orb

Hey guys, I am at the moment at the design stages of building my own large scale RC car.

The plan is, to keep it as SIMPLE as I can to make it as reliable as I can.

I have a 28cc McCulloch engine out of a petrol strimmer that i have been tuning and tweeking to run a little better and I plan to use this.

I was thinking about making a basic chassis out of 10mm box section and mounting the motor to this, I have decided that as it is set to be an off road bashing machine I am not sure that i want to go to the trouble of adding a diff to it, so I have instead opted for a solid rear axle.

That is the easy bit over with, now, this is where you lot come in!

I want to make it direct drive from the engine to the rear axle using a chain drive and sprockets, but I have no idea what ratio I should be using, I am not over bothered about MEGA top speed and LIGHTENING excelleration, I am more after a nice balance to this so I can generally have a bit of fun with it.

So, What do you guys recon? Can you assist with the ratio? Have you ever seen any models built with engines using Garden tools? Any Pics? Did they work ok?

Thanks for all your help chaps and sorry for the long post, I am just a little unsure, so i thought it best to ask the experts.

ORB

orb

Come on, someone here must have a clue?

I was thinking about using Cycle sprockets, a 13 tooth on the rear, and about a 20 on the front?

ORB

jimbo1890

Mate that is a little difficult to answer. there are so many variables like how fast you want it to go, how high the engine revs, the diameter of the tyres etc,etc,etc

trial and error is the answer

sorry

mbba2002

My Feedback: (10)

WEIGHT, TIRE SIZE and HP are the main ideas you need.
The motor you have is 1.5 hp
You need the tire size and weight of your project. EXP. 9" tire Weight EXP. 30-40 lbs. So gearing should be 15:1-20:1 to start with. The heavier you go the lower the gear ratio.
25 pitch chain is the best to work with.
Motorcycle chain is too large to stuff in a small space.

I have built 3 and plan to build more

OLD_SLOW and in the WAY

run a flex shaft off the engine or just tow one of these around
[link=http://images.amazon.com/images/P/B000087QXC.01._SCLZZZZZZZ_.jpg]weed walker/whacker/trailer/thingy[/link]

kiora

I bet that cuts through the post office que on pension day beats any zimmer i've seen.

Col

orb

25 Pitch chain?

I was thinking of using a cycle chain and sprockets?

Any more pics?

Drive train would be nice

mbba2002

My Feedback: (10)

Bike chain is overkill and the sprockets off a bike are junk. You can use the chain if you want but you will have to buy new sprockets with hubs. You can't get the gearing I suggested to you to work with bike chain and sprockets (TO LARGE). So it's best to start with smaller sprockets and chain to achieve the suggested gear ratio. Most large scale cars use chain drive, gear drive or belt drive. Look at the size of the parts that make up the drive end and see how small they are.

orb

you can get cycle sprockets from about 60 tooth to about 9, so i recon getting the range should not be a problem.

Are the ones you built yourself fast?

What gearing do you use?

ORB

chevyman_de

I don't think you'll be able to use a single stage direct drive with them. The sprocket on the rear axle will touch the ground before the tires do.
The gearing you'll need requires a two stage drive train (as long as you don't want to go with a worm gear ), no matter whether you use chains or spur gears.

orb

Do i really need the rear sprocket to be that big?

I thought i would get away with about a 13 tooth sprocket on the rear (about 60mm tall) and about a 25 on the front?

chevyman_de

That way you would have the rear axle at twice the engine speed. You need a reduction!

orb

Whats wrong with that?

The engine will not rev that fast will it?

lol

ORB

chevyman_de

The engine has not enough torque to move the car with that kind of gearing. Engines need a reduction. Look at a bicycle and then look at a motorbike. And the motorbike has an additional gearbox to get even lower gearing. Ever tried to launch a real car or motorbike in top gear?

orb

so, what would you reccomend?

How many teeth on the front?

How many on the back?

ORB

chevyman_de

There is no recommendation possible. As mbbaj2001 wrote some postings before, you have to design the car first, then you can guess the gearing. You will end up with a two stage reduction. Direct drive will be possible for a street racer only. Nevertheless some try and error will be required.

mbba2002

My Feedback: (10)

SO you want to use bike chain??? EXP: Your 13 sizesprocket is aprox 2.25' and the 60 sprocket size is aprox.10". Your mounting distance between the the 2 sprockets is aprox. min 11.5". Now you are stuck with a tire size of greater than 10" . Tires any smaller will drag on the ground and the gearing is 4.6:1. Too high for the 10"tire and 1.5 hp motor. The gearing I recommended you to start with is a starting figure for 9" max tire sizes. With 25 pitch chain you can use a double gear reduction in the same space as the single gear bike chain and get the recommended gearing. The rear axle gearing I would start with 5:1 and the gearing from the motor 3:1-4:1 adjustable with the recommended 25 pitch chain. With a smaller tire (EXP.6"-7") you can use a smaller gearing at the axle( EXP. 4:1-3:1). The bigger the tire and lower the gearing the slower in speed. So more HP with a higher gear and smaller tire will bo faster.

orb

Thats cool.

Ok, I am gonna start welding this week so will start postig pics as I go.

Warning:

THIS IS NOT GONNA BE PRETTY!!!