Need help with a braking experiment

[dr fabio]

To all non mag track owners, I need your help in conducting an experiment. On another forum a question was asked at to whether a 30/10 = 3.0:1 ratio would provide better brakes than a 24/8 = 3.0:1 ratio. Both are 3:1 so should provide the same braking. Now the 3:1 ratio is an average value and as the gears rotate the value will be slightly more or less than this value. Picture going up and down the teeth of a wood saw. The average may be 3:1 but sometimes youll be at the top of the teeth and sometimes youll be at the bottom of the teeth as you move along the wood saw. I hope the anlalogy helps rather than confuses.

OK now for the experiment. I dont own a track so I need a track owner to help out. Choose a gear ratio, say 30/10 and also 24/8. Both 3:1. The car must be the same and the motor must be the same. The only thing that changes are the gear sets. I dont think the weight and inertia difference between the two gears sets will be significant in a car weighing 80-100g. If you want, weigh the gear sets and add extra weight at the rear of the car to compensate for the smaller gear sets less weight (maybe 0.1-0.2g lighter??). Perhaps a slotit would be the easiest as the gears could be changed over relatively easily.

The test: Youll need to run some electrical or masking tape over the last 1/3 of the main straight on your track for this test. The tape is needed so that the car can coast brake to a stop with no power.

1. Place car at the exact same location at the beginning of the straight.
2. Apply 12V (controller is fully on and you just turn on the power supply switch). This will avoid differences in depressing the controller from run to run.
3. Car takes off, hits the taped section and coasts to a stop.
4. Measure the distance from the beginning of the tape to the front of the car.
5. Repeat 10 times and record the braking distance.
6. Change the gears and repeat.
I know its a big ask but is anyone up for it? I want to put this one to bed.

[Ember]

Timing shouldn't really be necessary Johnny. Distance travelled under coasting would be the indicator.

Can't help you Rick, I don't have a long enough straight that I can get at to mask the rails.

[Florida_Slotter]

dr fabio,

Well I really do not need to do the testing as I have already done a lot of pseudo-scientific testing on this exact question.

My research has shown that the brakes are better on the gear lash that uses a smaller pinion.

Why is that? I think it has to do with the diameter of the pinion and the smoothness of the gear mesh. I do know that a 10/30 gear set provides some outstanding smoothness in the lash and lots less braking then an 8/24 gear set. Perhaps there is something to do with the distance from the centerline of the motor shaft and fulcrums and all that stuff. I did not bother to sit down and sort all the details. All I know is that a slot car will stop quicker with a smaller pinion each and every time. Tests were performed on a 200 foot hillclimb track. The brakes were activated as the car exited the banking on it's way to the Deadman. Every time the smaller pinion stopped more quickly.

[dr fabio]

John, the are no variables (that change) expect changing the gears. Thats the whole point. Yes Ill accept the lube aspect. But then lube the gears the same way each time, or dont lube them, but keep it the same. Same car, same track, same voltage, same day/temp/humidity etc. Run the car 10 times, change gears and repeat.

[dr fabio]

Hi Marty,

Ill take your results at face value. So your results give the 24/8 being better than the 30/10. That is the car will pull up quicker with the 24/8. Dont not believe you. However on the other forum the poster was saying the 30/10 pulled up the car quicker. Hence my desire to be a bit more scientific about it and trying to control the variables better.

[slothead]

I'm curious what the outcome of this will be, and am reminded that when designing experiments there are so many variables to consider. Diameter of the pinion and crown gears must have some sort of effect on spin up and spin down of the motor and rear axle, even when the overall gear ratios are the same. If one gear set created a consistently shorter stopping distance wouldn't it also logically create slightly different torque and/or RPM profiles, meaning the speeds at the start of the 'braking' test were also different?

It's also possible that the natural variance (differences between trials with the same gear sets) will be larger than the effect size caused by the differences between gear sets. In which case it could take 100's of trials to do a proper analysis.

No doubt some engineering student(s) spent years working on a research question like this for their dissertation(s).

Slothead

[dr fabio]

slothead, if the variations in each run are greater than the variation between the two gear sets then that is also a good result. It says that there is F all in it and that all the who ha that people post is just that...who ha. I dont care what the resukts are, I just want to know.

Come on guys, who has a track that they can test this out on. Id love to test it but dont own a track.

[SRQSloter]

I have been told before that larger diameter gears will have more braking.

[ddyke]

I talked to a couple of engineers and the one said to make sure the gears are made of the same material, same break in procedure, and the same lube. The other said the larger gear should have less friction and so if friction is the reason for the difference then all other things being equal then the smaller gears should brake better because of more friction. Many variables to throw off the results. For example if the larger gears have less friction then their speed should be higher and the braking distance longer. Go with the set that works the best.

[SRQSloter]

Here is a test that was done. http://www.slotcarillustrated.com/porta ... hp?t=26528 Larger diameter gear had more breaking.

[paul gage]

Hmmm? Okay, confused. In laymans terms...

Are you testing the brakes or rolling resistance of the chassis. Wouldn't it be more precise to use an inclined surface and measure elapsed time over the fixed distance to measure rolling resistance?

If it's the brakes, most of the braking energy is created by the motor acting as a dynamo, not if it's free wheeling. If you taped/covered the one side, the circuit would be closed and the motor would not generate any electro-magnetic field, or what would also be friction in this application. The circuit needs to be open back to the controller's capacitor or what ever (not an electrical engineer) for there to be any draw.

Tire traction has a big impact here too. I would be guessing, however I'm confident saying the the tires convert 10 times the braking friction that the gears could possibly. The tires need to convert the rolling inertia into mechanical energy fed through the gears to the motor. Once the braking circuit is opened the motor generates its elctro-magnetic field which then acts as resistance which feeds back through the mechanicals as braking energy, further slowing the car. Provided of course the tires are hooked up.

I have always chosen gears by sound, less sound, less friction, that has always led me to smaller gears, 8/24 rather than 10/30. And, smaller gears fit in so many more RTR cars without cutting them all up.

What am I missing here?

[Nor Cal Mike]

I agree wih Paul that the complete circuit needs to be open to test for "brakes" due to the controller wiring transforming to a dynamo. AS for which combination of 3:1 is better for brakeing effect, They both should be the same EXCEPT for operating efficiency dfferences. 3:1 is 3:1 mathimatically. As to operating efficiency, I would predict that the numerically larger gear set would be the more efficient due to the slightly better mesh between teeth. That would mean the lesser efficient, numerically lower gear set would produce more drag and shorter stopping distances.

[dr fabio]

Paul and Mike,

In this very post we have 30:10 and 24:8 is better, hence my desire for a real test!!

The open braking test is still valid. Do you agree that if the ratio is 3:1 why would the dynamic braking be different? How could it be different? Yes I agree that testing under dynamic braking would be better but that would mean someone cutting up their braid to do the test. Pressing a controller trigger and then releasing it would have tooooo much variability. Hence the tape on the braid to cut the power at the same place every time. To have dynamic braking would mean cutting the braid so that 12V was cut from a length of track. Then you could short that section out as well to have full dynamic braking. Thats a tall ask for a track owner to do. The tape on the track is easy and do-able.

The ratio 3:1 is an average value. As the tooth engages and rotates at some point in time the ratio will be less and then more than 3:1. Do some simple Pythagoras triangle drawings on the position of the tooth engagement. The ratio changes as it rotates and the variation in the ratio looks like a sawtooth waveform. I think it is the amplitude in this change around the 3:1 avarage that produces the change, if any.

Anyways, someone must own a track ?? Rather than debating it couldnt a track owner just volunteer to do the test. You grab a slotit car. Run 30:10 gears and then swap over to 24:8 and repeat.

[Dangermouse]

breaker breaker - or maybe that should be beaker beaker!

the problem probably isn't who has a track but rather who has a set of 8/24 gears :)

Braking.... have a Carrera 458 Ferrari that has no brakes and a Carrera C6R Corvette that has good brakes - same motor same pinion set etc - how does that work?

DM

[paul gage]

Dr Fabio,

What is "dynamic braking"?

It still sounds to me like you are trying to measure which set of gears produces the most braking friction. Which should be zero, gears are not supposed to generate friction are they?

I'm not an engineer, but here goes. Gears are lever and fulcrum essentially. The ratio needs to change for there to be a difference in the energy conversion ratio. The energy used to slow a slot car is a carefully balanced mix of the cars inertia converted into mechanical energy, flywheel or rotating mass of the wheels tires axles gears and motor, by way of the connection between the track and tires, combined with the resistance created by spinning one of those flywheels (the motor) in an electro-magnetic field. Gear ratio changes effect the mechanical conversion ratio, and the type of controller used manages the electro-magnetic field values.

Wouldn't it be easier to buy a Slot.it electronic controller and dial the brakes in to perfection?