Dead man's handle

[paulhipwood]

Dear All

I have just fitted a conversion kit to my bike.
I checked that the motor cut out when I stopped pedaling and or operated the brake levers.

In industrial safety circuits any safety device is usually hard wired and does not go through a PLC or computor.

On Bike controllers does any one know how the safety cutouts are arranged? Are they fail safe?

best regards
paul

 

[flecc]

Not necessarily, many failed contacts leave a bike running and they are often omitted. I don't even use cutouts since I have a throttle, and we are only speaking of a fraction of one horse power which adequate brakes can easily overcome.

 

[rog_london]

Adding to Flecc's comment, it wouldn't be practical to arrange hard-wired cutouts as the controller has to deal with currents of 15 to 20 amps routinely, and you'd need serious switches on the handlebars to control this sort of DC load. Of course the pedal sensor is necessarily electronic and HAS to work through the controller.

The brake lever sensors are nonetheless a good thing, as operating the brakes is (or should be) a reflex action and cutting the power at that point is desirable from a safety viewpoint. Sensibly they would be 'normally closed' so that a disconnected cable would not defeat them, though many are 'normally open'.

Many pedal sensors - perhaps most - just (in effect) switch the system on or off depending on whether the pedals are turning forwards, and they're a bit of a blunt instrument - without the lever cutouts you could unintentionally move the pedals slightly and get sudden and unexpected full power. For example, a Wisper on the high power setting will deliver 80% of available power quite suddenly if the pedals are turned forwards.

My Wisper is left permanently on 'Low' (around 20% power) for this reason, and I use the throttle to apply power as I need it. This is totally intuitive to me and exactly the same as riding my motorbike. A motorbike of course doesn't have cutouts on the brakes.

In summary, the cutouts are not there to protect you from a system failure - more to save you from human error.

Rog.

 

[paulhipwood]

My bike has a Rohlof hub gear.
When you push the bike the pedals rotate in all gears.
I put a conversion kit on yesterday.
This has never caused me any problems - except the occasional bang on the leg
It does now, when it is set on the pedelec the bike disapears into the distance.
Gave me quite a shock.

 

[flecc]

My bike has a Rohlof hub gear.
When you push the bike the pedals rotate in all gears.
I put a conversion kit on yesterday.
This has never caused me any problems - except the occasional bang on the leg
It does now, when it is set on the pedelec the bike disapears into the distance.
Gave me quite a shock.

Nasty! This is where the bikes with crank torque sensors have an advantage, they need pedal pressure to give any degree of real power.

 

[rog_london]

It does now, when it is set on the pedelec the bike disapears into the distance.
Gave me quite a shock.

That proves my point rather well! I did know about the Rohloff tending to pull the chainwheel in the forward direction - of course it does have a freewheel but if I remember correctly it's one of those which doesn't have a ratchet and pawls, but instead uses a roller clutch (much more robust) and there's significant drag.

I wouldn't have minded being a spectator when you did that - ideally out of sight and especially out of earshot, as I don't think you would have appreciated my merriment! I certainly would have been incapable of being any help.

Rog.

 

[kitchenman]

Not necessarily, many failed contacts leave a bike running and they are often omitted. I don't even use cutouts since I have a throttle, and we are only speaking of a fraction of one horse power which adequate brakes can easily overcome.

I did a brake "test" recently. I currently don't have a brake sensor and had to break sharply at about 20 mph. I left some rubber on the road and had to re-bleed my right hand break but I did avoid going into the back of the car in front.

 

[paulhipwood]

I wouldn't have minded being a spectator when you did that - ideally out of sight and especially out of earshot, as I don't think you would have appreciated my merriment! I certainly would have been incapable of being any help.

Rog.

I was fairly quick to realise what was happening and managed to lift front wheel off the floor.

paul

 

[rog_london]

I was fairly quick to realise what was happening and managed to lift front wheel off the floor.

paul

You were lucky! One member a year or so ago did something similar in his hallway and ended up chasing the bike upstairs.

Rog.