. See here: RTP Hut Power Supplies

If you click on the image it gives more detail. For instance the description of the large one is:

Large Mains Power Supply Unit 4524

 

 

£ 150.00 each

Suitable for single or dual model flying on line lengths from about 3 metres to about 10 metres. Rated outputs are:- 24 volts, 30 volts, 38 volts, 46 volts and 54 volts at 6 amps. Unit consists of Heavy Duty mains transformer, bridge rectifier and smoothing capacitor housed in a plastic case. Voltage selection is by 5 position break before make rotary switch. Three pairs of D.C. outlet sockets are fitted.

Unit size: 175W x 110H x 150D

Weight: 5kg approx.

Edited By Robin Colbourne on 29/03/2020 16:19:16

[Phil Green]

Those seem very expensive for what they are. A proper 30v switch-mode current & voltage controlled bench PSU can be had for much less, and is a versatile tool for other purposes.

Our modest RTP setup used swapped-out car batteries, the weight helped tether the pole too, and kept voltage drop to a minimum by only extending the pwm pot wires outside the circle, rather than the power wires.  PWM speed controllers can be as simple (555+mosfet) or as complex as you like (processor controlled with envelope shaping etc) all very cheaply, theres absolutely no need to spend that kind of money !   

In fact if you have a spare car battery, an old brushed speed controller and one of those £1 servo testers from ebay, plus a few bits & bobs to make up a pole, you're already good to go without spending a penny!

 

 

Edited By Phil Green on 29/03/2020 17:21:24

[Simon Chaddock]

I first did indoor round the pole in the early 1960s using 3V early Japanese motors. Marginal flight and the motors did not last long with 12V transformer supply.

Much more success with later proper 12V motors which allowed more realistic planes to be built.

Given there were always two wires my big step was utilise them as a control line function as well. The centre pylon gets a bit more complex to not only move the wires but also to lead the control to the pilot outside the circle.

With elevator control RTP flying became rather more gentle allowing for very intricate models to be flown successfully.

Always a keen scale builder there was attraction in building small and very light yet with a reasonable prospect of it actually surviving. First a Sopwith Pup built late 1968 in classic balsa and tissue style.

20" span with a geared slot car motor driving a hand carved balsa prop. Just under 2 oz (40 g) but the motor alone accounts for nearly half of that!

Even on short 6' lines it flew well and at almost a true scale speed!

It prompted me to build a matching Fokker Triplane.

18" span and modelled on one of the planes flown by ace Wernher Von Voss. It weighs 2.25 oz (64 g).

Built in 1969 to almost perfect scale inside and out. This is the only picture I have of it under construction.

The fuselage with full internal bracing (cotton thread) is made from medium 1/32 round balsa to simulate the steel tube of the original.

A similar geared slot car motor and the Oberursel URII rotary actually goes round with the prop.

Just to confirm that control line RTP can be quite 'gentle' I still have the Triplane in the loft although at 50 years old it is firmly retired. .

That's quite enough of my reminiscing!

 

Edited By Simon Chaddock on 29/03/2020 19:00:54