How to Convert Specialized Demo?

[wardrop]

Hi All,

E-bikes have really caught my imagination. Since I got my first brushless remote control car a couple years ago, I've always had a fascination with electric bikes (pedal, or motorbikes). I recently saw last years model of the Specialized Demo at my local bikeshop for 2/3's of it's original price ($3000 AUD) and began wondering how it would go as a base for an e-bike. This is the exact bike (yellow and black): http://www.specialized.com/au/gb/bc/SBCProduct.jsp?arc=2011&sid=11Demo

I'd like to get at least 3kw out of it, so one of the high-end hub motors is what I'd like. It needs to be quiet (like the Stealth bikes), and have a good balance of torque and top-speed, though I favour torque. I'd love some motor recommendations.

The other even more important consideration are the batteries, or more to the point, how to attach them to the bike. I'd be aiming for at least 1kw/h, preferably closer to 1.5kw/h, but given the nature of the specialised frame, it only has enough room in the middle for probably 20 LiPo cells at the most (2x 10S or 3x 6S 8000mah). I've been thinking of maybe only have up to 500w/h on the frame, and maybe storing a set of spares in a backpack which I swap them out with. Some other ideas would be welcome, keeping in mind that I want to preserve as much of the bikes natural aesthetic as possible, though I understand LiPo's only have so much energy density.

My intention is to use it for a combination of trail riding and downhill, so durability is pretty important. The controller is something I can worry about later as it depends on whether we can make a motor and battery combo work for this bike.

Any and all ideas are welcome.

Thanks

 

[dogman dan]

Well, there you are. Edit, double post, see below

 

[dogman dan]

Well, there you are. The problem is always how to carry a big battery. Since you want to ride technical, carrying much of it on a rear rack is unacceptable. For the same reason, carrying much in a back pack is unacceptable too. Same for the bars. Sure you can put 10 pounds there for easy stuff, but I wouldn't want more than 5 pounds there for the tricky riding.

The only good place to put the bulk of the battery weight is the middle of the frame. Low, but not so low you are going to rub a wheel landing a drop. Saddlebag style is about your only choice, though you might fit a row of it along the bottom of the downtube. I wouldn't put too much there though, perhaps 10 ah of 20s-24s. About .8 to 1KW. Any more is just going to be getting bulky and inconvenient. For a longer ride, it would be possible to spread out another 1KW to the other locations on the bike, or maybe a backpack. Perhaps possible to ride to the trail on the backpack, stash it, then ride the techical stuff on the main battery?

Motor choice depends on what your actual needs are. I'm quite happy just using a lower speed winding of a 9c motor. More like the stealth fighter than the bomber, but the right choice of winding and voltage has me going up slopes where the real problem is staying on the bike at all. It's a slow bike, 25 mph top speed, but she climbs. 25mph over the bars is plenty of speed for me.

The other issue is how you are going to controll torque. Before you buy, take a good look at how the dropouts are made. Removable bolt on dropouts are the best, so you can get motor compatible ones machined. At the least, you want something wide enough and flat enough to accept a beefy torque plate, again, custom made for your bike.

 

[wardrop]

Yeah, I'm thinking side-by-side saddle-bag in the middle. I might get 500w/h in there. I'm also thinking I could wrap packs either side of the bottom and top tube. There's probably at least 30cm there of unobstructed real-estate up near the head tube. Even on top of the top head-tube. The problem will be finding the best way to secure them. I guess tight straps are the only way to go.

So far, these batteries are the most energy dense I've found: http://www.hobbyking.com/hobbyking/store/__18210__Turnigy_nano_tech_8000mAh_6S_25_50C_Lipo_Pack.html

Each pack has about 180w/h. I think it'd be pretty easy to secure at least 6 of those to the frame for just over 1kw/h (matching the Fighter), or maybe even up to 10 which would exceed the capacity of the Bomber at 1.7kw/h.

As for electric motor, I guess I'd rather overspec than underspec. The battery and controller cost to run at 1kw vs 5kw is little different, hence I may as well spec up the motor for those instance where I need the power. After all, I can always just back-off the throttle or cap the controller to achieve lower power. A 10kg motor is perfectly acceptable. I'm thinking something along the lines of a Hadron Mk IV or Crystalyte equivalent (how much do they weight?).

 

[dogman dan]

Yep, goes without saying you will lipo it. Those are great if your budget allows it. At the moment, the least cost way to go is 4s 20c packs in the hardcase. A bit more wire, but perhaps the hardcase is worth it. Bear in mind, once you have 10 ah of it, you can pull 100 amps at 10c. Nanos for the win in a race of course.

What motor, and the weight of it, again that depends on your needs. My personal needs were to climb steep hills, but not requiring it to be fast. What I REALLY required was to not lug a 25 pound 5304 around. The rocky terrain I ride just pounded my tires to death in a few rides with a 25 pound hubmotor. So I got a lot happier when I lightened back up to a 15 pound 9c motor and stopped walking pinch flatted tires back home.

If you really want the power, the hot item right now is the Cromotor. Search out the threads on that. Hal's been doing some outstanding stuff with frames for years, and now he's turned his attention to motors. If you have the big budget, you'd just want to order a frame and motor from him. Search Greyborg, that's Hal's company name.

The other hot alternative this year is the new Crystalyte design. You can't buy a new 5304 anymore. The HT would be the one for dirt. Slower winding for dirt, then add voltage till you get the speed you need.

Bear in mind, it's not just so simple as get the hugest battery and motor avaliable. It's got to stay nimble, if you are going to ride technical. Otherwise why go bike? Just get a 4 stroke honda 250 if you want to ride something heavy.

 

[MadRhino]

I have converted mt Demo 8, and it is my best so far.
You will be happy with it, no doubt, but it is not an easy bike to convert.

I have cut the swing arm tubing to insert strong steel dropout.
That is the worse part, not only to have the balls to put the angle grinder in such a good freeride bike, but also to shape the dropout to make a perfect fit.

You need a large, ideally, for it is the only one to have room in the triangle to fit an 18 fet controller, and also because the shorter sizes don't have the same stability under hard acceleration.

I Ride it with various motors, for all my bikes are made to quickly swap components, and I have 4 motors here that are ready fit for my Demo 8. I use slow and fast windings of both the X 5 and H series motors, according to the course I plan to ride. I also use various controllers, and carry battery capacity for specific needs.

I have assembled Lipo batteries in fork packs and frame packs.
Every pack is a series of 4 Zippy Flightmax 6s 5800mah 30C bricks, making 24s 1p, 100v hot 580 wh.
I always use one fork mount, and add frame mount packs if I need more range.
That is not often, and most of the time a frame mount is filled with disc lock, plastic rain coat, and small tool kit.
I prefer riding it light weight, for I can charge in 20 minutes or just swap a fresh battery pack in no time.

The Demo 8 is a very good bike for conversion. It is not my fastest nor the one that has the longest range, but definitely has the best handling. It is a playfull bike in the mountain trails, and a very agile city ride. It rides so good that I can't help leaving my A-Line sleeping in the garage, although it is the one that is specifically set for winter commuting. So I ride the Demo 8 in the dirty salted slush, on snow and ice everyday, but I am converting a new dirt bike with the Cro-motor for the spring.

Good luck with your build

 

[dogman dan]

Had meant to say also, do whatever Mad Rhino says. He's the real dirt bike expert here. I just dork around with cheap wallmart FS frames and moderate power. I'm just older and more easily amused these days, and don't want to repeat the double collarbones broken.

 

[Phoebus]

MadRhino is the expert.

Unless you have good (excellent?) fabrication skills - or are friends with one who is - suggest you stick with bike that has bolt-on dropouts, such as Norco A-Line, Intense M6, Intense M9.

I went the easiest route - geared BMC motor which bolts directly into 135x10 dropouts. Only fabrication required is torque arms (machine shop can do). Fewer and fewer DH bikes are compatible with 135x10, but they do exist (Specialized Status). Note that I only run 1200W - about 1/5 the power that MadRhino does.

Have backpack mounted battery. This is the most expensive option (backpack with proper spine protection $$$) and least comfortable. I am pigheaded in my refusal to use LiPo

 

[wardrop]

Thanks for the replies guys. It's much appreciated.

So it seems the big problem is the drop-outs. Can someone explain what the problem is with the standard Demo drop-outs? Do they not have the strength to support the weight and torque of a powerful electric motor, or is it more to do with the width between the drop-outs? What's the most power such a frame could handle without modification to the drop-outs, except for a torque arm.

 

[dogman dan]

Picture putting a square bar into the dropouts. Then apply a wrench to the bar. It's a wrench about 4 feet long. Long enough to just about twist the square bar into a spiral. That may be about how much torque you would be applying to an aluminum fixture designed to have zero torque applied.

That's why there are many many many torque arm, torque plate, and pinch dropout threads here. That's why a removable dropout bike is a great thing. You take off the old ones, and have really strong steel ones machined to fit. There are lots of options, but nothing is really one size fits all for rear motors. Too much difference in how the frames are in back. So everybody has to come up with his own solution.

If you are lucky, somebody made stuff for his bike, and it's the same as yours. Really lucky if he made several and will sell em.

This issue of torque arms is one of the reasons I often recomend that people start out with less power. Build a bike with 72v 20 amps and a cheap frame. Go break it. Then start designing your stuff for 120v and 40-100 amps.

There is a trend building, for fabricating entire rear swing arms for bikes. You get your strong droput, and some extra length to help with the wheelies that are coming. Check out Zombies new thread. His cromotor is so strong it just wants to flip the bike.

 

[MadRhino]

Yep, you have to do them yourself, or find someone local who can work on your bike.

I believe that you will be the second ever to convert a Demo 8, so can't hope to have ready made parts for the conversion.
The Demo is still actual, I mean it is the best bike that Specialized had produced for freeride and DH, and still one of the best to ride as of today. It has a good place as a gravity bike, so its used value is good even after many racing seasons. Few DIY hobbyists like to start a project with an expansive bike, and even when they do, they chose one that is easy to convert, one that has good triangle space and flat dropouts.

The compact 3D shaped dropouts of the Demo, are probably the worst for conversion. You just cant use the simple solutions, usual torque plates or arms won't do it. I stared at it for a while, before I got to admit that this one would need the dropouts to be inserted into the swingarm tubing.

Then, you have to realize that your brand new Demo 8 will need upgrades from the start. The rear brake won't fit with a motor, the best I found to replace it is the Magura Gustav M, for it is a very good DH brake that clears any hub motor. The front brake is good and will do for a while, but with the power and weight of the build, you soon will want better. I tried a few, and finally settled with the Hope Tech V2 EVO.

The rear suspension shock will need to be upgraded too, for the weight of the hub requires better damping that most DH shocks can be tuned to. I found that a big air shock is the best for that, but the choice is not plenty to offer a big air can. The Rocco air WC does it good, but it won't fit the Demo and I had to dremel the swingarm, and fabricate an excentric bushing set. A spring loaded shock that could have sufficient damping tuning range is way more expansive, and I'm not sure that it would fit the demo either.

Ideally, you will want the fork steer tube to be uncut, so you can cut it yourself to set the stem higher and use the extra space to install a solid clip-on holder for the fork mounted battery. A battery support made with alu can be clamp bolted to the fork tubes, but it is good to have the battery in a bag that can be taken off and swapped quickly. The extra height of the stem also makes space for the battery setup to clear the fender that you will want to do, sooner or later. It will also let you access the battery to monitor every cell and feel the temp when you want to quick charge on the bike. The stem will need to be replaced for one that is long enough to set the handlebar mount right in the middle top of the battery weight, so that if you draw a line between the handlebar mount and the wheel axle, this line would pass through the middle of the battery pack. That is how you will have the best steer handling, in fact it will be better than before, and you will find that you'll be able to ride the Demo without the hands.

Controller goes in frame, for it is safe there, and exposed to air flow for cooling. That is an easy setup, the 18 fet fit tight in the large Demo frame, and leave you with just enough space to make a waterproof connection box.

You can fit a 7 gear 11-34 freewheel with the Clyte motors, to clear the chainstay of the Demo. You won't use them much but it's good to have them. The rear shifter will need to be replaced for a twist grip and installed on the left, you remove the front shifter but keep the small inside chain ring, so you can manually shift on it if you ever have to pedal the bike in the mountain with a dead motor.

Half twist throttle on the right, with a 3 speed switch, leave you with just enough space to fit the rear brake lever. The Cycle analyst can be installed on the stem, and lights each side on the handlebar (hi and lo beam).

Well, I believe that you have enough to think about. If you build it, you may ask for solutions here. ES is a wonderful resource, you can find specialists in every fields to help you.

 

[wardrop]

Hmm, seems like a lot of work. I was hoping it would just be a matter of motor + batteries + controller, but I guess that's only the case up to maybe 500-1000 watts.

 

[emergence]

If you wanted to start simpler, I just got this setup running.

http://endless-sphere.com/forums/viewtopic.php?f=6&t=35921

For off road I've put the battery in my backpack. 2808 is not good for steep offroad climbs as it bogs down way to early but with a 2806 or even a much lighter geared hub you would go much better. Having the battery in the bag makes it feel much more like a mountan bike rather than a motorbike and you can experiment with pack size and config much more easily while you workout how to get what you want before you commit to an on frame battery design.

The demo has a pretty tight frame for batteries (the old DH Comp frames are becoming popular ebike donors because they ave so much space in the frame), but you should be able to draw up a torque arm and get it cut to fit without cutting into the rear arm.

after I get used to this setup I'll start experimenting with lipo etc... maybe... The greyborg looks pretty fun too..

 

[MadRhino]

Hmm, seems like a lot of work. I was hoping it would just be a matter of motor + batteries + controller, but I guess that's only the case up to maybe 500-1000 watts.

It is never that simple, but the Demo sure pushes it a step further.
The reward is an Ebike that has amazing offroad handling and performance.
To surpass this build on a DH single track, one is likely to spend alot of time and money on an RC build, that would be much more complicated, and would be noisy too.

I am starting a new build with the Santa Cruz V10 and the Cro-motor, and I doubt from the start that I can do better than the Demo.

 

[Phoebus]

Also, to make things a bit simpler, I had my first ebike - a full suspension downhill bike - put together and got all parts from ilia, owner of ebikes sf. He is extremely professional, uses excellent parts, and was able to fabricate what was needed. If you talk to him about what bike to get to make things work simply, and which motor etc to use, he can put something pretty awesome together.

Check out his website. I've put well over 100mi on my BMC V4T motor from ilia, and it's stood up to the abuse quite well.

 

[LegendLength]

My friend converted a full suspension specialized last year although it wasn't a demo

( http://endless-sphere.com/forums/viewtopic.php?f=9&t=28156 ).

From memory it had 0.8 kWh of range . No torque arms though unfortunately so not much help there. But I would like to say a couple of things about battery setup:

My bike has 0.6 kWh of lipo and still feels quite heavy. I'd recommend going towards the light end of the spectrum if you want to ride off-road, it feels a lot better. I'm unable to reduce my batteries to 0.4 or 0.3 kWh because of my wiring harness but if I could that would be a good number for me.

It all depends on where you ride of course and how close you are to the trails. There's the option to carry an extra 0.3 kWh block in your backpack and hot-swap them. Although that is 2.0 kg so it would be like carrying a 2 liter bottle of coke.

Fitting the batteries is obviously very hard on that type of frame but there are options. You can get the 3s lipo instead of 6s and tile those on the side of your frame ( http://www.hobbyking.com/hobbyking/store/__6501__ZIPPY_Flightmax_5000mAh_3S1P_15C.html ). You can fit 4 of those between your knees confortably and without hitting the pedals. About an inch of spare padding room.

If you do end up buying the bike and struggle with the battery setup I'd recommend cutting out rectangles at the exact size of the batteries (even just flat rectangles are useful). Allow a good amount of room for wiring and padding of the box. Also consider where the leads will run down the frame into the box. The connectors themselves seem to take up an annoying amount of precious space in the box.