Mammotion Luba 1 Wheel Hall Sensor Replacement

ID: 220075

Description: If your Luba 1 has started to go lame, ie one...

Steps:

1. To start with get the Luba on a bench, remove the safety key, remove the front bumper, turn it upside down, clean it, and remove the blade holders and the under guards, then the screws needed to open up the mower (there are a few videos on youtube on how to do this).
2. To positively prove it is a hall sensor failure you need to get inside the motor hub, so you need to get the wheel off the mower. This explanation is for a rear wheel hub, I wouldn't expect it is much more different for a front wheel.

3. To remove the wheel, trace the wire from the failed wheel, cut off the cable ties releasing the cables, unplug the two plugs from the wheel cable to the main board, the larger one is the power, the smaller white plug is the hall sensor and temp sensor connections.
4. Start to pull the cable back, freeing it as you go, if it is a rear wheel you will have to hack away the silicon sealant just in front of the rear axle. I used some thin nosed pliers to keep grabbing chunks and pulling it out. Be carefull to not damage the main power cables that run underneath the wheel cables.
5. Remove the five screws holding in the rear axle, there should be enough slack in the cables to turn the axle upside down exposing the four screws that keep the wheel holding plates on. Undo the four screws, clean away any rubbish, then if you rotate the wheel backwards and forwards it should knock the plate up enough to be able to lever it off.
6. The whole wheel spindle should slide out, feed the cable out of the rear axle casing, which can be tricky with the two cable connectors. You should now be looking at a complete wheel hub.
7. When I was diagnosing this issue for the first time, at this point I decided to switch the rear hubs around, so I removed both as described, switched the wheels over left to right, put the mower back together, and the fault had switched sides, so I had definitvely confirmed the fault was in one specific hub, not the main mower boards etc.

8. Undo the screws holding the wheel "hub cap" off, prise the hub cap off, and then prise the tyre off the hub with both hands holding the outside of the tyre and pushing with your thumbs inside the hub, so the tyre comes off.
9. Clean the outside of the exposed hub, you don't want anything getting inside the motor. Undo all of the screws on both sides of the hub. The outer side of the hub holds three planetary gears, so be careful when you split the hub open.
10. Start to split the hub by holding the main hub body spindle side up and pulling the inside cover off upwards towards spindle side, work you way round evenly so that the cover comes off all the way round, then remove the cover over the spindle and cable.
11. You should still have the hub with the spindle vertically up, and you can then pull the spindle upwards while still holding the hub, this will remove the motor whilst keeping the planetary gears intact.

12. From the outer side of the motor undo the three plate retaining screws, then the outer circlip, then remove the retaining plate and then the second circlip.
13. You should be left with the motor stator and rotor still attached to the spindle. We are now ready to test the hall sensors and find the faulty one.
14. Looking at the exposed circuit board you should see the three hall sensors inserted into the stator, mine were two green outer and one red in the centre. You will also see other cable which is the wheel temp sensor.
15. You need to scrape away the silicon sealant to expose the solder joints of the middle and right hand joint for each of the hall sensors, so you can get a multi meter on both joints.
16. Put your multi meter into diode mode, put the red lead onto the middle joint and the black lead on the right hand joint. A good hall sensor should have a value of around 0.63, my broken hall sensor gave no value at all.
17. Whilst at this point it is worth testing the continuity of the whole wheel cable, so I exposed all of joints on the circuit board, put a small copper wire in the cable plugs and checked for continiuty and any shorts across.
18. This is a lot of work just to get to the point of proving it is a hall sensor failure, as you can see, all of the motor control circuitry is on the main board inside the mower, so there is very little to go wrong, however I have read of some hubs getting water ingress which has failed the motor.

19. To get access to the sensor, you first need to pull the rotor off the stator. I clamped the spindle firmly in a big vice, and with both hands pulled the rotor very firmly off, there is a strong magnetic field so pull it evenly and strongly and it will come off.
20. Always be carefull how you handle the rotor as the permanent magnets are brittle, so treat with care.
21. After identifying the failed sensor, get your magnifying glass out and read the markings on the failed sensor. Mine was the right outer one and was marked Y3141 with a second number below.
22. I didin't know enough to know if I could use a "similar" hall sensor with close specifcation that I could source locally and quickly, but it wasn't the exact same Y3141. So I decided to play it safe, ordered on Aliexpress, and waited the 12 days for it to come, £5 for 5 including postage, so £1 unit cost.
23. Clear the silicon off the three joints of the failed sensor, with thin nosed pliers, and then with a sodering iron, pull off the three connectors, then use a solder sucker to clear the solder from the holes on the board, this is essential, as you will not be able to get the new sensor wires in before soldering.
24. Using a stanley knife, start to hack out the old sensor, you have to be quite brutal to get it all out, then clear out the sensor hole with a small file to make sure you have got rid of it all, the new sensor is a tight fit.
25. Trim the legs and the insulation of the new sensor so that it replicates the old one, then bend the ends of the sensor cables, push them through the underside of the board and resolder.
26. With thin nose pliers, gently fit the new sensor in the stator, when you are sure it will fit properly, prize it out a little way, put a drop of super glue under the sensor, push it back in fully and hold it until it sets.

27. I would recheck your new sensor with the multi-meter before recovering the board with silicon to re-seal the board.
28. Put the spindle back in the vice and put the rotor back on the stator, hold the rotor firmly with both hands and keep it inline as you put it back on, as you get near it will pull it back on strongly, so make sure it doesn't damage anything as it goes back on.
29. Put the circlip back on, then the retaining plate and three screws, then the last circlip.
30. The rest is a reversal of disassembly, I added a little more grease to the planetary gears while I had access, and make sure you reseal both end plates of the hub with silicon before screwing it together, it is imperitive it is water tight.
31. You will need to reseal the joint where all of the cables come into the main body of the mower in front of the rear axle, and secure the cables with new cable ties.