Well, I went out and made a sled similar to yours this afternoon (it made for a nice Sunday afternoon project!), but with a few differences. I’ll have to put it through some paces, and start a thread to review it.
Thanks for the inspiration.
-FC
Good shit bro, I’m envious, will build myself a similar set up when I leave Japan and my postage stamp sized apartment.
How much poundage do you have?
[quote]Keith Wassung wrote:
I would be proud to train at your gym, the sled does look intriguing, though I have found that if you have a sled that has a flat bottom, it will add to the difficutly in dragging it because of the friction against the ground. Your sled is designed almost like a sleigh that has slick runners, so more weight must be added-of course this is just an observation/specualtion on my part.
[/quote]
Interestingly, friction does not depend on surface area, but rather on the normal force (weight) and the roughness of the surfaces.
Friction force=(coefficient of kinetic friction)x(normal force).
Basically, if you have 100 lbs. spread out over a large area, the normal force per unit area is smaller than if the same weight was spread out over a small area. So in our example, 100 lbs on two rails will be just as hard to pull as 100 lbs on a large platform.
I know this is counterintuitive, it took me quite a while to wrap my mind around it.
Jeff
Great home gym! It’s really cool how you build some of that stuff! Way to go.
I would be proud to train here.
great job!
[quote]Jeff Parsons wrote:
Keith Wassung wrote:
I would be proud to train at your gym, the sled does look intriguing, though I have found that if you have a sled that has a flat bottom, it will add to the difficutly in dragging it because of the friction against the ground. Your sled is designed almost like a sleigh that has slick runners, so more weight must be added-of course this is just an observation/specualtion on my part.
Interestingly, friction does not depend on surface area, but rather on the normal force (weight) and the roughness of the surfaces.
Friction force=(coefficient of kinetic friction)x(normal force).
Basically, if you have 100 lbs. spread out over a large area, the normal force per unit area is smaller than if the same weight was spread out over a small area. So in our example, 100 lbs on two rails will be just as hard to pull as 100 lbs on a large platform.
I know this is counterintuitive, it took me quite a while to wrap my mind around it.
Jeff[/quote]
Wassung is half-right for the wrong reasons, most of the flat-bottomed sleds are steel or wood, both of which 1) are denser and 2) have a higher coefficient of friction than PVC.
ejjett,
Very nice (better than mine,I don’t really have time or patience for PVC) but several things:
- Keg
- Sledgehammer
- Tire
- Sandbags (My 'Depot carries “truck weights” for $1.80/30# bag)
Okay, maybe they’re not your thing, but they are immensely useful, very cheap, and most gyms don’t like you bringing your own (esp. the keg).
Very Nice