September 23rd, 2010
By Emiliano Jordan
As is the current state of the Eurobike / Interbike scheduling, the cat is out of the bag and we know that Polar and Look are working in a partnership to provide a pedal-based power meter. So I took the chance at Interbike to sit down and talk to Fredirck, Look’s lead Pedal Powered Product Project Proponent. Okay, he’s actually Look’s lead on the pedal-based power meter, and he has a lot to say.
First, there is a little intro to be done. The pedal-based power meter is something that has been sought after for a couple reasons. The main one, in my opinion, is the ability to isolate each leg for insight into a rider’s pedal stroke and efficiency. Potentially large gains in wattage could be uncovered with the right measurement tools, coaching and practice. The second is a little more common in the industry and involves “cool, that’s different.”
The Look / Polar collaboration is the closest I’ve seen to a production product. Testing on the pedals has moved out of the lab and onto the road by various teams. A targeted price of $2,000 – $2,300 US dollars has been set. We also know that the weight is going to be around 340 grams (excluding cleats) for the set, setting you back 245 grams when compared to Look’s top of the line Keo Blade model. For now I’m going to leave you with that and we’ll dive into some of the details on the pedal. Feel free as you read to leave me some comments below with your thoughts.
First of all, how accurate is it? Well, for starters, there are eight strain gauges per pedal, which means there are the same amount per pedal as the SRM has in the crank. But there are issues here to overcome. One thing to note however is that the SRM, Quarq and Power Tap units are measuring the moment placed on an axle. Therefore the force is much easier to measure. On a pedal, things get more complicated, and deriving your power requires more calculations. Look has placed a sensor on the body and axle of the pedal to measure your cadence, but for the most part this starts to get into math that is worthy of it’s own post. Again, this hasn’t proven to be a problem, and until there is real world comparable data (anyone want to ride this, an SRM or Quarq, and a Power Tap?) we won’t know the accuracy for sure.
Polar Computers and Head Units…
Considering the partnership with Polar, it’s not surprising that the unit is only compatible with Polar units, the CS600X, CS600, and the CS500 to be exact. Polar has obviously been in the game a long time. The only issue I can see here is GPS. None of the Polar units offer GPS, and I don’t imagine that polar is looking to get into that game anytime soon. As a tech geek I love numbers, and obviously GPS involves a lot of numbers — pairs of them in fact. It doesn’t seem like either party is considering a move to the already popular ANT+ system either. An issue brought up during ANT+ the discussion is current software limitations, considering the power meter’s need to send both left- and right-leg data. I do not consider software limitations to be good enough of a reason, there are plenty of talented and creative programmers.
Transmitting and Transmitters
For the pedal to effectively transmit data to the Polar Computer, a transmitter was mounted to the pedal behind the cranks (one on each side). One of the most commonly voiced concerns about the system was the vulnerable looking position of the transmitter. I spoke with Fredrick about this, and as with most things, the engineers had thought of every thing I had. Look could not mount the sensor in line with the crank (hidden behind is another way to think of this) due to chainstay clearance. A lot more discussing ensued and I left convinced that although I was still uneasy about it, it was in fact the best fit place. Keep in mind this is still a prototype and things could change, but I doubt they will.
Installation is very simple, the only difference to note is the extra set of threads on the axle. The reason for this is that the two sets of strain gauges, placed opposite each other on the axle, need to be aligned “just so.” When installing the pedal, you’d tighten the pedal down to snug as normal, then back it out until the line or dot on the axle is where you need it to be. Then, and this is where the second set of threads comes into play, you back a lock nut up against the crank, securing the pedal in it’s place.
After this, simply snap the transmitter into the back of the pedal, secure it with a zip tie, strap on your favorite Polar Computer (of the three that work) and head out!
The Look / Polar partnership has huge potential. Even if overcoming issues of force calculation proves difficult and accuracy ends up low by power meter standards, the benefit of training and racing knowing any discrepancy in your legs and fine tuning your pedal stroke would be advantageous. But for now you might be wondering, “wait, I thought we heard something about this last year.” Well, you would be right. Last year there was a lot of hype around MetriGear, which was a very similar concept in a Speedplay pedal. As of two days ago (Sept. 20th 2010), Garmin announced it’s purchase of MetriGear (read more on Velonews) and would continue development on what many of us had written off as an abandoned project. So for 2011 and beyond, I say, “let the battle begin.”