HighLUX Posted September 18, 2014 Share Posted September 18, 2014 How does one figure out what size pulleys to use. Im cobbling together a bit of a project that will be belt driven by a 3.5-5ish hp briggs and want it to do about 30kph. Needs to drive the weight of 2 adults Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 18, 2014 Share Posted September 18, 2014 Size of wheels and operating revs of Briggs? I had go kart size wheels and 25/90 tooth ratio from a 5hp bringgs with a 2:1 ratio reduction box and it could push along a motorized park bench that weighed ~80kg plus 2 people on it to pretty quick - I'm guessing 25-30Kmph. Quote Link to comment Share on other sites More sharing options...
Rookie Posted September 18, 2014 Share Posted September 18, 2014 I have a spreadsheet I could send you , pm me your email address. 1 Quote Link to comment Share on other sites More sharing options...
HighLUX Posted September 18, 2014 Author Share Posted September 18, 2014 wheel size 260mm and fuck knows what rpm a OG 70s briggs punts along at Quote Link to comment Share on other sites More sharing options...
HighLUX Posted September 18, 2014 Author Share Posted September 18, 2014 I have a spreadsheet I could send you , pm me your email address. Chur rookie What do I do in regards to the gear ratios and shit? Id prefer to do it straight drive with only 2 pulleys Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 18, 2014 Share Posted September 18, 2014 With 250mm wheels you may need a jackshaft because the driven pulley may nearly be bigger than the wheel or the drive pulley may need to be so small that it will slip with lots of load. Check your Briggs doesn't have a 2:1 reduction box on it cos they are an awesome headstart plus they have a centrifugal clutch in them. Quote Link to comment Share on other sites More sharing options...
HighLUX Posted September 18, 2014 Author Share Posted September 18, 2014 Doesnt look like it has one Jack shaft complicates things a bit but I suppose if its needed then I will use one Quote Link to comment Share on other sites More sharing options...
kicker Posted September 18, 2014 Share Posted September 18, 2014 Running rpm is normally around 3600rpm I think 1 Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted September 18, 2014 Share Posted September 18, 2014 That's the governed speed. They can rev to around 4000, but don't hold them there too long. (Or else you get a window in the front of the block) Lot's of goodies availble for thoses motors too........ 1 Quote Link to comment Share on other sites More sharing options...
Roman Posted September 23, 2014 Share Posted September 23, 2014 Wheel size of 260mm dia means it travels 816mm per rotation 1225 rotations per km To go 30kph = 36764 wheel rotations per hour 612 wheel rotations per minute So if your engine can do a max of 3600rpm (3600 / 612) You would need a 5.88: pulley ratio between the motor and the wheel. Assuming you had the torque available in the lower rpm range to get you there. 1 Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 23, 2014 Share Posted September 23, 2014 Wheel size of 260mm dia means it travels 816mm per rotation 1225 rotations per km To go 30kph = 36764 wheel rotations per hour 612 wheel rotations per minute So if your engine can do a max of 3600rpm (3600 / 612) You would need a 5.88: pulley ratio between the motor and the wheel. Assuming you had the torque available in the lower rpm range to get you there. To elaborate on that - using a bicycle sprockets (1/2" pitch) then a 58-60 tooth driven sprocket is 230-240mm diameter (which is only marginally smaller than the wheel) Plus you would need to find a 10 tooth driving sprocket which is a pretty big ask - they have them for BMX but they use very specific hubs. 10 tooth and 60 tooth sprockets are pretty much the far reaches of any common sprockets available on pushbikes. Alternatively you could find a go kart sprocket setup which is a much finer pitch (I think it's 1/4") but obviously more expensive Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 23, 2014 Share Posted September 23, 2014 Actually thinking about it, if this is running on the railway line then you could easily run a bigger sprocket than the wheels because it will drop between the rails. Just means it will be a pain in the ass to roll around when off the tracks. You could mount some swivel casters that also hang lower than the wheels that protect the sprocket and also allows you to move the jigger around with ease. Quote Link to comment Share on other sites More sharing options...
Steelies Posted September 23, 2014 Share Posted September 23, 2014 go jackshaft so you have more options to fuck with the reduction once it's rolling, cos you will want to once you're bored of doing 18kph, or 60kph after an hours run up and things can be more compact in size, final drive can be chain so the small sprocket can be tiny, allows you to work with a wider range of cheap/free belt pullies up front 1 Quote Link to comment Share on other sites More sharing options...
HighLUX Posted September 24, 2014 Author Share Posted September 24, 2014 Actually thinking about it, if this is running on the railway line then you could easily run a bigger sprocket than the wheels because it will drop between the rails. Just means it will be a pain in the ass to roll around when off the tracks. You could mount some swivel casters that also hang lower than the wheels that protect the sprocket and also allows you to move the jigger around with ease. Be a bit fucked with level xings/bridges with check rails if the sprocket is bigger. I have a jackshaft setup so will just use that and Manus idea of chain final drive to gear it nicely 2 Quote Link to comment Share on other sites More sharing options...
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