4 ms·

I don't know anything about FEA, but in reading this article and thinking it through, was the first time it hit me how bad a conventional chain and sprocket is.

by rconti 6y ago

I don't know anything about FEA, but in reading this article and thinking it through, was the first time it hit me how bad a conventional chain and sprocket is. On a brand-new set with perfect tolerances, you might be able to use many of the front side of many of the teeth, but as SOON as the chain begins to stretch (wear) even fractionally, most of the stress goes to the 'first' teeth in any given power stroke, and the same spot on the chain. I imagine if you're putting, say, 1000w through 2 teeth and 2-4 chain endplates, wear is an order of magnitude higher than if you're able to effectively transfer power through double the teeth and endplates. Likely the "pins rubbing" you mention doesn't really matter, because the wear from inserting and removing the chain as it cycles around has to be a miniscule fraction of the wear that occurs under load.

Obi_Juan_Kenobi 6y ago
Bike chain teeth do not have straight sides or a convolute profile. They are wedges that act as ramps for the rollers. As the chain wears, it is no longer possible for the rollers to all sit at the base of the teeth. Instead, to account for the increased pin-pin distance, they begin to ride 'up' the teeth at the point of first engagement. You can easily see this when looking at a worn cassette used with a stretched chain. The tooth profiles become sharply hooked as the roller wear works in from the 'side' of the tooth. https://pbs.twimg.com/media/EFYuxlJXYAA89-b.jpg https://pbs.twimg.com/media/EFYuxlJXYAA89-b.jpg Note that the lowest point of the profile remains at the original base of the tooth, and then is angled up. In a worn chain, the rollers engage high up, and then work their way down (under high load) until seated at the base. In the unworn condition, engagement begins at the base of the tooth where the forces are better spread over the roller. In point of fact, the forces are spread out over more teeth when worn. The first tooth engagement might begin 3mm high, then 2.5mm, then 2mm, etc. over ~6 teeth. Whereas the fresh chain might manage 2 or 3. But the wear and friction of the worn chain is much higher as you have a great deal of motion under high load as the loaded rollers creep down. The unworn chain has perhaps higher loads, but the roller is essentially seated and immobile at the base of the gear for this.
foobar1962 6y ago
> ..it hit me how bad a conventional chain and sprocket is. Not at all! The article claims 98% efficiency. Roller chains are used to transfer torque in bicycles and motor cycles, inside internal combustion engines to drive cam shafts... and many more applications covering a huge range of power levels and environments. Not only is it efficient, it's cheap. If that last 2% of efficiency was important (or easy to obtain) it would have been on a GP motorcycle already.
jacquesm 6y ago
A chain is an extremely efficient way of transferring power. A similar arrangement made with gears would be much less efficient (even if it could be made much more durable, but not at the same total weight).

by rconti 6y ago

Obi_Juan_Kenobi 6y ago

Bike chain teeth do not have straight sides or a convolute profile. They are wedges that act as ramps for the rollers. As the chain wears, it is no longer possible for the rollers to all sit at the base of the teeth. Instead, to account for the increased pin-pin distance, they begin to ride 'up' the teeth at the point of first engagement. You can easily see this when looking at a worn cassette used with a stretched chain. The tooth profiles become sharply hooked as the roller wear works in from the 'side' of the tooth. https://pbs.twimg.com/media/EFYuxlJXYAA89-b.jpg https://pbs.twimg.com/media/EFYuxlJXYAA89-b.jpg Note that the lowest point of the profile remains at the original base of the tooth, and then is angled up. In a worn chain, the rollers engage high up, and then work their way down (under high load) until seated at the base. In the unworn condition, engagement begins at the base of the tooth where the forces are better spread over the roller. In point of fact, the forces are spread out over more teeth when worn. The first tooth engagement might begin 3mm high, then 2.5mm, then 2mm, etc. over ~6 teeth. Whereas the fresh chain might manage 2 or 3. But the wear and friction of the worn chain is much higher as you have a great deal of motion under high load as the loaded rollers creep down. The unworn chain has perhaps higher loads, but the roller is essentially seated and immobile at the base of the gear for this.

foobar1962 6y ago

> ..it hit me how bad a conventional chain and sprocket is. Not at all! The article claims 98% efficiency. Roller chains are used to transfer torque in bicycles and motor cycles, inside internal combustion engines to drive cam shafts... and many more applications covering a huge range of power levels and environments. Not only is it efficient, it's cheap. If that last 2% of efficiency was important (or easy to obtain) it would have been on a GP motorcycle already.

jacquesm 6y ago

A chain is an extremely efficient way of transferring power. A similar arrangement made with gears would be much less efficient (even if it could be made much more durable, but not at the same total weight).