T-20 Output RPM ?

[swfleur]

Hi all - I'm trying to find the output RPM of the T-20 at typical max speed. I have a max II with 18 hp - I know that the RPM will vary based on the throttle I give it but here is why I'm asking - I am working on a dual propeller option that will be driven from the rear sprockets - axles. I can see that all the wheel axles are connected to center sprocket and the center sprocket is connected to the T-20 output shaft. I will share my very simple idea to add a prop for the left and a prop for the right side. I have seen all the posts on this site where this has been done but it seems out of reach for the typical weekend warrior - so I'm gonna make it EZ - I hope
( This site is awesome by the way and it has helped me rebuild everything on this Max II - engine to tranny to bearings - thank you )
SO back to my question .... What is the typical speed of the axles or sprockets or T-20 output shaft or even the tires themselves?? I'm not asking for surface FPM but RPM - this should not change from the tires to the sprockets to the T-20 output shaft. ( Unless the sprockets were different size and mine are all the same. Any help would be greatly appreciated. I may try to measure it but was hoping some one had an idea ?? Thanks

[Mike]

If you spin your T20 you can count the output shaft revolutions per revolution of the input shaft. I believe when I did this I counted about a 6:1 ratio.

[swfleur]

Got a question about RPM ... I'm trying to find the output RPM of the T-20 at typical max speed. I have a max II with 18 hp - I know that the RPM will vary based on the throttle I give it but here is why I'm asking - I am working on a dual propeller option that will be driven from the rear sprockets - axles. I can see that all the wheel axles are connected to center sprocket and the center sprocket is connected to the T-20 output shaft. I will share my very simple idea to add a prop for the left and a prop for the right side. I have seen all the posts on this site where this has been done but it seems out of reach for the typical weekend warrior - so I'm gonna make it EZ - I hope
( This site is awesome by the way and it has helped me rebuild everything on this Max II - engine to tranny to bearings - thank you )
SO back to my question .... What is the typical speed of the axles or sprockets or T-20 output shaft or even the tires themselves?? I'm not asking for surface FPM but RPM - this should not change from the tires to the sprockets to the T-20 output shaft. ( Unless the sprockets were different size and mine are all the same. Any help would be greatly appreciated. I may try to measure it but was hoping some one had an idea - comments or questions or even friendly insults are welcome ?? Thanks

[swfleur]

Thanks Mike - I would still have to get an RPM and do the math though - If the Tecumseh puts out 2000 RPM ( for example )- I could divide that and say that I'm getting reduced RPM of approx 400 ? BTW - you have been an inspiration to help me in many of my repairs on this Max II - Also - I saw your videos and it inspired me to clean my shop as well

[swfleur]

Mike - thanks for the quick reply and all the work you do keeping this site in order - Excellent place to share and learn about the 6x6's - Regarding propulsion... I have seen the trolling and outboard motors and the in wheel paddles, also the mad max with twin props. I have also read where a guy was gonna use a trash pump like a jet - not sure if he did - I even considered using a jet ski pump and cutting it into the tub but that takes high power and high RPM - is there any other method you know of? I' looking at using gear boxes driven of the rear left and right wheel shafts - I would up the RPM at the output of my gear box and have recessed female stubs in a flange mount bearing - this would allow putting the prop on and off with a through pin or maybe threaded wrench tight connection - I cant see leaving the props on when beating the brush - What are your thoughts on this ?

[thebuggyman1]

You have alot more to consider besides RPM. Prop diameter, pitch, height and distance from the tub.....to name a few.
I would think a larger dia. prop. with a more aggressive pitch positioned a fair distance behind the machine would work best. This would create issues with water angle departure, even if they were quick pin connected to a shaft so they were not on except when it the water. Do you know where your water line is? Can you even keep a prop below that mark without it being ripped off?

[thebuggyman1]

Quick math......assume 20mph typical high speed. 20mph/60(mph to mpm) = .3333 (miles per minute). .3333miles x 63360(inches in a mile)=21118"(traveled in a minute). 22" dia tires= (22"x3.1416) 69.12" circumference. 21118"(distance traveled per minute)/69.12( tire circumfrence)=305 axle rpm at full speed.

Somebody double check my math here......I'll blame it on a cheezy calculator. LOL

[racerone3]

yes-yes-no the tire/ axle/ sprocket will turn at the same rpm as they are all bolted together basically making them one unit. however the gear ratio between the axle and the T-20 will be different. For example in a machine with a T-20 running a 15 tooth sprocket driving an axle with a 30 tooth sprocket, the output of the T-20 will turn 2 revolutions for every one revolution of the axle

[thebuggyman1]

He was looking at driving the props off the rear axle.......t-20 rpm is irrelevant.

[LarryW]

I just found this Wheel And Tire Motion Calculator. If you measure your distance from the rim edge to the tread and enter your maximum speed you will get your axle rpm at wide open throttle. If you wanted it to be accurate you probably should actually measure instead of figure 22" tire actually = 22"(probably is not) minus 8" rim = 16" divided by 2 = 8" for your tire body size. But you will probably get more rpm out of it in the water with basically no load on the engine unless your props are working hard. Im not sure why it wants rim and tire body but must be for some of the other calculations its doing for the G force. Because you really only need the tire diameter to figure this out.

Wheel And Tire Motion Calculator