Need help with a braking experiment

[dr fabio]

What I call dynamic braking is when the motor's electrical output is being driven into a short circuit (Max braking), or into a resistive load of some description (less than max braking). No such thing as "zero" friction, only exists in text books. I suppose essentially its which gears will produce the max friction, must be the difference. Like I have said, even in this post people have said 24/8 and 30/10 give the best braking. So which is it? If no track owner is willing to do the test I'll have to do the test at one of my mate's track.....one day when I got time to kill.

[FootScoot]

This is very interesting. I do know that direct current motors become generators when the current is cut and the armature is still spinning. The amount of braking force is determined by the amount of electric current produced by motor when freewheeling with no current. An example would be a motor that is rewound with a completely different wind than it had originally, and you lose almost all of the braking force of the original wind, hence the need for stronger magnets to produce enough current to give it sufficient braking force. Gears even though the same ratio have little effect on braking. Just for an experiment take a motor and rig it up to turn with no electric and use a multimeter to measure the electric coming from the motor. It's not a lot of electricity but it will be there. :)

[RichD]

In order for this testing to be valid you would have to be certain that the car was going the same speed every time it hit the braking zone. If your track has a very long straight it might be safe to assume that the top speed would be the same every time around. The mere act of changing gears could introduce an unintended variable. In order to change pinion gears you have to pull the motor in most cases. Reinstalling the motor could change the axle alignmemt or something and create more or less drag. If drag from the gears gets you more braking it must also get you less speed. As far as I am concerned testing of this sort may not yield enough useful information to be worth the effort. In my case I do run without magnets. I have a controller with variable brakes, but in almost all cases I run with the brakes turned down. Once in a while I drive a proxy car that needs more brakes than usual.

[dr fabio]

I find it interesting that a lot of people are suggesting that the tests would be inconclusive. So hard to tell which would be better because of the variables etc even why you try and minimise the variables. Which may well be true!! And even that result would be a conclusive result. It would tell me that their is no "effective" difference. Then you will get other people that will say 30/10 is better than 24/8 or vice versa. These people must have super sensitivity to tell the difference, or the difference is real and measurable, or the difference is imaginary. We will never know though, not until someone actually tests it. :|

[VenturaAlfa]

Fabio,

The way you have laid out the test itself in your first post you don't need a slot car track. You can do it without any of us involved. Remove the guide from one of your cars. Place it on a slight incline but one that is sufficient enough for the car to roll. Have a long enough run off area for the car to stop after leaving the incline. Place the car at whatever distance you choose up the incline and let it roll. Measure where it stops. Repeat with the other gear set in the same car.

Your not actually measuring dynamic breaking in the experiment above or the one you described. All you are actually measuring in either of them is rolling resistance or friction created by the tires, bushings, gears, wind resistance and drag on the armature from the magnets in the motor.

Assuming the two gear sets are set up with the same amount of lash the difference in the distance one would roll versus the other would be negligible and not a function of dynamic braking at all just a function of the things mentioned above in this post.

Ventura Alfa

[2FER SLOTS]

[dr fabio]

[slothead]

A very simple friction test can be done with an inclined plane, and you don't even need the runoff area. Set a car up with a set of gears and place on a flat board with a slot for the guide. Lift one end of the board up slowly until the cars starts to move and measure how high (on average) the lifted end is when this happens. Repeat with a new set of gears. The more resistance the higher the incline will need to be for the car to start moving. If the car slides rather than rolls weight may need to be added.

I did this to measure the effect sanding my track surface material (hardboard) would have on tire friction. For standard tires sanding increased friction (had to incline the plane higher to get the car to slide), while wide silicone over foam tires had less friction on the sanded surface. Really grippy tires like a really smooth surface to grab on to.

Neat thing about this issue and discussion is that it would seem there has to be some effect, even if the way we're thinking of doing this isn't sensitive enough to get conclusive results. If 8/24 were the same as 9/27 and 10/30 because the gear ratio is the same, that would suggest 12/36 and 14/42 or even 20/60 would be the same too and the mass of the gears and distance of the mesh from the center of the axle has no effect. If this were true it would be counter-intuitive, like a 5 pound object falling as fast as a 1 pound object if you account for air resistance. THIS IS WHY I'VE ALWAYS LOVED SLOT CAR RACING, IT MAKES YOU THINK!

Slothead

[KnowtoriousWon]

An interesting request to answer an interesting question.
I'm sorry but I can not perform this test for you.
For an accurate test you need to compare a "baseline" then something new and then go back and double check the original "baseline".

[slothead]

Here's a reply from a related current discussion on this forum; Gears and ratios

by chappy » Tue Jun 10, 2014 9:22 pm
Hi Mayberryman, , boy what a loaded question that is, I bet you could get 6 people with 6 differing answers to, that one. People would be talking about variable factors in testing etc etc.
But if you promise not to bite I will give you the results of a test I conducted yesterday.
I ran a slot it inline chassis only with the orange endbell 21.5 k.
only thing I did was change the gearing .
10.5 volts on a mdf track, tires cleaned with water. Everything remained constant except the gears.
8/24,,,, and 10/30,,, both 3 to 1 ratio.
I'll cut to, the chase . Lap times virtually the same , acceleration better by a touch on the 8/24.
Handling better on the 10/30.
Braking distance measured on 10 times per gear set, result 1.5 cm shorter stop on the 10/30 gears
1.5 is not enough to say the 10/30 stops shorter as any driveing difference when brakes were applied could have been the difference.
10/30 fast lap 6.254,,,8/24 fast lap 6.244, 1/100th of a second, again could hve been my driving.
all gears were brass slot it, pinions and crowns.
Now if. I were to, have run 8/24 or 10/30 3 to1 against say 9/30 or 3.33 to 1 then I would have better brakes on the 9/30 just like Harry explained.
Remember that no matter what diameter spur you use , it is compensated by the appropriate pinion since the distance on a sidewinder between the motor shaft centre and the axle centre remains constant.
clear as mud right.
Bob

Pasted in by Slothead

[miveson]

Finally someone has undertaken some testing.... thanks Slothead or should I say Chappy.