Step Off

Today has seen the completion of the stepper control box. The electronics and power supply are now mounted and wired in to the switches on the front panel.

The power supply was fitted using 6BA bolts. As mentioned in the last post, the mains lead enters the enclosure via a strain relief gland.

Here is a photograph showing the internal set up of the electronics and power supply:-

Here is another photograph showing a side view of the electronics installation:-

And finally, a shot of the completed system in it's entirety:-

The control box was connected to the stepper on the rotary table. A full functional test was successfully carried out.

With this tool now complete, attention can again be turned to the design and development of the tube bundle thrust chamber concept. It also means the end of step related punning post titles. I can almost hear your sighs of relief. 

Three Steps to Heaven...

Greetings, dear reader. I am back in Blighty again and ready to resume rocket engine related activities.

To that end, I have done some more work on the rotary table control system. I'm putting together the control box that will house the power supply, switches and electronics.

Here is a photograph of the front panel, showing the LCD display, menu scroll through paddle switches and menu select button:-

The rectangular holes for the LCD display and the paddle switches were created on the milling machine. The paddle switches snap into the holes and are held in position by integral spring clips. The LCD is bolted in place using the protruding 6BA bolts that hold the PCB stack together. Here is a photograph showing the arrangement of the electronics and switches on the rear of the panel:-

The power supply will be fitted in the space next to the switches. The mains lead will enter the enclosure through a strain relief gland. A socket will be fitted for the stepper motor drive pulses.

I'm looking forward to getting the control box finished. The automated rotary table will then be ready for use. Just in time, as I am now going to order the material to begin the construction of the tube bundle thrust chamber.

Look out for more updates over the next few days.

The 39 Steps...

Over the past few days I have been working on the rotary table control electronics. This has involved reducing the profile of some of the boards, to ensure they will fit snugly into the enclosure.

On the LCD/Keypad shield, I was able to move the contrast potentiometer from the front to the rear of the board. This allows the LCD to sit closer to the front panel. I also took the ICSP header off the shield; it will not be required in the finished device. Flying leads have been soldered to the buttons to enable these to be piggybacked with the panel controls.

The stepper drive board had it's screw terminals removed. I have soldered flying leads to the stepper output pads on the board which will be connected to the output socket. The capacitors on this board have had their leads extended and led out to the side.

The Arduino has had the power leads soldered directly to the board. All three of the PCB's have been stacked together using various 6BA screws and stand offs.

This view shows the stacked boards and the contrast potentiometer. The conductors for the stepper output, control signals and the button extensions can also be seen.

Here is another view of the stacked PCB's:-

This unit will be mounted to the panel by means of the 6BA bolts through the LCD shield. The intention is to secure these through the panel with acorn nuts.

I shall be back earning a living again soon, so no more practical updates. I'm hoping to use the time to get some more details of the tube bundle chamber design published. 

One Step Beyond...

I have just finished sheathing the stepper motor cables and wiring the end connector. I used 6mm diameter expanding braid sleeving to cover the stepper leads. I secured each end of this with adhesive impregnated heatshrink tubing. I'm not sure how long this will last, only time will tell.

The connector is a five way locking type, obviously the fifth pin is not used. The locking feature means that the stepper cannot be inadvertently disconnected whilst being driven. The pin assignments in the connector are as follows:-

1 = White

2 = Green

3 = Black

4 = Red

I realise that the above means nothing to any of you, but the more places I write it down, the less likely I am to forget it.

As mentioned earlier, the major mechanical part of this tool build is now complete. I will still have to make a hand wheel for the other end of the stepper shaft. This will allow manual operation of the table if required.

Here is a photograph of the (almost) complete motorised rotary table:-

And here is a view of the end connector:-

Tomorrow I will begin boxing up the electronics. Now, the bare minimum of front panel buttons would be five. These would be UP/DOWN LEFT/RIGHT and SELECT. Various trial button layouts on the front panel always looked cluttered, so I wanted to find a simpler solution.

You already know that I like a recycled component or two. Rummaging through my stock of useful parts, I found some small spring return to centre SPDT switches. So I can use one each of these for UP/DOWN LEFT/RIGHT and then one push button for SELECT.

Here is a view of one of these switches:-

More updates to follow.

Step-ford Wife

If only...

The four holes to mount the stepper have now been drilled in the square end plate, and the stepper and mounting have been successfully mated up to the rotary table.

I decided to use M5 nuts and bolts to attach the stepper, as I've never been too comfortable with the idea of threads tapped into aluminium. So the holes ended up being 5.1mm diameter.

Here is a photograph of the stepper motor and mounting connected to the table:-

I ran up the stepper and shifted the rotary table round under power; the system worked perfectly.

Here is a photograph looking along the inside of the mounting, showing two of the table attachment screws, as well as the coupling:-

That is the mechanical portion of this tool build completed, now it is over to the electronics - ruggedising the motor leads and fitting all the PCB's into a die cast box.

Quick Step...

I have just finished milling the coupling access slot. I milled it slightly off centre. This makes getting to the offset grubscrews in the coupling somewhat easier.

Here is the part showing the slot and slipped over the rotary table drive sleeve, but not bolted on. You can see the bellows coupling peeking through it's newly created "window":-

Hopefully sometime today I will get the stepper mounting holes drilled and tapped to M5. That will then be the part finished. It is a good job as I am rapidly running out of Step related punning post titles...

Step-toe and Son...

...pation.

The experiment in bonding seems to have worked. After almost 18 hours of cure time - not strictly required but entirely due to my paranoia - the mounting is solid. Will it last with the weight of the stepper motor on it, and with general handling? That remains to be seen. All seems well so far, at least.

Here is a photograph of the mounting to show the three 120 degree spaced holes. These are 5.1mm, to suit the M5 attachment screws:-

And here is the part fitted to the rotary table:-

The next task will be to drill the mounting holes for the stepper motor in the square portion, then mill the coupling access slot. After that it will be time to assemble the electronics in the die cast case. Keep watching.