Case Assembly

I weep the loss of the post that was supposed to go up instead of this one. I spent several days (of here and there sessions) writing up my approach to acceleration complete with equations and graphs. I was preparing to make some final tweaks when I hit some random key combination and deleted some stuff. I believe I hit command-Z to undo it, but instead the entire contents disappeared. 'Round about the same time the Auto-Save Auto-Destroy feature kicked in and saved my post as completely empty. Much to my surprise there is no "versioning" of posts. All was lost. So it will probably be a while before I can resurrect it.

In the meantime, I've been working on the case and power supply. I purchased the HobbyCNC EZ Driver package which included everything needed except a 24V 10A transformer and case. A PacTec DM-4 case was recommended along with a couple of transformers. The transformers were out of stock. A friend gave me an industrial 24V 12A transformer mounted in a NEMA 1 case. It's much too big to fit inside the PacTec case so I'll be mounting it externally and deviating from the plans.

The plans call for a wiring path something like this:

• AC 110 from the wall
• Power switch
• Hot wire through 4A fuse
• Transformer
• Bridge rectifier
• Capacitor
• Negative wire through 10A fuse
• Driver board

I'll be going:

• AC 110 from wall
• Hot wire through 6A fuse (to be reduced to 4A)
• Transformer
• AC switch
• Bridge Rectifier
• Capacitor
• Negative wire through 10A fuse
• Driver board

So I've left out the 4A fuse in the case and the switch is on the 24V AC lines. Not being an expert in electricity, I had to run this by my dad to make sure the rating on the switch was good for this. It's marked AC 125V 10A so I should be fine. Apparently it's a big No-No to switch the DC lines as some fantastic thing happens in the motors and the driver blows up. I hope I don't blow the fuse...

I tested things as I went. The transformer secondaries produced 24V AC as expected. I temporarily connected them to the bridge rectifier but couldn't get a stable reading of DC output. This is because the AC/DC conversion produces a "wave" of current or voltage or whatever. After connecting the capacitor, things smoothed out and I got 32V DC output. I was expecting the output to be greater than 24V but I haven't had time to look up the theory that explains this.

Here's the transformer with wiring exposed with a 9V battery for scale (I didn't have a quarter handy). I studied it a bit to find out it was properly wired.

Here's the case prior to work.

Here's the case with all the parts in place. I haven't committed to anything yet. The capacitor and the driver board are just sitting in place. I haven't even put the heat to the heat-shrink tubing yet. I'd like to see some motors move first. I tested the DC output and I'm getting 32V. I applied this to the driver board and got 5V logic on the test pad. So far so good. Next is to solder on the driver chips and install the heat sink. I'll be using my mill for the heat sink, so I'll need good dimensions first for the screw holes.

Here's a shot of the front of the case. The plans called for 10 5/8" holes for ventilation. But I've got a mill and a DRO - I'm not afraid to use it! So I made 40 slots. That looks better.

And the transformer nicely wired and ready to go.