Midland Railway Centre

The darkside has our flounder by the short and curlies now ..... he's ordered up stepper motors, stepper controllers, and doing the control system himself

To aid him in his struggle, I'm trying to print up a GT2 gear 120T. combining this with a 20T gear on the stepper motor will give a 6:1 ratio i.e. 6 turns of the stepper motor will give 1 turn of the turntable, connected via a GT2 - 6mm wide toothed belt.
The stepper Toto has ordered up (Nema 17 - 1.68A per coil) has 200 steps per 360 degree rotation or 1.8 degrees per step, divided by 6 (the 6:1 ratio) gives a 0.3 degree movement of the turntable per full step.
The Sparkfun Big Easy Driver - stepper motor driver he has ordered will provide up to 2.0A per coil, and supports Micro Stepping, which is by using fancy electronics to control the coils, can divide the full step into half, quarter or sixteenth steps giving upto 3200 steps per revolution of the stepper motor (16 x 200), then with the 6:1 ratio gives 19200 steps per revolution of the turntable, or 0.01785 degrees per step - should acurate enough for Toto.

The other really neat feature of the Big Easy Driver, is you tell the software (arduino - what else ) you destination, and it works out from its current position, the direction and number of steps required to get there, and the acceleration and deceleration required for smooth operation.

The gear will be in two parts, the lower part having the outer flange to stop the belt coming off plus the gear teeth, the upper part is a thick flange to retain the belt and hold a 3mm dia neodyium magnet ('cos I have plenty of these ) to be used for the homing routine to set up the zero reference.

The gear is 45% through printing, so hopefully I will be able to post a pick up later today.

Paul

 

Does this mean another board will be added to the ever expanding Luib Bridge ?? Soon you'll be in the neighbours property...

Cheers, Gary.

 

...... he's in a quandry on that one as the turntable is wider that his standard baseboard

But it does mean that an O gauge depot layout may be on the cards in the future

Paul

 

4h20min later ..... I knew it would take longer than normal, as to allow for the fine teeth I had slowed the print speed to 40mm/sec rather than the usual 60mm/sec


Outer diameter is 86mm

Just the top section to do now.

Paul

 

nope not recently- I've been working on traversers , I do however have a Peco OO gauge turntable kit, bought an awful lot of years ago, still waiting for an unboxing , why ..........

Paul

 

what's this about me and an elephant - that's no nice, SWMBO has lost weight, ...... that's the two of us in the dog house now

For that beast you'll need bigger steppers - a bipolar Nema 17 with a Big Easy Driver as the controller will work fine. But would probably benefit from some form of gear box.

Something like this

Nema 17 + 5:1 planetary gear box

So there is your homework - google bipolar stepper motors, the Big Easy Driver, as you're just lounging around we'll expect a fully research solution when you get back - enjoy

Paul

PS - the Schnapps is usually on the top shelf, it doesn't actually help, but it does give the illusion making it all make sense.