BuddyPress.org

Hi, it would be nice if someone could help me here.
What i want to have is, that the default group avatar is generated by robohash.org with the current_group_name at the end of the url.

Like this: robohash.org/current_group_name

I tried it with this already http://premium.wpmudev.org/blog/how-to-add-a-custom-default-avatar-for-buddypress-members-and-groups/

but with no luck 🙁