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February 1, 2012 5:46 PM   Subscribe

Insane DIY project: build an exercise ski machine a la NordicTrack, only better. Venture ahead, or head straight for an insane asylum?

So it looks like despite my best efforts at being careful and taking it slow etc., I've managed to get a runner's knee (Patellofemoral Pain Syndrome). One of my knees is tricky due to a car accident some 30 years ago. I've been running on a concrete pavement 4 miles a day 4-5 times a week these past six months, but recently overdid it by not taking any breaks and voilĂ .

In any case, I suspect that my knee problems are not going away, and I'd really like to continue my cardio. Realistically, because my knee is permanently damaged (the above mentioned accident), I suspect the day may come when running is just not an option. For a variety of reasons, I like the indoor option of a ski machine, which puts minimal pressure on the knees (with proper technique).

Problem: the machines on the market, suck. Multiple issues, with quality of build, size, workout capacity. NordicTrack appears to have pretty much cornered the market, and their gear exemplifies all the problems.

So, I thought, foolishly, why not build one myself? The advantages are that I can tailor it to my requirements, and I can make sure I use the best materials.

On the face of it, there doesn't seem much to a ski exercise machine, and a determined individual ought to be able to build one for personal use. But of course, that's "on the face of it" and I recognize just how monumentally such projects tend to grow in complexity and difficulty once you bear down on it.

My main concern is the resistance mechanism. I've had stationary bikes with arm resistance, and elliptical machines with arm resistance, and my experiences have all been bad in that they never, ever last for more than a few months. I'm apparently really hard on them - and the workout never seems hard enough. I've given up in disgust - hence the running. Maybe the "gym quality" machines are better, but I also have a space issue, and can't have a hulking machine sitting in my apartment.

So I'd have to figure out what can provide good resistance, that is not going to (a) wear out lickety-split, so no cloth/rubber belts, wimpy magnets, softie breakpads etc., (b) not be the size of a fridge (c) require $10K worth of diamond/titanium space materials, and (d) not sound like a fighter jet taking off while I'm working out.

Then there's the size issue. What I'd like is something that I can easily fold and put away - this has to be quick and easy, so no 35 steps.

Budget - from experience I know it's always way more than I thought it would cost, but I'm hoping to get it done for $1K or under. I don't have a timeframe on this, and I can tinker with it for months.

The design itself doesn't seem too complicated, especially if the arm workout is decoupled from the leg workout (which is fine by me), but I'm stuck on how to provide resistance - I just have no experience with this aspect of exercise machine design, and I have not been impressed by what I have bought/seen on the market.

Durable. Capable of giving hard workouts. Foldable. Reasonably quiet. For personal use only (i.e. no commercial requirements). No fancy electronics, readout panels, calorie counters etc. - just the basics, ma'am.

I don't have a workshop myself, but I have friends who do. Is this the moment to take a cold shower and wake up to the real world, or is this within the realm of a realistic project?

I think the crux of the issue is going to be the resistance mechanism. Are there any DIY hobbyists, mechanical engineers, exercise machine designers in the house, who might point me in the right direction here?
posted by VikingSword to Sports, Hobbies, & Recreation (9 answers total)
Your complaint about the NordicTrack is pretty vague:

"Problem: the machines on the market, suck. Multiple issues, with quality of build, size, workout capacity. NordicTrack appears to have pretty much cornered the market, and their gear exemplifies all the problems."

I have one of the old wooden skiers from about 1990 and its held up well. I even put new rollers for about a $100 a couple of years ago. True, it takes up a lot of space, and its not exactly silent. But I would say the build quality is actually really good and I get more than enough of a workout. (Though, uh, its kind of been unused for about a year, but that's not the machine's fault.) I've thought about different ways of modifying it, but never gotten around to it.

But if that's not good enough, instead of starting totally from scratch, why don't you get one of those off craigslist or garage sale see if there's some modifications ("hacks" the kids might say) that you could do to make it closer to your expectations. The heart of it is an iron flywheel and rollers on bearings that only turn in one direction; its actually pretty cool. Maybe you could mount it on a bench and push the ski part with your arms.
posted by RandlePatrickMcMurphy at 6:04 PM on February 1, 2012 [2 favorites]

I know you said "build" but a Concept2 rower fits all your requirements.

Also, the NordicTrack machines are all well built and have seen many years of improvements, it's hard to believe there's faults with them - I've used the skier and other than being sort noisy (turn up the TV) it's bombproof.

Otherwise - get an old wind-resistance bicycle, cut the fan/flywheel unit off and attach it to something that you can generate power from. Unfortunately there's only so many ways the body can move, and there's already devices engineered for each them - ski, bike, row, run.

So anything you build is going to follow in the development cycle of an existing commercial product, but it'll take a *lot* of time to construct instead of just spending the money and using it.
posted by jpeacock at 6:10 PM on February 1, 2012 [1 favorite]

Response by poster: Sorry if I wasn't clear. It seems there is universal agreement that the NT skiers built in the 90's had far superior quality, and though the design has remained the quality has plummeted since the mid 00's - I've read that in several places, if you really need it, I can find those links, but I'm not making it up. I don't want to try to buy a used one from the 90's, because apart from the hassle of chasing one down, you don't know the condition you're getting them in (also, I've read they can frequently be warped). I've done my research, hence my idea to build it.

jpeaock - thank you for the suggestion, and I'm sure the Concept2rower is a great machine for many people, but unfortunately it's not for me, because of my requirements, in particular #1 - I'm trying to bend my knees as little as possible when exercising, which is the whole reason I settled on the ski machine to begin with, because with the proper technique you can almost not bend your knees at all (Chondromalacia Patella is due to the rubbing of the patella as it moves up and down as you bend your knee, if, your patella is misaligned, as mine is). I'm trying to do cardio without bending my knees, which is hard to do (swimming excepted). So rowers are 100% OUT. They also have the Concept2 SkiErg, but I'm afraid they totally misrepresent the product when they say "The SkiErg offers a total body exercise that helps you build strength and endurance specific to Nordic skiing". Then you see the video - the movement has nothing to do with Nordic skiing, or cross-country skiing, it's a travesty. Further, it does absolutely nothing for your legs - basically you may as well stand against a wall and do semi-squats... there is zero - repeat, zero - resistance apart from your own weight, so the design does nothing for you leg-wise. I'm looking for serious resistance, especially the legs - (not zero resistance) - as I've tried to repeatedly emphasize.

Now, getting back to DIY building...
posted by VikingSword at 6:46 PM on February 1, 2012

I think that building the actual machine is not that hard - mainly a matter of getting the geometry right and being accurate with the moving joints. As you point out, the hard part will be the resistance. What about making a flywheel that is heavy enough to provide the resistance you need? You could use standard round weightlifting weights, but you would probably need to turn the insides to accept a ball or roller bearing set, or maybe mount a hollow axle on bearings that you could slide the weights onto. That way, you could adjust the resistance although it's hard to imagine how you would make that easily adjustable. A flywheel has the advantage of being pretty much silent and the disadvantage of being heavy.
posted by dg at 8:04 PM on February 1, 2012

Actually, I wouldn't be so quick to dump the SkiErg. As a former XC ski racer, and having played with the ski erg myself, it does actually do exactly what it claims.

The ski erg supports both alternating arm swing (classical style) and double arm swing (skate style) of skiing. A full, aggressive, double arm swing involves pretty much every muscle. A constant, steady, alternating arm swing also involves every muscle. You will be out of breath and sweaty and get your heart rate up by using the ski erg. (dang, I sound like a C2 shill, but it's true)

As for leg resistance - running also has no resistance apart from your own weight ;) Without bending your knee you're not going to be able to apply serious resistance to your legs. What are you are going to do is apply serious resistance to your hips, abs, and lower back.

Proper XC ski technique (incl. on the nordictrack) requires about a 1/4 squat of knee bend, then an aggressive pull and extension of the leg. If that 1/4 squat is within an acceptable range for you, then you're good. If it's the actual pressure being applied while the knee is bent that's a problem, then you're not going to like it.

Doing the nordictrack or similar w/a straight leg is not going to develop any leg strength, and if you force it then you will likely develop hip problems. In all my use of nordictrack I never had sore legs or arms - but it is a great cardio workout. It's low impact, which is what you want, but also means you won't get serious resistance either.

As for the DIY - I agree with RandlePatrickMcMurphy that buying a some older, used fitness machines and improving/modifying them is the way to go. I have a strong DIY spirit myself, but I've learned that it's usually better to rip off an existing design than to try and replicate it from scratch unless you really want to spend lots more time than it's worth building your own :) Unless you have a pile of 2" square tubing and welder sitting in your garage, a used NordicTrack that you restored/beefed up is going to be the better choice.
posted by jpeacock at 11:13 PM on February 1, 2012

See if you can get hold of a strong electric DC motor, connect it as a generator and short the leads through a lightbulb. Changing the electrical resistance of the bulb changes the physical resistance you feel when turning the shaft. This solution is good because it's quiet and wear-resistant, but too expensive to put in a series-produced machine. For a DIY project, there's a pretty good chance that you can find a suitable motor on ebay. I guess you want to dissipate up to 500W or so, and need to dimension the motor and circuit accordingly.
posted by springload at 1:44 AM on February 2, 2012

On the DIY front I'm going to suggest this is capital-H Hard. You may be able to employ better materials (maybe - are you able to buy steel 1000lbs are a time in order to get a supplier to care about you?), but your manufacturing quality is going to suck and your tolerances are going to be miserable compared even to a manufacturing line that's stopped caring. Think about whether you can get all of your parts flat to within 0.001" and every element of your transmission parallel to within a degree or two (in a 10cm axle, that's 3mm). That's what influences smoothness of ride, noise, and lifespan as much as the materials you choose.

If one of my more talented undergrads proposed this to me I'd give them a full academic year to do it and expect it to not work at the end. Sorry to be depressing but I think this is a hard one.
posted by range at 5:50 AM on February 2, 2012

I'm much more positive than range, it shouldn't have to be so difficult and it sounds like a lot of fun. The prerequisite is that your friend's workshop has a mill and a lathe big enough to hold all the DIY parts, and that you know how to use them. It won't be possible to do with hand tools, but I don't think that's news to you. Can you please let us know what design you choose and how it works out?
posted by springload at 3:02 AM on February 5, 2012

Response by poster: Yeah, I'll check in, if it's the q is not closed by then, because a few things came up, and I'm gonna be a bit tied up for awhile. Also, yeah, the workshop has quite a few high-end machines so I should be good there, especially that my friend is a somewhat handy DIYer himself, and will be happy to pitch in on the more complex tools. *However*, I am not going to settle on a design until I settle on the resistance mechanism, which has to be (1) robust (2) controllable (3) high-capacity (4) quietish in operation (5) accommodate a foldable design - quite a list, so we'll see.

And thank you everybody for your observations. Indeed, this is, as I suspected, a bit of a challenge.
posted by VikingSword at 4:13 PM on February 5, 2012

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