Fitting a whoosh conversion kit to a Thorn Raven

[saneagle]

Any particular reason? Everything I’ve read says that torque arms are only usually used on aluminium forks but it’s ok on steel. My forks are steel so thought I’d be ok.
Happy to add one if folks think it worthwhile.

They might be steel, but there's not a lot of metal around the axle. 17A is quite a lot. For me, it's just a peace of mind thing.

The metal alone is not strong enough to resist the motor's torque. Most of the resistance comes from the friction of the nuts, and if a nut comes loose, the motor will twist its way out of the drop-outs. That will happen if you have lawyers lips on the drop-outs and you didn't centralise the axle, otherwise make sure your nuts are tight and pray that the metal is strong enough.

 

[Peter.Bridge]

That looks to be the same one I bought. Saw it on AE but wanted it today

I wondered how stable it would be - are you intending on using a jubilee clip at the top to secure the plate to the bike frame ? I was just checking my bike - think that would be above the battery mount

 

[Cadence]

That's the reason I bought this one:-


It has recesses at each end to use the steel "hose clip" type clamps that came with it. As my frame is steel with brazed bottle mounts I didn't find the clamps necessary, but I wouldn't want to trust a heavy battery on riv-nuts in an aluminium frame . The OP has a Thorn Raven - just about the strongest steel touring bike frame you can get and it will have brazed bottle mounts, so the one he has chosen should be OK.

 

[SafetyThird]

I looked at the one @Cadence mentioned but it's not as long effectively as the one I went for because of the section below the cutout for the bottle boss bolts.

I've now fitted it and, as you can see, there's just enough room for the bottle to fit on the downtube.



The bracket bends down slightly until the top bolt touches the downtube. I'll grind the bolts down so they're flush with the bracket and glue a piece of inner tube on to the back of the bracket so that it doesn't rub against the down tube. I think a single extra rivnut might be a good idea at some point, or perhaps get a proper one brazed in if I'm going to keep this as a long term option.



The bracket does flex a bit but there's room to put a jubilee clip around the bracket and clamp it in place. Because I'm not mounting it to the downtube directly, the little rounded plastic washers that come with the kit aren't used and I might trim them to fit underneath the bracket and then put a jubilee clip over the top, there's room between the battery mount and the bracket.

 

[Peter.Bridge]

Ah perfect - I will do the same

 

[SafetyThird]

I ground down the bracket screws so they didn’t protrude past the bracket.



Then I glued a couple of strips of old inner tube to the bracket and mounted it back up.

 

[SafetyThird]

Was up early this morning so went out to the garage to finish up. Installed the wiring as neatly as I could, though it might be changed later, will see if there’s anything that rubs or pulls after a couple of rides.





then took it for a quick test ride.

Wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee!

Everything works very well, I think it’s going to be a real boon on the local hills and encourage me to get out more now that I know I won’t be left pushing the bike up hills when my legs won’t carry me any further. I’ll be able to start working on my fitness again and also reduce the number of car journeys by doing grocery runs to the local town by bike.

Will update after a few rides with how it’s all going.

 

[Woosh]

I would put a cabletie near the fork's jaws to reduce the size of the drip loop and the chance that the motor cable gets tangled up.
Congratulations on a well done job and a great bike!

 

[SafetyThird]

I would put a cabletie near the fork's jaws to reduce the size of the drip loop and the chance that the motor cable gets tangled up.
Congratulations on a well done job and a great bike!

thanks, I’ll do that. Will make it a removable tie wrap so it’s easy to drop the wheel out for puncture repair etc.

 

[Az.]

Another successful conversion. Looks good, feels good. So much better than Swytch.

 

[SafetyThird]

Thinking about the torque arm conversation earlier, while it may not be necessary, is it a good idea for peace of mind given that it's a cheap thing to do? If so, what sort of kit should I be looking at?

 

[Peter.Bridge]

I'll be interested in what range you get. I have the rear hub version of that motor and also the 20Ah 36v battery. Using a multi meter to measure the voltage drop after a 43 mile trip (about 1/3 usable left), I estimated the range from full was around 65 miles on assist levels 4 and 5 on fairly undulating roads

 

[Woosh]

Thinking about the torque arm conversation earlier, while it may not be necessary, is it a good idea for peace of mind given that it's a cheap thing to do? If so, what sort of kit should I be looking at?

On steel forks, torque arms are not necessary. On aluminium forks, torque arms reduce the risk of breaking but don't eliminate the risk entirely. The jaws break because of the shock when your front wheel hit something hard. It's not the rotational kinetic inertia (0.5 * m * (ωr)^2) that breaks it, it's the usual mass inertia (also known as moment of inertia, 0.5*m*v ^2), the kinetics of your bike hitting an immobile object like the kerb that breaks the jaws of an aluminium fork. (ωr) is much less than v or v is much higher than (ωr) because ω is decelerating but not zero. The torque arms can't keep the wheel attached to the fork when that happens so it's not particularly useful under the circumstance. There is also the effect of metal fatigue thatb breaks the jaws. This time, we consider only rotational inertia which is proportional to mass. Your motor weighs 2.6kgs, saneagle's BPM weighs 4.5kgs so you don't have anything to worry about.

 

[saneagle]

On steel forks, torque arms are not necessary. On aluminium forks, torque arms reduce the risk of breaking but don't eliminate the risk entirely. The jaws break because of the shock when your front wheel hit something hard. It's not the rotational kinetic inertia (0.5 * m * (ωr)^2) that breaks it, it's the usual mass inertia (also known as moment of inertia, 0.5*m*v ^2), the kinetics of your bike hitting an immobile object like the kerb that breaks the jaws of an aluminium fork. (ωr) is much less than v or v is much higher than (ωr) because ω is decelerating but not zero. The torque arms can't keep the wheel attached to the fork when that happens so it's not particularly useful under the circumstance. There is also the effect of metal fatigue thatb breaks the jaws. This time, we consider only rotational inertia which is proportional to mass. Your motor weighs 2.6kgs, saneagle's BPM weighs 4.5kgs so you don't have anything to worry about.

Why do you keep referring to BPMs? I haven't used one in twelve years.

 

[Woosh]

Why do you keep referring to BPMs? I haven't used one in twelve years.

it's because the fork broke on your old bike and you worried the OP. I am not saying that front hub motors don't break forks, but they are rare and happen only when the fork is aluminium AND the motor is heavy. None with motors that weigh under 3kgs were known to break aluminium forks despite the large number of units in use.

 

[SafetyThird]

On steel forks, torque arms are not necessary. On aluminium forks, torque arms reduce the risk of breaking but don't eliminate the risk entirely. The jaws break because of the shock when your front wheel hit something hard. It's not the rotational kinetic inertia (0.5 * m * (ωr)^2) that breaks it, it's the usual mass inertia (also known as moment of inertia, 0.5*m*v ^2), the kinetics of your bike hitting an immobile object like the kerb that breaks the jaws of an aluminium fork. (ωr) is much less than v or v is much higher than (ωr) because ω is decelerating but not zero. The torque arms can't keep the wheel attached to the fork when that happens so it's not particularly useful under the circumstance. There is also the effect of metal fatigue thatb breaks the jaws. This time, we consider only rotational inertia which is proportional to mass. Your motor weighs 2.6kgs, saneagle's BPM weighs 4.5kgs so you don't have anything to worry about.

Thanks @Woosh thats put my mind at ease.

 

[Peter.Bridge]

On steel forks, torque arms are not necessary. On aluminium forks, torque arms reduce the risk of breaking but don't eliminate the risk entirely. The jaws break because of the shock when your front wheel hit something hard. It's not the rotational kinetic inertia (0.5 * m * (ωr)^2) that breaks it, it's the usual mass inertia (also known as moment of inertia, 0.5*m*v ^2), the kinetics of your bike hitting an immobile object like the kerb that breaks the jaws of an aluminium fork. (ωr) is much less than v or v is much higher than (ωr) because ω is decelerating but not zero. The torque arms can't keep the wheel attached to the fork when that happens so it's not particularly useful under the circumstance. There is also the effect of metal fatigue thatb breaks the jaws. This time, we consider only rotational inertia which is proportional to mass. Your motor weighs 2.6kgs, saneagle's BPM weighs 4.5kgs so you don't have anything to worry about.

Is there similar 'rules of thumb' for rear hub drives and torque arms ?

 

[Jodel]

On the 'Endless Sphere' web-site, torque arms have been / are discussed to quite a depth. If you want to gain additional knowledge, have a look at these threads:

Dropout Failure Experiments, and a call for Fork Donations

The strength of bicycle forks, their ability to handle the torque of hub motor axles, and the importance or non-importance of torque arms, has been a heavily debated topic in the ebike community. And rightly so, since failures that result in a wheel falling out of a vehicle can be more than a...

endless-sphere.com

2018 Torque Arm Tests, Splined Interface Design and Tabbed Washers

In some sense this is a decades old follow up to our initial torque arm experiments from this thread https://endless-sphere.com/forums/viewtopic.php?p=211356#p211356 The standard for imported ebike hubs back then was M12 or M14 axles that were ground flat to 10mm in order to use the dropout...

endless-sphere.com

 

[saneagle]

it's because the fork broke on your old bike and you worried the OP. I am not saying that front hub motors don't break forks, but they are rare and happen only when the fork is aluminium AND the motor is heavy. None with motors that weigh under 3kgs were known to break aluminium forks despite the large number of units in use.

The danger with OP's forks are not breaking. It's the motor twisting itself out of them. The drop-outs are tiny. There's not a lot of metal there, and he didn't mention filing the slots deeper nor reprofiling them to centralise the axle., neither did he mention whether the forks have lawlyers lips or not.

I just cannot understand why you want to discourage somebody from taking a basic safety precaution that costs nearly nothing. OP is absolutely nuts if he listens to you. It seems to me that you're more trying to score points in an arguement that let OP have an enjoyable and safe experience with his bike. You're gambling at his expense.

 

[Woosh]

I just cannot understand why you want to discourage somebody from taking a basic safety precaution that costs nearly nothing.

no, I never discourage anyone wanting to fit torque arms. You can search all my posts, I said it's not necessary if you have a steel fork or a motor under 3kgs. The OP has steel fork and a motor under 3kgs so there is no need to worry about adding torque arms.
I am neither pro or against torque arms.
I still fit torque arms on my Gran-Camino which has a heavy rear hub motor because the bike is meant for trail riding but I stopped making bikes Big Bears with heavy front BPM motors which have torque arms fitted to them. The Gran-Camino replaces the Big Bear.
The problem of motor wheels spinning out of the forks when the wheel nuts are not properly tightened affect only heavy and high power motors The OP's XF07 is neither.

Big Bear torque arms:

Gran Camino torque arms: