[Nonfractal]

Testing in readiness for the British nsr grand prix last Thursday provided the necessary impetus to work on the brake-choke.
(Type 4 braking defined in the OP above)
I'll finish the unit today and track test tonight, then test again on Saturday morning at Molesey.

A Recap:
------------------
4.Adjustable Start Point Sweep.
Using Sweep time braking, there is no method on the Slot.IT SCP2 to initially engage the brakes at anything less than 100%
Why would you need this?
I started thinking on this problem when I was driving a car where the initial bite of the brakes was triggering such bad behaviour in the car that I had to set the throttle to a fixed adjustment. (2 above)
Just as for "adjustable braking" , the brakes engaging 100% at the start of the sweep can cause the tyres to lose traction and the car to shudder.
------------------
I'll post again with full details after testing.
AlanW

[Kevan]

A very interesting and thought provoking thread...

I have recently changed my preference of controller after getting a SCP 1.1, prior to that I was using a Synapse which I love due to not having a wiper board (they use a pot like r/c transmitters).

I'm the kind of person that is willing to use something long enough to get use to it's foibles before making a final judgement. The SCP has a super light trigger with zero friction and the controller looks and feels big and clunky...thanks to Mr Flippants youtube video on SCP basics I quickly got a handle on using and tuning it.
The throttle spring had to be shortened, it's just too light for ageing arthritic fingers.

The one thing I don't like is the use of non-linear markings on the control knobs, I write down the controller settings for every car and have done for years, it get's me in the ball park immediately, saves time...and prevents the all too predictable smash when the settings are miles out.
I'm going to put linear scales on the control knobs, it'll be easier in the long run as some of the scales seem daft.  For example...how on earth do you write down what position the 'power trim' is in in this position? less than 1 but a lot more than 0, can't be 0.6 because it's not linear...how about 9.30 on the clock

   

As for braking, I tried all the settings on this controller and have grown to love 'sweep' but do wonder if it would be better if it worked the other way round, i.e. adjustable progressive braking increasing to 'max' rather than adjustable progressive braking decay after sudden 'max'.

[Nonfractal]

Urgency was added to this by a recent test evening at Molesey's wood track (last Thursday) as prep for the British NSR Grand Prix. 
I attended , primarily to get an initial feel for wood track, specifically:
- ride height
- guide spacing
- guide selection 
- tyres

I also wanted a chance to learn the track ahead of the weekend, not having driven this track since it was first installed , maybe 4 years ago.

As it turns out, the 4 items above were easily handled but braking was immediately identified as a problem. 
The brakes on the Molesey track are vicious and there is no rostrum plug point adjustment available. Coupled with the immense grip (truly immense) reducing the braking enough to prevent the car stopping on a sixpence was a problem.

I immediately noticed that Molesey members are heavily skewed in favour of tru-speed controllers. (I'm sure Steve is smiling as he reads this)
When  I visited 4 years ago, Molesey was heavily skewed in favour of the SCP2. Not the case any more and maybe braking control is a factor in the selection.
On the track, even setting the SCP2 to linear-1, the minimum setting, does not reduce the braking enough to traverse the corner optimally.
Using the Sweep time braking on Molesey track is a total non starter due to the scp2's 100% initial bite
Testing on linear-1 was bearable until the control was knocked slightly, removing all braking and causing an end of straight wreck.

So....
The inline brake choke project inferred in the OP, took on a new urgency.

Whether to build a separate box or integrate it into the SCP2 relay bypass box ?
A whole separate subject - covered by slot.it in the link here.
https://slot.it/wp-content/uploads/2020/...P1.en_.pdf)

My existing relay bypass box was not large enough for the components needed for the brake-choke. Thankfully, a trawl of my electronic dump-box brought up a suitable box of perfect size, along with scavenged diodes and a scavenged rotary switch (originally bought for a guitar pickup switch project)

The question of whether to use diodes or resistors was decided after enquiring at LSC about the braking technology built into their plug points. LSC use resistors and the general view is that this isn't really a good solution because it doesn't just soften the brakes, it changes the behaviour of the brakes. The voltage dropped by resistor is dependent on the current passing whereas a diode drops a fixed voltage.

I used this diagram as a base for the unit and built and tested a simple 4 position brake softer. This will certainly be good enough to have better control of the linear braking.

The only opportunity to test was at Nascot wood. Fri25th March and it worked well on cars using slot.it mx16 S-can motors.
Not an ideal test because NWSCC is Ninco Plastic, nothing like Molesey.

The only opportunity to test for Molesey was at the event.
As it turned out, any use of the softener circuit , deadened to power to the car.
It was almost like the brakes were on even if the throttle was being pressed.
This behaviour could be a result of:

- the wiring at Molesey
- using higher power motors at the event
- an unforseen issue with the SCP circuitary.

So..
3rd test will be at LSC on Tuesday.
Then I'll have to figure out the problem.
Maybe diode circuitary is just not compatible with some tracks.

AlanW

   
   
   

[Kevan]

Are you motor limited in the British NSR Grand Prix?

If not, try a motor with less aggressive braking.

[Nonfractal]

Handout King purple motors mandatory.
Without the brake softener, Sweep time braking was not possible
Brakes set to linear 1 and a piece of tape held it in place.

Finished right in the middle of the pack. 
An acceptable outing for a track and surface I'm not familiar with 
AlanW

[Kevan]

I have an SCP 1.1, I can't say the brakes are noticeably worse than my other controller (Synapse).

Another simple option (if you're allowed) is to gear it up (another tooth on the pinion or less on the spur), taller gearing will deaden the braking effect.

[Nonfractal]

Another simple option (if you're allowed) is to gear it up (another tooth on the pinion or less on the spur), taller gearing will deaden the braking effect.

Yep,
I was running the longest ratio permitted 
On the shorter ratio, even the linear-1 setting was too vicious to drive.
Alan

[merkit the grof]

The question of whether to use diodes or resistors was decided after enquiring at LSC about the braking technology built into their plug points. LSC use resistors and the general view is that this isn't really a good solution because it doesn't just soften the brakes, it changes the behaviour of the brakes. The voltage dropped by resistor is dependent on the current passing whereas a diode drops a fixed voltage.
AlanW

The variable resistance of the track wiring/rails is present all the time, I can't understand why adding some resistance  in the controller/separate box would make a difference.
In practical terms what is different about the brake behaviour between the 2 methods?


Joel

[Nonfractal]

The variable resistance of the track wiring/rails is present all the time, I can't understand why adding some resistance  in the controller/separate box would make a difference.
In practical terms what is different about the brake behaviour between the 2 methods?


Joel

"The variable resistance of the track wiring/rails is present all the time,"
- If you have anything less than infinite resistance between the rails "all the time",  this is a short circuit  and the track won't be able to power the cars.

"I can't understand why adding some resistance  in the controller/separate box would make a difference"
-When a dc motor is open circuit, no current can flow in the coil., If no current flows, no backEMF can be produced
-When a dc motor is closed circuit (shorted across the contacts) current flows through the coil producing a backEMF causing the motor to resist being turned.

Between the 2 extremes, the level of backEMF can be controlled by introducing a resistance between the motor contacts.
The resistance allows some current to flow. A variable resistance can produce various amounts of backEMF.

"In practical terms what is different about the brake behaviour between the 2 methods?
- diodes drop a fixed voltage 
- resistors drop voltage dependant on the amount of current flowing. 

In practical terms, control of diode based braking should be less impacted by the motor being used.

Alan

[merkit the grof]

- If you have anything less than infinite resistance between the rails "all the time",  this is a short circuit  and the track won't be able to power the cars.
-When a dc motor is open circuit, no current can flow in the coil., If no current flows, no backEMF can be produced
-When a dc motor is closed circuit (shorted across the contacts) current flows through the coil producing a backEMF causing the motor to resist being turned.

I think there a little bit of a misunderstanding.
I didn't say the 2 rails were shorted together, simply that when we apply the brakes, each side of the motor is still connected via the track rails/wiring. The diagram probably explains it better.
   

This wiring has a resistance which changes all the time depending on how far or near the car is to the controller.
The negative side of the motor is always connected to ground via the track wiring, the motor is never ""open circuit"
There is another situation where current will not flow across the motor, that is when both side are connected to the same voltage, important point because this is what helps us get the same braking effect all the way round the track.

Between the 2 extremes, the level of backEMF can be controlled by introducing a resistance between the motor contacts.
The resistance allows some current to flow. A variable resistance can produce various amounts of backEMF.

"In practical terms what is different about the brake behaviour between the 2 methods?
- diodes drop a fixed voltage 
- resistors drop voltage dependant on the amount of current flowing. 

In practical terms, control of diode based braking should be less impacted by the motor being used.

Alan

OK, so it seems that a resistance brake adjuster might need to be turned further than a diode one to get the same breaking effect, but no drastic change like some sort of sweep braking or worst still, reverse sweep braking.


Joel