Dangerous and inefficient pedal assist?!?

[handmadematt]

Hi guys, I've introduced myself in the new members area with pictures of the new bike that I've built myself.
Here:
http://www.pedelecs.co.uk/forum/threads/ive-just-finished-building-my-first-trail-ebike-pics.18787/

I initially only fitted the hand throttle to the bike. I also have hydraulic disc brakes so I chose not to fit the electric brake levers with the cut off. I come from motorcycling so I was happy to just be in control of everything myself.

Today however I fitted the pedal assist hardware (a sensor and a disc of magnets on the crank.) Just because I can. The system doesn't have any fancy torque sensors or anything. I wired it in with a switch so that I can turn it on and off.
Here's the switch panel and the side of the bike removed. One switch is to disable the hand throttle, one is for the headlight and the third the pedal assist. The switch panel will be hidden behind a layer of black foam that fits between the two bike side panels, this will help to keep it dry and clean.





My first thoughts of the pedal assist system is that it is both dangerous and inefficient. (I understand that this is bottom of the market stuff and that the switched brake levers would make it function better.)

There is a painfully long delay for the response of the power when pedaling meaning pulling away is hard and then suddenly you're catapulted forward. Also, when stopping pedaling there is a delay which is quite frightening.

I guess it's OK at speed but around town and in traffic it'd be a nightmare!
Maybe as a form of cruise control it makes sense to me but then why not just have a switch?

 

[JohnCade]

I suppose because most e bike users want to pedal as well. Though a significant number don't and just want an electric moped or even motor bike.

I think your bike will be dangerous without brake operated cut outs. Apart from the motor lag there are recent posts here which go into the possibility, which is not that small, of throttle failure in the open position. They do fail open when they fail apparently.

 

[Deleted member 4366]

Basically, it's a crappy controller. That sort of thing was common two or three years ago, but now there's much better ones; however, they still have a slight delay between stopping pedalling and the motor stopping, which is always going to be dangerous without a brake switch. You only have one power level with your pedal sensor, which is maximum. Worse still, it might be based on cadence, which is diabolical.. Unless you get a new LCD controller, I'd forget the pedal sensor.

You should fit at least one brake switch anyway. If you don't want to mess about with magnets and reed switches, fit a cable e-brake at the rear.

 

[handmadematt]

Good thoughts guys.
I want to pedal, if I didn't want to I'd just ride one of my motorcycles. I find that assisting my pedaling manually using a hand throttle is much more efficient and gentle. I understand economy in driving/ riding style and take joy in trying to maximise it. My hydraulic disc brakes would over power the motor easily if ever there was a fault. Additionally, there's a on/ off switch on the throttle assembly just by my right thumb. There are no safety concerns to me. I have two fail safes. Brakes and power switch.

It does appear that there are two assist powers, low and full. I'm sure it is based on cadence, that's the only hardware I installed. I think you're right, I'm just going to forget the pedal sensor unless I happen to be on a full speed long term open road cruise and I want a rest for my wrist on the hand throttle.

I was thinking about going to rear cable brake, I do have all the equipment for it but my current equipment is SO much better I'm reluctant. I have reed switches and small neodymium magnets in stock so maybe I'll have a play.

I do feel though that it touches on the issue I raised of economy. Simply if I'm braking and the motor is energised then my riding style is not economical enough.

Interesting chat, thanks.

(As mentioned, I am aware that my experience is based on bottom of the range equipment. It's not criticism of ebikes in general. I am also aware that the latest tech is very advanced. I look forward to exploring the scene more and trying out said machines in the future.)

 

[amigafan2003]

I've had a few friends I've helped build ebikes and a two of them declined my suggestion to fit ebrakes - for similar reasons you've given.

Funnily enough, it's only those two who have also crashed thier ebikes.

Seriously, fit one ebrake for the rear brake at least.

As for pedal assist - you;ve pretty much summed up what's wrong with a cheap controller and a simple crank rind sensor arrangement. I'd just dump it and use throttle only. A "switch" like pedal assist only really makes sense on a very low power ebike (<500w).

My commuter bike only has a throttle but it has a three speed switch and cruise control - so when I get to the speed I want, I hit the cruise control button and let go of the throttle and continue to pedal as much or as little as I like and a quick tap on the ebrake knocks the power off.

 

[handmadematt]

A "switch" like pedal assist only really makes sense on a very low power ebike (<500w).

I was thinking the same.

 

[Black Dog]

I'm from a motorcycling background too, and I don't like safety switches much either (I always disable clutch switches on my bikes, and usually also the side stand switch before it fails and leaves me stranded somewhere - it has happened). But I wouldn't be without the brake switches on my ebike. The lag in coming off the power is easily accounted for in normal riding (just stop pedalling before you need to), but for the 1% of times when you need to stop in a hurry they are vital. And also, having them saves me from turning the power off early when I get home. I have to manoeuvre round a tight circle on gravel and the ebrakes give me a nice bit of fine control for that. Otherwise, the bike would just lurch and throw me off.

A decent MTB with a motor and throttle - what you have got is a low-key sun-powered motorbike. I rather like that.

 

[Deleted member 4366]

My hydraulic disc brakes would over power the motor easily if ever there was a fault.

You'll pop the controller if you do that.

It's very difficult to hold a throttle steady on a bicycle while you're pedalling. You can make a cruise control, which is much more economical (on battery). I've built a few of these using a thumb throttle without a spring on the left as a cruise control, and any normal throttle on the right. A three pole switch switches from one to the other. Don't do it without at least one brake switch. You can use a simple linear 10K pot instead of a throttle as a cruise control :

 

[handmadematt]

My hydraulic disc brakes would over power the motor easily if ever there was a fault.

You'll pop the controller if you do that.

We were talking emergencies.

 

[handmadematt]

It's very difficult to hold a throttle steady on a bicycle while you're pedalling.

You are right. I'm used to off road motorcycle riding where one has similar problems but with time and experience it becomes easier. One trick is to push ones thumb across the bridge of the two twisting surfaces, holding the throttle in place as it were. I like your idea of a switched cruise control though. Thanks.
Here's my other ride on top of some hills in Portugal earlier this year:

 

[handmadematt]

...two of them declined my suggestion to fit ebrakes - for similar reasons you've given.
Funnily enough, it's only those two who have also crashed thier ebikes.

By that logic I'd hate to see them with any motorised vehicle!


Today I soldered and heat shrunk some wires onto a reed switch and cable tied it neatly in position on the underside of my rear hydraulic lever body. I've sealed it all in with a generous cover of black Sikaflex adhesive/ sealant. I've then stuck a small neodymium magnet to the lever itself. I've used JB Weld, two part glue, to stick it on. It triggers my voltmer well. Tomorrow when everything is dry I'll wire it in and go for a test ride.
Here are some photos before the black sealant.
Is this the kind of thing other people have done?

 

[Robint]

Hi HMM
see my hacks on the Ego bike. I think there may be many pedalers who dont come from a motorcy bg and therefore unused to automatic reaction to clutch throttle use as well as brake levers. It comes 2nd nature after a while and isnt an issue amongst bikers. So having a twist an go throttle on a weak hub motor doesnt seem dodgy to me. Agreed the twist throttle is a bit naff, but with the twist n go, there's no time lag or run on associated with pedelecs. Incidentally the cheap ring sensor type are really only and on/off sensor, ie cranks revs > set value = power full on depending on level preselected on the hand controller. You got to intiate it with a crank of minimum speed first and it will run on for 1/2 sec. I hated that.
With my system, you throttle back and dont use any juice when you dont need it.

 

[JohnCade]

Not sure what you mean about clutch though. I think a lot of people here have had and still have motorcycle experience. I rode bikes for many years and at one time my hobby was restoring old British bikes from the fifties. But they had clutches you could whip in if you needed to, and I've had a throttle stick open, as well as engine seizures on wet roads....

But what would HMM do if the throttle failed open on an e bike without a clutch, and he had no time to switch it off before he arrived at the scene of the accident?

 

[Robint]

sorry i didnt explain myself, i meant as a biker, you instinctively know what to do with your hands. not suggesting a clutch on an e bike. If you werent a biker you might have to learn how to use a throttle - once you learnt you never forget - like riding a bike ;-)

 

[JohnCade]

sorry i didnt explain myself, i meant as a biker, you instinctively know what to do with your hands. not suggesting a clutch on an e bike. If you werent a biker you might have to learn how to use a throttle - once you learnt you never forget - like riding a bike ;-)

Actually I confused your post with HMM for a moment. He doesn't want to bother with brake cut outs. I changed it later. Still can't really understand what you meant though....

 

[handmadematt]

All good points guys.
I'm now fitting this magnetic reed switch to my rear brake for a few reasons (see latest photos above.) Despite already covering over one hundred miles fine without it.

1) It is clearly highly recommended by this forum and I'm all for added safety measures.
2) I'd like to be able to let novices have a go on my ebike without worrying.
3) I want to experience this pedal assist system as it was designed to make a fair judgement about it.
4) I had all the materials and always like a project.

My only concern is that the more complex a system is the more chances there are of faults. I feel that it is well designed though.

 

[Deleted member 4366]

But what would HMM do if the throttle failed open on an e bike without a clutch, and he had no time to switch it off before he arrived at the scene of the accident?

Instinct makes you go for the brakes when your throttle jams. Then, you can't let go of them to reach any other on/off switch. By the time you figure out what to do, your controller has popped and your motor is smoking - as has been demonstrated by those that had to do it.

 

[handmadematt]

Here's a video I made to show people what I did.

 

[Deleted member 4366]

Perfect!