The efficiency of a chain drive transmission depends greatly on the selection of the transmission components, which here are the drive sprocket, driven sprocket and the roller chain. So how can one make chain drive components selection for Gokart and ATVbaja transmission?
Power source specifications
First of all we need specifications such as drive and driven sprockets rpm, the engine or electric motor power wattage (kW), the center distance between sprockets.
Let say we have a Honda engine with the following specifications: Engine displacement: 124.73cc, Maximum engine output: [email protected] rpm, Maximum engine torque: [email protected] rpm, Transmission four gears: First gear ratio= 3.3528 , Second=1.9624 , Third=1.3246 , Fourth= 1.0185 , Primary reduction= 3.350 .
Now we have the required specifications we can do some small calculations in 6 steps to determine the right components.
1- find The chain service factor (Ks)
for high impact and using an internal combustion engine as power source Ks=1.7, for electric motor Ks=1.5
2-Calculate the corrected design power (kW)
Design power=1.7×7.88=13.4 kW
3-Consult the design power (kW) vs speed of drive sprocket table (refer your chain supplier chain catalog) to select the suitable chain and drive sprocket for 13.4kW and 7500 rpm (maximum rpm of engine).
From the table we can see that RS140 or RS160 with a 15 tooth or 14 tooth drive sprocket will fit our application
4-Find the number of teeth on the driven sprocket
To find the number of teeth on driven sprocket we can use the formula:
Number of teeth in driven sprocket=number of teeth in driver sprocket × (engine sprocket rpm/driven axle sprocket rpm)
But I discovered, it’s quiet a bit difficult to find the rpm of driven sprocket or rear wheels in this case, since we need the final drive ratio or final gear reduction in order to find the rpm (reversely having the rpm help to decide the final drive ratio which is the ratio between the rear axle sprocket of the vehicle and the engine sprocket).
The most suitable solution to this issue I got is assuming first a final drive ratio then we can vary the ratio by looking it effect on the vehicle speed and the diameter of our rear axle sprocket with the chosen ratio.
Suppose we already have an engine sprocket of 15 teeth, if we choose a final drive ratio of 3:1 (for 3 rotation of engine sprocket the rear axle sprocket rotate once) the number of teeth on rear axle sprocket will be:
Number of teeth on engine sprocket × 3 =15×3=45 teeth
We can now look our vehicle speed and acceleration with the above ratio, if suitable now we check the diameter of 45 teeth sprocket if it can fit our application. For example in the design we have a distance of 100 mm as the center distance between engine sprocket and rear axle sprocket.Are the sprockets can fit within that distance? Even if yes in the case of Go kart the rear wheel diameter is 11 inches, a sprocket which has a diameter equal or greater than that value is not suitable.
For the vehicle speed or the sprocket diameter instead of going through a bunch of manual calculations, we can save time by doing it online there are many sites for that.
5-Confirm from the power transmission table (from chain supplier) that the selected chain meets the power requirements.
6-Calculate the length of the chain (number of chain pitches)
L= (N+N’)/2 +2C + ((N+N’)/6.28)^2/C
Where: C=center distance /chain pitch
N=number of teeth in driven sprocket
N’=number of teeth in drive sprocket
The RS140 roller chain pitch=44.45 (Tsubaki.ca)
Assuming the center distance between drive and driven shafts=300mm, doing the calculations L=52 links
I hope you enjoy this article and it can help you design a better chain drive transmission. If you like pleases comment and share, and if you will like us to cover any related topic suggest, we will do our best to satisfy your queries.
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