Diy Brushless Spindle

[m_c]

Jonathan, have you ever had any problems with cell balance using a LiPo?
I'm just wondering how actually using a multicell pack without balancing it works out longer term, as my current project needs a 2cell pack, and I'm trying to decide if I really need to include a balancer circuit.

[Jonathan]

Jonathan, have you ever had any problems with cell balance using a LiPo?
I'm just wondering how actually using a multicell pack without balancing it works out longer term, as my current project needs a 2cell pack, and I'm trying to decide if I really need to include a balancer circuit.

Not had a problem, except when the battery is already on it's way out. With a 2 cell battery I doubt you need to bother with balancing.

[m_c]

Not had a problem, except when the battery is already on it's way out. With a 2 cell battery I doubt you need to bother with balancing.

It's one of these things that gets mentioned alot, but not sure how much difference it's going to make in practice. I'm probably going to at least add the circuitry to the PCB as I've spare ADC pins on the uC anyway, and might built a couple prototypes with and without the extra components just to see what happens. I'm aiming for longetivity, so it may be a case of every little bit helps!

[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)

[njhussey]

Made some progress on this after concentrating on helis for the last goodness knows how long. The amount I've spent on helis recently I probably could have built a reallt top notch router by now.....oh well still having fun with the helis so not too worried :D

Anyway....below is the progress I've made with the spindle housing, will dig out the bits from the box in the cupboard tonight and see if I can put it together tonight (minus the bellville washers as I've forgotten to order them!!)

[njhussey]

Here it is roughly assembled....I know the shaft is sticking down by 12mm ish as I've not put it all the way in the motor bell, see last pic! I'm waiting on getting some Bellville washers then I can finish it off :)

[Tenson]

Brilliant work :)

What is your PSU?

[blackburn mark]

I'm waiting on getting some Bellville washers then I can finish it off :)

i could have sworn i sent you some

[njhussey]

Brilliant work :)

What is your PSU?

I can't take any credit as I followed what blackburnmark did, ok I adapted it a bit but the principle was the same :)

I'm going to be using one of the cheap 40A 24V psu's from eBay...