Hi Albert,
Thanks for your post. Regarding your 1st question about interfacing a RE40 82uH motor with the NI9505 (which requires 500uH for current sense) I would like to refer you to the KB article here which refers to using the MID-765x Drive with Low Inductance Motors. Although this is a different model power drive the principles described should be the same, I would also recommend researching the implications of using inductors in series with motors before considering this solution.
Can I also refer you to the forum here which details a similar configuration.
Regarding the reasons behind the strange behaviour you are experiencing with the old DC motor my initial thought is that this is also due to the current sense specification for the NI9505 not being met.
Hope this helps with your proposed application.
Thanks
Jamie S.
Jamie S.
Applications Engineer
National Instruments