• Warning!!

    Riding a tuned or deristricted EMTB is not a trivial offence and can have serious legal consequences. Also, many manufacturers can detect the use of a tuning device or deristricting method and may decline a repair under warranty if it was modified from the intended original specification. Deristricting EMTB's can also add increased loads for motors and batteries. Riding above the local law limit may reclassify the bike as a low-powered bike, requiring insurance, registration and a number plate.

    Be aware of your local country laws. Many laws prohibit use of modified EMTB's. It is your responsibility to check local laws. Ignoring it, has potential implications to trail access, and risk of prosecution in the event of an accident.

    UK Pedelec Law

    Worldwide Laws

    We advise members great caution. EMTB Forums accepts no liability for any content or advice given here. 


MEGABOBRA: Bosch Smart System Derestriction for Rim Magnet - DIY Project with Support

Sander

Member
Dec 29, 2022
56
29
NL
So if you're running rim magnet, the megabobra is confirmed working up to ~v5 on the motor firmware. After that point there hasn't been much luck.

If you're running rotor magnet, it should work regardless of firmware version.
Hey Megabobra! I'm still running your 1st gen MegaBobra for about 4k now ;-) A friend of mine also rides a Voima, but his motor has issues so it's gonna be replaced under warranty. We swapped his motor with a new one from another bike. Today we're gonna put the Bobra back. So if due to higher software version his Bobra won't work, the only solution is to switch from external to internal? And then "firing" the sensor input on the motor with the Bobra? Cheers Sander.
 

megabobra

Active member
Jul 24, 2022
263
267
Australia
Hey Megabobra! I'm still running your 1st gen MegaBobra for about 4k now ;-) A friend of mine also rides a Voima, but his motor has issues so it's gonna be replaced under warranty. We swapped his motor with a new one from another bike. Today we're gonna put the Bobra back. So if due to higher software version his Bobra won't work, the only solution is to switch from external to internal? And then "firing" the sensor input on the motor with the Bobra? Cheers Sander.

Hey Sander, ha that's outstanding. Did the motor that's being replaced have the megabobra running on it?

Do you mean switch from Rim to Rotor magnet? If so, yes I think that's safest. BUT let me send you a PM ;)
 

robbydobs

Member
Jan 31, 2021
101
91
Sussex, UK
I was thinking about this the other day as I took magnet off when chaning the valve.

I think the rim magnet is oriented so north-south is tangential to the wheel.

In which case, I think you'd need two coils, a longer one running up/down (as if coiled around the seapost), one running left/right (like you have already).
The up/down one needs to increase, then decrease and produce a strong field.
The left/right one needs to be weaker and incrase, then flip negative and decrease (as this crosses zero, it represents the rim magnet being perpendicular to the sensor)
These two magnetic fields should then add up to simulate the magnet on the rim passing.

I think this is exactly how the Speedfun rim magnet chip works, as there is space for the up/down coil in the longer raised part of the magnet emulator...

1726069565576.png

I did email about buying one but they aren't available yet.

I may get the bits and attempt to construct something similar with the megabobra schematic. I think the L9110 already has two outputs, so shouldn't be too hard to add another coil.
 

megabobra

Active member
Jul 24, 2022
263
267
Australia
Yes I think you're on the right track with this. I'd built up a three axis coil for the reasons you state above, but it was wound in a continuous strand so it wouldn't be possible to fire in sequence or with different power levels.

Again yes correct, you can use the second channel of the L9110 to do so.

Keen to hear how you go!
 

EMTB Forums

Since 2018

The World's largest electric mountain bike community.

555K
Messages
28,046
Members
Join Our Community

Latest articles


Top