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Tech Info - Roller Chains & Sprockets

#35 chain sprocketsRoller chain drives are, off course, a standard means of mechanical power transmission, however our interest in roller chains arose principally from the use of low cost Chinese built drive motors as the main motor type for our designs. These motors are more usually used in electric scooter/trike spares and often come with a chain sprocket already attached to the output shaft. My initial concerns about noise proved unfounded and we have found that roller chain drives, even at the high motor shaft output speeds (3000rpm +), are very quiet. Generally, for the same reduction ratio, chain linked shafts have to be a bit further apart than gear linked shafts, however they are more tolerant of slight shaft mis-positioning and removing the chain breaks the mechanical link between the shafts which can sometimes help in assembly or disassembly activities.

#25 bossed roller chain sprocketsSprockets need to suit the chain type used (or vice-versa) so pay attention to the specs. On the scooter motors type #25 chain is most common. This is 1/4" pitch American specification chain (ISO No. ASA-25) which is different from UK spec 6 mm pitch chain (04B-1) so don't mix up the two! Larger pitch chain is stronger so a step up to 3/8" pitch chain in the form of either the US spec #35 (ASA-35) or the UK spec 06B-1 will give more drive torque capacity. Again, don't mix and match chains or sprockets from the different specifications. A good range of larger sizes is available from 1/2" pitch and upwards if needed.

3/8" UK Spec roller chainSprockets are similar to gears insomuch as the number of teeth matters (to get the reduction ratios you require) and they are available in bossed or un-bossed (plate wheel) forms. For bonding to shafts the bossed form is best as this offers the greater bond area for joint strength, however the un-bossed sprockets are good for bolted attachment to the hubs on drive wheels without taking up too much space. 8 mm pitch UK Spec roller chain on MY1020 motorIf designing-in a chain drive particular attention needs to be paid to the shaft centre distance - this needs to be calculated to suit the chain pitch, number of teeth on the sprockets and the length of chain to be used. The equations needed to do this are available in several engineering design texts however they are most conveniently obtained from the chain suppliers themselves, check here. The common approach is to estimate chain length to suit the desired approximate shaft spacing, then to calculate the exact spacing once the precise chain length is selected. It is wise to allow position adjustment of one or other of the sprockets to enable the chain to be tensioned slightly on assembly to remove slack.

As with your steel gears you need to keep your chains lubricated in operation.

For a good on-line technical guide for chains take a look at chain-guide.com.


 

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