Servos: have you noticed ...
Servos: have you noticed ...
by jerome
Sun Nov 25, 2007 7:38 pm
Hello everybody,
Have you noticed, that once the power button on the CM5 is ON, the servos are all harder to rotate, although they should not apply any couple! When the switch is OFF, they rotate easier again.
I insist that this happen even if no program is running, in the bootloader for example. Does anybody know why? Does this mean they consume power even in the idle state?
Thanks,
Jerome.
Have you noticed, that once the power button on the CM5 is ON, the servos are all harder to rotate, although they should not apply any couple! When the switch is OFF, they rotate easier again.
I insist that this happen even if no program is running, in the bootloader for example. Does anybody know why? Does this mean they consume power even in the idle state?
Thanks,
Jerome.
by hivemind
Mon Nov 26, 2007 4:29 am
That's interesting... the DX-117's do exactly the opposite. We have a voltage monitor in our robots, and when the bots are unplugged and we move their servos, the low voltage light activates (and the servos are relatively hard to move). As soon as power is on, the servos become completely loose.
by jerome
Mon Nov 26, 2007 8:58 am
Indeed this is interesting. With the DX-117, as you describe, the low voltage light activates because the servo motor is acting as a generator.
If the behaviour is the opposite with the DX-117, then this must be a matter of resistive load, which is lower when the DX-117 is on, and higher when the AX-12 is on. If this is really the case, that would mean the motor does not actually consume power, which was what I am afraid of.
After all, when we rotate the servo horn, the motor must be spinning really fast in there ...
If the behaviour is the opposite with the DX-117, then this must be a matter of resistive load, which is lower when the DX-117 is on, and higher when the AX-12 is on. If this is really the case, that would mean the motor does not actually consume power, which was what I am afraid of.
After all, when we rotate the servo horn, the motor must be spinning really fast in there ...
by JonHylands
Mon Nov 26, 2007 1:25 pm
jerome wrote:Indeed this is interesting. With the DX-117, as you describe, the low voltage light activates because the servo motor is acting as a generator.
Interestingly, with BrainBot, when I move the servos manually (and it is switched off), the power LED for the bus lights up. Note that this is a custom switch/circuit, so the fact that the CM-5 doesn't do it may just be a circuitry issue.
- Jon
by hamid_m
Wed Nov 28, 2007 4:39 pm
Hello,
In Ax12 there are two Half Bridge switches which can be either low or high after power on. this makes it impossible to have the motor terminals floating, i.e connecting to nowhere. this means the motor terminals are shorted while you apply 0 torque, which makes a brake. this is an unpleasant feature of AX12(at least for me
) which is corrected in DX117.
Hamid.
In Ax12 there are two Half Bridge switches which can be either low or high after power on. this makes it impossible to have the motor terminals floating, i.e connecting to nowhere. this means the motor terminals are shorted while you apply 0 torque, which makes a brake. this is an unpleasant feature of AX12(at least for me
) which is corrected in DX117.
Hamid.