POST No. 2407939
How to lower the Max Torque of the X-series
2020-08-26 08:28:18 robotiscustomer

Hi, I read that in the past, there was a MaxTorque parameter to allow the user to lower the maximum torque of the dynamixel at will. However, I cannot find it in the control table of the X-series. Could you let me know how to do it on the X-series please?

2020-08-26 08:28:18
2020-08-27 16:33:24 Will Son


There are multiple ways to control the output current, but the easiest way to do it is to manipulate the Goal PWM(100) value.

If you have XM or XH series, you can set their Operation Mode(11) to Current-based Position Control Mode, then adjust Goal Current(102) to limit the maximum current.

Thank you.

2020-08-27 16:33:24
2020-08-27 17:35:43 robotiscustomer

Thanks. Under Current-based Position Control Mode, the emanual states "Up to 512 turns are supported(-256[rev] ~ 256[rev]). " What is mean by that? Probably it does not mean It can turn clockwise and counter-clockwise respectively by 256 times. 

Also, is it advisable to change the Operation Mode and the Goal Current values within my program which uses the Dynamixel SDK or do it via Dynamixel Wizard?

2020-08-27 17:35:43
2020-08-28 14:39:44 Will Son


The Position Control Mode only supports 1 rev(0~4095) while Current-based Position Control Mode supports 512 revs(-1048575 ~ +1048575).

The Operation mode(11) is saved in the EEPROM of DYNAMIXEL while Goal Current(102) doesn't so you have to set it every time power switches.

Thank you.

2020-08-28 14:39:44
2020-08-31 06:25:21 robotiscustomer

Thanks. In the emanual, 2048 is in the 12:00 direction while 0 and 4095 is in the 6:00 direction. In the case of Current-based Position Control Mode, how do these -1048575 ~ +1048575 position values correspond to the actual rotational in degrees? Is there a picture to illustrate the representation?

2020-08-31 06:25:21
2020-08-31 16:26:46 Will Son

The encoder counts from 0 to 4096 (= 0) within a single rotation, therefore, every rotation will add or subtract 4096 when passing the 6:00 position.

Multiplying the constant you get from 360 / 4096 = 0.08789 to the position value will give you the corresponding angle in degrees.

Please notice that 0 ~ 1048575 (1048576 encoder tick) is equal to 4096 x 256 rotations, therefore, -256 ~ +256 rotation is supported under the Current-based Position Control Mode.

Thank you.

2020-08-31 16:26:46
2020-09-07 09:53:22 robotiscustomer

Hi, from the eManual of the X-series, I read that the PWM Limit (36) is "commonly used in all operating mode as an output limit, therefore decreasing PWM output will result in decreasing torque and velocity."  Then, from the description for Current Limit(38), it states that it is "used in Torque Control Mode and Current based Position Control Mode, therefore decreasing the Current Limit (38) will result in decreasing torque of DYNAMIXEL:.

If I only do position control but want to also get the torque of the DYNAMIXEL, can I just use the Position Control Mode and then set the PWM(36) to lower value to reduce its maximum torque instead of using the Current-based Position Control Mode? 

In case of using the Current-based Position Control Mode, which is a better method to reduce to torque? Reducing the PWM output or the Current Limit? It seems that both can be used to reduce the torque at least in the Current-based Position Control Model. Thank you.

2020-09-07 09:53:22
2020-09-08 09:31:14 Will Son


Manipulating torque with PWM Limit(36) and Goal Current(Current Limit) have significant difference.

The PWM Limit basically controls the input source to the core motor and therefore affect to torque and speed at the same time.

However, using the Goal Current, PWM does not limit the input source, and Torque is monitored by the current controller, therefore, the speed can be maintained and precise torque control can be possible.

You may use any of these methods that is suitable for your application.

Thank you.

2020-09-08 09:31:14
2020-09-10 02:28:03 robotiscustomer

Thank you. So, for a project that uses position control but also gets the torque of the XM/XH series of DYNAMIXEL, it is better to use Current-based Position Control as it does not affect the speeds? The reason I want to lower the torque temporarily is to avoid damaging the DYNAMIXEL during the testing phase. 

2020-09-10 10:37:12 willson
You're right. The current base position control will provide the most appropriate condition for your case to minimize any mechanical damages.
2020-09-10 10:37:12
2020-09-11 09:59:25 robotiscustomer
Thank you. If I want the torque to be 1/x of the maximum torque, am I correct that I have to first set the Operating Mode to 5. Then, set the Current Limit (38) to 2047/x?

What will happen if I just lower the Current Limit but keep the DYNAMIXEL in the default Position Control Mode?
2020-09-11 09:59:25
2020-09-11 11:08:30 willson
You can also simply use Goal Current(102) which can be adjusted while Torque is turned on.

For setting Current Limit(38) or Goal Current(102) value, please refer to the Current Limit(38) of your product as each product have different maximum value.

Current limit is not used for Position Control Mode as written in Current Limit section of eManual.
Thank you.
2020-09-11 11:08:30
2020-09-10 02:28:03
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