Author Topic: Since the mini motors have a free wheel...  (Read 27101 times)

Offline Sangesf

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Since the mini motors have a free wheel...
« on: December 14, 2009, 06:55:53 PM »
I'm using the magic controller to power the 24v mini motor and for the alarm it would lock the wheel. Since the motor has a forward moving free wheel..  Could I turn the wheel around and set it up for using reverse constantly and make it so the alarm / wheel lock will work in that direction?

Would it hurt the mini motor to have it running in reverse constantly?

Frank

Offline muzza.au

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Re: Since the mini motors have a free wheel...
« Reply #1 on: December 14, 2009, 07:06:04 PM »
G'day Frank,

I think you'll find that the mini motor will not work in reverse because of the freewheel. Setting it into reverse would just make the freewheel.. well freewheel! It wont drive the wheel. Using the alarm with the mini motor will only prevent it spinning backwoulds, not forwards.

Muzza.

Offline e-lmer

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Re: Since the mini motors have a free wheel...
« Reply #2 on: December 14, 2009, 07:17:41 PM »
I don't have the motor, but it seems it should run in
reverse with the freewheel, it just won't let you pedal.
(I guess that violates some laws or something, but...)

Am I mistaken to think the motor drives the wheel against the
axle, and the freewheel is just to add to the wheel rotation,
having nothing to do with the wheel lock or alarm?



Offline Sangesf

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Re: Since the mini motors have a free wheel...
« Reply #3 on: December 14, 2009, 10:47:15 PM »
The reason I want to do this, is because when the alarm goes off and locks the wheel/motor it locks it from moving backwards, so I figured if I just ran the motor in reverse ( and turned the wheel around so that 'reverse' was actually forward ) it would lock it from moving forward. 

What do you guys think?

P.S.  Do you think it would also allow for regen braking?

Offline Russell

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Re: Since the mini motors have a free wheel...
« Reply #4 on: December 15, 2009, 01:33:41 AM »
When I was setting up a sensorless controller with my GM Mini Motor part of the process was to program the phase firing order. Once activated the controller sequenced through the possible phase combinations, some turned the motor forward and some spun the motor backwards but the wheel did not move due to the freewheel. A freewheeling geared motor will not run backward but if you want it to you can find a means to lock-up the clutch mechanism. I ended up doing just that on a Bafang geared motor to make it run better sensorless.


-R
'92 Raleigh hybrid, 24V 250W GM Mini-Motor, 36V/20Ah Li-ion, 23 mph, 53 lbs

'09 Kona Smoke, 36V Bafang QSWXB with locked freewheel running sensorless, 48V/10Ah LiFePO4, 23 mph, 59 lbs

Offline Bikemad

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Re: How the geared mini motor freewheel works.
« Reply #5 on: December 15, 2009, 02:40:34 AM »
Trying to explain how a mini geared hub actually works is not going to be very easy, but I'm going to do my best with the aid of these lovely photos that Russell has conveniently posted on the Endless-Sphere forum, and I'm sure he won't mind his pictures being put to good use. ;)

Let's start with the basics:
The stator (containing windings and hall sensors) is permanently fixed to the axle and does not move.
The outer drum of the motor contains a ring of permanent magnets securely attached to its inner surface surrounding the stator.
This drum has a small gear attached to the opposite side (see picture below) and the whole assembly is mounted to the axle by a bearing inside the gear, which allows the whole drum assembly to freely rotate around the fixed axle when power is applied to the windings via the controller.

The stator, axle and drum assembly above make up the basic motor unit.
So we have a motor that can spin freely, but it still needs to transmit its power to the hub and produce enough torque to turn the wheel and drive the bike.
This is cleverly achieved by the use of an epicyclic gear train, which provides a gear reduction between the motor and the hub, which greatly increases the torque (turning force) at the wheel.
The following two pictures show both sides of the intermediate gears (known as the Planet Gears) which are driven by the motor's small gear (the Sun Gear) and are mounted on a unidirectional clutch (a special type of ratchetless freewheel), which is secured onto the axle with a key and slot to prevent the centre piece from turning.
The clutch is very simple and comprises of three cylindrical rollers which are gently held by springs into the narrow end of a wedge shaped opening.
If the gear carrier in the first picture below is turned clockwise, it wedges the rollers between the carrier ring and the centre of the clutch, which effectively causes the carrier to become fixed in relation to the axle and will allow the rotational force to be transmitted between the motor and the hub.
This automatic locking action occurs whenever the motor tries to turn the wheel.
If the carrier is rotated the opposite way, the rollers will simply roll towards the larger end of the wedge shaped opening until the slight spring pressure prevents the friction from pushing the rollers any further.
As they are no longer wedged in, they are unable to transmit any load using the surface friction alone and the rollers will simply slip easily around the centre of the clutch, producing a noiseless and almost frictionless free-wheeling action.
This is how the hub manages to rotate easily, as it does so without having to turn against the resistance of the motor.

The picture below shows the side which faces towards the motor unit.

The outer gear (Ring Gear) is permanently fixed to the inside of the hub, and this allows the drive to be transmitted to the hub itself.


Now have a look at the following diagram and imagine your looking at the wheel from the left hand side.
The small gear in the middle is the motor, which only rotates clockwise when viewed from this side.
The three planet wheels are fixed to the carrier which is only free to rotate anticlockwise, as it will be fixed in relation to the axle when the motor tries to turn it clockwise.
This allows the hub to be driven anticlockwise (forward wheel rotation) by the motor.
If the motor is stopped and the wheel is moving in a forward direction, the hubs outer ring gear will try to turn the three planet gears anticlockwise around the stationary sun gear (it's stationary because the motor is stopped).
The free-wheeling action of the clutch allows the carrier to be freely turned in an anticlockwise direction with very little resistance.
So when you're pedalling without motor assistance, the planet gears will still be rotating, but as there is very little resistance, you're not usually aware of it.

The actual gear ratio is determined by the number of teeth on the sun wheel and the number of teeth on the ring gear.
So for example, if you had 9 teeth on the motor and 90 teeth on the hub you would have a 10:1 speed reduction and a 10x increase in torque!

Frank,

As Muzza and Russell have already mentioned, the motor will spin in reverse, but will not transmit any drive due to the unidirectional clutch in the centre of the gear carrier assembly, which is also why regen doesn't work with these motors.

If you were to fit the wheel backwards, the motor would not be able to drive the bike in a forward direction, but you should have very good regen!  :D
It's just that it won't be much use as a hubmotor if you can only use it for going backwards and regen!

Alan
 
« Last Edit: June 30, 2017, 05:47:36 PM by Bikemad »

Offline Leslie

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Re: Since the mini motors have a free wheel...
« Reply #6 on: December 17, 2009, 07:21:53 AM »
5 star post Bikemad.  Even though I don't own a Mini motor just yet I read every word.  Those Pics Russell did were the icing on the cake.

Bring it on

Offline GM Brazil

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Re: Since the mini motors have a free wheel...
« Reply #7 on: December 17, 2009, 07:09:14 PM »
Sure!!!

5 stars! :D

And is possible to see the quality of the GM mini motor, there is ball bearings all around, nice!

Offline Bikemad

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Re: Pictures are much easier to digest
« Reply #8 on: December 17, 2009, 09:17:50 PM »
Those Pics Russell did were the icing on the cake.

I don't think I could have described how it works using just text alone, and I don't suppose you'd want to read it without some form of visual stimulation either! ;)

Alan
 

Offline Sundsvall

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Re: Since the mini motors have a free wheel...
« Reply #9 on: July 06, 2010, 06:52:54 PM »
I know this topic is old but since it contains Bikemad's excellent post of the mini motor I'll continue this instead of starting a new. In the summer of 2009 I bought a mini motor front wheel kit and assembled it on my winter bike. I've biked through 1 meter deep snow, of course with a lot of pedaling, and that wouldn't been possible without the help motor. For the winter to come I've ordered a frog style battery to replace my heavy lead battery and I'm planning to order a mini motor rear wheel as well to improve the deep snow capabilites. The problem is that my front wheel motor drives backwards an my solution was to mount the wheel with the cables on the right side of the bike. The pedelec worked also in an opposite way, when I start pedaling the motor stopped and the battery indicator on the throttle never showed anything. My 28" (ETRTO 622) studded winter tyres didn't fit the rim because it was 28" (ETRTO 635) but that was easily solved with a new tyre, unfortunatly it wasn't as easy to fit it in the fork.

I don't miss the pedelec but I'm a little bit concerned over the rotation of the motor since it wouldn't be able to drive backwards.

Is this a potentional problem if I connect an additional motor to the same controller?
Midsummer sun = up 02:54   down 22:51   angle 51,0° :)
Midwinter sun =    up 09:19   down14:18   angle 4,2° :(
Mean annual temperature = 3,1°C

Offline Sangesf

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Re: Since the mini motors have a free wheel...
« Reply #10 on: December 23, 2010, 05:02:19 PM »
I know this topic is old but since it contains Bikemad's excellent post of the mini motor I'll continue this instead of starting a new.

Well someone brought up an interesting question to me today and I'd like to get some input.

The thing that has stuck in my mind is that Bikemad said, "I could run the mini motor backwards, but it wouldn't move the wheel but would give very good regen..

If I setup my normal motor on the rear and a mini motor running backwards on my front wheel... Would there be any resistance? In other words, would it act like a "super-dynamo" and not have any resistance so I could use it as a charger for my battery(s)?

Offline Hardcore

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Re: Since the mini motors have a free wheel...
« Reply #11 on: December 23, 2010, 05:09:32 PM »
No

Offline Sangesf

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Re: Since the mini motors have a free wheel...
« Reply #12 on: December 23, 2010, 05:36:49 PM »
No
Can you bea little more specific?
No doesn't tell me the why....  That's what I'm looking for.

Offline Bikemad

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Re: Fitting the minimotor backwards
« Reply #13 on: December 23, 2010, 08:10:20 PM »

With the motor fitted backwards there would be a fair amount of resistance, and the only way to eliminate this resistance would be to feed the motor with enough power to make it turn fast enough on its own so that the wheel would no longer be turning it through the gears.

I would also expect the regen braking to be very strong indeed, as the actual braking force from the motor would be increased many times over, due to the reduction gears within the hub.  This would probably put far more load on the nylon gears than they would normally have to withstand, and I would expect it to strip the teeth off gears (or even damage the speed controller with the excessively high current/voltage) very quickly under high speed regen.

Fitting a minimotor backwards is not something that I would seriously consider doing.

Alan
 





Offline Hardcore

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Re: Since the mini motors have a free wheel...
« Reply #14 on: December 23, 2010, 09:37:44 PM »
No
Can you bea little more specific?
No doesn't tell me the why....  That's what I'm looking for.

I see Bikemad, alan, already answered your question.

Good luck