Change Cm in Device

Change Cm in Device

Postby nicholsjon » Sat Dec 20, 2014 7:09 pm

I ride with a rear hub and I know it's efficiency (less than 98%), so I always have to Tweak Cm after the ride. Is there a way to change the profile and upload to Newton so I don't have to always tweak it afterwards?

Thanks.
Thanks,
Jon
nicholsjon
 
Posts: 15
Joined: Sun Jan 13, 2013 4:40 pm
Location: Austin, TX

Re: Change Cm in Device

Postby Velocomp » Sun Dec 21, 2014 8:32 am

Sorry, but Cm is not a number that the Newton stores at present. I will see if we can add it to the profile.
John Hamann
Velocomp
Velocomp CEO
 
Posts: 4336
Joined: Fri Jan 11, 2008 9:43 am

Re: Change Cm in Device

Postby nicholsjon » Sun Dec 21, 2014 11:22 am

Thank you John. Everything else seems to be adjustable or settable - I thought it might be nice for those of us with a non-standard drivetrain to be able to set that as well! You guys are doing a great job with this little device!
Thanks,
Jon
nicholsjon
 
Posts: 15
Joined: Sun Jan 13, 2013 4:40 pm
Location: Austin, TX

Re: Change Cm in Device

Postby tytrike » Thu Oct 15, 2015 1:18 pm

Hey John
Promises, promises.
For years velcomp folk have said they will make Cm "mechanical efficiency" a simple user entry.
I have several drivetrains, different profiles, none of which are 98%. Double mid-drive is ...don't laugh...
It would be superior for Newton/Issac to use my user entry during ride computations rather than me manually adjusting after the ride.
Like my unit alot.
PS: Recumbents need separate Speed and Cadence Ant+ sensors.
Thanks
tytrike
 
Posts: 9
Joined: Fri Jan 11, 2008 1:35 pm

Re: Change Cm in Device

Postby Velocomp » Thu Oct 15, 2015 9:35 pm

Actually, this thread started less than a year ago... :-)

Cm is a loss in the drive train, and is expressed as a percentage of your power output. So, for example, if Cm is 1.02, this means that 98% of your applied power is getting through to your wheels.

If Cm changes (say, for example that it is 1.03) this would mean that 97% of your energy is getting to the road. So, an additional, constant amount of 1% of power would be applied by your legs to move the Cm = 1.03 bike down the road. To put this in practical terms: suppose your ride file (with default Cm value of 1.02) shows an average applied watts of 200W, but your "actual" Cm is 1.03. Then, your "correct" applied watts would be 200 x 1.01 = 202W.

Now, Cm is a constant value of drag, in the same way that Crr (rolling resistance) is. So, in Isaac you can achieve the same effect of an increase in Cm, simply by increasing Crr by an amount needed to account for the extra loss.

Take one of your ride files, decide what you think Cm should be, then increase Crr by an amount that produces the desired increase in watts. Put that modified Crr into your profile and you will be all set.
John Hamann
Velocomp
Velocomp CEO
 
Posts: 4336
Joined: Fri Jan 11, 2008 9:43 am

Re: Change Cm in Device

Postby tytrike » Thu Oct 15, 2015 10:38 pm

For clarity, not to pick: Cm as a user variable has come up in my expierence as least 2 times before. I believe one was messaging with Trevor when iBike wasn't Newton.
Cm doesn't matter that much to me even though on my recumbent quad with a crank, N360 mid-drive and a a geared underdrive Cm may 1.10 .. big difference.
Correcting via linear Crr is one thing, what about CdA ... its power is 2, 3, or 4 depending on context.
A manual patch is helpful but not as simple as when a locally known value is entered by user after Velocomp recodes firmware and software.
Your crew does some pretty amazing complex programming. Cm is but a step above trivial.
Please consider. Close a small hole.
Terry
tytrike
 
Posts: 9
Joined: Fri Jan 11, 2008 1:35 pm

Re: Change Cm in Device

Postby Velocomp » Fri Oct 16, 2015 6:15 am

CdA is already customizable and in the profile, and you're right that it is much more important than Cm.

Regarding Cm: I just did a bit of playing around in Isaac. If you want to get the effect of a custom Cm into your profile it's easy:

1) Open a ride file
2) Look at your average watts for the ride
3) Tweak Cm manually to your desired value and observe the corresponding change in watts
4) Set Cm back to 1.02
5) Tweak Crr so you get the same average watts as in 3)
6) In Edit Profiles, set Crr to the value you determined in 5), and send the profile to your Newton

Unfortunately, recoding firmware and software is never a trivial activity, and the challenges are especially compounded when the two interact with each other in the profile. It has taken us years to get the profile structure locked down and reliable.

If and when we make do make changes to the profile structure, we will definitely look at adding Cm to it. In the meantime, this workaround will do the trick.
John Hamann
Velocomp
Velocomp CEO
 
Posts: 4336
Joined: Fri Jan 11, 2008 9:43 am

Re: Change Cm in Device

Postby tytrike » Fri Oct 16, 2015 9:09 am

OK. Good work John, as usual. Thanks.

Aside: regarding Cm and Powerstroke.
General principles do claim that rider motion that does not translate into forward motion is a loss of energy between the pedal and the road (which approximates Cm).
If so, would not PowerStroke's "Wasted Watts" value divided by "Propulsion Power" be a limit on the value of Cm?
Instance: If rider motion wasted 4 watts out of 130 propulsion watts, 4 / 130 => .031, 1 / 1 - .031 = 1.031.
¿ Cm would have a minimum value of 1.03, not including bike inefficiency ?
tytrike
 
Posts: 9
Joined: Fri Jan 11, 2008 1:35 pm


Return to Newton Setup

Who is online

Users browsing this forum: No registered users and 1 guest

cron