How to calculate gear ratio?

[Kerosene]

Anyone know how to work out gear ratios by counting the teeth on each gear/pinion?

[micro_Amps]

This is just a demo calculation for a set of 12:1 gears.
Motor pinion gear 6 teeth
Large cog on idler gear 18 teeth
So, initial gear reduction ratio = 18/6 = 3.00

Small cog on idler 6 teeth
Large cog on rear axel 24 teeth
Secondary gear reduction ratio = 24/6 = 4.00

Multiply the two reductions together to get the final reduction through the drive,
3 x 4 = 12.
So the reduction is 12:1
This means that the motor will have to turn 12 times to turn the rear axel once,
or as a ratio (12 turns:1turn) 12:1
I used the 12:1 axel as an example because it is the easiest, the others are calculated the same way but the numbers wont be whole numbers.
So there you go.
:)uA

Edited by – micro_Amps on 03 January 2004 17:53:49

[ph2t]

cool, I always wanted to know! now I can go and figure out my mini tank’s gear ratios…..

thanks mate!

:approve:

ph2t.

[micro_Amps]

Happy to help Ph2t, 😀
:)uA

[ph2t]

OK then, I think I’ve just found the lowest ratio setup ever.

This is from a Smartland MCV “Tank”

Motor pinion gear is 7 teeth, outer cog on idler gear is 16 teeth.
This ratio is 16/7 = 2.29

Inner cog on idler gear is 11 teeth, rear axle gear is 19 teeth.
This ratio is 19/11 = 1.73

Putting both reductions together gives me:

2.29 x 1.73 = 3.95

Therefore the resultant gear ratio is 3.95:1!!!

Now that’s a low ratio. The lack of power in this ratio is evident in that the Smartland MCV vehicles work only on very smooth surfaces, they have no “get up and go” power on carpet, etc.

Very interesting!

ph2t

[Kerosene]

Nice one 🙂 exactly what I was after. Thanks.

[betty.k]

very useful:) i was curious about the ratio on my enertecs and now i know! 7.1:1 if you’re wondering:8ball:

[leonli17]

THe is really helpful uA.
THe hardest part of calculating gear ratios is counting how many teeth there are.:dead:

[matic]

ph2t, BIT racer gears have 3.43:1 ratio….

[z-beam]

i just worked out my pink thunder charger clone gears, they are 6.57:1

they are my favorite gears for a standard bit.

[jamiekulhanek]

Quote:

ph2t, BIT racer gears have 3.43:1 ratio….

Remember there are 3 different kitt racer gear sets.

[micro_Amps]

Yes, there is,
Blue 4.75:1,
Red 3.95:1,
Green 3.43:1
They used to sell them in sets for the Bit Racers, but you will be VERY lucky to find them anywhere now, trust me.

:DuA

[z-beam]

i got a set of the blue ones modded to fit a bit.
and 1 red and green idler gear but no axles…

i wonder if the sbcg upgrade gearsets are the same as the standard bcg ones…. i’ll have a count and post the results…

[micro_Amps]

Zb, the SBCG ‘High Speed Set’ has only got two gear sets.
The red 8.25:1,
The orange 9.86:1 is sold as standard with all the cars,
and the yellow 12:1

But the set comes with front suspension, a 3.0 motor, and front knuckles as well.

So that makes the ratios on the SBCGs the same as the original BCGs, just different colours.
:)uA

[z-beam]

ok the sbcg yellow gears are 12:1 as well and the red ones are 8.25:1.

and just to complete this set of information a standard bit axle (orange) is 9.86:1.

with the motor ratings is it per second or minute? e.g. 1.0 = 1000 rpm

[z-beam]

ahh… i was too slow. you beat my post Ua

yeah igot lucky by getting one of those high speed sets, nice rims too. if only tomy would release some different rims with the good gears…

[leonli17]

the rating of the motors are:
1.0 = 10,000rpm etc.

[PandaBear]

If you’re changing the size of your tyres, then this also affects the “effective” gearing.

To counter this… some talk in terms of “rollout”.

This is just the Inverse of the gear ratio X the circumference of your drive tyre.

Rollout would be quoted in unit of “mm (travelled) per rev of motor”.

[leonli17]

I don’t get it. How does the size of the tyres had to do with the gears?
Please explain.:question:

[ph2t]

land speed, actuall speed, what ever you want to call it……. that’s what panda is saying. When he says “effective” this means the actual land speed the car will get with said gearing….

ph2t.

[micro_Amps]

So if I am correct it would be along the lines of…….
The gearing on the sample car was 12:1,
The rear wheel diameter (with average BCG tyres fitted) measured with vernier calipers is 13.84mm.
So if circumference is Pi x D (or 2 x Pi x r) then the circumference of the rear wheel is 13.84mm x 3.14 = 43.46mm
Now according to Panda….

Quote:

“rollout”…..is just the Inverse of the gear ratio X the circumference of your drive tyre.

That means that our 13.84mm wheel rear axel with a gearing ratio of 12:1 would have a rollout of…
43.46mm (circumference) / 12 (gear ratio) = 3.62mm of travel per motor revolution.

This makes perfect sense as a thicker or different tyre will change the rollout, and therefore the effective gearing.

Just to take this a little further.
If I have a microB 3.0 motor in that car, running at a perfect 30,000 rpm, what would the actual speed be?
Well if the car travels at 3.62mm per rev, and the motor is doing 30,000 rpm, then the car would be doing (3.62mm x 30,000) = 108600mm per minute. Or 108.6 meters per minute.
Times that by 60 to get meters per hour, 108.6 x 60 = 6516m/Hr or 6.516Km/h.
So a 12:1 geared car with average BCG tyres and a 3.0 motor should run at around 6.5km/h.

And then to take it to extremes….
The same car, running a 4.2 motor, 3.43 bit racer gears, and the same tyres, would run at…
43.46mm / 3.43 = 12.67mm per rev.
12.67 x 42,000 = 532163mm per minute
or 532.2 meters per minute
times 60 = 31929.7 meters per hour or….
31.9Km/h !!!

This is a theoretical maximum only, there are lots of ‘losses’ in the drive train, being friction, heat, noise, wind resistance, battery and motor production deviations, just to name a few.

I know from practical examples that using a triple cell car and the above setup, that this speed is possible, but the car is very difficult to control.

So there you go. Sorry for starting your Saturday with a maths lesson.blackeye:
:)uA

[leonli17]

Yeah…i know what panda means now. i just thought panda means by the tires had to do with the gears. i just misunderstood him that’s all.

I bet ph2t’s tri/quad cells will do that speed for sure. But he does have bigger monster wheels on the car so it should be more stable.

But just asking, dual cell does double the rpm of the motor right? and tri cell triples it. etc?

[micro_Amps]

Not sure on that one, I havent taken any rpm readings with the different batteries.
:)uA

[z-beam]

considering the context this thread is taking i’ve been noticing that certain clone motors behave very different to the tomy ones.
i prefer the clone ones because of what i termed “roll” factor, that is a tomy motor when not suplied with power tends to stop (resist) the the forward momentum of the bit whereas my clone ones idle and allow a gradual loss of momentum.

this rolling/idling is so benificial to acheive different degrees of steering on my tracks. the tomy motors just dont keep going like the clone ones, regardless of gear set up…

any ideas?

[leonli17]

It’s just that the clone motors are more loose than Tomy Motors which can be both good and bad. Good: u can use the slowing down time to turn better. Bad: the breaking distance is very long.

And over heating a motor for a long time can also loosen the motor.

[z-beam]

i’m thinking the loosness or idling ability is due to a different construction method, anyone clued in on how the micro motors are made?

[micro_Amps]

Yes, the clones (and other higher speed motors) have a finer wire in the ‘mesh’ that surrounds the core. (These motors are known as coreless motors because they dont have an armature that spins). The finer wire is needed to pack in more windings, which in turn, will produce a higher rpm but at lower torque.
The Tomy, and some slower motors, have thicker windings and because of this when the motor is powered off and let to roll, the Tomys will generate more back EMF (reverse voltage) and slow down quicker.
With the clone motors thinner windings dont create as much electrical resistance to spinning without the power on, so they will roll on for longer when you stop the power supply to them.
As far as ‘tightness’ all the motors use the same method of bushings, through the magnet at the front and a plastic casing on the back end.
The main achilles heel in this design is that is you run a motor hard, it heats up, and the heat on the shaft can melt the end cap and distort the hole where the shaft cames through.
:)uA

[ph2t]

Quote:

The main achilles heel in this design is that is you run a motor hard, it heats up, and the heat on the shaft can melt the end cap and distort the hole where the shaft cames through.
:)uA

And that’s how I killed my EM38 Vanquish…..:dead:

[z-beam]

thanx alot ua.

so if the wire inside the motor is resposible for the motor power through eloctromagnetic force, does this mean that the windings in the mesh can be damadged by contact with other motors and magnets?

what i’m asking in simplified words is can the wire inside be permanatly magnetized? and would this affect performance?

[micro_Amps]

Not likely, the windings are copper and therefore not magnetic.
Some people have said that perhaps putting a magnet beside the motor will strengthen it, but the chances of getting the poles in the right place are 100 to 1. Also the steel casing of the motor will divert any external magnetism around the internals of the motor, instead of through it.

I am reasonably sure that the magnets in these motors do weaken over time. I have a few 3.8s that have had some use, but not alot, and now a fresh 3.0 can leave them for dead.
:)uA

[betty.k]

copper is not magnetically attractive, and therefore the answer is no:8ball:

[z-beam]

thanx, i was asking this because i have heard that leaving your motors all bunched together side by side can damadge them.

even if it isn’t totally true they look neater when separated by a block of foam with holes cut in it…

[micro_Amps]

They sure do.
:)uA

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