• 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

manu.w

New Member
Aug 5, 2023
80
35
belgium
I preordered the new Speedbox 1.2B which is for the smart system + Rim Magnet and has Bluetooth connectivity. Scheduled to ship the end of January.
At which time I’ll be removing my Megabobra if anyone in the US wants to buy it.
Ok, they produce the magnetic pulse, and provide a sort of kiox display replacement by reading the motor data (they reverse engineered the communications protocol of the kiox display)
 

megabobra

Active member
Jul 24, 2022
220
237
Australia
I made my own setup (MEGABOBRA: Bosch Smart System Derestriction for Rim Magnet - DIY Project with Support)
On my original firmware i managed to have a quite easy rudimentary working setup.
When upgrading the motor system firmware from 4.21.0 to 8.16.0, troubles appears.
After a loooot up and downs i got a working setup.I
would like to share my experience, but if i see that others "steel" it an sell it over 300£ ..., i am a little bit reluctant. Sad, because i would love to share my findings.
What i will share is that the reedswich should work flawlessy, the way to generate the electromagnet pulse is also much more tricky on latest firmware! I only generated a "pusitive" pulse, no need to mimic the "passing by" permanent magnet signature...

That's great news Manu. I share a similar feeling with steeling the info. I'm quietly working on some improvements and new features that I'll look to share in the future, but I'll likely withhold the code and/or specifics for exactly that reason.

Ok, they produce the magnetic pulse, and provide a sort of kiox display replacement by reading the motor data (they reverse engineered the communications protocol of the kiox display)

Looks like they're picking up the mode changes from the controller (switching EMTB to Turbo for example) to turn their device on and off. Don't think there's any other data being drawn from the motor though, eg remaining battery percentage.


I preordered the new Speedbox 1.2B which is for the smart system + Rim Magnet and has Bluetooth connectivity. Scheduled to ship the end of January.
At which time I’ll be removing my Megabobra if anyone in the US wants to buy it.

Out of interest Alumi, why are you switching?
 

AlumiPro

New Member
May 1, 2023
130
64
California
That's great news Manu. I share a similar feeling with steeling the info. I'm quietly working on some improvements and new features that I'll look to share in the future, but I'll likely withhold the code and/or specifics for exactly that reason.



Looks like they're picking up the mode changes from the controller (switching EMTB to Turbo for example) to turn their device on and off. Don't think there's any other data being drawn from the motor though, eg remaining battery percentage.




Out of interest Alumi, why are you switching?
I haven’t been able to get the Megabobra to be consistent; I’ve never had a ride with out an error code at some point with it. Which can be dangerous with the type of cliff side tech trails I’m climbing……when an error code occurs assisted power shuts off. I would constantly wonder when it would happen next, which makes the ride not as enjoyable.
I put a sharpie mark on my reed switch to keep track of its position, while slowly rotating it to find its sweet spot with no luck. Also slowly moving the spoke magnet in different positions.
It gets frustrating because I also have a Gen3 S-Works Levo which is derestricted with a simple plug and play unit at the mastermind screen in the top tube that keeps the correct speed and odometer, which I have had zero issues with. I’m frustrated with Bosch not Megabobra, I understand the Megabobra installed on a Race motor with up to date firmware was not a 100% guarantee it would work.
I’m willing to spend a decent amount of $ for a device that is guaranteed to not trigger error codes and give me at least 28mph of assisted power. Hopefully the Speedbox 1.2B works as advertised, it’s essentially doing the same thing as the Megabobra and eplus unit. 🤞🏻
 
Last edited:

megabobra

Active member
Jul 24, 2022
220
237
Australia
I haven’t been able to get the Megabobra to be consistent; I’ve never had a ride with out an error code at some point with it. Which can be dangerous with the type of cliff side tech trails I’m climbing……when an error code occurs assisted power shuts off. I would constantly wonder when it would happen, which makes the ride not as enjoyable.
I put a sharpie mark on my reed switch to keep track of its position, while slowly rotating it to find its sweet spot with no luck. Also slowly moving the spoke magnet in different positions.
It gets frustrating because I also have a Gen3 S-Works Levo which is derestricted with a simple plug and play unit at the mastermind screen in the top tube that keeps the correct speed and odometer, which I have had zero issues with. I’m frustrated with Bosch not Megabobra, I understand the Megabobra installed on a Race motor with up to date firmware was not a 100% guarantee it would work.
I’m willing to spend a decent amount of $ for a device that is guaranteed to not trigger error codes and give me at minimum 28mph. Hopefully the Speedbox 1.2B works as advertised, it’s essentially doing the same thing as the Megabobra and eplus unit. 🤞🏻

Understood, appreciate the feedback!
 

manu.w

New Member
Aug 5, 2023
80
35
belgium
Hi Alumipro,
If you are brave and curious, you could open the electromagnet case and see and measure the resistance of the coil. I made different coils , some didn’t worked …
Maybe share, if they allow that, the installation instructions .
Let us know how this sb works
Thanks
 

megabobra

Active member
Jul 24, 2022
220
237
Australia
Preview of one of the new pieces I'm working on. The OLED display and buttons will show the true speed, true distance, reported speed etc, as well as providing the user options to set their own multiplier, change units, wheel circumference etc. It'll be set in a 3Dprinted case to suit either mounting on handlebars or top tube.

Other works in progress: new tiny electromagnet, hall sensor, no LPP.

1.jpg
 
Last edited:

manu.w

New Member
Aug 5, 2023
80
35
belgium
Well shoot!….I figured the stronger the magnet the better, and as close to the reed as possible! I ordered three different spoke magnets just to have options. The one I chose is a cylinder type and honestly I think it is the weakest one I ordered because it’s incased in plastic. Maybe the cylinder shape sometimes triggers double pulse!?
I ran the reed wire/sensor along the bottom of the rear brake line through the swing arm and used a long piece of electrical shrink tubing to secure it to the brake line and disguise it! I’m really happy with how hidden it is being shrink tubed tight to the bottom of the brake line. My next ride I will take all three types of spoke magnets to try out, they are very easy to swap out on the trail.
The red oval outline in my pictures indicate the reed, while the yellow oval outline indicate the spoke magnet.

View attachment 127793 View attachment 127794 View attachment 127795 View attachment 127796 View attachment 127797 View attachment 127798 View attachment 127799 View attachment 127800 View attachment 127801
magnet and reedswitch needs to be far away from other "spinning" metal objects...
 

megabobra

Active member
Jul 24, 2022
220
237
Australia
New coil in the works. Old version on the left, new version on the right. This will be small enough to be fixed directly to the motor, regardless of how close it is to the frame, as it sits within the bounds of the motor case's footprint. Similar to the OLED display, I'll print a small case for the magnet to protect it and the wires.

Coil.jpg
 

cozzy

Well-known member
Aug 11, 2019
746
786
Basingstoke UK
New coil in the works. Old version on the left, new version on the right. This will be small enough to be fixed directly to the motor, regardless of how close it is to the frame, as it sits within the bounds of the motor case's footprint. Similar to the OLED display, I'll print a small case for the magnet to protect it and the wires.

View attachment 130112
You also have a voima I recall? Isn't it easier to replace the rim magnet with a rotor magnet to open up more possibilities?
 

megabobra

Active member
Jul 24, 2022
220
237
Australia
You also have a voima I recall? Isn't it easier to replace the rim magnet with a rotor magnet to open up more possibilities?

Yes I have unit fitted in my Voima. Certainly, if you're able to move away from the rim magnet everything becomes easier for derestriction. I understand you're given the option of rim or rotor magnet with the Voima now, but sadly the earlier versions had rim magnet only.

I assume dealers can change the preference in the motor firmware at any time, but that'd be an interesting conversation to have...

The derestriction for rim magnet is fiddly, but reliable once it's in place. I suspect this is due to the fact that it's not interfering with intercepted signals like the rotor magnet-style devices do. I'm hoping that the changes I'm working on will take out the guess work from installation/setup others had been having trouble with.
 

cozzy

Well-known member
Aug 11, 2019
746
786
Basingstoke UK
Yes I have unit fitted in my Voima. Certainly, if you're able to move away from the rim magnet everything becomes easier for derestriction. I understand you're given the option of rim or rotor magnet with the Voima now, but sadly the earlier versions had rim magnet only.

I assume dealers can change the preference in the motor firmware at any time, but that'd be an interesting conversation to have...
Its definitely possible to convert, people have done it.
Instructions are vague and incomplete though. I'm currently going through this for my incoming voima, plus a wheelsize change for a mullet, will document the steps in the pole forum once it's done.
The magnet, slim speed cable and clip are about £45.
 

ready13

New Member
Sep 7, 2023
4
4
USA
Yes I have unit fitted in my Voima. Certainly, if you're able to move away from the rim magnet everything becomes easier for derestriction. I understand you're given the option of rim or rotor magnet with the Voima now, but sadly the earlier versions had rim magnet only.

I assume dealers can change the preference in the motor firmware at any time, but that'd be an interesting conversation to have...

The derestriction for rim magnet is fiddly, but reliable once it's in place. I suspect this is due to the fact that it's not interfering with intercepted signals like the rotor magnet-style devices do. I'm hoping that the changes I'm working on will take out the guess work from installation/setup others had been having trouble with.
Excited to see the progress on your projects and really appreciate you sharing the 1st gen ‘bobra directions with us.

I have a friend at Bosch and although it is possible to change from an ‘internal’ speed sensor to an ‘external’ speed sensor, the dealer can’t do it, and neither can Bosch.
Only the OEM manufacturer of the bike can do it from their side of the Bosch software.
All the dealer can do is plug your bike in and submit a “configuration change request” and hope the random engineer at the bike company who works on Bosch integration will receive it and be willing to make the change.

Also, the friend confirmed Bosch is following all of these threads so best to keep the code under wraps as long as possible to protect the rider’s ability to derestrict. Bosch really wants to keep us from owning our own motors.

Thanks again megabobra, can’t wait to see the new parts!
 

Naagra

Member
Aug 14, 2022
7
6
France
Also, the friend confirmed Bosch is following all of these threads so best to keep the code under wraps as long as possible to protect the rider’s ability to derestrict. Bosch really wants to keep us from owning our own motors.

As expected, Bosch is trash with their customers, don't understand the crusade against derestrict.. Brose and Yamaha don't care and Shimano is the same with bosch, except worse
 

megabobra

Active member
Jul 24, 2022
220
237
Australia
Little update on the display. Just about happy with the all the functions now. All the typical screens, current speed, max speed, distance (all true values of course), as well as total climb/descent. Additionally, there's a menu for the controls of the megabobra itself; setting the desired multiplier, units (metric/imperial), wheel circumference etc. I'm considering also adding an option to turn on/off distance catch up functionality, ie where the device keeps the trip running after being idle for a minute in order to clock up the true trip distance to the motor. Certainly not a feature I'd use, but some asked for it and it's only a few lines of code.

Some snips below to show comparison of trip distance reported by the bosch display vs the true distance on the megabobra display. Bosch shows 22.1km vs true distance of 31.06km. I'm running a 1.4 multiplier (for max assisted speed = 35kph), so 22.1 * 1.4 = 30.94km, or within 0.3% of what the megabobra shows. I'm happy with this tolerance!

Just waiting on some new cabling before I tidy up the display and install it in its housing. For now, it's attached with velcro :)

Wide.jpg CloseUp.JPG
 

manu.w

New Member
Aug 5, 2023
80
35
belgium
As expected, Bosch is trash with their customers, don't understand the crusade against derestrict.. Brose and Yamaha don't care and Shimano is the same with bosch, except worse
We buy but don’t really own it… and “with a click” they can brick it…
 

megabobra

Active member
Jul 24, 2022
220
237
Australia
Will you offer the new tiny electromagnet and hall sensor for those who already own your first Gen Megabobra?….provided they are compatible?
Hi Alumi,
It's something I've thought about a lot. Yes, I'm happy to send an upgraded coil at no cost to anyone with v1 who's experiencing trouble like you faced. It would just be a plug-in replacement.

As for the wheel pickup sensor, this will be trickier - at best, a hall sensor needs an additional wire core (3-core instead of 2-core) going to the rear wheel, meaning the existing reed sensor plug would be incompatible. I'd be happy to supply the new sensor along with a new female connector to suit, BUT it'd require some soldering at your end to attach the new connector to the megabobra and a code update.

Just noting though that the new-est pickup sensor (call it v2.5 if you will) which sits inside the frame at the motor, rather than at the back wheel, will not be an easy upgrade from v1 to v2 as it requires new hardware. Though, it doesn't offer any advantage over the hall sensor at the back wheel, we live in a world where less visible wiring = better!

I'll reach out directly when I'm in a position to offer the coil/sensor to v1 owners who need it.
 

AlumiPro

New Member
May 1, 2023
130
64
California
Hi Alumi,
It's something I've thought about a lot. Yes, I'm happy to send an upgraded coil at no cost to anyone with v1 who's experiencing trouble like you faced. It would just be a plug-in replacement.

As for the wheel pickup sensor, this will be trickier - at best, a hall sensor needs an additional wire core (3-core instead of 2-core) going to the rear wheel, meaning the existing reed sensor plug would be incompatible. I'd be happy to supply the new sensor along with a new female connector to suit, BUT it'd require some soldering at your end to attach the new connector to the megabobra and a code update.

Just noting though that the new-est pickup sensor (call it v2.5 if you will) which sits inside the frame at the motor, rather than at the back wheel, will not be an easy upgrade from v1 to v2 as it requires new hardware. Though, it doesn't offer any advantage over the hall sensor at the back wheel, we live in a world where less visible wiring = better!

I'll reach out directly when I'm in a position to offer the coil/sensor to v1 owners who need it.
So your new v2 you’re still finishing has no exterior wires outside the motor area?! But it’s designed for the Rim sensor Bosch?!
 

aegidius

New Member
Sep 30, 2023
39
25
brisbane
at best, a hall sensor needs an additional wire core (3-core instead of 2-core)
There are plenty of 2-wire hall sensors. Bosch themselves make one, and it's freely available. Connect between an input pin and ground with a 3k3 pullup to +3.3V (that's what Bosch motors appear to do - it draws ~1mA when magnet is present). Works fine that way with my arduino-based speed display.
 

megabobra

Active member
Jul 24, 2022
220
237
Australia
So your new v2 you’re still finishing has no exterior wires outside the motor area?! But it’s designed for the Rim sensor Bosch?!

That's correct.

There are plenty of 2-wire hall sensors. Bosch themselves make one, and it's freely available. Connect between an input pin and ground with a 3k3 pullup to +3.3V (that's what Bosch motors appear to do - it draws ~1mA when magnet is present). Works fine that way with my arduino-based speed display.

I've not seen a 2-wire hall sensor before, do you have a link? Are you sure you're not thinking of a reed switch?
 

aegidius

New Member
Sep 30, 2023
39
25
brisbane
I've not seen a 2-wire hall sensor before, do you have a link? Are you sure you're not thinking of a reed switch?
Example here (at a LBS chain here is Australia, but they're all over the place)
They are the ones used on pre-Smart System Bosch motors with the spoke magnet. They come in different lengths, and have the nanoMQS plug at the end (the one you can't get a socket for)
 

megabobra

Active member
Jul 24, 2022
220
237
Australia
Example here (at a LBS chain here is Australia, but they're all over the place)
They are the ones used on pre-Smart System Bosch motors with the spoke magnet. They come in different lengths, and have the nanoMQS plug at the end (the one you can't get a socket for)

Gotcha thanks. Those are reed switches, rather than hall effect sensors. Both detect a passing magnet, but the reed switches do so physically and are susceptible to vibration, and can be a bit particular with orientation. Orientation issues are addressed in the one you linked by the screw mount, ensuring it's always facing the way the manufacturer intended.

I had some early vibration issues with the reed switch where it was held in place loosely with a cable tie but could bounce around a little. Securing it firmly sorted the issues.

The hall effect sensors have no moving parts, instead detecting changes in electrical current induced internally by the passing magnet.

Reed switches can definitely work OK, as evidenced by most bike computers and ebike speed sensors, but moving to a hall sensor just removes one more variable when installing the megabobra, making it less sensitive to correct placement.
 

AlumiPro

New Member
May 1, 2023
130
64
California
That's correct.



I've not seen a 2-wire hall sensor before, do you have a link? Are you sure you're not thinking of a reed switch?
I understand you don’t want to give out all the details for good reason. But I am very curious how your V2 would work, keeping everything inside the motor area. Besides the screen wiring of course.
Will you be offering it without the screen option? Or I guess maybe it’ll be good to have the screen for at least set up mode, as I have no interest in having another screen on my bike.
 

aegidius

New Member
Sep 30, 2023
39
25
brisbane
The Bosch 2-wire wheel speed sensor is a hall sensor afaik - it uses a 2-wire hall sensor chip, similar to this one. (I've never taken one apart to check for certain which chip it uses, and they are potted, so it would be hard to see anyway). They are polarity sensitive (which a reed switch isn't) and are used commonly in automotive sensors (Bosch also makes a lot of those)

When I first encountered 2-wire hall sensors I thought they were black magic, but they are definitely a thing.
 

EMTB Forums

Since 2018

The World's largest electric mountain bike community.

513K
Messages
25,095
Members
Join Our Community

Latest articles


Top