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Wheelchair Motors Part 2: Service

Cleaning, Replacement Parts & Reassembly

Housing Cleaned
Housing Cleaned

The housing of the contaminated motor was left to soak in diesel for a few hours to loosen the grok, this has come very clean. I couldn’t have used a stronger solvent here – the magnets are glued in place in the steel housing, I certainly didn’t want them coming loose!

Brushboxes
Brushboxes

Next into the diesel bath are the motor end bells with the brushgear. Attack with a stiff brush cleaned these up very well, some cotton buds served to clean out the brass brush holders.

Armatures After Skimming
Armatures After Skimming

Here are both armatures, having had their commutators resurfaced. I’ve completely removed all traces of the wear caused by the contamination, luckly the commutator bars are very heavy on these motors so can take quite a bit of wear before there’s not enough left to skim. I’ve not yet pulled off the old bearings, but they are all going to be replaced with new SKF bearings, as they’ve been contaminated with grok over the years of use. I’m also going to uprate the front motor bearings to rubber sealed instead of metal shielded, to help keep lubricant out of the motors if the gearbox seals ever fail again.

Gearbox
Gearbox

The gearboxes have been cleaned out with some elbow grease, assisted by a long soak in petrol, I’ve refilled them here with engine oil as temporary lube & to flush out the last remains of the old grease & solvent. The worm wheel in these boxes is bronze – so a GL4 gear oil will be required. (Some Extreme Pressure additive packs contain sulphur, and will readily attack copper alloys, such as brass & bronze).

Commutator End Bearings
Commutator End Bearings

Here’s the armatures, after the new SKF sealed bearings have been fitted to the commutator end, above, and the drive end, below. These will cause some extra drag on the armatures, and slightly higher power consumption as a result, but keeping the crap out of the motors is slightly more important.

Drive End Bearings
Drive End Bearings
Fresh Commutator Skim
Fresh Commutator Skim

The commutators have been lightly skimmed with abrasive cloth, and finished with 1500 grit emery. The armature on the right has been run for a short time to see how the new brushes are bedding in.

Old Seal Removed
Old Seal Removed

Finally, the old oil seals are pulled from the gearboxes. The worm gear bearing on the inside is actually a sealed version, with the external oil seal providing some extra sealing. I haven’t changed the gearbox bearings, as they seem to be in good order, this might get done at some point in the future.

New Oil Seals
New Oil Seals

The new seals ready to be driven into the bores.

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Wheelchair Motor Service Part 1: Teardown & Inspection

Trolley Propulsion System: Wheelchair Motor Units

So it’s time to get the propulsion system underway for the trolley, a pair of wheelchair motors were sourced for this, from HacMan. Since I don’t know how many hours are on these units, or how they’ve been treated in the past, I’m going to do a full service on them to ensure reliability. I decided on wheelchair motors due to their extreme ruggedness & heavily built components – this project when complete is going to weigh in at about 150kg!
I suspected something was amiss with one of the motors from running them under no load: the left hand wheelchair motor was heating up to the point of being too hot to touch, so this one at the very least needed some investigation.

Motor Disassembly & Assessment

Rear Cover Removed
Rear Cover Removed

With the back cover removed from the motor the electromagnetic brake is revealed. This engages when power is removed to stop the motor freewheeling, which even though it’s a wormdrive box, it will do readily if backdriven.

Electromagnetic Brake Assembly
Electromagnetic Brake Assembly

The brake is rated 6.7W at 24v DC.

Brake Disc
Brake Disc

The brake disc is just visible between the plates of the brake here, with some green dust worn off the disc. When power is applied, the top disc, just under the magnet on top, is pulled upward against spring pressure away from the brake disc, which is attached to the motor armature.

Brake Disc
Brake Disc

Here’s the brake disc, removed from the motor. There’s only a little wear here, as I’d expect – these brakes don’t engage until the motors have come to a complete stop.

Brake Actuator
Brake Actuator

The steel disc above the magnet acts as one of the friction surfaces of the brake.

Brake Solenoid
Brake Solenoid

Finally, the solenoid is at the back, partially potted in resin. The strong coil spring in the centre applies the brakes when power is disconnected.

Gearbox Grok
Gearbox Grok

Removing the top of the gearbox reveals the state of the internals – There’s no wear at all on the gearset, but the lubricant is totally manky. The external oil seals have been leaking for some time, letting water in and grease out. The emulsified result is revolting! These gearboxes have a wormdrive first stage, the worm gear is underneath the left hand gearset. Steel spur gears then do the final gearing to the output shaft. The output gear is splined onto the output, and can slide along the shaft out of mesh – this is the freewheel clutch mechanism. At the moment it’s all obscured by the disgusting lubricant.

Input Shaft Seal
Input Shaft Seal

Here’s the failed seal on the left hand gearbox, the face damage was done by petrol immersion to clean everything up. (The seal is already compromised, so I’m not fussed about solvents eating the remaining rubber). The motor shaft is joined to the gearbox input by a rubber coupling.

Output Shaft Seal
Output Shaft Seal

The output shaft seals seem to be still OK, there has been some seepage past the collar that the shaft rides in, but nothing more. This can be resealed with some Loctite bearing sealant. The sleeve is held into the gearbox by the wheel hub when in operation, but this doesn’t seal the gap unfortunately. I don’t know why the manufacturer didn’t just machine the shaft to that larger diameter, instead of using an extra sleeve to accommodate the seal.

Bore Seals
Bore Seals

The bore seals covering the ends of the shafts are also fine, which is a good thing, since I can’t seem to find replacements for these anywhere. The input shaft seals will be replaced on both gearboxes though.

Motor Contamination
Motor Contamination

The oil seal must have been leaking for a long while! This is the gearbox end of the wheelchair motor frame, completely clogged with grease. Luckily only a small amount has made it down past the armature to the brushgear.

Damaged Commutator
Damaged Commutator

The commutator of this motor is badly damaged, and the brushes are very worn. This has been caused by the gearbox oil seal failing, and contaminating the motor internals with lubricant. The undercut between the segments is all but gone – filled with an abrasive mixture of brush dust, copper dust & old lubricant. Some repair work will be required here.

Second Motor
Second Motor

Here’s the brushgear removed from the second wheelchair motor, this one looks much more normal, and there’s not as much wear on the brushes or the commutator. Just the usual coating of brush dust.

Armatures
Armatures

Here’s both armatures together, with the contaminated one on the right, after some cleaning to remove most of the greasy old grok & brush dust from everything. The windings on the damaged left hand wheelchair motor haven’t darkened, which I would expect from severe overheating damage, so I’m hoping this armature is OK, and won’t require a rewind. Using an ohmmeter on these windings doesn’t tell me much – there’s only 7 turns of 0.86mm (20AWG) magnet wire in each coil, so they read as a dead short anyway. There was some leakage between the windings and the core before I cleaned things up – this was in the high (28+) megohms range, but this seems to have cleared now I’ve given things a real good cleaning.

More to come when new bearings & seals arrive!

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eBay Mini Gear Pump Teardown

Mini Pump
Mini Pump

I got one of these to test since I’ve been in need of some small DC pumps for fluid transfer use. At £2 I can definitely afford to experiment.

DC Motor
DC Motor

On the eBay listing, these pumps are rated at 3-12v DC, (I thought that was a bit wide of an operating range), I looked up the motor, an RS-360SH on Mabuchi’s website, they only have models in this range rated at 7.2v & 24v. Judging by the size of the windings on the armature & the fact that after a few minutes operation on 12v it gets rather hot, I’m going to say this is the 7.2v motor.

Pump Gears
Pump Gears

Removing the screws releases the end cover & the pair of gears inside. This operates like any other hydraulic gear motor, albeit with much wider tolerances. It has no capability to hold pressure when the power is removed, and can be blown through easily.
Flow & pressure under power are quite good for the pump’s size, even though it’s noisy as hell.