[Jojje Bergan]

And here with the fan on the top.

I'm only shoowing this for Mariss, if he like to do it the same way.

[Mariss Freimanis]

OK, I just edited the schematic to remove some idiotic errors.

Here's how the high-side short-circuit protection works:

1) The protection circuit is scaled to trip at 12A, a current that is just above the maximum normal operating current (all axis set to 3A, all motors running at high speed and loaded to stall torque simultaneously). All current to the mobo passes thru the 0.01 Ohm, 3W resistor.

2) The 0.01 Ohm resistor develops 120mV across it at 12A. The MPSA92 is a 300V PNP transistor. The BAS21 (200V Si diode) is biased via the 330K resistor to develop the same forward voltage as the MPSA92's Vbe. This temperature compensates and cancels the MPSA92 Vbe resulting in 120mV across the 470 Ohm resistor in the emitter path at 12A.

3) The MPSA92 collector current becomes 250uA at 12A thru the 0.01 Ohm sense resistor (120mV / 470 Ohms). In effect, the MPSA92 is a current-mirror scaled to 20uA per Amp of supply current. This current passes thru the 10K resistor to ground and it develops a ground referenced voltage of 200mV per Amp of supply current.

4) A CD4013 D-Flop is used as a fault condition latch. The logic threshold is 2.5V when Vdd is 5V. 4000-series CMOS logic is chosen because it is slow enough (300nS propagation delay) to ignore sub-microsecond noise impulses yet fast enough for the intended purpose.

5) A 12A current develops 2.5V across the 10K in (3). The voltage is clamped to 5V via the BAT54S Schottky, RC filtered (10K, 100pF) to produce a 1uS delay for noise filtering purposes and is applied to the R input of the flop. The flop resets at 12A and disables all drives. The flop is set via the RC network (1 second delay) acting as a power-on reset on its S input.

6) Protection circuits need protection against failure themselves. The most likely failure is the 0.01 Ohm resistor burning open. Should this happen the green LED forward biases and limits the voltage across the 470 Ohm resistor to about 800mV and the collector current to a safe 1.5mA. Should the MPSA92 fail, the 10K resistor in series with its collector limits the current to 5mA at 50VDC. The BAT54A clamps the resulting voltage to 5V at the CD4013.

In writing this I see there is a problem with how the power-on reset works. I need to correct that part of the circuit.

Mariss

[Mariss Freimanis]

I corrected the schematic. The D-Flop has been replaced with a CD4001 quad NOR gate. It should manage fault latching and power-on reset properly now.

Mariss

[pminmo]

I corrected the schematic. The D-Flop has been replaced with a CD4001 quad NOR gate. It should manage fault latching and power-on reset properly now.

Mariss

So what schmetaic tool do you use that allows you to crosslines without either a dot or hump to indicate connectivity? :stickpoke (IRF530 drain node)

[Mariss Freimanis]

I corrected the schematic again. Note to self: Do not attempt to design a circuit until drinking 1 gallon of coffee.

Mariss

[mlaws1172]

Why the HCPL2531s versus 74hc14 ? Sorry if this is a really stupid question
mike

[pminmo]

Why the HCPL2531s versus 74hc14 ? Sorry if this is a really stupid question
mike

The 2531's give you complete isolation of the ground paths.

[.xXACEXx.]

DOH! (homer simpson) simply amazed with every ones knowledge of elec-tricky ,.. ...
great reading!!.. would be nice to build that stuff instead of holding +/- .00025 inch tolerance,but thats another story (had a bad day at work )..oh to have that knowledge of electricity!!...

[microcarl]

...oh to have that knowledge of electricity!!...

Buy some electronics books and study them, read trade journals, set up a small electronics work bench and experiment.

I'll guarantee you'll be rewarded beyond anything you could have imagined.

Be it small, but take a stroll through Boarders and other book store technical sections. They usually have a small section on electronics, robotics, physics, mathematics, etc...

My budget allows for the purchase of a $100.00 book every couple of months. Yes, books are expensive, for sure. But now the question is, how bad do you want to learn electronics. It is a participation sport - without a doubt!

Over time, I've accumulated about 500 technical books. Those in my circle of life think I'm really smart. I'm actually much less intelligent then most individuals I know. But I have a technical library that is better stocked then some universities, and most community libraries. But if I want to know something related to the above, it's usually only a few short steps away.

I hope this advice helps you on your way...

[Mariss Freimanis]

I did a 4-axis design exercise:

1.jpg shows the mounting shell of the 4-axis unit. It is 0.085" hard-anodized aluminum and it will be the heat-spread plate for the 4 Cheap Drives. The anodizing provides electrical insulation for the drive MOSFETs.

2.jpg shows a single Cheap Drive mounted to the shell via a pair of 2-56 hex head screws. The shell is threaded for these screws.

3.jpg shows all 4 drives mounted. Connection will be via the 2 X 15 headers on the drives.

4.jpg shows the mobo 2 X 15 header sockets plugged into the 4 drives. It is the only thing holding it in place. The mobo circuitry and header sockets are on the opposite side.

6.jpg shows the cover snapped onto the mounting shell. No screws are used because the cover interlocks with the shell the same way as on a G100. The cover is flush with the DB connector mounting tabs preventing the mobo from slipping out of the sockets. The 12 position screw terminal block is the same as what's used on all our other drives. Power supply and miscellaneous I/O is made through this removable connector block.

The pencil is to give the unit a scale reference. The length is 5.6", width is 2.35" and the height is 0.93" (142mm by 59mm by 24mm).

Mariss

[Mariss Freimanis]

The pictures:

Mariss

[tauntdesigns]

I need/want/gotta have one or two of those........... Please..............

Very nice design, you SHOULD be very proud. More wine and cheese for the master...

Please,
Jack

[DR-Motion]

Absolutely brilliant design.
Mariss, you have certainly mastered the art of design for manufacturability.
Can I humbly add a further design consideration to your masterpiece?
How about some sort of gasket to prevent machining debris from entering the case and letting out the smoke?

best regards and congratulations.

[the4thseal]

the paaaaiiiinnnnnn,,,,,,,,,,,,,,,,,,,,,,, when can i buy some?????????????
please say soon......please

[pminmo]

Brilliant system!

[Ryan7777]

Its nice to see a company actively seeking suggestions and engaging with its costumers! I love the idea of a cheap drive packed with useable features at such a price point. Some of us DO have a tight budget and only want to CNC a small mill or lathe for hobby use and not for profit (like myself!). I'm well versed at electronics and could build a microstep drive myself and probably enjoy the whole process, but sometimes its a whole heck of alot nicer to pay $30 and get a finished product that can go right to work. Its sad however, to see someone knock a well made but low priced product all over "bottom line". you would put yourself out of business if you don't try to lower prices, because if you don't, someone else will! You ALWAYS have to innovate. And like its been said, if I'm impressed with the performance and engineering of the smaller, cheaper drive, I'll more than likely stick with gecko when I go to upgrade to something more powerful. And having these guys here taking the time to get involved with the rest of us really makes me more comfortable buying something off of them at any price.

[Chucks CNC]

Its a great design! Combat Ready. If only the black boxes I worked on the USAF were this nice. I like the d-sub / DB09 connectors they can take abuse and people can get cables and plugs from surplus or make there own.

[Chucks CNC]

Once again its nice to see such a great company.

[dex918]

Mariss,

Everything about this drives is really a brilliant idea.
Question,

1. How soon will it be available in the market?
2. Is is going to sold as a complete package (enclosure, MOBO & drives)?
3. Is it going to be sold as 3 & 4 axis or just 4 axis only?
4. What are the prices we are looking at if it is going to sold as complete package with 3 or 4 axis?

Thank you.

Dexter

[yantra3d]

How about the option of a 2-axis solution for use w/ a lathe, will that also be available for purchase?