Could not find codec parameters -- for gif?
It's worth a try using the concat demuxer.

First, create a text file like this:

file 'motor_animate_000.gif'
file 'motor_animate_001.gif'
file 'motor_animate_002.gif'
file 'motor_animate_003.gif'
...


Then run

ffmpeg -f concat -i list.txt motor.mpg


Do note that by just specifying a .MPG filename as output parameter, ffmpeg will encode to MPEG-1 at a bitrate of 200 kb/s. If MP4 is not acceptable and .mpg is needed, then add -c:v mpeg2video -b:v 1000k after list.txt to set codec and avg. bitrate. For MP4, just change extension; the defaults are decent.