Gearbox

[snaker]

I am going to buy replacement gearboxes for my chair. I found them on mobilityscooterpart.com and I contacted to the seller. They sent me the gearbox specs as in the attached images underneath. The ratio 25:1, shape, dimensions are all correct. But I do not understand about the parameters e.g 300W/5300RPM. Do they match the motor specs? My motors are 450W but I do not know their RPM.

The seller asks me if I need 300W/5300rpm/25:1 or 450W/25:1 gearboxes? I am confused, does a gearbox have a power e.g 300W/450W? And does a 450W gearbox has the same size as 300W or bigger? How can I calculate the RPM? My chair speed is originally 12.5kph with 14inch wheels.

[Burgerman]

I am going to buy replacement gearboxes for my chair. I found them on mobilityscooterpart.com and I contacted to the seller. They sent me the gearbox specs as in the attached images underneath. The ratio 25:1, shape, dimensions are all correct. But I do not understand about the parameters e.g 300W/5300RPM. Do they match the motor specs? My motors are 450W but I do not know their RPM.

Motor watts dont tell you a thing. Two identical motors, spray one black, and it radiates heat better. So now its a higher wattage motor. RPM is more useful. It tells us what gear ratio we need to go x speed. But the ratio is the same 25 to 1 so that will be the same speed.

The seller asks me if I need 300W/5300rpm/25:1 or 450W/25:1 gearboxes? I am confused, does a gearbox have a power e.g 300W/450W? And does a 450W gearbox has the same size as 300W or bigger? How can I calculate the RPM? My chair speed is originally 12.5kph with 14inch wheels.

Presumably they THINK a 450 watt motor is more powerful. It may be. Or it may not. That depends on impedance. Not watts. But I suppose tht their 450 watt gearbox may have stronger internals or a different sized cush drive motor coupling. The ratios are the same, so the gearbox will give the same speed.

[snaker]

Why do they offer 2 options: 250W, 4000RPM and 300W, 5300RPM? Does Watts parameter relate to RPM? More watts equal more RPM? To know the correct gearbox Watts, we have to know the motor's RPM. Is it right?

[snaker]

Is the formula to calculate RPM below correct?
RPM = 25 * SPEED / (PI * D)
SPEED = 14.5km/h (the actual speed) = 241.7m/minute
D = 14inch = 0.36m

The result is RPM = 5408 => the 300W, 5300RPM gearbox is suitable?

[Scooterman]

I found them on mobilityscooterpart.com and I contacted to the seller. They sent me the gearbox specs

I've purchase from them a couple of times. I reckon they're a really good company.

[Scooterman]

Motor watts dont tell you a thing. Two identical motors, spray one black, and it radiates heat better. So now its a higher wattage motor.

Good point (and it's the same principle with cables)

Most AC motors have lateral cooling vanes running down motor and a fan at one end to draw the air over them. DC mob motors could have low profile cooling vanes moulded into the casing. They wouldn't need to be that pronounced or necessarily need a fan, and would surely act as a better heat sink than a smooth steel/alu casing?

Yes/No?

But then I suppose if they were needed mob motor manufacturers would incorporate them?

[Burgerman]

Induction motors are actually rated in watts though... They dont draw zero or almost free running and huge currents under load, and a wild current stalled.

A typical mobility 250W or 400Watt Perm. Magnet DC motor is coupled with a 70A ot 100 Amp LIMITED controller.

My 4 pole 250 watt motors fitted to the salsa, are a typical example. That 250w just gives an approx guide to the power they are ALLOWED to sustain continuously. But then consider the ACTUAL electrical power they really use.

24V and a 120A limit (the max the controller allows) means 24V multiplied by 120A gives us 2,880 watts. Somewhat more than that rated 250W !!!

Now, lets consider the same with the 400 watt motor. The exact same 2,880 watts...

++++++++++++++++++++++

So to determine motor TORQUE and the chairs SPEED we only need some simple figures. And watts are no use to us.
We need the free running RPM not of the motor, but at the wheel. To equalise this over with different wheel sizes, and different gear ratios we just need to look at speed at 24V (max chair speed im MPH or KPH. And we need to know MAX stall amps, and free running Amps. We can call that zero, but because of some friction it will be 5 or 6 Amps. Which is pretty much the same regardless of motor. From this, and because of the controllers limit we know everything we need. With the exception of efficiency. This varies from approx 55% up to 70% across almost all powerchair motors at BEST efficiency. And thats usually at around 90% max speed. At slower or faster speeds its much worse. At stall for e.g. the efficiency is zero. You go zero miles, and maximim Amps.

Watts never enters into this. All that really matters is efficiency, stall current (or motor impedance, and lower is better as long as the wiring is adequate). Half the impedance = double the range at a given speed. So when somone tells you they have 450 watt motors you can laugh at the idea.

This is a 6S 100A (25.6V) motor. And it runs at this in flight continuously. So its rated as safe at 780 watts, but in use, its heavily overloaded and running as a 2560 watt motor... And its 95% efficient so barely gets hot at approx 45,000 rpm while making over 3 horsepower. This is due to good construction, brushless, and just 2 motor turns, so ultra low impedance. And 4,000rpm per volt.

[woodygb]

The seller asks me if I need 300W/5300rpm/25:1 or 450W/25:1 gearboxes? I am confused, does a gearbox have a power e.g 300W/450W? And does a 450W gearbox has the same size as 300W or bigger? How can I calculate the RPM? My chair speed is originally 12.5kph with 14inch wheels.

It's a bit more complicated than just watts.

https://www.parvalux.com/resources/choosing-your-motor

Personally I'd go with the higher 450W.

[LROBBINS]

Do remember that the RPM at the axle will be motor RPM/gearbox ratio. If the two motors have different RPM, the axle RPM will also be different unless you change the gear ratio.

[shirley_hkg]

If everything , casing , gear ratio … are indifferent , then hope they have difference in materials of the drive gears , synthetic / metal .

Or just marketing gimmicks otherwise.

[snaker]

The seller gave me the quote for a set of 2 gearboxes: $278 + $96 shipping = $374 + 2 months waiting. It is too expensive for 2 simple gearboxes.

Why do Chinese companies can sell a full chair with correctly those motors for $1.000? The chair is not a toy, it is fairly good. I am using it.
https://enjoycare.en.alibaba.com/produc ... 6a67CteraJ

[woodygb]

The price increases each time the gearbox is " bought and sold " ....

Let's say ... Gearbox is imported into the States from China ...Importer doubles or triples the price as it's landed... sold on to Monster Scooter parts.....then sold on to you at double the price Monster scooter parts paid.

Everytime someone handles it and passes it on the price increases.... and seeing as how it's "mobility" who knows what mark up they have all used!.

[Burgerman]

Not to mention tax, on top of profit, over and over.

Plus, the person building the chairs may be buying 1000 motors at a time complete. So gets much discount.
Buying parts which are sold in one or two at a time, involves storage, losses, inventory / stock keeping, parts left on shelves for long or indefinite time while a company is running on an overdraft, and paperwork, shiping and packing for one part at a time. And all of this increases cost.

I can sell you a pallet of batteries, about 48, at almost half the cost of individually. I can send you a container full at half of that again.

[Burgerman]

These are cheap https://www.alibaba.com/product-detail/ ... 3582Fs8umk

[snaker]

My dad decides to take gearboxes apart and replace oil inside them. He will use oil that is popularly used in bikes/cars here.

[Burgerman]

All the ones I ever looked in were grease.

However. It may be better to just have a spare set of motors on the shelf. They generally wear out as a unit. So ultimately pointless replacing bearings, gears, brushes etc. The magnets lose power and efficiency, armature gets out of balance, the commutator wears, brushes and bearings wear, brake wears out, cush drive motor coupling wears, gearbox develops backlash, etc. All together.

[ex-Gooserider]

Actually that is a relatively fancy AC motor - not 'typical' - it is a heavier duty 'industrial' motor intended for use in environments where there is dirt or other contaminants present that need to be kept out of the motor 'guts'.... It is described as a "TEFC" motor for "Totally Enclosed Fan Cooled". It is also going to be an EXPENSIVE motor for it's size / horsepower rating....

If you were to take it apart, you'd find the shell is a fairly heavy casting with NO openings other than for the motor shaft and the wiring, and those are gasketed or sealed.... The end opposite the output shaft, where the sheet metal cover is, has a fan under it that pulls air in through a grid of holes in the end and forces it out along the fins... The extra cooling is needed because there is no air circulation from the outside to the motor internals, and the heavier cast enclosure would hold the heat otherwise....

Lighter duty, less expensive motors that don't need to meet the environmental conditions that a TEFC motor is designed for will have lighter sheet metal shells, and often openings in the sides and / or ends so that air can circulate THROUGH the motor internals...

Our chair motors are somewhat of a middle ground - they are more or less sealed, but not as much as a TEFC motor, and won't have a forced air fan, but don't develop as much heat (we hope) due to the current limiting imposed by the controller.

ex-Gooserider

Motor watts dont tell you a thing. Two identical motors, spray one black, and it radiates heat better. So now its a higher wattage motor.

Good point (and it's the same principle with cables)

Most AC motors have lateral cooling vanes running down motor and a fan at one end to draw the air over them. DC mob motors could have low profile cooling vanes moulded into the casing. They wouldn't need to be that pronounced or necessarily need a fan, and would surely act as a better heat sink than a smooth steel/alu casing?

Yes/No?

But then I suppose if they were needed mob motor manufacturers would incorporate them?

[snaker]

All done !!!

My dad opened gearboxes, cleaned up, replaced new oil/grease, rubber rings. He also found that the bearing in the right gearbox got loose and he replaced it by a new one. Now no oil/grease leaks out, no strange feeling on the right wheel. I did a 80km trip SAFELY

I still feel a little difference while driving with these repaired gearboxes. When the chair moves at a low speed, I feel the right wheel is a little tight. May be it is due too new the bearing. When moving at max speed (14.5kph), everything is Ok. I also feel the chair gets a little more sensitive than before repairing gearboxes. And the chair seems consuming less power when moving on good and flat roads.