7i43 + 7i52 + 8i20 + servo motor

Hello,

I have a servo-motor but don't have too much information about it: supports up to 220V, internal resistance 4Ohms, weight 3kg.

I'm trying to make it work with an 8i20 that is connected to a 7i52 and then to a 7i43.

For the moment I'm limitiing the input voltage of the 8i20 to 64V DC.

Right now the current-maxlim is set to 1.5A, current-minlim is set to -1.5A and current-maxscale to 1.


My questions:
* What's the approximative the value for the regenerative resistance
* How to calculate the NVBRAKEONV and NVBRAKEOFFV

The brake resistor value must be high enough so that the maximum brake switch current (15A) is not exceeded.
for the default BrakeonV and BrakeOffV, this is ~25 Ohms minimum. Do note that a minimum value brake resistor at
340V VBUS dissipates ~5200 W (intermittently) so make sure any resistor you chose can stand the peak power
requirements (average power will be much lower, probably no more than a few hundred watts with lots of fast braking)

The brake resistor protects the 8I20, _and_ your power supply from excessive bus voltage
during braking (deceleration) when the kinetic energy of the mechanics is dumped back into
the power supply filter capacitors.

So if you have a rectified 240 power supply (340V nominal DC bus voltage) The default 8I20 values (on at 380V off at 360V)
are fine.

If you have a rectified 120VAC power supply you would set the values to say 200V and 180 V
(mainly to protect your filter capacitors)

You may have to tweak these values depending on your exact power supply voltage and voltage stability

Ok so for the resistance I have something around the 130 ohms so it should be able to maintain the current under 15A given my current tension.

Now for the NVBrakeONV and NVBrakeOFFV, the voltage is 60V so following the logic I tried a NVBrakeOFFV of 6200 and NVBrakeONV of 8400 and the card is always in breaking.
If I lower NVBrakeOFFV to 6000 (which corresponds to 60V due to 10mv unit) the card is not breaking.

Why is the card breaking when the voltage is lower than NVBrakeOFFV ?

First off I would always set the BrakeoffV at least 10V higher than the nominal PS output voltage
(and much higher if your power supply will take it)

Also note that you must power cycle (control power cycle not motor power) the 8I20 before
newly set NV parameters are used

Hello,

So indeed it's the case (is it in the 8i20 documentation ?).

I found those parameters:

NVBUSUNDERVMAX

NVBUSUNDERVMIN

What is the meaning of those 2 parameters ?

Also,

My HAL file is almost empty, I haven't configured anything for the motor but
I set current_maxlim to 3.5A and current_minlim to -3.5A current_scalemax to 2.5

The motor's torque seem to be null as I very easily rotate the axis.

Intially I tried with current_minlim 1A current_maxlim 3.5A (as I didn't know that maxlim and minlim should have the same absolute value) and in this case the motor has signifiant torque (it was pretty hard to rotate the axis with the hand).

NVBUSUNDERVMAX and NVBUSUNDERVMIN set the limits of the 8I20s operational range versus VBUS

PWM will be disabled outside of these limits, unless you know exactly what you are doing they should not be changed.

torque is expected to be null unless you set a current

unsymmetrical bounds may cause an offset current, not sure (and unsymmetrical bounds make no sense here)