So now that we have the entire Neato robot vacuum system including charging dock, it’s time to see how did they perform at the job they were built to do. Not that their performance was important, as I bought my Neato intending to scavenge it for parts and it was only a happy accident to end up with a fully functioning robot vacuum. But before I start having fun with robot experiments, I should at least see how it works in its original capacity. Mostly just from curiosity, but if I’m going to show up at places with a modified robot vacuum, I also expect to be asked by people if it’s worthwhile to buy one to vacuum their home. Those who paid full price for their robot vacuums will have very different expectations from people like Emily and I who picked up our robot vacuums for cheap at a thrift store.

The common wisdom with Roomba robot vacuums is that they still miss a lot of surface area due to their random walk nature. A Neato, with its laser distance scanner, is supposed to provide full ground coverage. In reality, all open spaces are indeed very efficiently covered. However, the laser scanner meant a Neato is less effective at cleaning edges and corners. Because they’re smart enough to not run into edges and corners, a Neato’s cleaning brush never get close to those areas. We can see this most clearly in this picture of a dusty doorway after a Neato vacuuming pass, showing the smooth path it took swerving around a door frame instead of digging in and cleaning out those corners. (Note: my house is not quite as disgusting as the photo implies: the contrast has been exaggerated via Photoshop.)

And naturally a little robot vacuum would not be able to move furniture out of the way. For example, floor under the dining table is not vacuumed, because the dining chairs legs all around the table blocked access. But it turned out the dining table itself was an obstacle. Just as my earlier experiment with Neato scanner had problem seeing certain furniture features, an actual Neato was unable to see the ramp-like shape of my dining table legs and managed to launch itself into an awkward angle and got stuck.

As a home of a tinkerer, my house had many other features unfriendly to robot vacuums. My Neato kept getting itself tangled up in power cords for various AC-powered electronics gadgets, and of course there are piles of stuff all around the house in odd shapes, some of which share the “important features are out of sight of laser scanner” problem with office chair and dining table. There may be homes where a Neato would be a productive little housekeeping worker, but I’m afraid my home is just too much of a hazardous environment for this little Neato to be effective.

Which is great! I now feel less guilty about relieving it of vacuum duty and put it back to work for the reason I bought it: as a chassis for robotics projects. But it was fun to see a Neato in action doing its job. It was enlightening to see its own mapping and routing software at work, a benchmark to compare against for my own code driving this chassis. It is a really endearing little robot, with friendly messages on its LCD screen and my favorite part: the way it cuddles its charging dock. And now that one Neato is back up to full running condition, [Emily] and I will team up and try to get them both running.

The Neato XV-21 I found at a thrift store has bee joined by a XV-12 found by [Emily]. Both Neato robot vacuums found at thrift stores have degraded batteries. This was not a surprise as robot vacuums work their battery packs hard. Not just frequent charge and discharge cycles, but with a heavy power draw under use to run vacuum motors. This means both of these vacuums were retired by their previous owners when the battery no longer hold enough charge to perform its duties.

Fortunately, this common failure also meant there’s a robust aftermarket for replacement batteries. Curiously, the economics of the markets are such that whole replacement packs can be ordered online for less than ordering individual cells and rebuilding the packs myself.

With previous experiments, I have gained confidence I can verify functionality of individual components using test mode accessible via USB port. And since this XV-12 was found with an official Neato charging dock, it’s time to install replacement batteries and test the full system.

The replacement batteries claim a capacity of 4000mAh which, on paper, is an increase from the original battery’s label capacity of 3800mAh. However, battery manufacturers play pretty loosely with these ratings so I expect the difference of 200mAh to be fairly insignificant in practice. When I took apart the original pack, I saw a thermister for monitoring temperature, an overcurrent protection fuse, and an overheat fuse. I assume the replacement pack has a thermister because the Neato computer can read it, but there’s no immediate way to tell if the overcurrent or overheat protection also exists on the new pack.

With new battery packs installed, it’s time to put the robot up against the charging dock and verify the charging system works as expected. But before we do that, let’s take a closer look at this charging dock.

When I looked over my Neato XV-21, I thought it was far too clean to be a high mileage appliance. There were several possibilities:

1. The previous owner was meticulous about keeping things clean (supported by the plastic protective wrap.)
2. The Neato was barely used.
3. A Neato is very good at keeping itself clean.

Thanks to a second Neato found in a thrift shop, this time a XV-12, we now know #3 is false. This one is well used, and very much looked it! The previous owner didn’t bother cleaning the vacuum before dropping it off at the thrift store. I have several loops of hair tangled up in the roller brush. The largest loop has even snagged what looked like furniture padding foam.

The largest loop has also tightened enough to damage the roller brush. Once I cut that loop of hair and debris off the roller brush, I see a slot cut into the rubbery blade.

There was also debris tangled on the motor shaft driving this roller that had to be cleaned off before the roller brush could function properly again. The cavity for the roller brush showed extensive wear from a life as a working household vacuum (above), whereas the XV-21 showed barely any wear (below).

Those were problems found on the suction side of the vacuum. What about the exhaust side? The vacuum is generated by a fan which sat downstream from the dust bin filter, so its cleaniness would be a clue at how effective the filter was. Everything seen here are dirt particles that have made their way past the filter.

But even though this vacuum lived a harder life, its battery was actually in better condition and could run the vacuum computer for several minutes before fading out. As a result I was able to query all components individually using its USB port without having to hack a battery into this vacuum. All signs indicate that this robot vacuum is likely fully functional except for its battery.

And fortunately, with the arrival of replacement battery packs, we don’t need to drill holes and hack external battery packs for a full system test. We can install the new batteries into this XV-12.

 

I thought I was pretty lucky to find a Neato robot vacuum in a thrift store for $8. It didn’t work in the store and that’s why it was cheap, but I have since determined it was fully functional except for its battery pack. While waiting for its replacement battery pack to arrive, Player 2 has entered the game! [Emily] managed to find another Neato robot vacuum in a different thrift store. The new find is a model XV-12 and it included the charging dock for $11.

A little web research indicated that these two robot vacuums are contemporaries, both followed up Neato’s XV-11. The XV-12 is the direct successor that replaced the XV-11, and the XV-21 is a premium offering sold simultaneously with the XV-11. Aside from the cosmetic difference of purple plastic top on the XV-12, there are a few functional differences.

The cleaning brush roller is different. The XV-12 uses a bidirectional design with flat flexible plastic blades. The XV-21 uses a unidirectional design with a combination of flexible plastic blades and bristles. The XV-12 brush can be mounted in either direction – note that geared teeth to engage the toothed belt on both sides of the roller. The XV-21 is designed to spin a specific direction – brushing debris towards the center of the vacuum – and only has geared teeth on one end of the roller because it won’t work properly if mounted the other way.

The dust bin filters are also different between these two models. While the XV-12 uses a flat sheet, the XV-21 uses a pleated design for greater surface area. This partially compensates for the more restrictive filter used in a XV-21 that captures more particles from the vacuum air stream.

The XV-21 was sold as the upgrade model. Its roller brush with curved flexible blades and bristles combine to pick up more dirt, and its pleated filter keeps more of that dirt in the dust bin instead of passing it into the exhaust. These two differences reportedly improve vacuum capability at the cost of greater power consumption which translates to shorter run time on battery.

In addition to the design differences between the XV-12 and the XV-21, there are additional differences between these two specific thrift store finds. The XV-21 was surprisingly clean hinting at a very low usage in its previous life, but the XV-12 shows signs of a well-used robot vacuum.

 

With a successful all-up system test of Neato XV-21, running on hacked-up battery packs through a full vacuum cycle, we have confidence everything works on this thrift store bargain except for the battery pack. So focus returns to these NiMH battery packs.

The default option is to buy some battery packs specifically built and sold as replacement batteries for a Neato robot vacuum. A straightforward Amazon search for “Neato battery pack” will return this “Amazon’s Choice” item (*) at $30 for 4000mAh NiMH packs.

A tempting choice is to purchase some lithium-ion batteries that would also fit in the Neato battery bay. However, battery packs sold on Amazon are typically designed for very high draw applications like multi rotor aircraft. Batteries designed to survive such use tend to have lower energy density. Thus lithium packs that fit within the bay’s dimensions actually don’t have much significantly higher capacity than 4000mAh.

Another concern with installing lithium batteries is the fact the Neato’s on board charging circuits are designed for NiMH battery cells, which has a different charging profile. Charging lithium cells as if they were NiMH cells risks damaging the lithium cells and possibly lighting them on fire.

There is, however, this item (*) which are lithium replacement packs intended and designed as an upgrade option for Neato vacuums. Not only are they sized appropriately to fit, they also have an integrated battery management system. Presumably, the circuit will make the Neato brain think there’s a NiMH battery pack installed but treat the lithium cells properly. At 4400mAh it offers 10% higher claimed capacity relative to default option, but at over double the cost, the cost/performance ratio is poor.

There is also the option to purchase new NiMH battery cells and rebuild the battery pack myself, reusing all the associated parts from the existing pack. I had expected this to be the lowest-cost option by supplying my own labor, but when I searched for NiMH battery cells in 4/3A form factor with 4000mAh capacity, I was surprised to find that they were selling for more than $3 per cell. There are 6 cells per pack and a Neato requires two packs, for 12 total cells. This means buying raw cells and rebuilding them myself would cost over $36, more than just buying a prebuilt pack from Amazon!

With this little bit of research into lithium upgrade option and rebuild option, it looks like the default $30 option is the best way to go. But before that replacement battery pack arrived, my Neato got a friend!

---

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

Using small batteries I hacked into existing battery bays, I was able to query sensor status and command individual motors. However, those small batteries were not powerful enough to run multiple motors simultaneously, which meant a full system test would not be possible until larger batteries are installed. At this point I could order some Neato-specific replacement batteries and have decent confidence it will work, but I would like additional confirmation before I spend money.

But I didn’t have any batteries that were more powerful and still small enough to fit within Neato vacuum’s existing battery bays. This meant batteries had to be installed externally. And if they’re going to be external, I might as well go with the biggest batteries I have on hand: those I purchased for Sawppy the rover.

But where could I install those batteries?

The most obvious place: is to put them on top of the dust collection bin. This is a popular location for Roomba battery retrofits, because it preserves weight balance and does not hinder Roomba operations. However, it won’t work for a Neato: this position blocks the line of sight for the laser distance scanner.

Installing the batteries on the front bumper would be out of lidar line of sight, and might help improve vacuum performance because their weight would help push the dirt brush roller into the ground. But this would change the behavior of front bumper which might confuse vacuum mapping algorithms, and using fragile batteries as your front bumper is never a good idea.

If we put batteries off to the sides, it preserves front clearance but now it interferes with side clearance. The vacuum would no longer be able to follow along walls closely to vacuum near walls if the batteries are attached to the sides.

Installing behind the vacuum disturbs the weight balance – battery weight is now trying to lift the brush roller off the ground. The back is not flat, making installation difficult. And that circular shape is there for a reason – its clearance helps the robot turn in tight spots. Batteries install behind the robot would get bashed against obstacles as the robot turned.

And obvious we don’t have any way to mount batteries on the underside of the vacuum, as there is only about 5mm of ground clearance. That exhausts all the potential directions we can go for external mounting.

Time to get creative.

Rethink top mounting, we recognize the problem is that we can’t block laser distance scanner’s line of sight. It looks out all around the top of the vacuum, except for one place: the raised protective cap above the lidar housing. Batteries mounted on top of that cap would not block laser scanner’s line of sight.

Wires were run from battery compartment, which required drilling two small holes. To keep the power wire out of sight of lidar, the wires were routed through existing grooves on top of vacuum body and then followed existing  support pillars for lidar housing. This way, the wires should not introduce additional blind spots.

With this hack, the robot vacuum can run on my pair of Sawppy rover batteries, which are plenty powerful enough to run all vacuum systems simultaneously. Now this little Neato is alive and can run through a full vacuum cycle, verifying that all systems worked.

Obviously, this won’t be the final long term solution. For one thing, Sawppy wants its batteries back. For another, the additional height on top of the robot hampers its ability to get under furniture for vacuuming, and the exposed wires are vulnerable to tangling on protrusions. What we need next are batteries powerful enough to run a Neato and fit within existing battery bays.

With the experimental batteries in place, the computer boots up and stays up for longer than three seconds. I tried to run a vacuum cycle but that was too much for these batteries to handle, so for now I’ll stick with digital exploration starting with the standard UI to dump revision information on components inside this particular Neato XV-21 robot vacuum.

After that, it’s time to go exploring through its USB serial port diagnostics!

I went straight to the most interesting component: the laser distance scanner module. First I had to put my vacuum into test mode with testmode on. Followed by setldsrotation on to turn on the motor that sweeps the laser. And finally, fetch a set of laser distance data with getldsscan. This gave me a large set of numbers. According to the legend given in the first line of the response, a distance and intensity number per degree of sweep. Partial excerpt below:

AngleInDegrees,DistInMM,Intensity,ErrorCodeHEX
0,2378,82,0
1,2397,88,0
2,0,88,8021
3,2494,85,0
4,2505,82,0
5,2509,12,0
[…]
355,2289,99,0
356,2303,103,0
357,2303,99,0
358,2315,94,0
359,2367,91,0
ROTATION_SPEED,5.10

Future experimentation will determine what range of distance values are typical, similarly for intensity values. A quick web search failed to find a reference guide for error hex codes, but hopefully there’ll be a small set that I can infer from context. More exploration to come!

In the meantime, I repeated the getldsscan command to verify the values are getting updated. They were – I received a similar but slightly different set of numbers. Hooray! the most important sensor looks like it is functioning.

Next item on the exploration list: querying analog sensor values with getanalogsensors.

SensorName,Value
WallSensorInMM,63,
BatteryVoltageInmV,16120,
LeftDropInMM,60,
RightDropInMM,60,
LeftMagSensor,-2,
RightMagSensor,-3,
UIButtonInmV,3317,
VacuumCurrentInmA,0,
ChargeVoltInmV,132,
BatteryTemp0InC,34,
BatteryTemp1InC,31,
CurrentInmA,622,
SideBrushCurrentInmA,29,
VoltageReferenceInmV,1225,
AccelXInmG,-8,
AccelYInmG,-12,
AccelZInmG,1092,

I see three distance sensors – wall and two drop sensors, one in each front corner. It’s not immediately clear what “Mag” in left and right “MagSensor” referred to. Do they detect magnetic fields? Or are they measuring magnitude of something? Bottom three lines indicate the vacuum sensor suite includes a three-axis accelerometer which can measure in units of thousands of G, implied by a Z value nearly 1000 in this vacuum sitting on the floor. Remainder of the values are related to power management.

The 3-axis accelerometer values above from getanalogsensors partially overlap with results of getaccel. As the name indicates, this one is completely focused on accelerometer readings and includes results of additional calculation in the form of pitch and roll in degrees and a sum of acceleration vector.

Label,Value
PitchInDegrees, -0.64
RollInDegrees, -0.53
XInG,-0.012
YInG,-0.010
ZInG, 1.079
SumInG, 1.079

The list of digital sensor values from getdigitalsensorsis shorter, and for whatever reason, labelled in all capital letters.

Digital Sensor Name, Value
SNSR_DC_JACK_CONNECT,0
SNSR_DUSTBIN_IS_IN,1
SNSR_LEFT_WHEEL_EXTENDED,0
SNSR_RIGHT_WHEEL_EXTENDED,0
LSIDEBIT,0
LFRONTBIT,0
RSIDEBIT,0
RFRONTBIT,0

Here we can see whether the dustbin is installed, whether either or both wheels are at full extension, and it looks like there are four switches associated with the front bumper. The top line shows if a charging plug is connected, but that’s only one of many parameters around power management. Most of the rest are in getcharger.

Label,Value
FuelPercent,88
BatteryOverTemp,0
ChargingActive,0
ChargingEnabled,0
ConfidentOnFuel,0
OnReservedFuel,0
EmptyFuel,0
BatteryFailure,0
ExtPwrPresent,0
ThermistorPresent[0],1
ThermistorPresent[1],1
BattTempCAvg[0],33
BattTempCAvg[1],31
VBattV,16.03
VExtV,0.16
Charger_mAH,0

If I were to create my own control logic for driving my Neato around, the most important parameter here is FuelPercent. I’ll have to be responsible about not draining the battery too far, beyond that I can leave the rest in the capable hands of Neato’s existing battery management system. Speaking of power consumption, the biggest drains are the motors, and I can monitor them all with getmotors.

Parameter,Value
Brush_RPM,0
Brush_mA,0
Vacuum_RPM,0
Vacuum_mA,0
LeftWheel_RPM,0
LeftWheel_Load%,0
LeftWheel_PositionInMM,-1
LeftWheel_Speed,0
RightWheel_RPM,0
RightWheel_Load%,0
RightWheel_PositionInMM,-1
RightWheel_Speed,0
Charger_mAH, 0
SideBrush_mA,28

Not very exciting at the moment, because all motors are at a stop. I imagine these numbers will get more interesting once the robot gets underway.

One final discovery in inputs: when in test mode, the user interface buttons on the top of the robot no longer trigger their usual functions. I could check for status of all five buttons via getbuttons which implies I could use these buttons in my own projects without worrying that I’ll trigger the default vacuum behavior. Cool!

Button Name,Pressed
BTN_SOFT_KEY,0
BTN_SCROLL_UP,0
BTN_START,0
BTN_BACK,0
BTN_SCROLL_DOWN,0

But if I want to actually have my own user interface using those buttons, I would need to also display my own information on the LCD. Which brings us to phase 2 of playing over USB: start sending commands to see if components follow orders.

My Neato XV-21 vacuum couldn’t power on when I found it in a thrift store, and the problem (or at least, the first problem) was its battery pack: it could only deliver enough power to boot up the onboard computer and run it for about three seconds before its voltage dropped and the computer shut down again.

In order to assess the rest of the vacuum, I need to find a replacement power source. Since the actual condition of vacuum components are still unknown, I’m not inclined to spend money buying batteries specific to a Neato robot vacuum. The next experiment, then, is to wire up something out of batteries already on hand. I looked through my pile of batteries to see which would satisfy the following criteria:

• Delivers roughly 7.2 volt power of a six-cell NiMH battery.
• Fits within Neato battery compartment.
• A pair of identical batteries, one for each bay.

The winner was a pair of batteries I had for my E-Flite remote control helicopter. The aircraft itself had long since been crashed and trashed, but I kept its batteries. Two cell lithium polymer batteries have nominal voltage of 7.4 volts, within operational range of 6-cell NiMH batteries. Physically they were small enough to fit within the battery compartment, but at 800 mAh their power capacity is too low for full vacuum operation. They were designed to deliver high power to fly a small helicopter toy though only for a few minutes. Ideally they can run the vacuum motors briefly to verify their operation, but mostly I just need them to run the Neato computer for more than three seconds.

To connect these batteries, I first disassembled the old tired original battery pack. Before disassembly, I noticed a rectangular bump visible in the battery pack. I had thought this was the thermistor but I was wrong. It appears to be a temperature safety fuse. There was also an over-current protection amperage fuse in the pack. NiMH cells are relatively safe but it’s still good to see additional safety measures inside these packs.

 

I needed the battery pack’s wiring harness for my battery experiment, so it was cut free. I kept the temperature monitoring thermistor and wired the positive and ground battery power wires to a JST-RCY connector that will mate with my E-Flite battery pack.

Once soldered, I connected the pair of batteries and plugged them into my Neato XV-21.

I was greeted by the same boot-up screen I saw before, but this time the screen stayed on instead of flickering off after three seconds. Now it’s time to try talking to the vacuum.

 

The batteries from a Neato XV-21 were found to be flat and possibly damaged. This would certainly explain why the little robot vacuum failed to power on in the thrift store where I found it. Since the thrift store didn’t have its associated charging base, my fallback was to leave its batteries to trickle charge (at 100 milliamps) overnight on a bench power supply.

The battery packs nominal voltage was listed at 7.2 volt per pack, so the voltage limit for charging the pair in series was set to 14.4 volts. Fully charged six-cell NiMH battery packs can be up to 9 volts each, for 18 volts total, but setting to 14.4 volts leave us with a bit of headroom in case these batteries didn’t behave as expected. This turned out to be a good idea.

When I checked in on the batteries the next morning, I saw voltage sitting at 14.4 and amperage had dropped to 40 milliamps. If all goes well, the voltage would be evenly divided across the two packs at 7.2 volts each. This was not the case: one battery pack (I’ll arbitrarily name it pack A from now on) was holding at 7.9 volts and the other (now designated pack B) at 6.5. If it weren’t for the headroom, we might have inadvertently pushed pack A beyond its limits.

At this point I got distracted by other events and left the batteries sitting for a week. Checking in from time to time, I measured their open circuit voltage and wrote them down. It was an unplanned test of the batteries’ self-discharge rate.

Pack A:

• Overnight trickle charge: 7.9 Volts
• After one day: 4.67 V
• After three days: 4.44 V
• After a week: 2.0 V

Pack B:

• Overnight trickle charge: 6.5 Volts
• After one day: 2.77 V
• After three days: 2.68 V
• After a week: 2.61 V

While it is normal for NiMH batteries to self-discharge over time, this observed discharge curve was far more severe than is acceptable. Looking at the voltage discharge behavior for pack A, it appears to have two almost-useless cells, three weak cells, and one good cell. Pack B behavior hints at four almost-useless cells and two good cells.

But even if they are unusable to actually run the vacuum, they are still better than dead weight: these batteries can hold a charge for a very brief period. So they’re reconnected to the power supply to trickle charge again. I don’t expect them to actually power any motors, but perhaps there’d be enough to power on the electronics for a short while. Hopefully long enough for me to assess if the rest of the vacuum is healthy.

After another overnight charge, I plugged them into the vacuum and pushed the power button. Good news: they did power on the electronics for a short while. Bad news: It only lasted for three seconds, far too short to assess anything else about the vacuum. But the vacuum computer did boot, and that’s enough motivation to keep going.

We’ve pulled the battery packs out of a Neato XV-21 found in a thrift shop. We’re pretty sure the red and black wires are battery positive and ground, but if so we expect to see a few volts across those wires. The fact we measured less than a volt indicates this battery is flat and may even be damaged. Well, at least this would be consistent with the fact it wouldn’t power on in the thrift shop.

Fortunately, rechargeable NiMH battery cells are hardier than lithium batteries and they might possibly revive with a charge. And even if they were permanently damaged, they are less likely to turn themselves into fireworks as damaged lithium batteries sometimes do. Since we read a nonzero voltage, none of the cells have failed as an open circuit. Some might have failed as a short circuit acting as a resistor dissipating energy but not holding the charge. With this unknown, we shouldn’t charge the batteries anywhere near as fast as we could if they were known to be healthy.

A bench top power supply was set to a maximum voltage of 14.4 volts and maximum amperage of 0.1 amp (= 100 milliamps). Using a piece of wire, the two battery packs were connected in series. (Which is where the 14.4 came from: adding up their nominal 7.2 volts per pack.) Once connected in series, they were connected to the bench top power supply and we watched the meters.

If we instantly hit maximum voltage and maximum amperage, it indicates a short circuit somewhere, possibly in a dead battery cell acting as a resistor turning that 1.44 watts into heat. Fortunately this did not happen. We hit the 100 milliamp limit immediately as expected and the voltage started rising, which is consistent with a battery pack trying to charge.

After a few minutes, we disconnected the power supply and measured battery pack voltage: they now measure a few volts, higher than before. This increased confidence that our positive/negative wiring guesses were correct and also proof at least a few cells can hold some amount of charge.

The batteries were reconnected and, for the first half hour, we periodically touched each of the cells to see if they were hot to the touch. Some of the cells were warmer than others, but none were alarmingly so. We’ll let the power supply continue slowly feeding the battery pack overnight and see how they behave.