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by Matt Wikstrom
August 19, 2016
Photography by Matt Wikstrom
TECH NEWS BROUGHT TO YOU BY BIKEEXCHANGE
Verve Cycling is a relatively new Australian company and their first product is the InfoCrank powermeter. Rather than emulate strategies adopted by other companies, the InfoCrank was conceived as an integrated powermeter purpose-built to provide accurate power measurements without the need for ongoing calibration, or indeed, zip ties.
After taking a look at the first release of the InfoCrank last year, Australian tech editor Matt Wikstrom updates his review to consider the impact of new firmware that allows users to do away with magnets to measure cadence.
There has been enormous growth in the number of powermeters on the market in recent years. Part of the reason for the growth can be attributed to society’s growing fascination with data; another has been a clear demonstration of the effectiveness of power-based training; yet another was the expiry of the patent held by SRM for the design of a crank-based powermeter.
The majority of powermeters utilise strain gauges to determine a rider’s power output. SRM ushered in crank-based powermeters in 1987 with its design for a spider fitted with a series of strain gauges, while Saris installed gauges in the hub for its Powertap design. More recently, Garmin’s vector pedals have strain gauges located on each pedal shaft, while Quarq and Power2Max have essentially emulated SRM’s spider strategy. In contrast, Stages and Pioneer have developed discrete units that attach to the spider and/or crank arm to measure torque.
At face value, Verve Cycling’s InfoCrank resembles any other crank-based powermeter, however it is unique in that the strain gauges are integrated into each crank arm. According to Bryan Taylor, Verve’s president, the idea behind the InfoCrank was a very simple one: “We want to stop with the use of zip ties on bikes, and we want to integrate the technology into the bike.”
Work on the InfoCrank began in 2008 with a request from the Australian Institute of Sport to design a powermeter to suit their test jig. Five years later, Verve Cycling was formed to build a crankset around the technology (which was dubbed the KIP module at the time). Richard McAinsh, a former technical director at 3T and motorsport engineer, designed the crankset, electing to use alloy so that a niche could be machined in each arm to house the load cells.
Measuring 35 x 20 x 5mm, each niche essentially positions the strain gauge within the crank arm while serving as a battery compartment. The niche design allows the strain gauges to be positioned so as to exclude competing forces, thereby improving the overall accuracy of all torque measurements. Working with precision-machined crank arms also affords enormous reproducibility when comparing one arm with the other, as well as one crank with another.
Verve claims that the InfoCrank has an accuracy of ±1% for loads up to 3,000W. Independent testing with static loads reported a maximum error of 0.11Nm for loads below 17Nm and 0.57% for all loads above that, as shown in the extract below:
Summary of independent static load testing performed on the InfoCrank June 2014. Absolute or percent deviation are shown for a range of loads over a series of ten tests.
Verve also performed comparative testing against an SRM crank and found that the InfoCrank matched or bettered it, both in static load testing and track tests. While these results do not automatically extend to every set of InfoCranks, they provide a clear demonstration for the capabilities of the design.
Verve claims that the power measurements made by the InfoCrank are insensitive to temperature. In the first instance, the strain gauges are compensated against the thermal expansion of the alloy crank arms; and in the second, four strain gauges are arranged in each crank arm in a Wheatstone bridge that automatically removes the influence of temperature. As a consequence, there is no need to zero the InfoCrank before use, or indeed, at any point in the life of the crank.
During the course of developing the InfoCrank, it became apparent that reliable cadence data was as crucial to the accuracy of the powermeter as a high quality load cell. While some manufacturers are utilising accelerometers to indirectly measure cadence, Verve found that this strategy was far too noisy for its design goals so installed a Reed switch in each crank arm instead. Thus two magnets must be installed on the bike (one on each side of the bottom bracket) to trigger the switches.
An equally important consideration relates to data sampling. Each load cell generates an analogue signal that must be digitised for processing, wireless transfer and display. Thus, the accuracy of the powermeter depends, in part, upon the frequency of sampling. How many data points are required to accurately measure the torque signal?
Verve settled on a rate of 256Hz (samples per second) so that every pedal stroke is sampled more than 50 times, even at very high cadences (>200rpm), to provide a clean measure of torque. To put that sample rate into perspective, SRM’s powermeter (that has historically served as the gold standard) samples at a rate of 200Hz, while Power2Max, Quarq and PowerTap all have a sample rate of 60Hz.
There are a variety of optional extras for the InfoCrank including o-synce’s navi2coach GPS computer and cadence magnets, however an ANT+ USB stick (lower right) is supplied with every crankset for firmware upgrades.
Verve recently unveiled new firmware for the InfoCrank dubbed the “Revolution Update” (or more simply, RevUp) that allows cadence to be measured without the need to mount magnets on the bike. Not only does the new firmware bring InfoCranks closer to Verve’s vision for the powermeter, it improves the compatibility of the crankset with different frame designs. This is an issue that is helped further by lower profile pods associated with the load cells that sit at the back of each crank arm.
Verve doesn’t go into details on how it manages accurate cadence measurements in the absence of magnets (or any other dedicated hardware), however they refer to the new “Crank Positioning System” as both proprietary and intelligent. Users are free to use magnets if they wish, since the system will incorporate data from one or both Reed switches if they are triggered by a magnet.
Extensive testing by the company as well as British Cycling confirmed the accuracy and precision of the Crank Positioning System, and indeed, the most recent results from dynamic tests demonstrate that the current iteration is more accurate than the prototype. One set of results showed that the error at 3,000W was 0.006% and that there was linear development of torque over the entire range 0-3,000W.
Verve’s InfoCrank initial release comprised a crankset with a bottom bracket, chainrings and magnets for the cadence sensors, but as of April 2016, the cadence sensors have been relegated to an optional accessory. An ANT+ USB stick is still supplied with the crankset for firmware upgrades along with a pair of batteries for each crank arm with no change in the asking price of AUD$1,949/US$1,399/£1,149. Buyers can obtain InfoCranks from Verve Cycling online and through its network of local bike shops and affiliates (in Australia as well as the US and throughout Europe).
The InfoCrank crankset is currently available with a an alloy 30mm axle with a compact (110mm BCD) five-bolt pattern in three lengths (170, 172.5, 175mm) with another three on the way (155, 160, 165mm) and a choice of two chainring combinations (Praxis 50/34T, Praxis 52/36T). Verve is working on a second version of the compact crank design with a 24mm steel axle that will be compatible with Shimano bottom brackets; also in the works is track version of the crankset with 144mm BCD.
It’s important to note that the 30mm axle is not compatible with standard BB30, PF30 or BB386 bearings, since the axle makes use of Praxis’ proprietary M30 design that has differential drive- and non-drive-side diameters. At present, buyers are able to select from M30-compatible bottom brackets to suit BSA, BB30, PF30, Specialized OSBB, and BB86.
The load cell in each crank arm requires a pair of 303 batteries (aka SR44) that can be easily installed and replaced by the owner. While these batteries are identical in size to the more common alkaline LR44 battery, the 303 is a silver oxide battery that has a much greater lifespan and is better suited to the power demands of the InfoCrank than LR44 batteries (however the latter will serve in an emergency). Verve expects a run time of around 500 hours for each pair of 303 batteries.
InfoCranks broadcast their data using ANT+, so any capable device can be paired with the cranks, though some devices won’t be able to display data on separate left and right pedal measurements. o-synce’s navi2coach is one device that will display this data, otherwise it can be analysed with post-ride software.
The 175mm crankset sent for review weighed 854g with an alloy 30mm axle and a set of Praxis sub-compact (52/36) chainrings installed. The InfoCrank is therefore heavy by current standards, where the penalty is in the order of 200-300g.
Another, less important, consideration is the aesthetics of the InfoCrank, which are bold, industrial-like, and perhaps best suited to an off-road bike. Regardless, the crankset integrates well with the rest of the bike; however, the magnets ruin the effect a little. I expect most buyers will elect to use the InfoCrank with cadence magnets for a clean integrated result.
The InfoCrank crankset has a two-piece design, where the axle is integrated into the right crank arm, while the left arm has a single bolt with a built-in extractor. As such, installation is straightforward. As noted above, Verve’s 30mm axle utilises a proprietary bearing design, so a new bottom bracket will have to be installed in the frame, which is best left in the hands of an experienced mechanic.
The cranks sent for review were supplied with two Praxis bottom brackets, one for a BSA-threaded frame, and the other for BB86. The former was easily installed, requiring only Praxis’s purpose-built tool to tighten the cups in the frame. The BB86 bottom bracket was more demanding in terms of tolerance, with Verve warning that the cups may not fit all frames. In this instance, the frame selected for installation satisfied the required tolerance and I was able to install the bearings with a conventional bearing press.
Verve’s optional cadence magnets were a little hit-or-miss in my hands. One version has the magnet attached to a plastic ring that fits over of the external cups of the bottom bracket and is easy to use but flimsy; the other employs adhesive backing that quickly failed on the matte-painted bike I was testing. For those that prefer to install the magnets, I’d recommended hiding them in the chainstays (if possible) with double-sided tape or an adhesive for the cleanest result.
While the magnets seemed like an afterthought, I was impressed with the battery compartments in each crank arm. Each compartment has an LED that provides immediate feedback on whether the batteries have been installed correctly, the device is working, and the cadence magnets are detectable (the LED lights up with each revolution of the cranks if the magnet is within range of the cadence sensor). Another nice touch is that the small bolt is secured to the lid of the battery compartment with a clip, so there is no danger in losing it when changing out the batteries.
Updating the firmware was a simple matter once I downloaded a suitable version from Verve’s website. The company provides versions that will run on Windows, Mac and Linux systems along with easy to follow instructions. The key to the process is having plenty of power in the batteries (in both crank arms) and positioning the crankset close to the ANT+ USB stick. I was able to complete the update in about 5mins, as promised by Verve.
The alloy axle is 30mm in diameter but uses a proprietary design from Praxis so it will not fit BB30, PF30 or BB386 bearings.
Putting the Infocrank to use is very simple, just turn on the data unit and start pedalling. Since there is no need to zero the powermeter, the only delay is waiting for the data unit to initialise and acquire GPS satellites. In this regard, the navi2coach GPS device that was supplied with the InfoCranks was noticeably slow compared to any Garmin device, but in the space of a couple of minutes the unit was alive with the data I had programmed for each display page.
InfoCrank provides all of the expected power measures (average and maximum power for various intervals; normalised power; intensity factor; and training stress score) as well as data on power balance, pedal smoothness and torque effectiveness. The latter two are relatively new metrics: pedal smoothness provides a measure on how much of each pedal stroke is spent producing the average power output; torque effectiveness compares the power produced on the downstroke with the upstroke. At present, it’s not clear if these pedalling metrics have any value to a cyclist in training, but owners can marvel at them nonetheless.
The InfoCrank is rated for use in all weather conditions. I’ve already noted that the load cells are not susceptible to fluctuations in temperature. The crank arms have an IPX7 rating, so they can be submerged, but Verve warns they may not resist a blast from a high-pressure hose. On balance, I expect there is a greater risk of the cadence magnets coming off the frame or bottom bracket cups than there is of weather damaging the cranks.
The firmware update worked flawlessly, allowing me to dump the cadence magnets without losing any data. I’m not in a position to formally validate the performance of the InfoCranks, but a comparison of power and cadence data before and after the upgrade agreed well, so I’m inclined to accept Verve’s claims.
The InfoCrank generates an enormous amount of data that is best handled with a sophisticated analysis program. Sure, you will be able to view basic ride data using Strava, but you won’t be to mine the data to any great extent. I found that Cycling Analytics provided an easy way to have a look at the power balance, torque effectiveness, and pedal smoothness data provided by the InfoCrank, but a paid subscription is required to make full use of the application. In this regard, it’s worth noting that Verve is working on its own software called the “Pedalling Analysis System” that should be launched in the coming months.
Ultimately, power data is best used in conjunction with a formal training regimen. The InfoCrank is a tool, and while it will quickly satisfy the curiosity of most riders, it will not improve their cycling until they use it to guide their workouts. Thus, one worthwhile prerequisite is experience training with a heart-rate monitor.
Verve’s InfoCrank is an impressive product. There is enormous appeal in the company’s approach to the design of the crankset, where the position of the load cell within the crank arm is intuitively sound. I’ll leave it to the engineers (and Internet experts) to debate the approach, but Verve’s (and British Cycling’s) lab and track testing suggests that it allows for gold-standard levels of accuracy.
In my first look at the InfoCrank, I was critical of the design for the cadence magnets, so I’m pleased that Verve has been able to address this shortcoming so quickly. The RevUp firmware upgrade that was released in April gives buyers the option to use or ignore the cadence magnets, though I expect most will opt for the latter, if only to simplify the installation and operation of the InfoCrank.
As for the price of the InfoCrank, it’s high enough to exclude mainstream users, yet not so high as to be out of reach like SRM’s powermeters. Aspiring racers and data geeks are still likely to be frustrated by the expense but when put up against an SRM powermeter, the InfoCrank looks like an absolute bargain that also happens to be much easier to maintain.
InfoCranks are supplied with a choice of bearings to suit different bottom brackets. These bearings are designed for BB86 and press directly into the frame.
A look at the optional cadence magnets designed for external bottom bracket cups.