I feel the same - the middle part of a research project is always the worst and I hate the feeling of despair at how much further there is to go until the end. I definitely had doubts as to the worth and purpose of my project, so you are not alone!

I found that the best way of overcoming the dip in motivation is to stick it out, and in the meanwhile take motivation from anything and everything you can. I found that thinking about what originally motivated me helped to put things into perspective. Also another thing I found helped was to write down all that I had achieved up until now (rather than focussing on the things that I hadn't) and this meant I could feel more positive about the position I was in.

I also found that taking small steps such as setting realistic targets for just one day meant that I wasn't forever chasing big goals that made me feel I wasn't getting anywhere. Support from my supervisor was vital as he reassured me that what I was doing was along the right lines and that I was making the right progress. Hope this helps.

If you are passionate about what you have found then this is surely half the battle! I think when you are not happy with what you are doing it is so difficult to convince others it's interesting. If you are excited by your discoveries then you have to have confidence in your ability to convey them in your writing - I'm sure you are very capable!

Although writing up seems like a massive task now, the answer, I find, is to break it down and set short term goals so that you will see your ideas progressing. Perhaps concentrate on what you really want to say in each section in the way it comes to you - then spend some time working with the ideas to write them convincingly for others.

I also found this link to some tips on boosting motivation: http://ezinearticles.com/?7-Tips-For-Boosting-Motivation&id=2245272. Hope it helps!

Does anyone else find that there are particular times of year that also bring on the slump. I know this thread started looking at the overall PhD, but personally I always struggle through October / November. Perhaps it is the weather in the UK, although I wouldn't say I had Seasonally Affected Disorder.

I also think that universities are just so hectic and busy at the start of the new academic year it can be a bit distracting.