khatfull

...but not with my massive guads pumping out 800W and not my "real" KK...read on.

Some of you may have followed that I got a demo Road Machine, had an issue, and Kurt replaced the resistance unit. All fine and good. Very happy. But, when I asked what I needed to do with the old unit customer service said, "It's a sealed unit, we don't repair them, just toss it."

Well, to the avid tinkerer tossing such an assembly is simply out of the question. I had the wild idea to get the flywheel off the old one and somehow attach it to the current one to double the weight to 12 lbs. and make a semi-pro resistance unit. Kurt adds 4mm to the axle size for the Pro unit at 18 lbs. (12mm to 16mm) so I'm guessing that 12 pounds of flywheel weight on the standard axle will be just fine. Things like this usually get over-engineered anyway. Well, I'm here to tell you....

I couldn't simply unbolt the flywheel....NOTHING I did to turn that hex head worked at all. So, I ended up wasting two Dremel reinforced disks to cut the bolt head off. It took 30 minutes to make it through the hardened bolt but I finally got it and got the flywheel off. It's just a chromed disk of steel. One of my clients has a full machine shop so I'm going to get the machinist to open the hole to 1" or so (I'll figure out the correct measurement) so that the second flywheel can simply butt up next to the existing one. Now, how to attach them? Hmmm...clips, nah, probably not strong enough. Glue? Nah, don't want it permanant. Hmmm.... MAGNETS! And I know where there are 12 neodymium rare earth magnets! Right inside the resistance unit!

So, I proceeded to pull the bolts out that hold the two halves of the resistance unit together. Got them out and after a few whacks with a dead blow hammer, both halves separated. On the drive side the magnets are out in the open but glued into a plastic carrier. I was able to remove five of the six without damage. I'm thinking I'll need six so I unsealed the sealed portion of the resistance unit and the fluid is draining right now. so I can clean it up and get to a few more magnets.

Let me tell you folks, these things are built. Well. I'm really good at deconstructing stuff and this thing was a beotch to get into. I can't imagine it failing under any normal use circumstance. I'd think you'd wear the aluminum roller dangerously thin from your tires before you'd even begin to affect the resistance unit proper. And when they say sealed, they MEAN sealed. Tight.

Once I get the second flywheel machined, the magnets out and cleaned up, and get the flywheel attached I'll post up some pics. I'll grab a few of the inside of the resistance unit before I toss it as well.

I used to drive my parents nuts when I was a kid...I always took crap apart...doing this kind of stuff makes me feel 12 again

zatopek

Sweet idea. I love your Rube Goldberg DIY approach. I will be interested to see how this beast works. I'm not exactly sure how the attachment of the second wheel might work, but it sounds whacky to me. You go boy!

bdcheung

I predict you'll snap the axle in the new resistance unit.

You also might damage the trainer frame.

khatfull

Here's the exploded pic:



The hex head on the far right sits flush (with a washer) on the surface of the flywheel. I'm going to have the hole in the second flywheel machined out big enough to fit over/around the existing bolt and washer. That will bring the second flywheel flush with the existing flywheel. Then, 6 of the neodymium magnets in between should provide more than enough "glue" to keep the two flywheels together. I might face the magnets with thin rubber sheet just to give it a little more friction. Let me tell you, these magnets are between the size of a dime and nickel and about 3/16" thick...and they're a real pinch hazard if you're not watching what you're doing. 6, maybe 8, should provide all the force necessary to keep the second flywheel in place.

Rube huh? That's a compliment to me

khatfull

Why?

bdcheung

KK has a whole writeup on the structural (can't think of a more accurate word) difference between the Road and Pro models. It extends beyond just the axle.

Frames are different, bearings are different, I think even the fasteners used are different.

jrobe

I am kind of a DIY'er myself but I don't think I would even want a unit with a heavier flywheel. A lot of the training DVD's involve short interval work (accelleration sets like 10 sec on/10 sec off, 30-60 second intervals, etc.) which would be frustrating with a heavier flywheel. It would probably make the unit feel a little more realistic though for longer steady state riding with a longer coast-down time.

I bet KK doesn't sell too many of the units with the heavy flywheel. That definitely wouldn't be an upgrade for me.

R900

+1

Gluteus

Interesting.

But why are you doing this?
Is the resistance of the new unit, not enough?

khatfull

Axle size is all I can find on the website...and larger bearings would make sense given a larger axle.

That's most of the reason, other than I wanted to deconstruct the old unit for fun anyway . If I can get it to attach magnetically it'd be real easy to put on and take off for different workouts as you indicate. I've been on a Pro and yes, it does feel quite a bit different.

As Kurt will point out the weight of the flywheel has nothing to do with the resistance, only the feel as you ride. The heavier flywheel extends the coast down time and just makes it feel more like the road. If you rode the standard and Pro units side by side you'd feel the difference. I'm hoping that this mod will give a little more of the Pro unit feel.

gregf83 

If you're using a power meter the only difference you'd notice is the speed would ramp up slower. The power you put out during the interval shouldn't change and it should provide a more realistic feel.

fordmanvt

10mm/2=5mm
5mm*5mm*3.14= 78.5mm^2

14mm/2=7mm
7mm*7mm*3.14= 153.86mm^2.

That is nearly DOUBLE the cross sectional area. I predict you'll break it as well.

Dubbayoo

I do like to use the bigger flywheel for tempo rides and longer intervals. It's a nice option. I think I tightened mine too much; last time I tried to remove it I couldn't. I haven't really given it a concerted effort though, no need to at this time of year.

Jinker

How are you going to locate the second flywheel and magnets to keep everything concentric and balanced?

tadawdy

Are you sure the magnets are a good attachment method? If they're so secure, how would you ever get the flywheels apart, assuming you might want to? You might want to.

AEO

neodymium magnets, when given enough surface area, can crush your hand as well as support at least 180lbs off of a wall.

but I think the axle might be the biggest limitation.

remember, it's the outside diameter that matters the most in tubes and axles. hollow core or not, the extra weight and leverage can bend or snap it.

khatfull

I thought of that last night myself...drill and tap three holes at 120 degrees into the edge of the new flywheel and bolt on small tabs that capture the original flywheel...or something like that.

By the time I face the magnets with rubber to prevent marring and provide more friction I'm thinking I'll actually need fewer magnets to have it be secure, especially with the tabs mentioned above. They will be nearly 1/4" think by that point which will be more than enough room to get a non-marring pry of some sort in there.

Given what I did to try to get the bolt off the old unit to release the flywheel I can't imagine it snapping. The axle is solid...most assuredly.

I don't know, we'll see...if anything deconstructing the old unit was a lot of fun and it was interesting to see the inside of a real unit rather than the LBS cutaway display

achoo

Doubling the flywheel weight won't break the axle. If the engineering margins were THAT small there would be the occassional axle failure on non-modded units. The larger axle on the Pro unit is probably a "perceived value upgrade".

The different weight distribution might impact bearing life, though.

f4rrest

Hey, where's the pics!?

Also, given the rotational speed of the flywheel, I'd be concerned about it becoming out of balance if you slap on the 2nd flywheel without some way to keep it absolutely centered. E.g. extra tabs and things can make it vibrate.

GUGS

I just got off the phone with Pam at Kurt about getting the 12 lb flywheel for my pro. She said if my model has a hole drilled and tapped in the bolt that holds the 6 lb flywheel on then they have a solution. I just placed the order over the phone with her. They will ship it Monday. Cost is $79 plus shipping.

Stads

I wonder if in your exploring of the road machine unit, you might explain to me, how cadence works. Mine will go up to about 60, and no higher.

seypat

Noooooooooo! I thought we were past Halloween this year. Somehow this thread clawed it's way back to the surface. Must be some black magic involved.

choddo

What happens? The resitance gets too high to push any harder? What gear are you in?

Stads

The cadence has measured by KK, is not accurate and will drop off, even though I maintain 80 RPM, the highest it will read is 60.
Yesterday on Zwift, I maintained 80 RPM, and did a couple U-turns on a steep slope.
The cadence was reported to have changed by a large amount, even though I maintained 80 RPM.

I also have PowerTap petals installed, at the end of a workout. There is a large difference in speed, wattage, etc..

Just a guess, but if oil is used to move the cadence recorder, perhaps it is low on oil, or the resistance within the unit is too high.
I do calibrate with the KK app before each ride, and check tire pressure, etc.
I have another KK Road machine at a different house and have been using it for years, it works fine. And I’ve been riding swift for years.

ls01

resistance is futile, he shall be assimilated.