Diy Brushless Spindle

[paul.hunaban]

Yep power output would easily do the job. But, given the supply will be PWM then this shall have a resultant affect on the current drawn, dependant on speed required / length of pulse. What I hoping for is the input from those members who are now using these brushless motors to cut wood to help by letting us know from their experience, motors used – power supplies etc. I will poach with pride!! I’m happy to be told information resulting from experience as it does not always relate to theory...
Regards Paul

[Jonathan]

Power supply is tricky (unless you have a large budget) since 70 amps is a pretty large current:

http://www.ebay.co.uk/itm/HOT-Univer...ht_2890wt_1037

£40 for 20A .. not great, but there's another way. If you place a battery which can deliver the peak load in parallel with the ESC&PSU then the PSU only needs to supply the average current. This is where it's easiest to just measure how much current the motor draws when cutting and get the PSU to match. A standard multimeter wont measure 70 amps since they tend to be fused at 10-20A. Something like this is excellent as you can measure the current and it records the peak current:

http://www.hobbyking.com/hobbyking/s...Analyzer_.html

Or the cheap way is to use a multimeter to measure voltage across shunt resistor, which can just be a short length of wire of known resistance. I used one of the following batteries, with a 0-50V, 0-20A lab PSU in parallel on mine:

http://www.hobbyking.com/hobbyking/s..._Rex_500_.html

That battery is rated for 60A constant, or 90A for 10 seconds which is plenty. Since my PSU has variable voltage output and current limiting I can set it to just below the fully charged voltage of the battery (i.e. <22.2*4.2) and it will never overcharge the battery, which is very important since overcharging a lipo battery is a good way to start a fire. So whatever PSU you get if you decide to use in combination with a battery will need to have good stable voltage regulation below 25.2V. Two computer ATX PSUs in series is nice and cheap and will give very close to 24V, however it is CRITICAL to ensure they are electrically isolated before putting them in series. The battery would never fully charge, but that's a good thing if anything as it increases it's life expectancy. You could get the battery first, use it to power the motor to measure the current then buy a PSU to suit.

We can estimate what power you require; what cutter diameter and depth of cut do you generally use (at 2.5m/min presumably)?

For example:

12mm cutter, 2.5m/min and 60% stepover at 6mm depth of cut is 108cm^3/min material removal rate (12*0.6*2.5*6=108). That's about 740W required...and a pretty rigid machine to sustain that. So you'd ideally want a PSU rated for a bit more than that to be safe. Also it's a good idea to put better capacitors on the ESC, especially with such long wires, to reduce the impedance...

Hopefully it'll turn out the motor draws a lot less current and you can just use a standard PSU.

[vtcnc]

That battery is rated for 60A constant, or 90A for 10 seconds which is plenty. Since my PSU has variable voltage output and current limiting I can set it to just below the fully charged voltage of the battery (i.e. <22.2*4.2) and it will never overcharge the battery, which is very important since overcharging a lipo battery is a good way to start a fire. So whatever PSU you get if you decide to use in combination with a battery will need to have good stable voltage regulation below 25.2V. Two computer ATX PSUs in series is nice and cheap and will give very close to 24V, however it is CRITICAL to ensure they are electrically isolated before putting them in series. The battery would never fully charge, but that's a good thing if anything as it increases it's life expectancy. You could get the battery first, use it to power the motor to measure the current then buy a PSU to suit.

Thanks Jonathan for this very helpful information. I hadn't realized that it was possible to connect ATX PSUs together in series to increase voltage -- just assumed they were regulated in a way that would prevent this. Makes sense really, when I think about it. Battery cells have nominal voltages and can be series connected into a battery of higher voltage. Somehow I got hung up on the regulated part of it.

Anyway, I've gone ahead and ordered two ATX supplies with 12V 30A outputs, and looking forward to making a 24V supply with them for a spindle PS. I will isolate the negative buss from the case, and I know about setting up the switch line and adding a starting load resistor on the 5V lines to keep the supplies running.

I build and fly R/C planes, so I'm familiar with the rest of the motor side components. I have two 5055 1500W rated motors -- one 400 kV and one 540 (I believe) -- both have 8mm shaft dia. I have an 8mm ER-11 collet spindle, and collets.

ps. I also wanted to post a possible correction to the above -- I think the bolded text above should read "(i.e. <6*4.2)"

Thanks for your PSU info!

[vtcnc]

(deleted and prior post corrected)