Dirtsurfer electric build

[benj]

The time has come! I'm finally starting my conversion after much thought and searching around.

The donor is a Dirtsurfer FS. This is the freestyle version with the flexy deck, 16" wheels and disc brake.

I spent a while deciding if I should use an electric hub, or try a mid mount, and have decided to go the mid mount route. I haven't seen a Dirtsurfer converted like this before, so it's going to be a good challenge. The good news is I have the electronics from my Alien powered longboard which I can use to get this project rolling.

Looking at the back end of this beast, there is quite a bit of room for a motor in the rear well area...and it looks like a chain or belt would have a clear line between this area and the current rear hub.

 

[benj]

So my first main job was to find a way to get a sprocket onto that rear hub. The current hub is standard narrow front fork dimensions...100mm..and with a standard 6 holes for a disc brake.

I wanted to keep the disc brake, but also get a sprocket on there somehow. Through all of my searching and contacts it was impossible to find a hub that was 100mm with disc holes and a thread for a sprocket, but eventually I turned up this little guy:

From http://www.choppersus.com/store/product/1095/Std-Rear-Hub-FW-Disc-BLK-32/

Damn, 112mm! Pretty close, so I ordered him and offered him up....didn't fit and really didn't want to bend the frame of the Dirtsurfer.

Luckily I noticed the stock Dirtsurfer hub had thinner lock nuts:

What a bit of luck! Swap over the lock nuts between old hub and new...bingo:

Just a small bit of tweaking on the disc brake alignment and it's looking solid So that's the rear hub sorted - almost. I know the current freewheel is too small, only 22 tooth and a gear ration of 1:2 isn't going to cut it on this thing!!!

 

[benj]

Now that the hub is in place, I made a temporary motor mount and put together a mockup of the drivetrain...

It's looking great. Clearance is probably a bit tight for the chain, but I think I'll get away with it

Now it's time for my buddies at the engineering shop to take a look. I don't have the tools or skills to make a proper motor mount so that's their job.

For the rear sprocket, I've dug out a 44 tooth sprocket which I hope I can get threaded or mounted somehow onto the hub thread

 

[stuntmanmike]

I'm dying to see this done..
I demo'd one of these years ago at the Killington bike park in Vermont & its lots of fun, but very sensitive turning at low speeds. It took a minute to get the hang of, but I felt it was more like a snowboard at higher speeds, for sure.
Please put up some images.

 

[made_in_the_alps_legacy]

So nice to see extra ordinary project like this one,
i guess u chose the challenging option with the mid mount rather than hub and i look forward to see ur transmission

 

[bee]

One of these for the rear: http://bikemotive.myshopify.com/products/custom-acs-crossfire-flanged-freewheel

 

[benj]

Thanks Bee - that link was very handy! I'm in the UK, I'll see if I can source over here or if they ship. I might just end up welding onto the existing 22t sprocket...those bits aren't expensive, so worth a shot.

 

[Jonboy]

I'm so liking this.. I spend alot of time at the beach.. those big wheels & the motor tucked up (& / covered)

Please fill us in on the reduction ratio, what alien motor ETC

 

[bee]

cyclone has the flanged freewheel and a variety of sprockets up to 48t for it:
http://www.cyclone-tw.com/order-chainwheel.htm

 

[benj]

I'm looking at a 4:1 reduction ratio right now (44t rear, 11t front). I'm hoping it will be good...but might be too much speed with those big 16" wheels I've estimated about 40mph.

The motor is the Alien 63mm 6374 170kv 3Kw running through an Alien 120amp ESC from a 8000mAh 5s lipo.

I can't wait now - the engineering shop have the bits, so just waiting for their call back! They seemed happy to be working on something a bit mad

 

[james_baja]

Sounds like an awesome build!

FYI your speed calculations are correct but you will not get much torque from one 170kv motor needing to move about 100kg?
We use 4 X170kv motors on the bajaboard and our top speed is about the same as you have calculated.
See how you go, but i think you may need to increase the gear ratio and sacrifice a bit of top speed. otherwise you may experience alot of cogging and little movement.
Brushless motors deliver a large amount of power but only when they have rotational momentum.

 

[benj]

Thanks James!

I would be happy to sacrifice top speed for torque...I don't need to go 40mph (well, not on the flats anyway!)

It will be interesting though, as I don't think I need the torque for starts. As the Dirtsurfer only has 2 wheels, you have to kick or push to get it rolling and balanced, then I'll apply the electric power once it's rolling. It will no doubt take some getting used too, but I think it should be OK. Fingers crossed

 

[benj]

Exciting times, I got my Dirt Surfer back from the engineering shop and it's looking great Everything lines up really well and it's looking strong. They welded a small bracket to the bottom of the chassis, and by using part of my APS mount, it allows some chain tensioning too.

I've run a quick bench test with the electrics and it's all good so far.

Now I just need to work out how to lace my 32 hole hub into a 28 hole rim....not sure if that will work. If not I'll have to wait until the new year and find a 32 spoke 16" rim.

So close to be rideable!!!

 

[benj]

Bench testing the drivetrain:

[youtube]http://youtu.be/Q-cBxckEavE[/youtube]

 

[adrian_sm]

[youtube]Q-cBxckEavE[/youtube]

[youtube]Q-cBxckEavE[/youtube]

 

[made_in_the_alps_legacy]

I've run a quick bench test with the electrics and it's all good so far.

Note that this is a "no load test".
(a representative test would include "dynamic resistance" like inertia of the wheel and of urself, + aerodynamic drag, and "steady resistance" - like brake, hills)
Maybe u could add some braking during this test to simulate how it behaves with "some" load and if it cogs...

+1 regarding the eventuality that the 4:1 transimssion ratio might be temporary

 

[benj]

So after learning lots of lessons about wheels, hubs and spokes, I finally found the right parts to lace my back wheel! Here is the end result, the first rideable version:

I'm not happy with a couple of things with this - firstly the motor is too low and the clearance is not great. This is because I had to use a slightly larger rear wheel which is my second problem.

I am using a 32 hole hub, and it wouldn't lace into the original Dirtsurfer 28 hole rim. I looked all over for various ways to fix this but most people suggest not trying to lace a wrong hub to a wrong rim. I eventually went with a new rim, with 32 holes to match my hub. For anyone else thinking about doing this, there is lots of other options. There is a 36 hole version of the hub I used, or you could used a flip flop hub with screw on disc brake adaptor.

What I didn't realise is that not all 16" rims are the same! The Dirtsurfer original is a 305 rim, and I ordered a 349 rim - the 349 rim is 44mm bigger - so it rubbed against the motor with my new motor mount The choice of 305 rims is very limited so I need to rethink this area. The 349 rim also suffers from a lack of tyre choice, there isn't any offroad/mtb tyres for it, so I've got some horrible road tyre on it right now...maybe good for power slides, but not good for grip on grass

Anyway, still exciting because this version is rolling and rideable, and so far - all good. Just had a very short and quick blast in my back garden and so far it seems pretty good. Cogging at low speed was always expected, and it certainly does that. It also requires a very smooth trigger finger whilst kicking which is proving tricky, but I'm sure practice will iron everything out.

I should probably wait until I can get the motor tucked up a bit more before I ride it properly, so updates coming after that is sorted.

 

[parajared]

Maybe put the motor on a bicycle rack like the 2 stroke bicyle guys do it?

Looking forward to seeing this thing come together, and the youtube video of you blasting around on the thing.

How does two wheels feel compared to the feel of a 4 wheel mountain board?

 

[benj]

Hey parajared. Not a bad idea, but there is plenty of room to tuck up the motor - it's just because my wheel is too big that I had to hang it so low.

2 wheels feels great when moving, it's a lovely thing to ride downhill and carving is super fun. The turning circle is pretty big, and the board is pretty heavy, but it does feel nicer to ride than a 4 wheel MTB. It's just a lot smoother, less shakey, more stable...and the faster you go, the better it feels.

However, pushing to start is it's main downfall. Because the front wheel wobbles a lot until you get speed, it is difficult to start unless you start on a hill. I'm hoping the electric drive will fix this.

It's certainly not beginner friendly But I'm fine with that

 

[sn0wchyld]

What about adding some simple shock absorbers to the steering? Just to dampen rapid swings?

 

[kfong]

I just picked one up, same model. Came in the mail today. Ordered the Magic pie 3 16" wheel for the build. Should be a simple conversion. Going with a wireless throttle setup and custom battery build. It's going to be a fun summer

 

[benj]

Awesome Good luck with the build. How do you make the MP3 work wireless?

 

[benj]

Finally had some dry weather and a chance to take this Dirtsurfer for a proper blast around!! The bad news is my phone was too flat to grab any video But I did manage to get some GPS logs.

Overall - this thing is a blast to ride I got about an hour out of 2 5000mah 5S batteries across a mix of cruising and uphill.

Top seed was 20mph. I'd like it to go faster Torque is really good, but steep hill climbing makes the ESC cut out. Moderate hills where no problem.

Power slides in the mud no problem either! General cruising around getting a good carve on, it's really fun. Here's some post-mortem pictures of the mud - next time I promise to get some video!!

So I'd call the mid-mount idea a great success I think. I'll probably try some 6S batteries on it, and I'll consider looking at the motor KV to fine tune the speed/torque. I might also look at some boat ESCs as I don't need an electronic brake and I'd like to reduce bulk (make room for more batteries!!).

In the end I found a 20 hole flip flop hub and matching 16" 302 rim. I used a screw on disk brake adaptor on one side and my custom chainring on the other. It runs really smoothly, the chain isn't really very noisy, and there whole thing seems pretty bullet proof mechanically. I managed to get the motor tucked up enough so even when the board bails there is no risk to the motor hitting the floor.

I'm off to charge the batteries and get some more EV grins back on!

 

[benj]

Finally some video of this thing being ridden. Sorry it's not the best....holding an iPhone and trying to ride this was kinda interesting

So much fun. This video is now on a 6S setup and I probably hit about 80% throttle I think. Top seed was 20mph.

[youtube]iWkW7nW9JPo[/youtube]

Hit a few roots on my way, and ended up bending the hell out of my battery box. Scary how much it bent considering I didn't even notice. Everything inside was find though but it does show that battery protection is very much needed and not to be under estimated.

 

[made_in_the_alps_legacy]

Thxs for the vid', I am surprised how smooth the ride looks, I would love to try it