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Wie funktionieren Bandbremsen? (Quelltext anzeigen)
Version vom 13. Juli 2018, 06:57 Uhr
, 13. Juli 2018→Aufbau einer Bandbremse: Verlinkung zu wikipedia
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The rotation of a band brake's drum tends to pull the band around it. This results in a capstan effect, which multiplies the braking effect. You can experiment with the capstan effect yourself by wrapping a rope around a tree. Hold each end of the rope in one hand. Pull on one end hard and on the other lightly. If the rope is wrapped by 1/2 turn, you can get it to slip by releasing tension on the lightly-tensioned end. If it is wrapped by 1 1/2 turns or more, no matter how hard you pull on it, it will not slip. | The rotation of a band brake's drum tends to pull the band around it. This results in a capstan effect, which multiplies the braking effect. You can experiment with the capstan effect yourself by wrapping a rope around a tree. Hold each end of the rope in one hand. Pull on one end hard and on the other lightly. If the rope is wrapped by 1/2 turn, you can get it to slip by releasing tension on the lightly-tensioned end. If it is wrapped by 1 1/2 turns or more, no matter how hard you pull on it, it will not slip. | ||
A Wikipedia article describes echnical details of the capstan effect, but here's a simpler explanation: where the lightly-tensioned end of the rope pulls away from the tree, it is in line with the side of the tree trunk, and it isn't pressing on the tree at all -- so the tree trunk isn't pulling on the rope there, at all. After a quarter turn, the tension on the rope is pressing it directly inward against the tree trunk, so friction allows the tree trunk to resist the tension from the other end of the rope. That friction, in turn, allows the rope to resist more tension after the next quarter turn, and so forth. So, starting at the lightly-tensioned end, the tension increases as the rope wraps farther and farther around the tree. If the rope is wrapped far enough, a light pull on one end of the rope, or even the weight of the rope itself, generates enough friction to resist a hard pull on the other end. | [https://de.wikipedia.org/wiki/Euler-Eytelwein-Formel A Wikipedia article] describes echnical details of the capstan effect, but here's a simpler explanation: where the lightly-tensioned end of the rope pulls away from the tree, it is in line with the side of the tree trunk, and it isn't pressing on the tree at all -- so the tree trunk isn't pulling on the rope there, at all. After a quarter turn, the tension on the rope is pressing it directly inward against the tree trunk, so friction allows the tree trunk to resist the tension from the other end of the rope. That friction, in turn, allows the rope to resist more tension after the next quarter turn, and so forth. So, starting at the lightly-tensioned end, the tension increases as the rope wraps farther and farther around the tree. If the rope is wrapped far enough, a light pull on one end of the rope, or even the weight of the rope itself, generates enough friction to resist a hard pull on the other end. | ||
In the image above, pulling up on the lever one end of the band (at a1) tightens the band against the drum. The other end of the band is attached (at a2) to the lever on the other side of the pivot, so the capstan effect rotates the lever around the pivot and pulls the band tighter. This makes the brake self-locking: if it is applied strongly enough, the band will hold the lever up and keep the drum from turning until the lever is actively pushed down. This is a differential band brake, similar to our example of wrapping the rope around the tree because both ends of the band are active. | In the image above, pulling up on the lever one end of the band (at a1) tightens the band against the drum. The other end of the band is attached (at a2) to the lever on the other side of the pivot, so the capstan effect rotates the lever around the pivot and pulls the band tighter. This makes the brake self-locking: if it is applied strongly enough, the band will hold the lever up and keep the drum from turning until the lever is actively pushed down. This is a differential band brake, similar to our example of wrapping the rope around the tree because both ends of the band are active. | ||
