Crab canon

I guess most of us know Bach's crab canon from him Musical Offering. 

I have already tried doing a crab canon, but the result was pretty ugly, I did it with little knowledge about counterpoint.

If anyone has any idea of this subject please leave a comment because I would like to try writing a canon using the same technique Bach used.

Bach's crab canon:

My attempt:

Plus:

You've got the right idea, but I'll go through the basic procedure below anyway. Your main issue is your counterpoint. You need to learn basic two-part counterpoint, including double-counterpoint, if you're going to be writing canons.

For a crab canon, start off simple: 8 bars, 4/4, in C major, canon at the octave, one whole note per bar. And use only diatonic notes for your first practice tries.

There is no proposta and risposta, since both voices enter at the same time. 

Yes, that will be boring, but it's better to learn the procedure first.

In the treble clef: put a C4 whole note in the first and last bar.

In the bass clef: put a C3 while note in the first and last bar.

Now you have just the 6 bars to fill in.

Overall, the procedure is to write from both ends—in both voices—with every note decision you make. So...

Choose (and notate) a note for bar 2 in the treble clef. If you chose, say, an F4, then after notating that, you'd also notate an F3 in bar 7 of the bass clef, since that provides the necessary retrograde movement.

Next choose and notate (in bass clef) a consonant to the F4 in bar 2. If you chose contrary motion for an A2, then after notating that, you'd also notate an A3 in bar 7 of the treble clef.

You just carry out this procedure from there until everything meets in the middle.

You can now elaborate those whole notes—conservatively, in several passes—using adequate voice leading technique. It goes without saying that the rhythms also must occur in retrograde.

From this basis you can gradually write more elaborately with each new canon.

If later you want to be able to write the canon on a single line, it has to be a canon at the unison, and you still need to composer it on two staves. After that's all squared away, you can write it on a single staff with a backwards treble clef at the end.