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Reversing MiniPro Steering sensor


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11 hours ago, FreeRide said:

Modifying the signal electronically should be very simple stuff, the specific type of Hall Effect sensor used is of a linear type and essentially one needs to invert the signal which is biased at 2.5V according to measurements made on the german site.  A simple Inverting OpAmp with biased output should do the trick.  That's 4 resisters and one small chip in a typical circuit with a couple small caps to prevent and noise/feedback issues.  It should be very low power so hopefully could be powered right from the connector that connects the sensor. However until I measure the circuit myself, this is all theory.

In order to avoid any issues with going back to standard operation if need be I've taken precautions.  1st I bought a second machine, 2nd I ordered parts so I don't have to modify the original parts, 3rd I intend to only make the changes if I can measure the operation of the circuit all powered up and record the current operation.  So in the end I'm less worried about the mod and more about just general issues of disassembly and assembly especially if I'm working with it under powered conditions.  I also believe the mechanical approach should actually work if done carefully and/or with measured calibration.  In the end though I'm thinking of it as a fun project and I'll learn something either way and I'll be happy... just much happier if the mini-pro runs 20-25km/hr reliably and safely.  Then I change the tires, then I work on the battery capacity issue.  

It's easy to take the MiniPro apart and put it back together.  I had no problems working on the sensor position with the battery and fin re-attached so I had power for testing without having to re-assemble the machine.

If your idea works, and predictable, comfortable steering reactions in reverse is achieved, you will go down as a legend in the MiniPro community - at least in my opinion. You can sell the circuits to some of us, I hope.  I wish you good luck!

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Ok guys, what about this idea: 

Swap the motors over so that when riding in reverse at the higher speed, I would actually be standing on the device in the normal forward position, keeping the steering functioning normally. The MiniPro would think it's going backwards and allow the full 25kph but the left motor is bolted on the right side and the right motor on the left, so the device would actually be going forwards. Cutting and extending the motor wires will likely be required.

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34 minutes ago, RooMiniPro said:

Ok guys, what about this idea: 

Swap the motors over so that when riding in reverse at the higher speed, I would actually be standing on the device in the normal forward position, keeping the steering functioning normally. The MiniPro would think it's going backwards and allow the full 25kph but the left motor is bolted on the right side and the right motor on the left, so the device would actually be going forwards. Cutting and extending the motor wires will likely be required.

I don't think it matters which way around the motors are installed (as long as the phase wires are connected correctly). Likely for the motor, there is no "forward or backward", at least from the winding and electronics point of view... And even if it did run in the opposite direction (probably achievable if the phase order is changed to "correctly" reversed), wouldn't that mean that when you lean forwards, the motors would run backwards and faceplant you?

At least most if not all wheels (as in electric unicycles) run similarly no matter which way you turn it, in the early days, people were actually confused which way around some of the wheel should be ridden ;)  There's of course a rotation direction marked in the tires, but that usually has to do with the pattern in the tire, when running in "correct" direction, the patterning throws water away from the middle towards the sides to prevent hydroplaning (but with the speeds and area touching the ground these things got, I doubt it's easy to hydroplane even if running it "backwards"), and some wheel casings are built so that there's a distinctive forward and backward-side, but they still could be ridden "the wrong way around".

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1 hour ago, esaj said:

...And even if it did run in the opposite direction (probably achievable if the phase order is changed to "correctly" reversed), wouldn't that mean that when you lean forwards, the motors would run backwards and faceplant you?

 

My thougths exactly.

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2 hours ago, esaj said:

I don't think it matters which way around the motors are installed (as long as the phase wires are connected correctly). Likely for the motor, there is no "forward or backward", at least from the winding and electronics point of view... And even if it did run in the opposite direction (probably achievable if the phase order is changed to "correctly" reversed), wouldn't that mean that when you lean forwards, the motors would run backwards and faceplant you?

At least most if not all wheels (as in electric unicycles) run similarly no matter which way you turn it, in the early days, people were actually confused which way around some of the wheel should be ridden ;)  There's of course a rotation direction marked in the tires, but that usually has to do with the pattern in the tire, when running in "correct" direction, the patterning throws water away from the middle towards the sides to prevent hydroplaning (but with the speeds and area touching the ground these things got, I doubt it's easy to hydroplane even if running it "backwards"), and some wheel casings are built so that there's a distinctive forward and backward-side, but they still could be ridden "the wrong way around".

With the MiniPro there's a clear distinction between forwards and backwards, because one way allows 7-8kph more speed than the other.  So the machine knows the difference.

At first I thought the same thing as you guys about the faceplant.  But I'm not sure if it would work that way. Please correct me if I am wrong but if the device does not sense tilt using tilt sensors that are independent of the motors and instead it detects when the motor is being turned by the COG of the rider being moved to the front or the rear, the swap should work.  And when the device detects the motors being turned by the COG shift it turns them the opposite direction to compensate and create balance. I would keep all wiring intact without switching the phases, but lengthen the wires so the motors can be swapped.  It would be as if I cut the unit in half horizontally, turned the bottom half 180 degrees and glued back on. 

Of course if I am wrong about how the tilt is detected and it is actually done with an independent tilt sensor (ie. gyro) then you are right, it would result in an instant face plant the moment the unit is powered on unless the gyro is also rotated.

 

Edited by RooMiniPro
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Well i've started my attempt at reversing the steering. First thanks to SpeedyFeet for his foot-pad dissasembly video, and RooMiniPro for his update that mentioned that removal of the rear light panel was not required to get the foot-pads off. This is the quickest way to get to the screws to remove the Control Cabin (fin). 

I will add a dissasembly tip; i used a steel spudger on the top side to release the two clips for the bumper area/front light assembly, this made it pop off easy as i didn't want to risk breaking the clips. My nylon ones were too thick.

Step One: Setup so i can measure the sensor output. I didn't have another connector set to match the one used for the steering sensor and was not ready to cut wires for this quite yet so i hacked in a temporary extension cable. (see attachment). Operates fine so no signal problems in my test environment. It's not pretty, but i wanted to get started. 

 

IMG_5487.JPG

Edited by FreeRide
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Good News!

Step Two: Measure the sensor when idle.  Stock sensor and control shaft measured 2.5xxV as expected based on measurements done on the German forum.  

Step Three: Change Control Shaft.  Wow the screws for the steering bar/Quick-Connect were some tight... they used Red Loctite on these ones, Blue is used everywhere else so far.  The shaft sold by More4Mini unfortunately is the Chinese version and it is cheap metal and it doesn't use a screw to retain the magnet assembly it uses epoxy (bas***ds).  The shaft is nicely lubed on the original, you'll have to do that yourself on the new one.  They use a good grease, but I don't know what it is.

Step Four: Measure the idle sensor voltage with new control shaft.  Also measures 2.5xxV, so far so good.  no calibration needed with the new shaft.

Step Five: Reverse the magnetic field.  Of course the adhesive on the Cheap control-shaft went where you don't want it.  It took significant effort and two small hand wounds to free one of the magnets. I slightly chipped the magnet, and some damage to the housing. It would have been easier to do the quality component.  The Chinese assembly also does not label or mark the poles on the magnets so do that before disassembly.  Re-assemble again.  It still works there is no slight turning of the MiniPro when idle. So far so good.

Step Six: Measure the control voltage with the reversed shaft.  The voltage measures 2.5xxV / 2.6xxV that is it is on the very high side like 2.59x, and sometimes 2.6xx so it has moved further away from center this was somewhat expected because I damaged one magnet and the housing so I could not get exact placement.  The good news as reported in Step Five, this change of roughly 0.04-0.05V appears to be within tolerance.  I did not have to switch off Automatic Steering Sensitivity in the app, and the steering control seems to operate exactly as before but in reverse. I may try tweaking it before final assembly.

Step Seven: Reassemble completely suitable for short road test.  Pending

Step Eight: First Road Test. Pending

IMG_5516.JPG

Edited by FreeRide
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So to summarise, you just did what I did, ie. turn the magnets 180 degrees?  You mention a new shaft and a reversed shaft.  Maybe I have missed something but can you explain what you mean by new shaft or reversing the shaft? 

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5 hours ago, RooMiniPro said:

.... can you explain what you mean by new shaft or reversing the shaft? 

The 'reversed shaft' I refer to in step six, is the new shaft with the direction of its magnetic field reversed.

More details as road operation and safety tests are done, taking a slower scientific approach and only have so much time in a given week. 

Edited by FreeRide
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On ‎05‎/‎06‎/‎2017 at 3:16 AM, FreeRide said:

The 'reversed shaft' I refer to in step six, is the new shaft with the direction of its magnetic field reversed.

More details as road operation and safety tests are done, taking a slower scientific approach and only have so much time in a given week. 

This is still not clear.  What new shaft?  Did you buy a new shaft?  It sounds to me like you just did the simple magnet polarity reversal that has already been done.

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2 hours ago, RooMiniPro said:

This is still not clear.  What new shaft?  Did you buy a new shaft?  It sounds to me like you just did the simple magnet polarity reversal that has already been done.

See Step 3 above.

See Earlier post: 6990-reversing-minipro-steering-sensor

See Earlier post: 6990-reversing-minipro-steering-sensor

Yes others have tried reversing the magnetic field, and that is why I took the scientific approach since as I stated there is no known reason yet that it should not work.  The steps I'm taking are very controlled and as such reveal information about the system and how it is designed to work, this information is analyzed to see if there is any reason that the mechanical approach cannot work due to components or construction.  The tests so far show there is no such reason.  I prefer to post only when I have solid information, so I'm documenting the steps so others can understand as they may need to make their own judgement call.

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Step Seven: Reassemble completely suitable for short road test. Completed.  

I completed the reassembly, but I left the front bumper (now rear bumper) off.  This is not critical and it saves a bit of reassembly time and wear and tear.  It has rained all day here today and most of yesterday so I was not able to start the first road test yet.  I rode it a very short distance indoors and it is working as the measurements and earlier steps would suggest.  At this low speed though indoors it only makes me more excited about the road test.

Thanks to donaldduck8 for reporting the information on the steering mechanism and sensor details, and thanks to Jes who first reported the increased speed limit in reverse.  This is a fun little diversion project for me; it is not complete until road tests and safety tests are complete.  Wednesday and Thursday are supposed to have nice temperatures and sun so hopefully a short road test in the evening will be possible.

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Step Eight: First Road Test. Completed  - Failed.

This was interesting. The steering worked perfect on level ground, but in my first general tests I found an issue so I never did ride to a place for a speed test.

It appears once the steering is altered there is another problem.  I'm pretty sure it is separate from the steering issue, and that is the vehicle does not respond correctly to uneven terrain.  There is probably something about keeping the wheel speeds synchronized or something that still seems to be in reverse.  

It's possible as that this is related to the pressure in the foot pads when titled is opposite to what it expects.  Is this what jojo33 is referring to above? What is the roll of the foot pad sensors, more that just you have your feet on the device so that it can keep things balanced?  

This issue bade the machine feel unstable even at slow speeds so i didn't attempt a longer ride where speed could be tested.

Some more tests and measurements are in order, but it looks to me like the solution is more than just reversing the steering sensor.

Edited by FreeRide
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Step Nine: reevaluate sensor bias significance.  In Progress

I did a few basic tests of the steering on a smooth surface rather then carpet and there is a offset still in the lag between left and right as one direction require more of an offset of the control arm to activate any motion.  This indicates to me that although the output of the sensor for the center position was not enough to cause the minipro to turn on it's own it was enough to affect the dead zone for the steering.  This would have affected the steering of the device when the surface was tilted as keeping the device going straight when have been more complicated and sensitive to which side was tilted.  This may be the answer, but certainly needs to be resolved first before other experiments.  The main problem here may have been having to bust the magnet out of its epoxy which distorted the housing and chipped the magnet.  Back to the lab for a day or two.

 

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  • 2 weeks later...

I'm almost sure that next official firmware release will have the check of the speed either in reverse. ...:pooping: :innocent1:

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I still stay and will remain with 1.1.7 :thumbup:

Having bought last month another unit, this time white,  I was afraid about which firmware I should found on it. ..:unsure: Luckily it was a tedious 1.2.2 so I was able to rollback either the white unit to the V. 1.1.7:thumbup:

 

Please, you're great Donald:clap3:

Saw your Video, can you test it and confirm the 25kph in reverse ?? :confused1:

Thanks

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@donaldduck8

Another question...

Going "reverse" we will have the bar attached in front, between our toes as is in the Elite and in i2 Segways ;)

Well, how to menage the illumination? ?? :confused1:

Because,  going "reverse" we will have the actual 2 front led projectors pointing rear... ad actual 2 rear led bars acting as stop when we brake,  pointing front ... :unsure:

Can the led parts be dismounted and mounted reverse ?? :confused1:

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11 hours ago, zugu said:

Saw your Video, can you test it and confirm the 25kph in reverse ?? :confused1:

No, because I have already driven with the turned magnet in the steering sensor the 25kph.
However, the steering sensitivity was very bad.
Now with reduced gain this is much better.

1 hour ago, zugu said:

Going "reverse" we will have the bar attached in front, between our toes as is in the Elite and in i2 Segways ;)

Yes indeed.

1 hour ago, zugu said:

Can the led parts be dismounted and mounted reverse ?? :confused1:

No no way.
I would disable both, in which the plugs unplugged

 

Donald

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