thotalion / bldc-design-help

Tests on BLCD controller to understand robotic articulation design

Help to design BLDC articulations

BLDC controllers are very new with respect the classical DC motor controllers, mainly taking into account position control. The objective of this repo is to gather studies to help design of robots (small and big) with BLDC.

STL files

Find in this Repo the STL Files used to test the two motors. Find also STL files for the USB-CAN Box for the Tinymovr kit.

Motors

	Motor 1	Motor 2
Picture
Ref	Eachine 2204-2300KV	MAD component 5005-280KV
Resistance/phase(milliOhms)	170	100
Inductance/phase(microHenri)	10	76
Outer diameter(mm)	28	56
Max quadratic current Iq in coils	12 A	18 A
Purpose	Fast/silent animatronics (eye)	Powerful robotic articulation

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Tinymovr controller

Documentation Here, the tinymovr controller board is powered by a DC power supply 15V - 10A. The communication is done via a standard FTDI USB - UART device (for experiment purpose here... Later via CAN bus) By default, Iq is limited to 10A and speed to 300000ticks/s 1 turn is 8192 ticks.

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Theory about BLDC

The motor current

Iq = (Ia/sqrt(3) + 2*Ib/sqrt(3))cos(theta) - Iasin(theta)

The torque constant

Torque (N.m) = Kc*Iq(A)

The speed constant

U(V) = Kv*Omega(rad/s)

Knowing that Kc = 1/Kv

The power in the system is used in internal resistor, controller and to general mechanical movement

P_in = P_Joule + P_controller + P_mecha

P_in = U_in.I_in = I_q.I_q.R + P_controller + C*Omega

P_controller in control state is here 0.060A for 15V => 1W

To get the input current when motor is blocked (consider power of controller is small enough) :

I_in = R.I_q.I_q/U_in

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A small motor (2204-2300KV) + Tinymovr controller - push test

the motor is set next to a weighing scale with a lever arm of 95mm. Input voltage : 15V.

Measures

Position target (ticks)	Motor current Iq (A)	Input current Iinput (A)	weight (g)	torque (N.m)
0	0.918	0.060	0	0.000
1000	-0.165	0.060	5	0.005
2000	-3.640	0.120	13	0.012
3000	-6.112	0.230	21	0.020
4000	-8.710	0.420	29	0.028
5000	-10.040	0.570	34	0.032

Find below the input current of the Tinymovr controller function of the current delivered in coils.

Find below the torque generated by the motor function of the current delivered in coils

Kc = Torque/Iphase = 0.032/10.04 = 0.0032 N.m/A

Kv = 1/Kc = 310.8 rad/s/V

KV = 2970 rpm/V

And find below the torque produced function of input current

A bigger motor (5005-280KV) + Tinymovr controller - push test

the motor is set next to a weighing scale with a lever arm of 98mm. Input voltage : 15V.

Measures

Position target (ticks)	Motor current Iq (A)	Input current Iinput (A)	weight (g)	torque (N.m)
0	0.277	0.050	0	0.000
1000	-1.983	0.090	50	0.048
2000	-4.547	0.200	112	0.106
3000	-6.995	0.420	175	0.166
4000	-9.527	0.740	236	0.224
5000	-9.973	0.840	247	0.235
6000	-10.025	0.860	249	0.237

Find below the input current of the Tinymovr controller function of the current delivered in coils.

Find below the torque generated by the motor function of the current delivered in coils

Kc = Torque/Iphase = 0.032/10.04 = 0.0234 N.m/A

Kv = 1/Kc = 42.7 rad/s/V

KV = 407 rpm/V

And find below the torque produced function of input current

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A small motor (2204-2300KV) + Tinymovr controller - speed test

the motor is without load

Speed target (ticks/s)	Input amps (A)	Measured speed (ticks/s)
0	0.060	168
7000	0.060	506
8000	0.060	2373
10000	0.060	9880
20000	0.060	17605
40000	0.060	38343
80000	0.060	79606
160000	0.070	147904
320000	0.080	278386
640000	0.090	281503

See that until 10000 ticks/s, the measured speed is far from the commanded one. The rotor slips and is too slow. On the contrary, the high speed does not go above 300000 ticks/s. This is nominal since the speed is limited (can be tuned in Tinymovr)

A bigger motor (2204-2300KV) + Tinymovr controller - speed test

the motor is without load

Speed target (ticks/s)	Input amps (A)	Measured speed (ticks/s)
0	0.060	-0
5000	0.060	-292
6000	0.060	4173
7000	0.060	4915
8000	0.060	5408
9000	0.060	7836
10000	0.060	8835
20000	0.090	75905
160000	0.140	166808
320000	0.470	270000

See that the motor can reach slower speeds even if it slips.

Reactivity tests with a LeapMotion

This part is in progress, waiting for CAN controllers. Here is a small video with serial communication. The position gain is small by default, that is why, the phase inversion occurs at a very low frequency (with respect to a classical DC controller like Dynamixel) The code is in this Repo (Leap2BLDCUART folder)

Motor control with pygame

The folder MotorControl contains a Python3 script to control a brushless motor with a Tinymovr controller. Change the name of the serial port in the script before starting.

The key hacks are :

• Up arrow : hold position
• right arrow : decrease and hold position
• left arrow : increase and hold position
• z : set current position as zero
• c : calibrate
• r : reset the controller
• p : oscillate position between max and min current
• space : soft emergency stop

With a belt reductor

The belt reductor design is under progress, based on Open Dynamic Robot Initiative