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Tandem Power Measurement

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Tandem Power Measurement

Old 09-29-11, 10:49 AM
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Originally Posted by p2templin
For anyone still tracking this thread, we've successfully implemented two independent power meters on our daVinci tandem. The DV drivetrain "made it easy" - no math needed, just some metalwork on behalf of our dealer to mate the Quarq units to the DV cranks. No need to flip the pedals (we ride Look, so it'd be messy to reverse them), and Quarq was able to program them to read power in the opposite direction. Unfortunately it's not a solution for standard tandem drivetrains.
Thanks for the follow up. Very very interesting as we use DV cranks but without ICS. I am correct that your solution would work on anyone using DV cranks?

Was the metal work on the Quarg or the cranks?
How extensive was the work?
Do you have pictures?

Thanks, Wayne
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Old 09-29-11, 02:11 PM
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If I understand your question correctly, our solution is dependent on the ICS. With ICS, each bottom bracket spindle is only handling one rider, so each Quarq is only measuring one rider. All measurement is done before the power is summed at the ICS intermediate driveshaft.

The cranks were not modified whatsoever (except perhaps for some accidental cuts during "engineering"). The Quarq center was cut large enough to fit around the "square taper section". Our dealer chose to minimize any "fastener torque", and therefore chose to sandwich the Quarq between the crankarm and an inner fastener. This inner fastener started life as the DV 34T ring that came off the arm, which was then cut down to a diameter that would cover the screw holes without interfering with the Quarq itself.

Because the DV 34T ring is "thin" and the Quarq is intended to have a 50/34 ringset ("thick"), the 34T-only Quarq is inset, and therefore presents a problem given how short the stoker chain is. A longer-spindle BB resolved that problem; since the Rear Admiral is already riding with pedal extensions, the BB change was perhaps a benefit. Some other BB "misadventures" led to an unfortunate scrape of paint on the R chainstay.

I don't have any pictures of the inner mechanics at the moment. The finished units can be seen in a pair of pictures on our dealer's website, houseoftandems.com (scroll down a little more than a screen's worth). If you'd like other views, let me know and I'll work on those next week.

For the moment, I'm using a Garmin Edge 705 and she has an Edge 800. I'm hoping to add two more Edges so that each of us can see both riders' efforts (I want to help her train smarter, as that was much of the justification for the project, and I'd like her help managing my efforts when the going gets tough in "the peloton").
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Old 09-29-11, 05:56 PM
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Originally Posted by p2templin
If I understand your question correctly, our solution is dependent on the ICS. With ICS, each bottom bracket spindle is only handling one rider, so each Quarq is only measuring one rider. All measurement is done before the power is summed at the ICS intermediate driveshaft.
It would be very interesting to determine what would become of the power measurements on your bike, if the ICS could be bypassed, and the cranks joined conventionally with a sync chain. How would the captain's power transmitted through the stoker's spindle affect the measurements taken the in stoker's CinQo spider?

It is, however, a moot point. In a few short months, the Garmin Vector and Polar/Look pedal based power meters will be available, and if these work out, they will be the obvious choice for tandems, as the pedal spindle strain gauges will be isolated from the tandem sync drive peculiarities, and they can be easily transferred to owner's half-bike as well.
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Old 09-29-11, 06:53 PM
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A traditional drivetrain has three spiders. Both left-side spiders would read captain power, and the right-side spider would read total power. It'd take a head unit that could take two power meters as input and do the math to derive the stoker power.

You're right about the pedal-based power meters, IF they make it to market as suggested. I'm also curious to see how accurate they are - there will be two new layers of imprecision with them. Crank length will have to be entered into the head unit, and that'll complicate the head unit's math (probably handled by a firmware update). Also, the strain gauges won't all be aligned with the direction of deflection like hub/crank systems, so they'll have to combine readings "between" gauges.
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Old 09-30-11, 08:39 AM
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Way to go, and please keep this updated. I have had a pedal based power system in my head for some time. Start with the difference of each capt and stoker and display it as a percentage ratio on both computer displays, for real time effort matching. Then fill in the rest of the software info/calculations that are available. The best average ratio will be different for each team.
I would not be too concerned about the overall precision/accuracy, they would just have to be repeatable and consistent to have something to reference and compare your effort. I would guess they could be built with enough strain gauges, and placed/calibrated to be very accurate.

Those Spinnergy tandem wheels on their website look sweet. Rim or disc brakes.
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Old 10-03-11, 06:27 AM
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My take on the pedal power meter status @ Interbike, in order appearance in market:

1. Look/Polar: most expensive, proprietary head unit communication protocol (not ANT+, may go to low-power BlueTooth at some point in future), force detection only (requires pedals be carefully aligned, uses magnet for approximate cadence determination)... no accelerometers. Fully functional units have been distributed, so close to available. Demo'ed in Interbike w/ Polar head unit... not sure if open road tests were available.

2. Garmin Vector (formerly Metrigear): Presently Look-compatible pedals, but technology is applicable to almost any pedal if they decide to expand (early prototypes were Speedplay, but Speedplay wouldn't allow for good warranty support). ANT+ Sport protocol (good with many head units). Uses accelerometers for "instant cadence" and automatic orientation determination (if pedal thread orientation changes, it will figure it out eventually). Electronics are inside spindle instead of on spindle as w/ Polar (may make for stronger or lighter spindle, not sure if this affects accuracy). Demo'ed in Interbike on trainer w/ Garmin head unit.

3. Brim Brothers: cleat-only solution, using cleat adapter plate for Speedplay, so won't work with 4-hole Speedplay-specific shoes. Disadvantage is cleat position relative to propulsive force direction is constantly changing, which requires accurately and instantly tracking that, while the spindle orientation relative to force position only changes when threads are rotated. Demo'ed in Interbike on trainer w/ Garmin head unit. Trainer tests are easiest, though, because vibrations make it much harder to determine cleat orientation from accelerometers.

Various companies are looking at crank-arm based power meters, and these would also work for tandems if a tandem set were designed.
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Old 12-25-12, 02:43 PM
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According to DC Rainmaker, on the Garmin investor conference call, the long-awaited, multiple-delayed, Garmin Vector is set for introduction in Q1 or Q2 this year.

Originally Posted by DC Rainmaker

The quoted answer from Cliff Pemble, President and Chief Operating Officer of Garmin:

“We are making progress on Vector and we’ve been evaluating new design changes and we do feel like things are looking promising and are sticking to our early next year first quarter (Q1CY13) or early second quarter (Q2CY13) deliveries.”

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Old 12-25-12, 02:53 PM
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Those tandems using right side timing chains could use a regular Quarg or SRM power meter on each set of cranks. The torque input from the captain isn't going through the stokers crank spider so they should both read normally.
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Old 03-04-13, 10:43 PM
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The latest on the Garmin Vector from DC Rainmaker is, per usual, another delay. Q1/2? Not so fast.

Originally Posted by Garmin CEO earnings conference call
“We continue to make progress with our Vector Power Meter, and anticipate it will be made available this year.” – February 20th, 2013
This year, it is surmised, means the end of the year.

A hopeful sign, sort of like the first crocus peaking up from snow, is a detailed listing at Excel Sports, which indicates product is developed enough for the marketing people to write product description copy, and send it to a retailer.

Garmin Vector Pedal

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Old 03-05-13, 09:15 AM
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The Look/Polar system apparently is available now.

I'd go ahead and buy that except for the fact that it's not Ant+.
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Old 03-05-13, 12:35 PM
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Originally Posted by merlinextraligh
The Look/Polar system apparently is available now.

I'd go ahead and buy that except for the fact that it's not Ant+.
What is needed is a Polar -->ANT+ converter and relay, then the Look/Polar system would be the bees knees.

Polar has devices that send information to a smartphone using Bluetooth Smart.



If the Look/Keo pedals send a Bluetooth Smart signal, a smartphone potentially could then convert these signals to ANT+, and thus to the Garmin.

How stupid Polar/Look is for not at least offering ANT+ as an option for their pedals? They have managed to do what Garmin has thus far failed at, and are sacrificing their market lead on the altar of their proprietary standards.
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Old 03-05-13, 12:42 PM
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Supposedly the Polar Look Pedals are going to be Bluetooth Smart capable. But they aren't as of now. Polar says they'll be a retrofit, but whether that actually happens and whether it will cost more money are up in the air.
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Old 03-05-13, 01:48 PM
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Originally Posted by merlinextraligh
Supposedly the Polar Look Pedals are going to be Bluetooth Smart capable. But they aren't as of now. Polar says they'll be a retrofit, but whether that actually happens and whether it will cost more money are up in the air.
The new Garmin 810/510 have Bluetooth.

The major hardware upgrade on the Edge 810 is the addition of a dual band ANT+/Bluetooth wireless chip that enables you to connect the device with both iOS and Android phones using Garmin’s own Garmin Connect mobile app. Pairing the two devices is straightforward.
So, with all these Bluetooth signals going about, all that is needed is a Bluetooth Polar-->ANT+ conversion dongle, or iPhone app. All those iPhone apps, and not the one that is really needed!
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Old 03-05-13, 02:28 PM
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The garmin 810/510 use a legacy bluetooth though, not the new lower power bluetooth smart
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Old 03-11-13, 06:56 AM
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iBike is an intriguing option. Since tandems don't draft as much as solo bikes, it would likely work relatively well, although it won't separate total power.

There's spider-based power meters and crankarm-based power meters. Crankarm meters should work for both stoker and captain, but the only 2-sided option here I know is Pioneer. I'm not sure how well it works, but avoids the assumption of L-R balance of Stages (which I wouldn't use). If it does work it would be perfect. One pro team (Blanco, formerly Rabobank) is using it.



There's still Garmin Vector on the horizon. They've been plugging away at the project and have announced something will be available this summer. Time will tell, however. Garmin's limited to Exustar pedals, though.
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Old 03-11-13, 08:24 AM
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I went ahead a bought the Look system. (one pair for the captain)

I do a lot of my training on the tandem, and not having power data for that leaves a big hole.

I got tired of waiting on Garmin. Also allegedly, the Bluetooth upgrade for the Polar system will only require a firmware update.

So it may work out in the long run, if the do go low powered blue tooth, and that improves the head unit options.

If not, I at least have something to use in the interim, and can probably get a portion of my money back ebaying the Polar system.

I'll report back when I've gotten it installed and used it.
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Old 03-18-13, 09:29 AM
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I'm really excited to see how the Look works for you. It's a simpler system than the Garmin: for example, it doesn't automatically determine its orientation, so it needs to be carefully aligned so it can accurately determine what portion of force is propulsive torque, and what part is perpendicular to this. I keep scanning Garmin team bikes, looking for the power meters, but so far they've been using just the pedals (without pods). If the pedals appeared on pro bikes I'd view that as a good sign. If you do end up getting the Garmins as replacement, I'm interested in seeing what you think of them.

For me an issue with both of these systems is they require Look pedals, and I like Speedplays for several reasons (double-sided, light, can be used with walking shoes comfortably). For mountain biking or touring or randonneuring I prefer mountain bike shoes (I use Frogs). So limiting my power meter to one pedal type is an issue.
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Old 03-18-13, 11:48 AM
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Originally Posted by djconnel
I'm really excited to see how the Look works for you.
From a post on another thread:


A tandem with Look Keo Power Pedals, on the Cyfac-sponsored riders John Saccomandi and Olivier Donval, World Paralympic tandem champions.





This a screenshot of this video, in which they race against singles.


https://www.dailymotion.com/video/xsxx4h_tandem-bavay_sport

The Look Keo Power Pedals can be seen below their shoes.

It would be interesting to see uploads of their rides, with the power measurements.
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Old 03-18-13, 03:02 PM
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SO far, I hate them. Most of the problem is the head unit, Polar cs600 is terrible. It's display interface, ease of use, cnfigurability, and ease of uploading data pail in comparison to a Garmin.

Setting the system up was not very tough. Actually using it, and getting useable data uploaded to Training Peaks, not so much.

If a garmin 800 was Windows 7! The Polar is MS.DOS.

Have used it twice. Saturday, I got data for 39 minutes of a 3 and half hour ride. I chalk that up to operator error operating the head unit.

Sunday, it ran out of memory, half way through a 7 hour, 121 mile ride. Bizarrely, the head unit has summary data including power for the entire ride. The file that downloaded however was obviously wrong data ( max power 29000 watts) for 13 miles of the ride.

If it doesn't improve it's going back
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Old 03-18-13, 04:10 PM
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If you get a new bike with right hand timing chain/belt you would be able to use a conventional (proven/available/reliable) crank based system.
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Old 03-18-13, 04:18 PM
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Originally Posted by Dean V
If you get a new bike with right hand timing chain/belt you would be able to use a conventional (proven/available/reliable) crank based system.
I would think that power coming from the stoker would have some effect,

One good thing about the pedal based system is that the stoker does not appear to affect the Captain's power.

When I take my feet out of the pedals and just the stoker pedals, the power goes to zero.

Not sure that would be true with a crank based system.
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Old 03-18-13, 04:35 PM
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Originally Posted by merlinextraligh
I would think that power coming from the stoker would have some effect,

One good thing about the pedal based system is that the stoker does not appear to affect the Captain's power.

When I take my feet out of the pedals and just the stoker pedals, the power goes to zero.

Not sure that would be true with a crank based system.
I haven't had the Quarg cranks on the back of our tandem yet but the readings from them on the front are certainly comparable to what I get with them on my solo bike.
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Old 03-18-13, 04:51 PM
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Good To know. When I talked to Quarq about this awhile back, they weren't big on the idea. However that wasn't in the context of a single sided drive train.
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Old 03-26-13, 02:26 PM
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I'm considering investing in a couple CycleOps PowerCal straps. They would probably meet our "needs" and < $100/ea is a very economical addition to the dual Garmin Edge 800s we already use.

From a setup point of view, it's my understanding that we would simply replace the Garmin HR straps with these PowerCal straps, and then sync the new Ant+ straps accordingly. This would provide HR & calculated power readings independently to both Garmins. No L/R pedal analysis though.

Among the various "reviews" found online, I found this one (or two) was of particular interest:
Pre discussion: https://teamrodrigo.com/2011/06/27/th...eops-powercal/
Actual usage: https://teamrodrigo.com/2012/07/20/ri...eops-powercal/

Also this review is well done: https://www.dcrainmaker.com/2012/11/c...th-review.html

Another of minor interest: https://bikehabit.blogspot.com/2012/0...-quarq-is.html

This recent review has a less positive outlook, but people seem to be panning the review as somewhat shabby work: https://www.bikeradar.com/gear/catego...powercal-47026

While the PowerCal does not appear to perform well for short period efforts (< 40 secs), overall it may be of general interest for ballparking power output of longer durations.

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Old 03-26-13, 05:09 PM
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Originally Posted by twocicle
I'm considering investing in a couple CycleOps PowerCal straps. They would probably meet our "needs" and < $100/ea is a very economical addition to the dual Garmin Edge 800s we already use.

From a setup point of view, it's my understanding that we would simply replace the Garmin HR straps with these PowerCal straps, and then sync the new Ant+ straps accordingly. This would provide HR & calculated power readings independently to both Garmins. No L/R pedal analysis though.

Among the various "reviews" found online, I found this one (or two) was of particular interest:
Pre discussion: https://teamrodrigo.com/2011/06/27/th...eops-powercal/
Actual usage: https://teamrodrigo.com/2012/07/20/ri...eops-powercal/

Also this review is well done: https://www.dcrainmaker.com/2012/11/c...th-review.html

Another of minor interest: https://bikehabit.blogspot.com/2012/0...-quarq-is.html

This recent review has a less positive outlook, but people seem to be panning the review as somewhat shabby work: https://www.bikeradar.com/gear/catego...powercal-47026

While the PowerCal does not appear to perform well for short period efforts (< 40 secs), overall it may be of general interest for ballparking power output of longer durations.
I've been riding with HR since 1997. I don't think this technology is worth as much as experience with your own body and an ordinary recording HRM, which your Garmin already has. It's not just a 40" thing, it's over many minutes, many hours, many days. I do wish I had a PM, but for my perceived benefit it isn't worth the money. Besides time@power, other things that go haywire is that power vs. HR varies a lot with conditioning, current training stress, hydration, and fueling. This gadget doesn't take any of those into account, nearly as I can tell. With experience, I can evaluate all those factors by observing my HR and speed on known routes or grades. Still doesn't give me power, but knowing the state of those factors is kind of the whole point of using power. I really couldn't care less about my watts/kg numbers. I just want to go fast. Or well, faster anyway.
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