More questions out of Northir, this time about gears

[Northir]

im working on a go-cart part of it will be the gears off of a old bike just trying to figure out how to set them up, big-big, small-small, big-small, small-big, ive all ready tried researching on google but i figured id pick your brains too

[inonickname]

You haven't given us enough information.

How heavy are you? How many people will be on the go-kart? How heavy is the go kart? How much torque/horsepower does the engine have? How big are the tyres?

Small-big will decrease RPM and increase torque, big-big will keep it the same and big-small will increase RPM and decrease torque.

[Northir]

well thats a totally valid point,i havent even started building it, but i was thinking of a angle iron frame 3X5 feet maybe 4X5', with 3/4 plywood "flooring" the engine will either be a 5.5 HP gasoline or a much smaller electric motor from a sat dish, the tires are going to be old 16" bike tires, not sure if the steering will be a single wheel or 2 wheels yet, i weigh about 200 pounds, im thinking ill need the torque over the speed, as far as supplies i have quite a bit to work with and am total open to ideas, im trying to use some of my more abundant mats, like the angle iron, and bike peices, i also have lots of rebar and pan decking, kinda limited on my engine selection, i only have the 2 side drive motors, the rest are vertical drive, more or less i dont care about speed

[jackssmirkingrevenge]

the engine will either be a 5.5 HP gasoline or a much smaller electric motor from a sat dish, the tires are going to be old 16" bike tires, not sure if the steering will be a single wheel or 2 wheels yet, i weigh about 200 pounds, im thinking ill need the torque over the speed

Given those specs small gear on the engine, big gears on the drive shaft, no question.

[Technician1002]

the engine will either be a 5.5 HP gasoline or a much smaller electric motor from a sat dish, the tires are going to be old 16" bike tires, not sure if the steering will be a single wheel or 2 wheels yet, i weigh about 200 pounds, im thinking ill need the torque over the speed

Given those specs small gear on the engine, big gears on the drive shaft, no question.

A good resource is the info for selecting gear ratios for model RC race cars. They give lots of good info an how the torque and speed translates to track performance.

http://www.rcuniverse.com/forum/m_2587132/printable.htm

This ratio theory applies to designing the go cart. More people are into building RC race stuff than designing go carts so there is more info on the subject there.

http://www.rcracing.com/Gear_Ratio_Program_1100.cfm

Don't be put off by "spur"gears. RC cars use gears instead of sprockets. The ratios apply to chain drive just like they do to gear ratios. The ratio of either can be calculated by counting the teeth and making a ratio. For example 30:30 = 1:1 90 :90 = 1:1 11:55 = 1:5. Chain sprocket or gear spur, the ratio still works the same.

http://www.rccartips.com/rc-cars-ezine-14.htm

Knowing the engine RPM range, the gear ratio that reduces RPM and increases torque (by the same ratio) will give the final wheel RPM. Using the wheel diameter, Circumference can be found. (Pi X Diameter) that will give the distance traveled per wheel revolution. Distance per revolution X revolutions per minute (RPM) gives distance per minute. Further conversions can give feet/second and miles/hour.

I won't spoon feed the last two. Keep track of what units you are working with at all times. Distance.. feet.. inches.. miles.. etc. Time seconds.. minutes.. hours.. Don't confuse feet per minute as miles per hour.
If you do, NASA may have a place for you.

[psycix]

Make them detachable so that you can experiment with different ratio's. Or even shift like a bike with dérailleur.

[geardog32]

do you have a centrifugal clutch for the gas engine? and is the electric motor ac or dc? electric motors have more instant torque than gas motors but the drawback is heavy batteries, thick wires, speed controller, possibly a big inverter. i would for simplicity go for the side driven gas motor and pick up a centrifugal clutch from tractor supply.

[ramses]

Yes, you need a clutch of some kind. also make sure the engine (assuming 4 stroke) is a horizontal shaft engine. I think vertical can be adapted to work, but is more trouble than it is worth.

[Northir]

do you have a centrifugal clutch for the gas engine? and is the electric motor ac or dc? electric motors have more instant torque than gas motors but the drawback is heavy batteries, thick wires, speed controller, possibly a big inverter. i would for simplicity go for the side driven gas motor and pick up a centrifugal clutch from tractor supply.

dont have any sort of clutch for the gas, the electric is a DC will take quite a bit to get the power ill need for that, it runs slowly off of a single car battery if i use that ill want to add a alternator or a power regen of some kind, and i was thinking 5-10 batteries, it will depend on how many i can get

[inonickname]

An alternator will be useless with an electric motor. Thermodynamics say no.

[geardog32]

yeah an alternator is pointless with an electric motor. you could add a bank of capacitors to that when you roll to a stop it "charges" the capacitors and lets you have that extra energy to start moving again.

[Northir]

i was more or less thinking to keep a small charge in the batteries, so i could maybe use less batteries