Triple Rewind of Unite 500W Motor

[duivendyk]

The power output is roughly proportional to the armature volume multiplied by the speed.Manufacturers most likely have preferred diameters,so may first increase the power output by increasing the length before going to a larger diameter. Increasing speed is a sure fire way to increase output for a certain motor size.Rewinding for more power essentially boils down to doing this.

 

[safe]

The Maiden Voyage

Rode the bike for the first time today. Speaking of "higher rpm" no load speed there are limits to that. When I rewound the motor on this bike it ended up with a 10,000 rpm no load speed.

That's way too high... I can't even get to the true no load speed...

So this bikes motor is going to get another rewind.

The no load speed should be between 5000 and 6000 rpm and no higher.

 

[duivendyk]

How come?.I thought you had seen the light.You need twice as many turns or half the battery voltage.

 

[safe]

I did that rewind before I started this thread. (in the middle of winter)

At that time all I knew was that my first rewind had been a big success, so I tried to simply copy that experience. It was obvious that you can increase current flow with more winds, but the increase in the no load was something I didn't know about... well... you remember... and thanks again for pointing me towards the answer.

What's interesting is how this Triple wind behaved. First of all it flowed current really easily so you could get some pretty impressive torque at low rpms with it. But since the "theoretical" no load was 10,000 rpm and the actual turned out to be something like 5,000 rpm I very well might have repeated my error just by basing things on experience. (because the no load speed "seems" like it doesn't change that much)

It's interesting how two overlapping physical properties can mask and confuse someone trying to figure it out. Now I understand it and I've already taken the motor apart as the present 10,000 rpm is largely useless.

I'll get there... it's just good to have crossed that threshold which is to actually have a bike that has run.

It handles really well, in fact, I think that my cornering is already about as good as on my old bike. Plus, this bike only weighs about 70 lbs so it's really light. Once I get the motor situation cleared up it will be an awesome ride.

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Strange Flywheel Effect

Here's an interesting oddity...

The 10,000 rpm has a built in geardown unit and when I spin up the motor the geardown acts like a flywheel and want's to keep spinning. Now on my old bike I used a derailler and when the motor continues to act like a flywheel it actually makes the shifting smoother. With this 8 Speed Sturmey Archer internal hub the gears don't want to shift until you get off the power, so the flywheel effect is actually making my shifting slower. Hopefully when the hub loosens up the shifts will get smoother.

Also, if I drop the no load down to 5,000 rpm that might lower the flywheel effect somewhat... but come to think of it... I'm not actually exceeding 5,000 rpm much right now. Well, we'll see...

 

[safe]

Motor Apart, Rewind Beginning

The iron core cleaned up well and is ready to get rewound.

Unfortunately the bolts that hold the motor together are badly stripped (they used phillips heads, which is bad news) and I've had troubles finding replacements. In the end I'll probably need to buy the bolts online somewhere because they are too specialized.

The bike "ran" and I know what it's going to be like (excellent handling) now I need to mentally regroup for the long struggle that it's going to take to refine the bike to as close to perfection as I can get it.

So I'm probably going to be a "slacker" for the near term. Attaining a "big goal" (getting it running) was a major milestone.

There will be more work... later.

 

[duivendyk]

Good luck !,I like your drive set up, what is you ratio to the rear sprocket from your motor ?

 

[safe]

At present I'm running:

9 motor gear one
88 motor gear two
10 motor sprocket
55 pedal sprocket
38 rear wheel sprocket

...but that will change to a 25 tooth rear sprocket with the replacement rewind.

The Sturmey Archer 8 Speed has the following ratios:

1.00
1.28
1.45
1.64
1.86
2.10
2.38
3.05

...and that translates to the following land speeds in mph (flat land for actual):

Peak ------------ Actual ----------- Efficiency ----------- Maximum

17.2 --------------- 18.5 --------------- 17.5 --------------- 19.3
22.0 --------------- 23.4 --------------- 22.5 --------------- 24.7
24.9 --------------- 26.3 --------------- 25.4 --------------- 28.0
28.1 --------------- 29.4 --------------- 28.8 --------------- 31.6
31.9 --------------- 33.0 --------------- 32.6 --------------- 35.9
36.0 --------------- 37.2 --------------- 36.8 --------------- 40.5
40.8 --------------- 40.8 --------------- 41.8 --------------- 45.9
52.3 --------------- 41.2 --------------- 53.5 --------------- 58.8

When the pedal speed reaches 109 rpm that will be matching the peak power of the motor. The typical cadence for pedaling is about 76 rpm and high torque pedaling is at about 50 rpm. So the idea is that the pedaling will pull the rpms up into the peak power area and then the motor takes over. You would enter a turn, lean and survive the cornering (not pedaling) then on the exit you stand up and torque the bike up to full speed so that the motor takes over and you can get back into the tuck.

Each exit of a turn is a short sprint. (a burst of about 750 watts extra power)

It's a lot like BMX...

 

[safe]

Ice Cooling

It's a little bit of a side project, but one I've wanted to do for a long time now. The idea is fill the container with water and put it into the freezer the night before. On the day of your ride you strap the Ice Cooler to the motor shell and get a lot of cooling that way.

...this will allow more heat to be produced without burning up the motor.

I made the container by just fiddling around with fiberglass. I'd start off with nothing but aluminum foil and get an outline of the shape going, then gradually refine it until where it is now. It weighs very little. The container will hold one cup of ice. (250 ml) The water will weigh a lot more than the fiberglass container.

At 80 calories per mole (for ice) I've done the calcuation before, but basically it should be able to absorb most of the heat produced for an entire batteries worth of riding. Will have to refresh my memory on the heat absorption calculation.

I still have two motors in need of rewinding.... which I'll get to eventually...

 

[safe]

Day One

First layer complete. Cleaned up the little tab thingies and all looks good so far. After the tragedy with AussieJester I went the extra step and put some masking tape on the starting locations of the windings so that I would not make a mistake and get it out of alignment. I'm using broken pieces of pencils (three) to act as placeholders for the grooves so that the wires don't fluff up while I'm working on it. Hopefully that will help to produce a tighter final wind.

14x2=28 20 AWG

Stock was 21x1=21 20 AWG, so I'm hoping this is going to fit. It's going to be tight, but I'm optimistic.

 

[Fuzzo]

I'll be amazed if the ice has any effect at all. It's quite warm inside an igloo. The fibreglass will insulate the ice from the motor. It could even prevent heat from radiating out of the motor. How hot does it get?

I'd think an air scoop would do a better job, forcing cold air to pass over the motor, or even better, through it. It doesn't matter if the air is warm, so long as it's colder than the motor, and it's constantly moving, it will take the heat out efficiently. I'm sure that's why so many electric motors have corrugated shells - to maximize the surface area of the metal so that air flow will take the heat out more efficiently. If you can also get more air flowing, that's got to help.

The same could go for the batteries, if they're in any danger of getting hot. It was my first thought when I saw your container with the PVC pipes holding the batteries - "that'll keep them toasty warm, but with a scoop, you could keep them extra cold too!".

But hey, there's no substitute for experimenting! Maybe your ice box will work.