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I spent most of the day working on the Class D Amp. I got a roughly sawtooth oscillator based around a 555 timer going after I sorted out some problems with power supply filtering. I then added in a buffer amp stage to make sure I wasn't going to be loading up the oscillator, after going through the buffer the waveform was a little mangled but I pressed on.

I then tried to put a PWM stage with the output from my iPod and the buffer stage. In the process of doing that I managed to knock some critical wires loose and spent the next few hours trying to work out what had changed to stop it working. During this process I realized that even with all of the capacitors in my collection in use there was still ripple on the power rails in time with the bottom of the sawtooth. The other thing I realized that to get the PWM working with Audio frequencies I'm going to need to up the frequency.

To solve the first problem I'm going to go into Jaycar tomorrow and pick up some LM7905's if they have them and  possibly some generic BJT's in case I need to make a constant current supply for the Sawtooth oscillator.

To solve the second problem I have just substituted a smaller capacitor in the oscillator. This has definetly increased the frequency by an order of magnitude; so hopefully that problem has been solved.

If anyone wants some diagrams or pictures of my setup let me know in the comments and I'll put some up.

Cheers,
Rex Write comment (0 Comments)
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I know it's been a while since my last update, I have been quite busy moving out of my parents house.

I have just bought 6 of these and 1 of these packs.

I'm pretty sure that the current motors on my CNC's are NEMA 17's but even if they are not I can buy or make some kind of alternate mounting plate or just use them for a 3D printer if I can't make it fit.

In other news having moved out I don't have anywhere to put my HF antenna but soon I should be able to get my 2m rig online from inside so I won't have to go out to my car to talk to someone.

Cheers,
Rex Write comment (0 Comments)
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I finally tidied up my electronics desk so I could see how I would need to drive the original spindle motors.

Short version:

They are DC motors that seem to be able to go fairly fast at 30V.

Long version:

This is the assembly for the mill option on the converted lathe I had to throw away.
On the top you can see the the speed controller with a switch and a pot to vary the speed.
This is the bit I really wanted to look at as it would be the part to simulate.

After I got a few screws undone it came apart fairly easily.

From there it was a fairly simple process to unscrew the ground cable and take the plastic backing off. From there I could see the conductor side of the PCB.
From there looking at the board it looked like there was a diode either as a reverse polarity protection or as a half wave rectifier. Working on the theory of it being a half wave setup I decided to hook it up to my power supply and see if it would turn or at least produce some kind of cogging effect. When I connected it up and slowly ramped up the supply voltage/current I was rewarded with rotation. Upon experimentation I found it to start spinning with about 0.55A and to just keep turning over at 0.50A.
It's not very obvious but the motor is spinning slowly in this photo. I ramped the voltage all the way up to the maximum that the power supply will provide at about 29.7V which rewarded me with a nice whooshing noise from the air getting blown out of the motor. It looked like it was going pretty fast so I was glad there was a limit to stop me from going any further without having to bolt the thing down. Now I just need to confirm the voltage/current capacity of the PWM supply of the BeBoPr so I know if I need to build a buffer amplifier. The buffer should be able to be a fairly simple design with just a power transistor (probably some kind of FET) attached to a relatively small heatsink.

Being able to easily use these motors and spindles means that I can shave a fair bit of the potential cost of this project and I can focus on more important things like how to get the rotational speed of the spindle when it uses a plastic belt and a DC motor to drive it. I'm thinking some kind of back EMF based system. However the lighting conditions probably won't change too much so some kind of light based system could also be used. This is particularly true of the lathe which has all of the mechanism inside the headstock and is fairly well sealed to light.

Cheers,
Rex Write comment (0 Comments)
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I got the bearings for the bogies on the Heisler at work the other day. I might need to stop getting stuff delivered here, some people are starting to look funny at me.
And here's a comparison to the axles that we've bought. There's a bit of material to take off so I'm glad for the CNC's to run automatically.
Hopefully I can get the G-Code written by the end of the week and start machining this weekend.

On the BeBoPr front; I have got the bridges and the components to assemble them. However when I look at the Element 14 webpage I see that I need to call to get the availability for the BeBoPr's themselves. I called and they'll be in the UK around the 16th so I should see them near the end of September. At the rate these are going I might have the new hardware running by early next year.

Cheers,
Rex
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