I'm trying to make a swing rotor centrifuge and find a proper BLDC motor to reach 6000G with capacity of 4x50ml Falcon tubes. I did the calculations roughly but I'm not so sure about them and also couldn't find a proper motor for my calculations.
My rotor will be something like this;
Well for my calculations;
- Mass of the system : 250gr (50gr for body and 4x50gr for tubes)
- Radius of the body : 6.5cm (I'm trying to minimise it to minimise the inertia)
- RCF : 6000
- Ramp-up from 0 to 6000G : 10s
And probably my supply voltage will be 12V or 15V and my custom ESC can deliver up to 20A.
And from those inputs I get;
- Inertia : 0.000528125 kg*m^2
- Angular Acc. : 95.1056763541775 rad/s^2
- RPM : 9100
- Torque (with %20 safety margin) : 60.27mNm
- Power : 57.4W
But for example when I go and search for a motor such as this; https://www.alibaba.com/product-detail/500W-High-Power-Brushless-Outrunner-DC_60283824747.html?spm=a2700.7724857.normalList.33.4ab2c274DKm1Vs
It seems the torque is well within specs. But to get 9100RPM I need to supply 10.1V which may cause decrease in torque (?).
Also taking Torque Constant into account I get; 5.7A and it seems too low to me. I mean can I really make this thing spin from 0 to 9100RPM in just 10 seconds with just 10V and 5A?
And there is also Back EMF which I still didn't quiet understand. For the motor in the link, BEMF constant is 0.0011V/rpm and when I calculate torque producing voltage I get 0.6V, does this mean that I actually drive this with 0.6V? If so, than I need 95A to spin it with 9100RPM? But with terminal resistance involved, my available current is 0.6/0.1 = 6A, so I can't drive this with 95A, because of terminal resistance?
As you can see, I'm really confused and I'm really new at this things, so any help would be great.