Author Topic: Brompton swytch conversion  (Read 1507 times)

bhoot

  • MemSec (ex-Mrs RRtY)
Brompton swytch conversion
« on: June 30, 2020, 12:49:24 am »
Does anyone have experience of this? My father has just received his kit but is having some problems. One is that with the new wheel and its special washers/spacers, it doesn't go into the forks as far as the old wheel. The result is that the brake arms are not really long enough, given that the pads were right at the bottom of the slot anyway.
Very interested to know whether anyone else has had the problem and want they did about it.

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton swytch conversion
« Reply #1 on: July 03, 2020, 12:26:22 pm »
Is this problem because the new axle is a larger diameter than the original? If so, filing out the dropout slightly should solve the problem.

Brompton front axles are 8mm diameter, standard front axles are 9mm and most rear axles are 10mm.
Wheel meet again, don't know where, don't know when...

Re: Brompton swytch conversion
« Reply #2 on: July 03, 2020, 04:34:43 pm »
Given that Swytch supply a Brompton specific kit, I'd assume that they have supplied an 8mm axle to suit - unlike the normal kit I have, where the axle is 10mm and needs a small amount of filing the normal 9.5mm dropouts width.

The other problem, which is what I think is happening here, is that fitting the lock washer (essential to keep the motor from rotating in the dropout) has meant the axle won't seat as far up as it should. This requires filing out of the dropout depth.
HTH

LittleWheelsandBig

  • Whimsy Rider
Re: Brompton swytch conversion
« Reply #3 on: July 03, 2020, 11:20:27 pm »
Their website suggests that the Brompton motor axle is larger than 8mm and the fork seems to have suspiciously large slots. I would guess that some fork modification is required for everything to fit properly (for the washers at least, as you suggest) but I have never actually got my hands on a Brompton kit.

A Brompton-specific kit is expected. A Brompton front hub is quite a bit narrower than the normal 100mm OLD, so a standard hub motor would never fit without replacing or coldsetting the fork anyway.
Wheel meet again, don't know where, don't know when...

Tigerrr

  • That England that was wont to conquer others Hath made a shameful conquest of itself.
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    • Humanist Celebrant.
Re: Brompton swytch conversion
« Reply #4 on: July 04, 2020, 07:06:08 am »
I have one of these. The forks need widening, and I also filed the cutout back a bit. It’s because the motor used is a standard nano motor and it’s wider than the original axle.
It’s a nuisance but the alternatives are very much more expensive. Once fitted it works like a dream and he will love it.
I found it was a good idea to buy a second battery, and in the end I upgraded to a bigger battery altogether for more range.
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bhoot

  • MemSec (ex-Mrs RRtY)
Re: Brompton swytch conversion
« Reply #5 on: July 06, 2020, 08:02:59 am »
Good news, he is electrified now. Apparently (not seen a picture yet) the brakes are just (but only just) low enough to clear the tyre.

ppg has it right "fitting the lock washer (essential to keep the motor from rotating in the dropout) has meant the axle won't seat as far up as it should." In fact I think the axle is smaller in diameter than standard but then there is the special sapcer/washer which prevents the rotation.  I will attempt to post a photo later in case anyone else has this question in future.  There is no instruction from Swytch to file out the drop outs and he wasn't too keen on doing this.

bhoot

  • MemSec (ex-Mrs RRtY)
Re: Brompton swytch conversion
« Reply #6 on: July 24, 2020, 03:21:46 pm »
Just an update in case anyone else has been considering this. Overall he is really pleased with it - at 86 he was struggling a bit with some of the local hills and/or worried about head winds on the way back home!  Range isn't great as he has the smaller battery pack but he reckons 25 miles or so which is fine for what he wants to do - ie go for a coffee in the next town!
Still some minor problems in that he reckons the power cuts out when in top/top gear (he has a 6 speed bike) but he is still waiting for the correct Brompton pedal cadence sensor so is keeping an open mind until he fits that.

bhoot

  • MemSec (ex-Mrs RRtY)
Re: Brompton swytch conversion
« Reply #7 on: September 24, 2020, 03:43:10 pm »
A long time has now passed and he still doesn't have the special Brompton sensor but the issue with 6th gear is confirmed.  I and other family members have tried it out. It seems to us that the power cuts when the pedal cadence drops to a certain percentage of the wheel rotational speed - which would be logical to avoid power being delivered if you are "soft pedalling" - given that there is no torque measurement, it's probably the only way to detect that you have eased off and don't need power even if you are still gently rotating the cranks.  Assuming that is correct, then it would appear that the pedal cadence is always too low in top gear, which could be because any specified ratio has not taken into account the very small wheels of the Brompton which necessitate a high rotational speed of the wheel in relation to the crank rotation.