Motobecane 40T moped conversion

[northernmike]

+ Phoenix HV 110, (extra caps arrived today) 48V SLA (saving up for LiFePo...), you probably already saw it in the wrong forums, here is it's rightful home, I think!

Lots more aluminum chewing tomorrow, my eyelids are gaining serious downward momentum ...

 

[etard]

That's gonna be real classy, Mike. I like the protection sleeve for the motor, is that aluminum? Please put Lipos in that gas tank, this thing should be stealth. Well, except for the lack of smoke and loud ICE motor. Are you planning to gear the pedals to actually work above 2 MPH?

Nice pics, give us some more details about the actual moped, I don't think I've seen this done yet.

 

[northernmike]

Thanks etard!

Pedals are just for legalities and emergencies. I'm planning on winning the lottery and kidnapping Gary for the LiPo-in-tank feature! I think there's room.

The bike is a 1973 Motobecane 40T. Was originally orange, then blue, then green, partially "restored" by a little asian girl... Came with a 49cc AV7 2-stroke, DiMoby clutch, but was converted to MobyMatic Variator transmission by yours truly. I was setting it up to be a speed demon - 62cc Malossi cylinder kit, tuned pipe, etc - when I realized that 1. It stank, 2. I would have to insure it, and 3. It would always break down, no matter what.

Protection sleeve is aluminum, yes - I want to (be able to) ride this in all kinds of weather, and don't need the shiny bit hanging out attracting any more attention than it already will.

I love the sound of this motor (HXT 80-100-B) hooked up to the Phoenix. I had it on the bench yesterday screwed to some plywood - man, it just howls.

Now, to dig up some 5mm screws... the aluminum beckons!

 

[GGoodrum]

Interesting setup. I'm anxious to hear how this motor works out. If it doesn't run too hot, it could turn out to be an affordable option to the more expensive, but high-quality variants, like the AF 3210, or Matt's Pletti.

What is the gearing?

Did you ever figure out how many a123 cells you can fit in the tank?

-- Gary

 

[northernmike]

Gary, I bought too fast - I was copying Karen Nakamura's Piaggio (Vespa) Boxer moped build and didn't know about the Astroflight motor til a few weeks after I had the Turnigy in hand. I would take that 3210 over my motor in an instant, but we'll see how it goes.

I will be adding a few pancake power supply fans on the open end of that sleeve with some kind of piece to keep dirt out - maybe a foam filter? I do expect it to get warm, from what I've read so far.

Gearing is currently set up for about an 70kph top speed - I forget the numbers, but it works out to something like that with the motor wound out - 130kv @ 48V.

However, the rear sprocket is currently a 41 tooth, I have on my shelf a 45 and a 50 as well, and I can also decrease the size of the motor pulley - pictured is a 4 inch, I also have 3.85 and a 3.45, if memory serves me. Basically the Moby's CVT was able to 'variate' between about a 2 inch and 4 inch effective diameter (the engine swings on a pivoting top mount with a sprung rear point), so I picked the largest point as a starting point.

Hopefully it won't totally bog, but if it does I can re-gear pretty easily.

As for the tank - there's a steel sheet between the halves, so getting into the left side is pretty much improbable without some surgery. I am thinking about cutting out the "chrome" parts under the Motobecane stickers - these are just covered with chrome stick-on R/C airplane graphic material from a hobby shop (fitting, eh?) - anyway, if I cut those out I could slide the cells in easily, but I think that might hurt the structural integrity of the frame... more thinking to do...

Here's a few more of the weekend's work. The drive is all mounted up, I need to trim the sleeve, and am considering a 12mm flanged bearing on the back side to take some of the side load off the bearings.

 

[GGoodrum]

Looks great. Is the ratio fixed, or are you using the CVT feature?

Do you have anymore shots of the tank. I'm still trying to visualize this.

-- Gary

 

[northernmike]

It's fixed ratio, for the moment. I've been reading a lot of the discussion about the advantages of changeable ratios, though, it has me tempted to make a variator fit - there's some great aftermarket ones, too. Another lottery-winnings priority!

Here's a shot of another bike, for the tank:

I'm not in front of mine right now, actually I'm back in the city - the Moby lives in the burbs - for now! Anyway, the tank is the 'downtube', of course...

 

[etard]

Ahh, that things a tank, and it probably uses a steel spar backbone which splits the tank in two. Chop it up man, or at least convert it for lockable storage. That rack on the back is another good spot for batteries. Something in a nice wood container with a deck like the extracycle would complete the retro look.

 

[northernmike]

etard, I'm not really going for a "retro" look.

The bike just happens to be 36 years old - so it's kind of a "vintage" look - I think of the New Beetle, the BMW MINI, the Ford Flex when I hear "retro".

I also hate the term "steampunk"... but that's a whole other conversation.

Battery placement is a big sore point for me. I don't want to denature the bike. I don't REALLY want to make it look like it has a lot of luggage space, either, since it won't, but panniers are probably the best route for me for the interim.

I really want this bike to look like a complete, intentional, whole design - not a science fair project.

No offense to those who's bikes do - I love the Short Circuit "Johnny Five" aesthetic - I'm just going for something different here.

Ideally, if I have to stick with Panniers, I'd like to mold some fiberglass ones that compliment the lines of the bike, and paint match them. We'll see.

 

[Drunkskunk]

what about pulling the seat off a 50, like this one? I have one in the garage. it might not hold all the batteries, but there is a good amount of storage under that seat.

 

[northernmike]

Skunk, thanks, but I have to keep it at least looking legal. No doubles on e-bikes in Toronto allowed.

I was toying with the idea of one of those seats, but having the rack for my lady to side-saddle on is going to work out OK.

Besides, that's too nice a bike to part. (!)

What year?

 

[northernmike]

Ran it today!

Easily outperforms the gas engine. Took it about 1.5kms, did a good hill climb, estimating 50kph top speed on flats.

Fed it with tired 7AH SLAs, embarrassing but true. Found one battery hot after recharging, so replaced with a fresher one for the second run.

Forgot to check the voltage before connecting, and poof. 54V = no more Phoenix.

Boxed up the charred remains for return to their maker and preparing to buy a new one.

New details you now can know:

Fused thusly =

100A BUSS - shows signs of heat after short running despite huge interrupt rating. Skeptical.

Batteries carried in =

Question. Can I electronically protect my next HV 110 from over-voltage somehow? I would really like to keep it longer...

 

[lawsonuw]

For my experiments on my Linear 'bent (see my signature for the link) in addition to adding extra input capacitors I added a TVS diode with a ~30v rating to the input of the controller. 30v bi-directional TVS diode I haven't checked the voltage rating of my cheep controllers FETs, but the stock input capacitors were rated for 35v. I specifically added the TVS to clamp any excessive voltage I might hook up to it, or to clamp any voltage spikes the ~4ft supply wires might generate. 5KP43CALFCT-ND or 5KP48CALFCT-ND might blow the main fuse before they go up in smoke.

A far better solution would be to add a proper Crowbar Circuit to the input of the controller. Some Crowbar Circuit Schematics (this assumes that the battery has a fuse that can be blown)

Lawson

 

[northernmike]

Lawson, thanks!

Checking out your build now..

edit: sorry - can you explain how the diode is connected?

 

[lawsonuw]

Lawson, thanks!

Checking out your build now..

edit: sorry - can you explain how the diode is connected?

Hm... I really don't lay that out clearly do I

First picture of mine on the second page of my linear thread shows my combo TVS diode and extra input capacitors. It's part of the black lump below the controller in the white plastic box. The particular TVS diode I chose is bi-directional so polarity is not an issue, I just hooked it up across the battery input leads of the controller. My capacitor bank is about 1.5x the stock input capacitor bank of low ESR electrolytic capacitors. I didn't use a fuse in my system. But if I use a fuse, the fuse would be on the battery side of the TVS diode.

Another nice detail I added is the 60ohm resistance I have bypassing my main power switch. This pre-charges the controller's capacitors and keeps the connector and switches from sparking. I needed 60ohms because any more resistance and my controller would trip it's under voltage shutoff when it beeped the motor.

Lawson

 

[northernmike]

Thanks for the help sir.. and nice build

OK - I'm beginning to get how this diode works, I think.

Does the TVS diode work as a kind of 'soft' short circuit?

Would this mean that if I have a battery voltage of 54v and put one of the diodes you mentioned across it, I could safely draw 100A at 48V?

What I'm trying to accomplish is a way to feed my HV 110 with 4 12V SLA bricks. Seems redundant, I know. Sadly, they're outputting 54V hot off the charger.

I suppose I SHOULD go with 42V of nominal lead, but 6V are hard to find in the dimensions I want, and I already have a bunch of 12V 7Ah.

36V would just be too slow.

 

[12p3phPMDC]

I'm for anything that keeps you from popping stuff,
but a soft short from a TVS or zener will continually draw current until the voltage drops below the "trip" point then it will
turn off. It'll protect your circuits, but you'll be wasting juice shunting current to get the voltage to drop at the zener.
A couple of big rectifier diodes in series would knock the voltage down and wouldn't act like a shunt.
Lets say the forward voltage of the rectifier diodes is 1.5V. Three in series would be 4.5 volts.
54V - 4.5 = 49.5V. So maybe you throw one more in series for 6 volts to give you a little more margin at 48V.
Now, you're throwing away voltage here only out of necessity to keep from popping the ESC fets. like you said, you'd pick a lower voltage if it met your other requirements for size. But you are not throwing away current with this method.

+54 Volt Term -|>|--|>|--|>|--|>|--|>|--|>|----- +48V (sorry for the crummy text art)
D1 D2 D3 D4 D5 D6

Now, these need to be big diodes, obviously. But they make em.

I'm not saying that shunts are bad. But they are better for protecting against transients, not batteries that have too much voltage. They would protect the system, but just waste juice. Why waste current if you don't have to? Now if you wanted to put a TVS on there, well put it after the diodes on the 48V side.

 

[georgeycc]

hi Mike,
the aluminum motor shield jar......does it heat up rapidly as you run the motor at high rpm?? i suspect that there's a lot of eddy current induced on the jar body as my same motor has bad flux leakage problem. i think plastic enclosure of the motor would give you better efficiency and no eddy current.


-george

 

[northernmike]

George, tell me more please!

I haven't noticed any heating yet, but you have me worried now.

 

[georgeycc]

Mike,
eddy current is induced to conductors when the magnetic line "cuts" through conductor, that is why your stator iron has to be made laminated to isolate the "eddy" current to minimal. the same applies to any conductors that's close to moving magnets. R/C motors have too thin back iron so the shielding of magnetic field is not enough, so it's expected that the aluminum shield you placed closed to the motor rotor would have eddy current on it and make heat on the aluminum and lower your motor efficiency.

 

[northernmike]

Interesting ... I'll post some pics up tomorrow - the aluminum sleeve has become a structural component and would be hard to replace at this point, unfortunately ... I'll keep my eye on temps for sure

 

[northernmike]

 

[northernmike]

 

[Drunkskunk]

Nice!

you are inspiring me. My poor pug 103 doesn't have chome anything like that, though. amazing.
With all that brightwork, have you thought about getting the sleve polished and anodized? I think it would look good under there that way.

 

[northernmike]

Thanks Skunk. I'm not sure what to do with the sleeve. I'm leaning towards flat black, honestly, but there's so much to do before making it 'pretty' counts!

Speaking of pretty though ... my dad had this great idea:

Take the gas cap out and make a form fitting vase to insert in it's place - have some flowers poke out where the 50:1 used to go!

Like the old VW Blumenvasen

Seriously though, I need to sort out a brake light switch, a horn, and a new controller before that.