sharp corners

Excellent! For me, the best levels have more than one solution. This one offers that and more. Also features multiple clever instances of the subtle no-go effect, to block B from where he thinks he can go.
Great fun - Thanks!

@meko

Spoiler

One of my methods, which matches the designer's hint, is to sacrifice B. This is more of a shortcut, i think, than the other way which gets around his cunning no-go traps.
Sounds like you have two methods too? A precision method, and a shortcut?

@meko - all solutions that are achievable within the confines of the game are valid, in my opinion... Whether or not the designer intends for there to be multiple solutions to his puzzle.

Each solution, intended / alternative / shortcut, is a source of enjoyment when mastered. And therefore it is to the credit of the designer if his challenge supports multiple solutions.

Don't you agree?

I'm not sure what you mean about "cheating with luck", but regarding how shortcuts affect the final rating, this puzzle is a good example: the intended solution might be simple, which could earn it 3 stars; but since the alternative solution provided further enjoyment, I'm quite happy (if not compelled) to give it some more.

I'm not sure which is the intended solution, but here are the ones i found. I'm sure you'll agree that removing either one would detract from this excellent puzzle..

Spoiler

Solution 1:
Send B to block 1 and wait until the leftmost R (above) comes around and kills him, turning him into an obstacle in R's path. R will then turn right at block 2, and find the win in consolation!

Solution 2:
Notice that B can't step onto the slider from block 3, due to a crafty use of the no-go effect (which prevents B from stepping onto a slider whenever it occupies its start-time position). B can, however step onto the slider from block 4... choosing the right moment to avoid both R bots. The trick is to follow the leftmost R around one circuit of his rectangular path, and then wait on block 4. When the other R passes by to the left (our left from the perspective above), he will leave the slider unguarded, and you just need to step B onto it as it pauses in front of him, and hitch a ride to the win.

Nice!!!