Design Request - Deceleration Activated Brake Lights

[crutschow]

Here's my basic circuit concept:

What is the brake light bulb type and how many are there on your bike?

 

[AnalogKid]

In an old PE or RE article, an off-center aluminum or steel weight was attached to the shaft of a potentiometer. Pot output voltage was proportional to acceleration. I think it was a log taper pot connected backwards for a pseudo-linear output.

$1

ak

 

[sign216]

Here's my basic circuit concept:
View attachment 107025
What is the brake light bulb type and how many are there on your bike?

There is a single brake light bulb, 12V and 21 Watts. Standard incandescent, although I was thinking of going LED, but that's a different project for a different time.

AnalogK,
I like your old-school technique. It's not for me, but it's good to keep in mind.

Joe

 

[crutschow]

Can you do some tests to see how long it takes your bike to slow down say 10 or 20MPH when you back off the throttle under the conditions (speed and gear) that you want the brake light to come on?
(Just don't kill yourself in the process).

That will allow the calculation of the negative G forces involved and thus how much signal to expect.

 

[sign216]

Can you do some tests to see how long it takes your bike to slow down say 10 or 20MPH when you back off the throttle under the conditions (speed and gear) that you want the brake light to come on?
(Just don't kill yourself in the process).

That will allow the calculation of the negative G forces involved and thus how much signal to expect.

I think you are looking for what's called "engine braking." I used to work in traffic accident reconstruction, and book values for engine braking are available for passenger cars. None are published for motorcycles, but they would be greater (greater engine to vehicle weight ratio). Standard book values are:

less than 20 mph = -1.3 ft/sec sq or -0.39 meter/sec sq
20-40mph = -1.6 ft/sec sq or -0.48 meter/sec sq
over 40 mph = -2.6 ft/sec sq or -0.78 meter/sec sq

Does this help?

 

[crutschow]

Does this help?

Some.
But it would really be more so if you could measure some values for your bike on a deserted road.

 

[KeepItSimpleStupid]

FWIW: Nationwide https://www.nationwide.com/smartride.jsp considers hard braking > 7.7 mph/s, so that's somewhat of order of magnitude limit/linear range.

 

[crutschow]

FWIW: Nationwide https://www.nationwide.com/smartride.jsp considers hard braking > 7.7 mph/s, so that's somewhat of order of magnitude limit/linear range.

I'm looking for the braking effect of the motorcycle engine, not hard braking from the brakes.

 

[sign216]

It's not a problem. I'll do it this weekend; I'll measure the time it takes to slow down in gear in average traffic. Say from 40 mph to 30 mph, or from 40 mph to 20 mph. Should be a few seconds.

I see that the accelerometer measure acceleration in "g," a multiple of the force of gravity (9.81 m/sec squared or 32.8 ft/sec squared).
The figures from my earlier post, converted to g: vary from 0.040 to 0.079 g. I expect my bike should come out around 0.08 g.

Is that the kind of information you need? The range of "g" of the deceleration?

 

[KeepItSimpleStupid]

That's the "downward" component. You want the same units distance/time^2. The derivative of miles/hour is acceleration. So, mph/(time^2) or whatever units, you need.

s = distance; first derivative
ds/dt = speed; second derivative
ds/(dt^2) = acceleration; 3rd derivative of s; 1st derivative of speed.

A derivative is essentially the (instantaneous slope).

Conversions to other units: https://www.convert-me.com/en/convert/acceleration/mile_sec2.html?u=mile/sec2&v=1

 

[crutschow]

Is that the kind of information you need? The range of "g" of the deceleration?

Yes. If you measure the time it takes to slow 10MPH, the average g force can be calculated.
The worst-case is likely the slowest initial speed in high gear that you want the device to work.

Since the accelerometer output is give in V/g, I need to know the g to determine the output signal we will be getting.

 

[KeepItSimpleStupid]

g is just another unit. e.g. 1g, 2g meaning 1x the acceleration of gravity, or 2x the acceleration of gravity,
The acceleration vector does not have to be in the direction of gravity.

 

[sign216]

Okay, I'll make some test runs this weekend and get the data.
I'll do it at mid-speeds (40 to 20 mph) since this replicates city traffic, where accidents are more likely.

 

[crutschow]

Okay, I'll make some test runs this weekend and get the data.
I'll do it at mid-speeds (40 to 20 mph) since this replicates city traffic, where accidents are more likely.

Try to measure for a 10MPH drop in speed, if you can.

 

[Reloadron]

Looking at the instruction manual for the listed unit where they mention mounting: Mount flat or on edge with arrow pointing forward. Mount module as level as possible +/- 20 Degrees. I think we can pretty much figure they use an accelerometer to detect deceleration. I liked crutschow's circuit. If I went with a uC I would consider a simple 8 pin flavor maybe like a PICAXE 08M2. Also with the originally linked unit they mention Sensitivity and how to adjust for Sensitivity.

4. Adjusting Sensitivity
When calibrated, the module sensitivity is set to
an ‘average’ level based on a number of bikes
tested from large cruisers to sport bikes. Most
customers find they want to adjust the
sensitivity based on their bike and/or riding
style. To adjust sensitivities adjust the angle the
module is mounted
1. To make module MORE sensitive change the
angle so that the arrow points more DOWN
towards the ground.
2. To make module LESS sensitive change the
angle so that the arrow points more UP away
from the ground.

Being a retro type dinosaur I have a 1992 Harley Davidson Electra Glide Ultra Classic. My bike weighs in at around 750 to 800 Lbs. When approaching a stop I generally downshift before I use any braking but that is not always the case. Also, originally my bike came factory with an 1157 tail / brake light bulb plus additional brake lighting on the tour package. The standard 1157 bulb on bright brake draws about 2 Amps. Depending on configuration a bike could draw 4 to 8 amps when braking. I replaced my lights with LED (keeping the original parts) which required adding a few load resistors on the turn signals as the controller looks for incandescent loads.

Anyway one concern here is deceleration on any bike will depend on the bike and the rider and believe me stopping a few hundred pounds of dirt bike or small light road bike is not the same as stopping or decelerating a large road bike like the 900 pound BMWs, Harleys or similar. A guy riding a bike wants high visibility. Just about every time a motorcycle rider is hit by another vehicle the other driver claims they never saw the bike. When braking a biker is always looking in his mirrors making sure the guy behind them has noticed them stopped or stopping and looking for an out just in case. Bikes want and need bright attention getting brake light systems but also you don't want a brake light for every time you moderately decelerate. When I brake I have a system which does three bright quick flashes followed by a steady on as long as I am using my front or rear brake which I am good with. Would I buy another system to brake light on deceleration? I doubt it but obviously there is some demand.

All in all there are a good number of things to consider when looking to trigger off deceleration. Engine RPM really is not a factor as when accelerating I roll off throttle to up shift. My tachometer looks like an intermittent yo yo getting on an interstate.

Ron

 

[Nigel Goodwin]

Engine RPM really is not a factor as when accelerating I roll off throttle to up shift.

Surely everyone does?.

Likewise, you 'blip' the throttle as you change down (to equalise engine and gear box speeds, particularly important with non-syncromesh gearboxes, but should really be done in cars as well).

 

[Reloadron]

Surely everyone does?.

Likewise, you 'blip' the throttle as you change down (to equalise engine and gear box speeds, particularly important with non-syncromesh gearboxes, but should really be done in cars as well).

Yup!

Ron

 

[sign216]

Bikes want and need bright attention getting brake light systems but also you don't want a brake light for every time you moderately decelerate.

Ron

I use engine braking quite a bit. Why not? Saves wear on components. Having the brake come on when I use engine braking is a benefit, and it's not such a bother to the guy behind me (I think).

I'll be out later today to do the test runs to figure out the engine braking deceleration. I'll let the board know.

 

[Nigel Goodwin]

I use engine braking quite a bit. Why not?

Any competent driver does, cars as well as bikes.

 

[crutschow]

I use engine braking quite a bit. Why not? Saves wear on components.

May save wear on your brakes but it puts added stress on the engine, clutch, gears, and chains.
Brakes are cheaper than those items.
I never down-shift to brake on my bike.

In the distant past I knew someone who had two broken crankshafts sequentially happen on her VW bug.
After the second failure the mechanic determined that she was aggressively downshifting when slowing down and popping the clutch during the down shifts without blipping the throttle.
The continued shock to the crankshaft from that caused the breakages.