Servo register map

The servos use the Feetech STS register map. This dump was read on 2026-10-03 through the stock ATOM (GET_SERVO_DATA, one byte at a time) with tools/python/dump_servo_registers.py. Present position, load, voltage and temperature are live values. J1’s goal position was written during the tests; on the other joints it reads 0 (not written since power-up).

Names

The names follow Feetech’s STS register table (as in LeRobot’s table). Elephant’s documentation names registers 22 and 23 the other way round (“position loop I” and “position loop D”). Its own descriptions, Feetech’s table and the values on this arm show that 22 is D and 23 is I. See Stock protocol commands.

Feetech’s table also has factory registers 80–86 (for example the acceleration multiplier that applies when the acceleration is 0). They are not read yet.

What is not known

Register	Status
2	Not in Feetech’s table (reserved). Reads 0.
19, 20	Unloading condition and LED alarm condition. These are bit masks of the protections; the meaning of each bit is not checked. 19 reads 44/38 with the stock firmware and 0 with the custom firmware.
50–54	Not in Feetech’s table (reserved). Read 0.
64	Named “async write flag” from older Feetech documentation. Not checked.
67–68	Not in Feetech’s table. They follow the present position within a few steps.
71–79	Read 0 (71–77) and 255 (78–79). Not used.
80–86	Factory registers. Read on 2026-10-04; see Factory registers. The units are not checked.

All the other registers in the dump have a name in Feetech’s table, and the ones that the players use are confirmed below.

Encodings

• Little-endian: low byte at the lower address. Present position = reg[56] | reg[57] << 8.
• Speed (46–47, 58–59): bit 15 is the sign. Load (60–61): bit 10 is the sign, 0.1 % units.
• Offset (31–32): bit 11 is the sign. J3 0x0F7C, J4 0x0D1D and J6 0x0D4C are negative.
• Goal position (42–43) uses the same units as present position (56–57) in position mode.
• Voltage (62): 0.1 V. Temperature (63): °C.
• Register 19 (unloading condition) read 44/38 with the stock firmware and 0 with the custom firmware. The stock firmware probably writes it at power-up.

Registers confirmed by observation

Register	Observation
5 ID	1–6 on J1–J6.
6 baud rate	0 = 1 Mbaud.
33 mode	Writing 1 put J1 in velocity mode. Writing the mode turns torque off.
40 torque enable	A goal write sets it to 1.
41 acceleration	The stock firmware writes 50; the players write 0 (no ramp).
42–43 goal position	Same units as present position.
46–47 goal speed	0 = no motion in position mode; otherwise the speed cap. Drives the joint in velocity mode.
56–57, 58–59	Present position and speed; match the stock firmware’s get_angles.
62 voltage	J1–J3 ≈ 7.6 V, J4–J6 ≈ 6.4–6.8 V.
67–68	Follows the present position within a few steps. Meaning not known.

Full dump

Addr	Name	J1	J2	J3	J4	J5	J6
0	firmware major	3	3	3	3	3	3
1	firmware minor	9	9	9	9	9	9
2		0	0	0	0	0	0
3	model (L)	9	9	9	9	9	9
4	model (H)	8	8	8	7	2	2
5	ID	1	2	3	4	5	6
6	baud rate (0 = 1M)	0	0	0	0	0	0
7	return delay	0	0	0	0	0	0
8	response level	1	1	1	1	1	1
9	min angle (L)	0	0	0	0	0	0
10	min angle (H)	0	0	0	0	0	0
11	max angle (L)	255	255	255	255	255	255
12	max angle (H)	15	15	15	15	15	15
13	max temperature	70	70	70	70	70	70
14	max voltage	130	130	240	240	240	240
15	min voltage	60	60	60	40	40	40
16	max torque (L)	232	232	232	232	232	232
17	max torque (H)	3	3	3	3	3	3
18	phase	4	4	4	100	100	100
19	unloading condition	44	44	44	38	38	38
20	LED alarm	47	47	47	38	38	38
21	P	32	32	10	10	10	10
22	D	8	8	0	0	0	0
23	I	0	0	1	1	1	1
24	min startup force (L)	0	0	0	0	0	0
25	min startup force (H)	0	0	0	0	0	0
26	CW dead zone	3	3	3	3	3	3
27	CCW dead zone	3	3	3	3	3	3
28	protection current (L)	44	44	44	232	232	232
29	protection current (H)	1	1	1	3	3	3
30	angular resolution	1	1	1	1	1	1
31	offset (L)	146	102	124	29	192	76
32	offset (H)	0	4	15	13	0	13
33	MODE	0	0	0	0	0	0
34	protective torque	20	20	20	20	20	20
35	protection time	200	200	200	200	200	200
36	overload torque	80	80	80	80	80	80
37	speed loop P	10	10	10	10	10	10
38	overcurrent protection time	200	200	200	0	200	200
39	speed loop I	200	200	200	10	200	200
40	torque enable	1	1	1	1	1	1
41	acceleration	0	0	0	0	0	0
42	goal position (L)	111	0	0	0	0	0
43	goal position (H)	8	0	0	0	0	0
44	goal time / PWM (L)	0	0	0	0	0	0
45	goal time / PWM (H)	0	0	0	0	0	0
46	goal speed (L)	0	0	0	0	0	0
47	goal speed (H)	0	0	0	0	0	0
48	torque limit (L)	232	232	232	232	232	232
49	torque limit (H)	3	3	3	3	3	3
50		0	0	0	0	0	0
51		0	0	0	0	0	0
52		0	0	0	0	0	0
53		0	0	0	0	0	0
54		0	0	0	0	0	0
55	EEPROM lock	1	1	1	1	1	1
56	present position (L)	224	53	206	209	35	86
57	present position (H)	7	14	14	14	4	9
58	present speed (L)	0	0	0	0	0	0
59	present speed (H)	0	0	0	0	0	0
60	present load (L)	0	0	74	37	1	0
61	present load (H)	0	0	4	4	4	0
62	present voltage	76	75	76	68	64	64
63	present temperature	25	26	27	33	29	31
64	async write flag	0	0	0	0	0	0
65	status	0	0	0	0	0	0
66	moving	0	0	0	0	0	0
67	? position-like (L)	221	52	206	208	36	86
68	? position-like (H)	7	14	14	14	4	9
69	present current (L)	0	0	1	0	0	0
70	present current (H)	0	0	0	0	0	0

Factory registers 80–86

Read on 2026-10-04 from the Raspberry Pi (read only). The names are from Feetech’s table (via LeRobot). The units in the last column are a guess and are not checked.

Addr	Name	J1	J2	J3	J4	J5	J6	Possible meaning
80	moving velocity threshold	1	1	1	2	1	1
81	DTs (ms)	20	20	20	10	10	10
82	velocity unit factor	50	50	50	50	50	50
83	Hts (ns)	1	1	1	1	1	1
84	maximum velocity limit	68	68	68	120	150	150	× 50 steps/s: 3400 / 6000 / 7500 steps/s (≈ 300 / 530 / 660 °/s)
85	maximum acceleration	50	50	50	250	250	250	× 100 steps/s²: ≈ 440 / 2200 °/s²
86	acceleration multiplier (applies when acceleration = 0)	1	1	1	4	5	5

The values follow the three servo types (J1–J3, J4, J5–J6). The players write acceleration 0, so register 86 may set the real acceleration of each joint. This can explain part of the lag of J1–J3. Test it with the acceleration step tests in the roadmap.