How to use SOEM EtherCAT master on PC to control an EtherCAT slave device

Question

I'm trying to control an EtherCAT slave which is a robot gripper. The slave info is as follow, which is retrieved using the sample program slaveinfo inside the SOEM package:

SOEM (Simple Open EtherCAT Master)
Slaveinfo
Starting slaveinfo
ec_init on eth2 succeeded.
wkc = 1
1 slaves found and configured.
Calculated workcounter 3

Slave:1
Name:netX
Output size: 128bits
Input size: 128bits
State: 4
Delay: 0[ns]
Has DC: 1
DCParentport:0
Activeports:1.0.0.0
Configured address: 1001
Man: 0000ffff ID: 0000000b Rev: 00000000
SM0 A:1000 L: 128 F:00010036 Type:1
SM1 A:1080 L: 128 F:00010032 Type:2
SM2 A:1100 L:  16 F:00010074 Type:3
SM3 A:1d00 L:  16 F:00010030 Type:4
FMMU0 Ls:00000000 Ll:  16 Lsb:0 Leb:7 Ps:1100 Psb:0 Ty:02 Act:01
FMMU1 Ls:00000010 Ll:  16 Lsb:0 Leb:7 Ps:1d00 Psb:0 Ty:01 Act:01
FMMUfunc 0:1 1:3 2:3 3:0
MBX length wr: 128 rd: 128 MBX protocols : 04
CoE details: 33 FoE details: 00 EoE details: 00 SoE details: 00
Ebus current: 0[mA]
only LRD/LWR:0
End slaveinfo, close socket
End program

, and the register map of the slave device is as follow:

What I want to do now is to set the rACT bit, which is bit0 in byte0 of the output register, to 1, so that I can activate the device.

I modify the simple_test sample code in SOEM. After making the slave device into operational state, I tried:

uint8 * data_ptr;
data_ptr = ec_slave[1].outputs;
*data_ptr = 0x01;
ec_send_processdata();
ec_receive_processdata(EC_TIMEOUTRET);

I'm not sure if this really write the value 1 to bit0 of byte0. All I can see is that the gripper is not moving at all, which is not an expected behaviour.

I'm completely stuck here and don't know what's the next step I should try, or what kind of material I should study. Any suggestion are appreciated! Thanks.