so i made my self a fixed gear about a week ago and so far everything has been great except today i got some slipping action and im not really sure what it is. when im pedaling my crank seems to slip and its not like the back wheel is slipping its just my feet slip half a rotation to a full rotation with no difference in the momentum of the bike, this has happened while accelerating cruising and stopping so its just kinda random. i ride an old motobecane if that helps