Speed sensor vs torque sensor

Electrically assisted bikes, trikes, etc.
UpWrong
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Speed sensor vs torque sensor

Postby UpWrong » 25 Oct 2017, 6:50pm

I haven't ridden any yet but from what I've read a torque sensor provides the more natural power assistance because it operates as power amplification. Also I think the assistance comes on quicker from a standing start. Have read that a speed sensor can take one and a half revolutions to activate the power.

All the conversion kits I've seen are speed sensor only. Bikes with torque sensors are considerably more expensive (£1200+).

The assistance latency of the speed sensor bothers me. Suppose you are powering up a hill and have to stop. Getting going again is going to be an issue unless you can change down to a lower gear. Hub gears have the advantage there. I'm tempted to go for a conversion kit (around £450) but think I'd want an IGH, so motor will probably drive a front wheel. In which case a downtube battery would add weight to the front to help traction.

kwackers
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Re: Speed sensor vs torque sensor

Postby kwackers » 26 Oct 2017, 9:30am

So I got mine into a fit state to have a go last night (still got wires unrouted etc etc)

I've never ridden one either so this is absolutely my first impression.

Firstly. I thought there was too much assistance on the lowest level (so manoeuvring in traffic I suspect may need the assistance turned off although with a bit of practice perhaps it'll be fine.)

I thought that I'd be able to regulate the speed with the pedal rpm - I can't. Moving the pedals is a bit like a switch, the motor simply starts up and you move off, doesn't matter how slowly you pedal the motor drives the bike forward).

The 15mph cut off is a bit harsh, it'd be much better if it reduced power from 15mph onwards (I'm pretty sure I'm going to disable this, or perhaps set my wheel size to 16(?) inches so that kph is actually mph). In reality I doubt the limit adds much, I suspect it runs out of go long before you get much faster but it would probably make it easier to get to and hold 20mph and without abruptly cutting out at 15).

So if that sounds 'bad', I think it's just a matter of changing how you ride.

For me using the gears to keep the pedal rpm around 70 seems to work, if I start to pedal faster the motor reduces power, slower and the motor ups the effort.

Starting on hills seems to be easy peasy, the first quarter rotation or so will kick the motor in and tbh unless it's near vertical the motor seems well up to the job of getting you going. You may also want to consider a thumb throttle in which case you can get started without even pedalling (might be handy for fine control in traffic too???)

Apart from the weight (which I didn't notice when moving, perhaps slightly slower on turns but then my tourer is fairly slow turning anyway) I found it surprisingly easy to pedal. Didn't notice any drag from the motor at all. It's slightly odd on the system I chose that when you back pedal the 'freewheel' ratchet is actually on the pedals so the chain is stationary!

I've only done a loop round the block (5km) so it's early days but I think it's quite promising. Just need to finish some much needed servicing on my bike and tidy up the installation.

But; I think if a torque sensor was available I'd have one (assuming it works as well as I imagine)

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meic
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Re: Speed sensor vs torque sensor

Postby meic » 26 Oct 2017, 9:35am

I suspect it runs out of go long before you get much faster but it would probably make it easier to get to and hold 20mph and without abruptly cutting out at 15).

Yet the legal exemption from this being classified as a motor vehicle is absolutely and rigidly based on the power not being available in excess of that specific speed.
Yma o Hyd

Ruadh495
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Re: Speed sensor vs torque sensor

Postby Ruadh495 » 26 Oct 2017, 9:50am

UpWrong wrote:The assistance latency of the speed sensor bothers me. Suppose you are powering up a hill and have to stop. Getting going again is going to be an issue unless you can change down to a lower gear. Hub gears have the advantage there. I'm tempted to go for a conversion kit (around £450) but think I'd want an IGH, so motor will probably drive a front wheel. In which case a downtube battery would add weight to the front to help traction.


Hill starts (any starts, in fact) are what the "throttle" is for. This should be called an "override" rather than a "throttle" because what it does is to override the pedal sensors while you get going. Also very useful if you find yourself in the wrong gear at a junction. Unfortunately full power overrides are only legal on conversions (and then only in the UK). An override up to 6Kph would do the job and be legal, but I don't know of a bike or kit which has this.

I've never ridden a torque sensor bike, but I understand from the other forum (Pedelecs) that climbing hills is more difficult with torque sensor systems. If you can't maintain the level of torque on the pedals the assist drops off as well, just when you need it to increase. Speed sensor riders change down and spin to get more assist.

Front wheel traction can be an issue with front motor systems, though it's unlikely to fetch you off. I have my battery rack mounted over the front wheel which helps a lot.

Ruadh495
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Re: Speed sensor vs torque sensor

Postby Ruadh495 » 26 Oct 2017, 9:57am

kwackers wrote:So I got mine into a fit state to have a go last night (still got wires unrouted etc etc)

I've never ridden one either so this is absolutely my first impression.

Firstly. I thought there was too much assistance on the lowest level (so manoeuvring in traffic I suspect may need the assistance turned off although with a bit of practice perhaps it'll be fine.)

I thought that I'd be able to regulate the speed with the pedal rpm - I can't. Moving the pedals is a bit like a switch, the motor simply starts up and you move off, doesn't matter how slowly you pedal the motor drives the bike forward).

The 15mph cut off is a bit harsh, it'd be much better if it reduced power from 15mph onwards (I'm pretty sure I'm going to disable this, or perhaps set my wheel size to 16(?) inches so that kph is actually mph). In reality I doubt the limit adds much, I suspect it runs out of go long before you get much faster but it would probably make it easier to get to and hold 20mph and without abruptly cutting out at 15).

So if that sounds 'bad', I think it's just a matter of changing how you ride.

For me using the gears to keep the pedal rpm around 70 seems to work, if I start to pedal faster the motor reduces power, slower and the motor ups the effort.

Starting on hills seems to be easy peasy, the first quarter rotation or so will kick the motor in and tbh unless it's near vertical the motor seems well up to the job of getting you going. You may also want to consider a thumb throttle in which case you can get started without even pedalling (might be handy for fine control in traffic too???)

Apart from the weight (which I didn't notice when moving, perhaps slightly slower on turns but then my tourer is fairly slow turning anyway) I found it surprisingly easy to pedal. Didn't notice any drag from the motor at all. It's slightly odd on the system I chose that when you back pedal the 'freewheel' ratchet is actually on the pedals so the chain is stationary!

I've only done a loop round the block (5km) so it's early days but I think it's quite promising. Just need to finish some much needed servicing on my bike and tidy up the installation.

But; I think if a torque sensor was available I'd have one (assuming it works as well as I imagine)




A harsh cut-out is odd, it should taper off the power as speed approaches 15.5mph, reaching 0 at 15.5mph.

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meic
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Re: Speed sensor vs torque sensor

Postby meic » 26 Oct 2017, 10:03am

A harsh cut-out is odd though, it should taper off the power as speed approaches 15.5mph, reaching 0 at 15.5mph.

To a first time rider (I have ridden one ebike once) that taper may still feel harsh.
The way it flings you up to speed (even uphill) then leaves you on your own is a new enough experience that you may well fail to notice the tapered effect.
Yma o Hyd

Ruadh495
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Re: Speed sensor vs torque sensor

Postby Ruadh495 » 26 Oct 2017, 10:19am

Good point. I came to e-bikes from motorcycles, so I suppose I was expecting the thing to power itself. Only time I notice the cut-out is coming off a down hill. Then you get that "riding through treacle" feeling as you try to maintain speed above the cut-out, until speed drops and the motor cuts in. The other thing which comes with my not being a "cyclist" when I started was not expecting to maintain 20mph on the flat (I'm only just beginning to realize that is possible). I'm quite happy to cruise at 15mph. At that speed I get about 150W of assist and it feels like riding a frictionless bike. You have to not mind being passed by unassisted cyclists, though...

BTW you can "legally" have assist up to 17.2Mph (the legal cut out point of 15.5Mph plus 10% for "instrument error"). Not sure how you would stand if you deliberately set your cut-out 10% high but I suspect some commercial e-bikes are exploiting the "error" margin. I do have mine set at 26Kph rather than 25Kph as I think that is closer to the UK legal point of 15.5Mph (rest of the EU it's 25Kph).

kwackers
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Re: Speed sensor vs torque sensor

Postby kwackers » 26 Oct 2017, 10:27am

meic wrote:Yet the legal exemption from this being classified as a motor vehicle is absolutely and rigidly based on the power not being available in excess of that specific speed.

I'll just fit taller tyres. ;)

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meic
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Re: Speed sensor vs torque sensor

Postby meic » 26 Oct 2017, 10:52am

I'm quite happy to cruise at 15mph. At that speed I get about 150W of assist and it feels like riding a frictionless bike.


I would have thought that 150W was about the amount of power required to cruise at 15mph.
That is about the sort of power that I estimate that I am creating for normal long distance riding, which would go along with 15mph cruising on the flat.
Yma o Hyd

Mark R
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Re: Speed sensor vs torque sensor

Postby Mark R » 26 Oct 2017, 11:06am

I'll just fit taller tyres. ;)


Exactly. If the law was applied rigidly then something as simple as fitting larger tyres would suddenly make you a motor vehicle user!

Can you not add a throttle to your conversion? I reckon it would make it a lot more user friendly.

I've never ridden a bike with a 'pedal sensor' but I have to say I don't like the sound of the idea. With a twist throttle you just dial in the power however you feel is appropriate - what's not to like about that?

I suppose the pedal sensor is supposed to prevent you being lazy and using the machine as a moped instead of as a human/electric hybrid.

kwackers
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Re: Speed sensor vs torque sensor

Postby kwackers » 26 Oct 2017, 11:12am

Mark R wrote:Exactly. If the law was applied rigidly then something as simple as fitting larger tyres would suddenly make you a motor vehicle user!

Can you not add a throttle to your conversion? I reckon it would make it a lot more user friendly.

I've never ridden a bike with a 'pedal sensor' but I have to say I don't like the sound of the idea. With a twist throttle you just dial in the power however you feel is appropriate - what's not to like about that?

I suppose the pedal sensor is supposed to prevent you being lazy and using the machine as a moped instead of as a human/electric hybrid.

I have a thumb throttle as part of the kit. I wasn't going to fit it but now I think I will (although at the moment it's a fight for space between the thumb throttle and my bell).

I do actually want to cycle, I just want it to be easier.
To me the difference between a motorcycle and an ebike isn't the arbitrary 15mph limit (I easily average more than that) it's whether you need to peddle or not.
Obviously I'm not suggesting throttles should be banned or anything daft like that, I just 'feel' if I'm not pedalling then I'm on a motorbike and if I am then I'm on a pushbike.

UpWrong
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Re: Speed sensor vs torque sensor

Postby UpWrong » 26 Oct 2017, 9:20pm

If a throttle is still legal for a conversion then that persuades me to do a conversion rather than buy an e-bike.

kwackers
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Re: Speed sensor vs torque sensor

Postby kwackers » 27 Oct 2017, 10:11am

Mark R wrote:
I'll just fit taller tyres. ;)


Exactly. If the law was applied rigidly then something as simple as fitting larger tyres would suddenly make you a motor vehicle user!

I looked up how to get into the settings menu of the controller last night and spotted the wheel size was set to 26" (mine are 700cc) so I guess it's either 1 or 2 inches undersize (integer settings only) which means 15mph was actually a little over 16 (although still within 10%).

I also gave it a go up and down the road without the speed limiter and I have to say it felt so much better behaved. (Private road obviously ;) )

Whilst the kit was a doddle to fit I must admit with some shame I hadn't realised what a poor state my little bike was in. I usually stay on top of it but since I moved house I've just ridden it with no consideration apart from swapping out consumables.
The crank bearings had given up although they're replaced by the motor anyway (plus I'd already bought a replacement), brakes were seizing on the pivots and way out of adjustment, crud everywhere and I'm amazed the cassette was capable of carrying the chain at all - a couple of the gears were near bald.

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meic
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Re: Speed sensor vs torque sensor

Postby meic » 27 Oct 2017, 10:15am

(Private road obviously ;) )

But was it accessible by the public? You can not escape the legal requirements that easily.
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Ruadh495
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Re: Speed sensor vs torque sensor

Postby Ruadh495 » 27 Oct 2017, 10:22am

UpWrong wrote:If a throttle is still legal for a conversion then that persuades me to do a conversion rather than buy an e-bike.


Just make sure you have ridden the bike as a pedal cycle first (i.e. don't use a brand new one). The reason is that the presence of a throttle/override introduces a requirement for type approval, which in the case of a conversion would be dealt with via the Single Vehicle Approval process. However there's no standard for SVA as an e-bike, so the DfT have stated that the requirement is waived in the case of converting a pedal cycle which has previously been used as such.