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Gear Ratio Help PLEASE!

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tawd77 View Drop Down
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    Posted: Mar/08/2018 at 3:07pm
Hello, My daughter is working on a buggy project. We are trying to determine what the buggys speed will be, with the engine at 3500rpm.

Here's whats she's working with...
Engine at 3500rpm
CVT clutch 1:1 at 3500rpm
13.25:1 gearbox/differential 22" tires
Then a combination of sprockets between driven clutch, and gearbox to obtain around 60mph at 3500RPM. So, we are tring to figure out which sprockets will be necessary to obtain this speed.

I attached a picture she drew, using a 35 teeth sprocket on a jackshaft with the driven clutch, and a 10 teeth sprocket on the gearbox. Would that get her to about 60mph at 3500rpm?

Thank you all for the help!  uploads/4680/ratio1.jpg - uploads/4680/ratio1.jpg


Edited by tawd77 - Mar/08/2018 at 3:11pm
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tawd77 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tawd77 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/08/2018 at 3:12pm
I'm not too sure why the picture won't show up...
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RLM View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RLM Quote  Post ReplyReply Direct Link To This Post Posted: Mar/09/2018 at 8:10am
This is very basic gear speed calculations.

Since it's Friday, i'll help you out, but your doing the math, i do enough of that sh*t every day. 

basically you need  to find out how fast you need to spin the drive wheels. 
find the circumference of the tire. this will tell you the distance the vehicle will travel per revolution. then figure out from there how many revolutions per minute you need to do to go 60mph.

now, since you have a gearbox, multiply the wheel rpm through the gearbox to get the input shaft speed. 

looking at the input shaft speed and the engine speed, find out the multiple by which they are different. this will be the overall reduction you need from sprockets. you can then either do it with a single reduction or multiple reductions to achieve this overall ratio. 

Best of luck, and if you get stuck, there is likely a prebuilt calculator online, or check out a machinery component design text book for the chapter on gear ratios. 
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Bantu View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bantu Quote  Post ReplyReply Direct Link To This Post Posted: May/10/2018 at 6:49am
I get what you saying above. I am from South Africa, I am doing a similar project. In fact I am doing a CVT optimization. I am using Briggs & Stratton engine with 7.5kW and 3700RPM. The transmission is a single reduction, (driving and driven gear). But I want to know how to calculate the overall gear ratio and why do I have to calculate overall gear ratio? When do I consider transmission and CVT efficiency?
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