Pedelec modification to enable hill start

[PAB855]

MBH has an electric powered trike which has 4 power levels . Each one requires the cranks to be rotating in order to signal the electronics to supply power to the motor. There is also a 6kph button which, once pressed overrides any of the 4 power levels so that the rider can freewheel legally up to that speed. That's a good idea, except that it is not capable of working on anything other than a level surface! So, how will she cope if she has to do a hill start? Part of the reason for having an electric motor is to have a way of assisting the rider. The gearing range is 37in to 74in. If the rider is expected to rotate the cranks on a hill start with that bottom gear, then it is a lot to expect, even from a fit rider. So, without changing the gearing, it looks as if a minor addition/ alteration to the electrics would do it. Any suggestions? Not that I would do anything illegal of course!

[Redvee]

Would a anti clockwise rotation of the cranks fool the electronics? I can remember riding an early electric bike where you could pedal backwards from a standing start and zoom off into the distance.

[PAB855]

Yes Reeves. That sounds great. There is room to the side of the largest sprocket or I am wondering if a duplicate sensor on the chainring but reversed would give the same result. In any case, the luxury of having a choice of two places to set it is a bonus. Thanks.

[[XAP]Bob]

Unfortunately they normally can detect the direction of rotation.

Depending on the 'brain' you might be able to fit a throttle as well (so she could use either the pedelec sensor or the throttle.

[georgew]

I have a system which gives an extra boost when starting off by compressing both brake levers. My conversion was done by these people:

https://arccinnovations.com/?gclid=CjwK ... oCH6Lw_wcB

[Brucey]

I agree most modern systems won't take off if you pedal backwards (this would be a gross design fault).

You can (with some systems) adjust the settings in the software so that the assistance kicks in earlier/harder.

However I'd counsel caution here; I have ridden one or two machines that I thought were actually dangerous because of the way they took off at low speeds. When manoeuvring with full lock on, a touch of the pedals at the wrong time can cause the motor to kick hard enough that it might tip the machine over, or shoot the machine out into traffic etc.

cheers

[Ruadh495]

Perhaps some reprogramming of the 6Kph button. Starting assist is exactly what this is intended for, but it sounds like it's not supplying enough power. It should provide full power (usually about 400 Watts) up to 6Kph. That should be enough to start on most hills.

[[XAP]Bob]

Really ought to only be 250W....
But yes - if that is the purpose of the button, then is it working at all?

[PAB855]

Thanks everyone. We will persevere for a bit longer and keep trying the 6kph button since that's the only safe way to go until we have had much longer to try it in all cases. Your cautionary note, Brucey is appreciated.

Cheers

[Ruadh495]

Really ought to only be 250W....
But yes - if that is the purpose of the button, then is it working at all?

The standard / law is 250W continuous rating, which allows whatever the battery / controller can provide in short bursts, i.e. for starting. Mine tops out at 468W.

[Elizabethsdad]

The Bosch crank drive system on my e-assisted bike combines cadence, speed and torque sensors to determine power assistance required when pedalling. Pulls away going up hill just as easily as on the flat.

[bobc]

I've not used a modern commercial ebike solution, so anything I say is not gospel, just observations based on the limited constructions and experiments I've made over the years...
Setting off uphill is not easy. The cheapest motor controls, the radio controlled plane ESCs are all "sensorless" meaning they have no feedback of the motor's mechanical position. This actually works fine on a bike if you give it a turn of the pedals before applying the electricity, If you want reliable high torque from stationary it's usual for the system to utilise hall effect position sensors built into the motor. FWIW all systems revert to sensorless operation when they get up to a certain speed - it gives better and more reliable results than the position sensors. note this paragraph is just about making the motor turn.
Controls: Pedelecs need a pedal sensor. Again 2 sorts - position sensor or torque sensor. The position sensors are cheap and reliable (no sensitive analogue amplification required) but there has to be a change of position for them to be able to detect it - i.e. a (say) 1/4 turn of the pedals. Torque sensors must be based on some sort of strain gauge somewhere (chain stay?) and will be expensive and tricky to engineer right - but will work from the get-go.
So to get assist from first pedal pressure application on an uphill, I'd say you need all the expensive options - maybe that's what the bosch system mentioned above gives.
If I'm way behind the state of the art I apologise, I've never bought any sort of ebike, never mind a "smart" one, just played with radio control plane parts & arduino (nano) controllers on a couple of 'toy' bikes at home

[ANTONISH]

I think you need to know the stalled torque of your motor.
It may be that the required starting torque for your proposed hill start will exceed this.
If that is so there isn't anything the control system can do to obviate it.