Stopping a train at an exact spot

[Cosmik42]

Hi everyone,

So when you have a train going full speed and cut its engine, it might be hard to predict exactly where a train will stop.
Do you have any idea of 'braking system' to force a train to slow down and even stop?

Thanks!
Vincent.

Edited January 10, 2019 by Cosmik42

[Pdaitabird]

Which system do you use? The answer may be different depending on whether you run 12v, 9v, PF, PU, etc.

[Cosmik42]

Powered Up.

Actually, I wonder if reverting power for a short time would help decelerate faster.

[JopieK]

It would of course halt faster but that is an unrealistic scenario of course and might lead to abnormal wear of the motor. A normal train also can't stop very fast when it is traveling at higher speeds.

Solution: create sections where the train can accelerate / decelerate.

[Bartosz]

Is PU the same as PF in this regard? From the PF protocol I recall there were two messages to stop the motor: one was 'brake', the other was 'float'.

If I understand you correctly, the behaviour you describe would be more like 'float'..maybe there is some equivalent of 'brake' in newer protocol?

[Cosmik42]

9 minutes ago, Bartosz said:

Is PU the same as PF in this regard? From the PF protocol I recall there were two messages to stop the motor: one was 'brake', the other was 'float'.

If I understand you correctly, the behaviour you describe would be more like 'float'..maybe there is some equivalent of 'brake' in newer protocol?

Indeed, PU seems to act more like 'float'. For now 'braking' is simply a 'Set Motor Speed to 0'. 
Maybe there is an official 'Stop'. Will investigate.

[JopieK]

You can issue an emergency stop indeed by sending a 0 (forward) or 255 (reversed).

In Swift the command looks like: let value: [UInt8] = [0x08, 0x00, 0x81, motor, 0x11, 0x51, 0x00, speed] where motor is 0x00 or 0x01 and speed will be either 0 or 255 for an immediate stop. If I remember correctly pressing the red button will invoke this command with speed == 0x00.

[Lok24]

Hi,

with my automated layout I used the follwing:

Accelerate to 70

If sensor in the engine is triggered first(!) it decelaretes to app. 30, if sensor is triggered second time speed is set to 0

 

Edited January 10, 2019 by Lok24

[Mr Hobbles]

1 hour ago, Cosmik42 said:

Indeed, PU seems to act more like 'float'. For now 'braking' is simply a 'Set Motor Speed to 0'. 
 Maybe there is an official 'Stop'. Will investigate.

Speed value 127 is a hard stop/"brake". :) Obviously there will still be a bit of a "float" depending on the weight of the train and the speed it is going, but it's the closest you'll get without using sensors and a slowly decreasing speed to stop at an "exact" spot.

Edited January 10, 2019 by Mr Hobbles

[Cosmik42]

9 minutes ago, Mr Hobbles said:

Speed value 127 is a hard stop/"brake". :) Obviously there will still be a bit of a "float" depending on the weight of the train and the speed it is going, but it's the closest you'll get without using sensors and a slowly decreasing speed to stop at an "exact" spot.

If anyone, it would be you who would know! Thanks a lot!

[dr_spock]

Years ago, I used track side sensor to detect the train and slow it down to a stop.  I suppose you can use multiple sensors (or color tags if you using a color sensor).  First one to trigger a slow down the train and then the next to trigger stop.

 

[Roadmonkeytj]

5 hours ago, dr_spock said:

Years ago, I used track side sensor to detect the train and slow it down to a stop.  I suppose you can use multiple sensors (or color tags if you using a color sensor).  First one to trigger a slow down the train and then the next to trigger stop.

 

I think this will be the closest to "exact spot" programmed decel and stop and wait after sensor trigger.   Just have to play with sensor location and decel amount/time

[XGBC]

you could also if you are willing to mod lego build a so called "kurzschlussbremse" dont worry it will not short out your electronics it works by putting positive or negative voltage on both of the motors terminals and it will stop your motor more or less imediatley. but as always when you are dealing with electronics

Be Careful

i've also posted a diagram of the circuit below

XGBC

 

[Mr Hobbles]

9 minutes ago, XGBC said:

you could also if you are willing to mod lego build a so called "kurzschlussbremse" dont worry it will not short out your electronics it works by putting positive or negative voltage on both of the motors terminals and it will stop your motor more or less imediatley. but as always when you are dealing with electronics

 Be Careful

i've also posted a diagram of the circuit below

XGBC

 

The PUP motors and hub have this built in, this is what speed value 127 triggers (As opposed to value 0, which lets the motors float to a stop).

[XGBC]

you could also build something like this:

it is a machanical brake wich brakes the inside flanges of the weels

XGBC

[Cosmik42]

On 1/14/2019 at 7:22 PM, XGBC said:

you could also build something like this:

it is a machanical brake wich brakes the inside flanges of the weels

Thanks for both suggestions! I use PUP trains and managed to use the fast brake from @Mr Hobbles suggestion.

Now I wonder how to build such braking system in Lego. Thanks for showing such real-life system!

[XGBC]

these braking systems are mainly used for shunting wagons and are not used to slow locomotives down. They work using pneumatic or hydraulic cylinders. If you want to build such a system you have to raise your rails by a brick or two in height so you are able to fit the mechanism in there.

Hope to see such thing soon from you

 

XGBC

[Xifeng]

Hi! I am interested in this question as well, so I come up with an idea and used LDD to build a prototype shown below:

It is just a prototype, all the bricks can be altered, it just interprets my idea. I just utilize the friction between the rubber wheel and the tube piece to slow down the rotating axle. And the switch part in red should connect to another small motor to achieve the remote control. The power-output-axle should connect to the axle that the switch is on (whatever how you connect them). When you use this system to stop your car, you should stop the XL motor first and turn the switch, in order to let the deceleration part work. You can see that the wheel deceleration part is split, rather than directly install onto the axle connecting to the motor. I think if I connect them directly, the axle will still stop immediately when the motor is stopped, the brake system won't work. I think it makes sense. According to this prototype, I think its volume may not allow fitting into an 8-studs train.

Edited January 17, 2019 by Xifeng

[Cosmik42]

1 hour ago, Xifeng said:

Hi! I am interested in this question as well, so I come up with an idea and used LDD to build a prototype shown below:

Great idea! Share with us a video implementation if you can!

[Xifeng]

On 1/18/2019 at 12:37 AM, Cosmik42 said:

Great idea! Share with us a video implementation if you can!

I tried to make an implementation today. Unfortunately, when I was testing it, I found that if I turn the switch to make the axle out of power, the axle wouldn't be rotating because of inertia. So I may need to change the idea.

[Roadmonkeytj]

On 1/19/2019 at 9:32 AM, Xifeng said:

I tried to make an implementation today. Unfortunately, when I was testing it, I found that if I turn the switch to make the axle out of power, the axle wouldn't be rotating because of inertia. So I may need to change the idea.

Connect your "switched side" to a free axle so the movement of the train causes the other half of the mechanism to rotate. 

[treczoks]

On 1/10/2019 at 5:01 PM, Cosmik42 said:

Maybe there is an official 'Stop'. Will investigate.

Yes. there is. Speed 0 is "float", speed 1 to 100 and speed -1 to -100 are, well, speeds. And speed 127 is a hard break.

[Cosmik42]

1 hour ago, treczoks said:

Speed 127 is a hard break.

Thanks! Nathan shared that earlier too and it works great indeed!