September 23, 2010 at 5:09 pm #93027Keymaster
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.”September 23, 2010 at 9:55 pm #93028Ian Carr
Did the engineer you spoke to say anything about how they planned to deal with non-rotating forces. How would they deal with a heavy rider hopping down a curb or bunny hopping? I realize the transmitter would only send information every so often but if the timing were right I feel like this could cause a spike in the read out, skewing the riders max wattage.September 24, 2010 at 4:29 am #93029Keymaster
There are two situations here. One, is that the rider is not pedaling and just dropping of the curb or bunny hopping. In this case there is no, or very little, movement in the pedals so although there’s pressure on the axle there is no work being done. This is why the cadence sensor in each pedal is needed. The second case is that you pedal off the curb (not really applicable to bunny hopping). Here the pedaling action is more removed from the action of dropping of the curb. Power will be calculated normally and the drop will be considered a “vibration.”
The unit needs to filter out vibrations if it’s going to measure the specific type of work and power we’ve come to expect our power meters to measure. That is to say to measure the work and power done to move the bike forward not to balance or absorb shock and vibration. To answer your question, data will be “cleaned” and unnaturally high spikes are calculated out, smoothed or disregarded.
This all touches on the reasons we really need to wait and see some third party real world testing and data before we draw any conclusions on overall accuracy.September 28, 2010 at 8:09 am #93030Brian Fleming
Why would anyone design a product like this which uses RF to transmit data and not use the Ant+ Sport technology? Would you design a computer peripheral which did not have USB or Bluetooth connectivity? It is the lack of Ant+ Sport connectivity which has already adversely affected my buying decision. I will wait for the Garmin/Metrigear.December 13, 2010 at 10:03 am #93031Majk
Polar is the last choice on my list, when buying a cycle computer. The main reason is the lack of ANT+, second is no GPS. Plus a number of minor stuff, such as non-replacable batteries in speed/cadence sensors.
Too bad, once they were at the top of the game, now just another computer manufacturer.December 22, 2010 at 3:15 am #93032Jono
If its so complex building it into the pedal why not move the electronics into the shoe or a special cleat. You could really go to town with a shoe that detected the exact points where pressure was being applied. eg Nike and IpodJanuary 20, 2011 at 8:02 pm #93033JP
Still waiting for the Metrigear (now Garmin) Vector. Why? ANT+, and presumably a better price point. I’ve seen them on the road locally for 2 years now, and wonder why it doesn’t come to market. It clearly works.
Polar was always proprietary, and a battery change used to require sending the head unit to them.