I'm using GIM6010-8 + GDS68 on a lifting axis. When the load comes down the bus voltage spikes. Does the GDS68 support an external braking resistor, is there a recommended part, and do I need one per driver?
Yes, the GDS68 has an interface for an external braking resistor. The driver manual describes it as dissipating regenerative energy when the back-EMF voltage exceeds the relevant threshold.
SteadyWin does not give a fixed standard resistor for this. You size it from your motor and load:
Their guidance, roughly translated: calculate the theoretical back-EMF voltage from the motor parameters and the speed the falling load reaches, add a threshold, then work out the resistor.
As for quantity, SteadyWin's current recommendation is that one braking resistor can be connected to the braking interface. The final configuration depends on your actual system and how much regenerative energy you need to absorb.