I created a draft for a press release for the 24 hour record attempt – It is still a work in progress, but you can check it out here if you like:
http://www.adventuresofgreg.com/24hour.html
Then I made plans for a long training day today (Thursday) on the water with the boat gathering some really solid speed/watts averages over about 5 hours. This is what I need as my final sort of confirmation that breaking Carter’s 242 km distance record is even remotely possible for me.
I’m not sure I mentioned this before, but I found some spring steel to use as a flexible propeller shaft, but it was 1/4″ rather than my 3/8″ stainless shaft. I had to get my machinist wizard to whip me up some new couplers to mount the shaft onto the gear box, and to mount my 3/8″ bore prop and hardware onto the other end of the new 1/4″ shaft. I picked up the new parts from Manny yesterday and installed them along with a new 55 tooth chain ring and new Dura-ace chain. Of course, the new chain ring meant adding a link to the chain which meant moving the gear box back to tension the chain, but I didn’t think twice about it and assumed everything would be great.
Wrong. (loud buzzer inserted here!). I drove 45 minutes to Ghost lake today prepared to spend the day out there and right away the prop started smashing into the hull. DAM! When I adjusted the gear box position, I had inadvertently reduced the shaft angle and now at 150 watts (about 83 rpm with my new gear ratios), my razor sharp prop starts to slice through the thin carbon hull. Basically, two knives spinning at 400 rpm.
I stopped in time to save the hull from being cut open and messed around with the chain length and gear box angle to fix it lake-side. I was able to lower the prop so it didn’t hit the hull when I spun-up by lengthening the chain. The chain was floppy and derailed continuously, but I did get a couple of out and back runs in at my target 150 watts. My speed was disappointingly slow – I think just over 11 km/hr – that sucks! I was expecting an additional .2 km / hr speed GAIN. The reason is that I was speaking to George from Mitrpak about the preload on the gear box. He had run some tests and determined that I should back-off the lock nuts and remove the seals. I did, and instantly REMOVED the 5 watts it took to spin the gear box! This is really new news, as an 5 additional watts is now magically ADDED to my power which according to the calculator, should result in an additional 1.5 to 2 tenths of a km/hr speed gain. For free! I have no idea why I wasn’t seeing anything close to what I was expecting for speed, so I packed everything up and drove the 45 minutes back home. It was getting windy as freaking usual, so that could be one reason for the lack-luster speeds.
Back into the shop yet again. I decided the best way to isolate the gear box angle from the chain tension is to add a spring loaded chain guide. Luckily I had a Surely chain guide that I was able to fit onto the frame. It actually works really well. I can adjust my gear box angle, or swap the 12 tooth gear for a 13 tooth and not have to add or remove links from the chain.
The plan is to test this at Elbow tomorrow morning first thing before the wicked wind starts to roar. I have two shafts ready to test – the free, strutless shaft and a version with the old strut. I’m trying to get everything set so I can focus on planning the 24 hour event and my training. I expected that I was there – done. Ready to move on. This is very frustrating. I’m also trying to get everything set for a long testing day at upper Kananaskis lake on Saturday with my friend Chris Comfort.
ah well, if this was easy everyone would do it. Actually, no. I think they would all rather be doing something else. Non-stop pedalling for 24 hour straight isn’t exactly a luxury cruise.
I also changed the steering –
this works WAY better and I guess it was one thing that happened today
Anonymous on June 27, 2008
I guess all you can say is "Doe!".
"And what have you learned from this, grasshopper?" Each set-back in life is meant to teach us something.
Maybe, we learn how to swear better.
With your kind of tenacity, this problem is 'nuttin'.
Koen on June 27, 2008
Why use a 12 or 13 tooth gear? I am no expert at all, but according to what I can remember it takes away more power than a 16 tooth gear. You can easily keep the same ration by using another number of tooth at the front.
I think it's just a very small difference, but it might help.
Neil Martyn on June 27, 2008
Tomorrow is another day, as they say.
On the second comment about sprocket sizes, I too had read (perhaps in Bicycling Science?)that more teeth = higher efficiency, possibly because on a bigger cog the chain links are swivelling through a smaller angle. Will the transmission geometry allow say, 78/18? Might give you a watt or two.
Jarl on June 27, 2008
An eccentric bottom bracket would probably be a better setup for adjusting chain tension then that spring loaded chain guide you've opted for. I had just one like that for a single-speed mountain bike and it added a noticeable drivetrain drag compared to "magic gear".
Anonymous on June 28, 2008
Almost any tandem company can sell you an eccentric bottom bracket premade. You might also talk them into the matching bottom bracket tube that you could weld directly onto your frame. I'd suggest CoMotion or Santana. They both make frames from multiple materials.
It does sound like a search for the biggest chain ring you can find would make sense too, so that you can use a larger cog.
Peter Raymond