Single Gear Stealth Build - Battery in Frame Tubes

[LawrenceEaden]

Hi All.

I'm a little way into my build now and I thought I would share my experiences. My main goal for the project is to build an eBike that doesn't look like one. I recently got a single gear bike to try because i like the aesthetic and simplicity. A bike like this has a compromise with the gearing though, you can choose to make it easy to take off at the lights and get up hills, or have a good top speed.

This lead to my eBike project, could i gear the bike for a good top speed pedalling, then have electric assist for hills and getting off the line.

The Bike
This is the bike I'm starting with from Hackney Cycles, London. (£160)

All the components feel extremely cheap but considering what i had planned for it I wanted to keep the risk capital low and I can always upgrade components later.

The Battery
This is where it starts to get a bit tricky. I don't want a visible battery on the frame, so i had the idea of putting the battery IN the frame using 18560 cells. I could only fit 20 cells in the frame (top tube 6, seat tube 6, bottom tube 8). This would let me do a 36v (10s,2p) battery. So I did some maths.

Cells Used - Samsung ICR18650-26F (£3.95 each)
http://batteriesplus.co.uk/acatalog....7-V-2600-mAh-Lithium-cell-1957.html#SID=1123

Weight
20 x 45g = 900g

Voltage
3.7 x 10 = 37V

Capacity
2.6Ah x 2 = 5.2Ah

Max Current Draw
5.2A x 2 = 10.4A

Max Power
37 x 10.4 = Approx 350w

WattHours
37V x 5.2Ah = 192.4Wh

I was then trying to work out what range this would give me i found lots of different estimations of how many WattHours per Mile you use, between 5 and 20. So I took the top estimate to be conservative.

Range
192.4Wh / 20Wh/m = 9.62 Miles

For a first build I think this will be okay. My commute to work is 7 miles, so i can charge at both ends, and it's fine to get to the shops and back. I always have the option for longer journeys to add another battery in parallel in a rucksack.

10s is quite a common setup so findng a BMS PCB is very easy. I will add the balancing wires when I build my pack.

The Motor

The maximum power my internal battery could provide is 350w so that's a good start for my motor spec. I wanted to keep the rim that came with the bike for the oem look. The rim has 32 spokes, most hub motors are made for mountain bikes which have 36 spokes, and 135mm drop outs.

The options were very limited so I went for the Q100C CST 36V350W (£117.88 inc shipping)
https://bmsbattery.com/ebike-kit/65...driving-hub-motor-ebike-kit.html#/213-rpm-201

I am waiting for this to arrive. but I have tried to work out the spoke configuration using a great online calculator here. http://www.ebikes.ca/tools/spoke-calc.html

The Controller

I have done a few home automation projects before using raspberry pis and arduinos so I would like to go down this route eventually to add my own features like gps and data logging. There are so many cheap controllers around though I wanted to get one to reverse engineer the circuit and use it to get the bike going.

I went for this one on amazon (£15)
https://www.amazon.co.uk/dp/B00EB84L70

I'm still not sure where to package this on the bike. I have seen you can get nice leather frame bags for tool kits. This could work well because it butts up to the frame so wires can go between them discretely and it's something seen on non electric bikes.

Power Control

For simplicity to start the power will be completely controlled by a thumb throttle.

I found an inconspicuous one on ebay. (£8.99)
http://www.ebay.co.uk/itm/-/162194486812?roken=cUgayN

Final Specs

Voltage
36v

Power
350w

Range
9.5 Miles

Weight
Motor = 2.1kg
Battery = 0.9kg
Controller + Wiring + BMS = 0.8kg approx
Total = 3.8kg

Battery Build

Finally I get to start making things! I have seen a lot of people build battery packs spot welding nickel strips to the cells, but because mine has to take on the form of a tube, i thought that soldering wires should be okay. I used 0.75mm2 wire for the parallel connections and 1.5mm2 for the series ones. The balance wires are rated to 2 amps, i only expect to charge at 1amp.

To fit in the tubes I am building 3 packs which will be joined in series.
Top Tube - 3s,2p
Seat Tube - 3s,2p
Bottom Tube - 4s,2p

I started by making the 10 parallel pairs

Then linked 3 pairs together to make by first pack, and added wires for the balance charging. I tried to keep a 5mm gap between all the cells, and insulated all the ends with electrical tape to stop any shorts.

Once it was done i put heat shrink on it for a little rigidity and insulation. Two finished with ample wire at each end to route in the frame and add connectors.

This is as far as I'm up to with the battery. I have ordered more cells to finish the final pack. I am concerned about my soldering cracking after some time, so I think I will get some 20mm ID tube cut it into quarters down its length and heat shrink it to the packs for extra rigidity.

Frame Modifications

Okay so you may be wondering how i'm going to get these battery packs in the frame? I had a couple of options. The seat tube is easy, you can slide it right in but i can't get to the top or bottom tubes without drilling somewhere. a scary thought! I originally considered the bottom bracket after reading how over-engineered they usually are. but to get the right angle of hole i would come in contact with some welds for the drop out arms. So! Both holes could go through the head tube. I found some cool looking FEA for a bike frame and it looked like very little force went through the front face of the head tube.

Drilling a 15degree and 30degree 25mm hole in the centre of a tube freestyle didn't sound appealing at first, I designed some sheet metal jigs that would give me the angle and position i wanted. But with a 10 day lead time and extra cost I scrapped that and made paper templates i could stick to the tube and drill up to the line.

I got the angle grinder out to try and make a flat surface on the tube perpendicular to the tube the battery was going in. then centre punched and drilled a 5mm hole. I widened this with a stepper drill bit. finishing off with a die grinder to get the right profile.

I've only done one of the holes so far, but i'm pretty happy with the result! I removed the smallest amount of material to get the holes lines up to get the pack in the tube. I haven't done much modification work like this before, so i'm still learning the best ways to do things like this.

The pack fits! I haven't been able to find anywhere online someone making a DIY eBike like this so I'm going a little blind, but that makes it more fun as well! I will be left with two holes once i'm done, this could be perfect for designing a little custom front light and horn?

Video of Battery fitting in the frame.
https://player.vimeo.com/video/185115360

What's Next?

There's still a lot to do on this project, but as it's getting dark earlier now I have more motivation to stay after work and crack on with it. My list at the moment is

Bottom tube battery pack
Final wiring diagram
controller/bms packaging design
hub motor lacing to the hub when it arrives

Any comments, especially if you've seen any huge errors!, would be appreciated.
(I already posted this on electricbikereview forum before discovering this one).

Thanks,
Lawrence.

 

[motomech]

Actually, this is not the first time the "battery in frame tubes" has been done. There was a build here, maybe 4 years ago, but I can't remember his name. He strongly stated that he would never do it again :lol: He used a Cute motor too.
I've done several Q100CST installs and the motor requires severe dishing. On one bike, a Rocky Mountain, I could not get it over far enough and rather than spreading the chain stays and spacing out the caliper, I changed motors. The other, a GT I Drive, everything lined up and less dishing was required. I guess eevry bike is different.
Your link to BMS Battery doesn't work, what motor speed did you order?
That controller will work fine, but there are much better units available. But, all of them require some sort of display and I'm sure you don't want to go there.

 

[footloose]

I'd normally shy away from drilling big holes in bike frame, but that FEA does suggest that the head tube is relatively safe spot.
And project is far enough along that it seems likely that you'll complete it.
Will be interested to follow the project, see if you are happy with the results.

Question to others. Seems like this approach ideally wants a lugged frame for safety. Thoughts?

 

[drew12345]

I believe grindz145 was doing something like this for Kickstarter project.

 

[leelorr]

I realize that you may be tackling the "invisible battery" idea for the challenge, but I thought that the new Luna Cycle 6AH battery might also be a solution. I have seen photos where it fits completely in a small seat bag meant to hold a tire tube and patch kit.

https://electricbike-blog.com/2016/05/08/the-most-power-youll-ever-be-able-to-fit-in-your-pocket-6ah-3-3-lb-30q-luna-mighty-mini-cube-pack-reviewed/

 

[drew12345]

Yup, I just did that. Had to put in large Topeak. You can find in my thread. Would be much easier than what your doing.

 

[MrDude_1]

Cool build. You just need to run a smaller controller.
Maybe a VESC like the skateboard guys use?

 

[Lurkin]

Interesting. The bike looks to be a fixie/single gear bike, but you have bought a CST motor? This is designed to be used with a cassette... i.e. to use gears. I would have thought you would be better off with something narrower and a single gear freewheel unless you are also converting this to have gears...

Your frame has no gusseting at the head tube area. I think the FEA could be leading you a little astray here, that frame has elongation at the joints and note the periodic redness at the joint to the top tube. Do you know what frame it is exactly? just from the shaping of the frame/joins, looks carbon.... interesting, but if it is its not really comparable. Always makes me a little nervous in that scenario as you could be grinding away at the inside of the very welds holding the front of the bike on. I've snapped off a headtube before, not pretty.

Soldering direct to cells is one way... it can damage the cells with the heat. Alternatively, solder to a nickel tab, then spot weld the tab to the cell (or buy cells with tabs, solder with something acting as a heatsink at the cell end). This way you get the same functionality without the cell damage.

How much difference is there between the ID of the frame pipe and the OD of your packs? Is there enough room to sneak the entire battery stick into a plastic tube before going into the frame?

 

[LawrenceEaden]

@motomech That's cool! I'm not an innovator, but it felt like a challenge worth trying!

I have seen the dishing problem when calculating the spoke lengths. The motor I have ordered is wider than my drop outs, so I'm going to look at a few different options that I'll post about when it's here. Dishing, biasing the frame when cold pressing the drop outs, or modifying the motor, not married to any ideas yet. Like I said, i want to design my final system using arduino control for extra features. so the controller now isn't critical.

@footloose. I'm about a week into it. hopefully it will be finished within a month. The FEA may be wildly off, so i may look at some reinforcement.

@drew12345 / leelor I'll check it out! I'm going to see this project through as I've spec'd it. Then all options are open for the next one.

@mrdude_1 I have taken the controller out of it's case to design a leather frame bag for all the external components. It's pretty tiny really. Photos will follow later in the week.

@lurkin I had serious issues finding a hub motor that had the right size drop outs and 32 spoke pattern to keep the same rims. Do you know of any suppliers that make these?
I agree the FEA is wild. It's a great idea actually to get a bit of steel cut and weld in a gusset between the front 2 tubes. The tubes are welded from the outside, I tried to leave a slight rim so the tubes weren't affected too much. Reinforcement sounds like a plan!.. The spot welding would have added cost (to buy a spot welder for this), or time (to make one from a microwave transformer.) I'm quite happy to plow on with this project, if i'm going to fail, i want to fail fast and learn quick. If it works i'll be chuffed. I only mean to put a quarter section of the pipe down one side. i'm sure i can find some 1-2mm wall tube somewhere that should keep it snug.

 

[drew12345]

It sounds like a fun project. Look forward to hearing how it goes.

 

[PRW]

Actually, this is not the first time the "battery in frame tubes" has been done. There was a build here, maybe 4 years ago, but I can't remember his name. He strongly stated that he would never do it again :lol: He used a Cute motor too.

this build? https://endless-sphere.com/forums/viewtopic.php?t=59225

 

[footloose]

It's a great idea actually to get a bit of steel cut and weld in a gusset between the front 2 tubes. The tubes are welded from the outside, I tried to leave a slight rim so the tubes weren't affected too much. Reinforcement sounds like a plan!.. The spot welding would have added cost (to buy a spot welder for this), or time (to make one from a microwave transformer.)

FWIW, brazing in a simple steel reinforcement gusset might be both adequate and inexpensive. I've done some brazing on steel frames with a basic kit that cost ~$60.
http://www.bernzomatic.com/product/ox2550kc-cutting-welding-and-brazing-torch-kit/
It's fun 8)

 

[motomech]

When I had problems fitting one of my Q100C's, I toyed w/ the idea of converting it to a single gear and it looked quite easy w/ no or little machine work.
If the cassette is not used and the inner threads for the cassette locnut are not needed, about 12M/M of the spline can be trimmed off.
Then, using a cheap cassette(the kind that falls apart when removed), select a gear(12T & up) to use.
Locate on the spline w/ some fab'd round pipe(2 pieces? inner & outer) & secure the ASM w/ a C-clip(cut a grove on end of spline).
(Sheldon Brown actually sells gear spacers, but the amount needed would be pricey.)

 

[LewTwo]

I realize that you may be tackling the "invisible battery" idea for the challenge, but I thought that the new Luna Cycle 6AH battery might also be a solution. I have seen photos where it fits completely in a small seat bag meant to hold a tire tube and patch kit.

I did the battery in a bag thing for my light-weight bike with a handlebar bag.(see the tread in my signature). I have moved the bag to the headtube. Battery = 36 Volt 6.5 Ahr, 15 Amp controller, 250 watt hub. Level ground up to 18 MPH. Still a work in progress ...

 

[LawrenceEaden]

Thanks for all the feedback guys, really useful!

I've done a drawing of the internal layouts for the frame and frame bag for the controller. I'd quite like it to be a nice polished product at the end so I'm going to have my controller and bms in a bespoke leather bag I'll make to the design below.

I've added a key ignition (£2.25) for a bit of security, to act as a kill switch, and because it has multiple positions it could come in handy down the road if I add an integrated light system to control that as well. i.e. pos 0 = off, pos 1 = drive on, pos 2 = lights on, pos 3 = toggle lights flash or non flash.
http://www.ebay.co.uk/itm/AUTO-12V-Ignition4-Position-Switch-2-Keys-Equivalent-Replacement-SPB501-V1J6-/201618699607?hash=item2ef1693557:g:jiwAAOSwEjFXfNuU&clk_rvr_id=1104826078997&afsrc=1&rmvSB=true

To keep an eye on the batter as well I'm going to have a small voltmeter/ammeter under a flap on the bag that is held down by a magnet (like an ipad cover). (£5.99)
https://www.amazon.co.uk/gp/product/B00Y0PIAAS/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

The style of the bag to help your imagination will be like the one below, but perhaps a bit softer round the edges and butting right up to the frame to allow wires to go between frame and bag.

There's a bit of spare space in the bag to fit the connectors stuffed in there. I'm going to have the FET side of the controller along the bottom edge of the bag. I'm thinking this could allow me to cut a few sqaures along that edge to act as washers and put an external heat sync? but something discrete that would go with the leather.

I've just found out that there is a week long national holiday in China at the moment waiting for parts. so my motor may not land until the 14th Oct. But I have lots to get on with. I'm waiting on a carbide die cutter set tomorrow to do the second headtube hole.

 

[MrDude_1]

I have an idea for the heatsink part.
See how that bag has a flap? imagine if you had an aluminum plate as a large flat heatsink, under the flap. stain it brown to blend in better, and then have the flap over it... but curl or space out the flap so there is still a tunnel for air to flow over it.
done correctly, I could see it working for your motor size and remain invisible.

 

[LewTwo]

To be even more discreet you could strap a phase runner to the seat tube (less wires as well)... of course it would not be cheap.
http://www.ebikes.ca/c-phaserunner.html

 

[MrDude_1]

To be even more discreet you could strap a phase runner to the seat tube (less wires as well)... of course it would not be cheap.
http://www.ebikes.ca/c-phaserunner.html

The phaserunner is awesome. I have one of the first ones he released. 100% worth the price... however he already has another controller, so I can understand him wanting to make that work first.
on the next bike.. buy one.

 

[LewTwo]

The phaserunner is awesome. I have one of the first ones he released. 100% worth the price... however he already has another controller, so I can understand him wanting to make that work first.
on the next bike.. buy one.

I just ordered one along with CA ver 2 to redo my Weight Weenie bike. Sort of overkill for a 36V 250 watt hub motor but then with that small a motor every little bit helps.

 

[LawrenceEaden]

@MrDude_1 That does sound cool! I like the idea of wherever it is getting good air flow when travelling at full throttle.

@LewTwo That looks mad good. It could easily fit in a tidy frame bag. I got this controller though to learn how it works and try and develop my own for extra functionality. All about the DIY and learning instead of buying more. I think the frame bag will be the most discrete way to do it. A, they already make them for non ebikes, so not conspicuous. B, where i've positioned it whilst riding my legs will shield it from the side profile. It all depends if it all actually fits in that profile.

 

[LawrenceEaden]

Battery Reinforcement

I managed to pick up some 25mm conduit from screwfix for about a quid for 2m. It has a OD just smaller than the ID of the frame tubes. I cut down it's length using about a 160 section per pack.

I added some a few more wires down the pack as redundancy incase i wanted to add a pedal assist sensor later and heat shrinked/shrank(?) a section of the pipe to the pack. It's starting to look a bit more like a battery now. I need to find some good connectors to go on the ends.

This reassures me a little that the solder connections shouldn't break as i put the battery in and out countless times I'm sure before the project is done.

 

[LewTwo]

Looks good so far. I tend to agree with some of the others regarding the gusset plates. I have used to same brazing kit the footloose mentioned. It runs out of oxygen quickly but I would think one bottle would be sufficient for three gusset plates. I did structural detailing back in the 1970's and the rough rule of thumb for reinforcing plates around holes was 2 to 2-1/2 times the material removed.

As far as stealth is concerned those Flaming Red tires/rims we draw anyone's attention away from the motor.

 

[Dumsterdave]

Im interested in how this thing will play out

 

[LawrenceEaden]

@LeoTwo Thanks for the advice. I'm looking at a few different reinforcement options. Ha, i'm yet to decide what the final colour scheme will be yet.

Frame Modifications - Second Head Tube Hole

I got some carbide die cutter bits this week to make the second head tube hole a bit easier than the first. It made such a difference with them actually cutting the metal instead of grinding it off with the stone bits.

Both holes finished! The next frame modifications I need to make are a cable route through the bottom bracket between the seat and down tubes for battery cables. Also making slots in the seat and top tube where the controller bag will be for cables to go between there.

Controller Bag

I'm trying to make the frame bag for the controller as small as I can. This is my first layout of the components to go in. I think i can tighten up some of the gaps and get a smaller ignition switch. For material I'm trying to get hold of a cheap leather jacket on ebay this weekend I can cut up, it may also have some useful clasps or zips on it.

 

[i2000s]

Do you plan to make a hard-case in order to fix the positions of switch and other boards?

For the key ignition, why do you use a 12V one while the battery is 36V?

Looks interesting!