Measuring speed and distance correctly

The Halfords bike computer needs to be "calibrated" in order to measure speed and distance correctly. In the accompanying manual there is a table of different wheel diameters and types shown together with the setting value (circumference integer)  that needs to be input into the bike computer. If it  had been the case that you could only select a wheel size listed on the table then I would have been stuffed, as the smallest wheel diameter listed is for 387.5mm. Fortunately, it is also possible to put in a custom setting value. The only thing that might be an issue is if the bike computer can actually cater for small diameter wheels such as those found on a skateboard. The manual goes into detail about measuring the wheel circumference. But we know that already for my long board specifications.

The setting value can be simply calculated as wheel size (mm) x PI. So for the case of my long board with its wheel diameter of 90mm the calculation is: 90mm x PI = 282.74. Converting to an integer, the setting value is 283. I entered this value into the bike computer, threw on my trainers, and went outside to conduct my first run on the long board:

It works!!! The maximum speed I recorded in this run was 12.1 MPH!

But disaster struck whilst performing this experiment. Just as it looked like I was going to approach top speed, the magnet that I had mounted  in the wheel flew off (see time stamp 0:25). Damn, I got carried away and forgot that everything so far was only held on by Blu-tack. It looked like the magnet rolled off under a caravan trailer. After 20 mins of looking for that magnet I am resigned to the fact that I need to purchase another magnet.

Initial set-up and test with the bike computer

As the title says - Initial! - hence the use of "Blu-tack" to attach the magnet, magnet sensor and bike computer to the skateboard:

Mounting of the bike computer magnet and sensor

For a bicycle, the magnet sensor (10) is positioned vertically along the bicycle fork. The magnet (11) is positioned on one of the wheel spokes so that for each wheel rotation it passes  near the vertical end of the sensor either at point (7) or the same position at the other end.



Mounting the magnet so it activates the sensor in the orientation as shown in the image below also works well. Using my hand to pass the magnet past the magnet sensor several times activates the bike computer and the distance value recorded is incremented.



Using "Blu-tack" I mounted the magnet on the inside of one of the front skateboard wheels. In addition I mounted the magnetic sensor with its length in parallel with the truck stem connecting to the wheel.

Chased by dogs!

I had some business to attend to on the other side of town today. I could've gone by car but the journey would have taken more than 20 mins each way, and at my destination there would have been the added stress of trying to find somewhere to park.

The other side of town is separated by  two large civic parks. Cutting across the parks allows travel almost as "the crow flies". The weather this afternoon was mild and sunny and it was very easy to get to my destination and back by my electric longboard.

These parks comprise several open fields with paths at their boundaries. Dog owners typically let their hounds of the leash to enjoy all this open space.

On my way back today I was chased by two dogs. Fortunately,  I was on a nice flat and smooth path and those dogs were of the small variety. Their little legs could not keep up with the pace, and within about 20 seconds I left them for dust.

The following Google'd  image seems quite apt :)

Bike computers - more bang for your buck

Yesterday I went to Halfords and purchased their 5 function bike computer (item code 679286). This seems to be a common model. You can buy them on eBay and Amazon too but with different names on them.

Unpacked it all, and boy you sure do get more bang for your buck You get the bike computer itself and the cradle it sits in. Cable ties for attaching the cradle to the bicycle handlebars, cable ties for attaching the magnet sensor to the the bicycle front wheel fork, and the magnet and screw attachment for attaching to bicycle spokes and the instruction manual. The manual  is a double sided A4 page but gives enough detail to cover all aspects for fitting to a bicycle. There is a wheel size chart that allows conversion from wheel size to setting value. The chart lists the smallest wheel size diameter as 305mm. However, I see from the manual you can also use a calculation to determine the setting value, so in theory smaller wheels (90mm diameter) such as those on my longboard should still be possible - the only thing in the back of my mind is that the bike computer might have a limitation to smaller wheels. This is because the magnet on a smaller diameter wheel would pass the sensor at a higher rate than for a bigger wheel and the bike computer may not be able to keep up. The only way to find out is to experiment!

Bike computers - a mature market

When looking at the various bike computers on the market I had quite  a few considerations for an odometer for my skateboard. Originally measurement of distance was my  main concern. But since all the bike computers include a speed function, my selected bike computer would  have to have a reasonably sized screen so that I could see the display whilst travelling on the board. Also it shouldn't be too big that there was a risk of kicking it off! Finally, I wanted a bike computer which had its own battery power and would not need regular battery changes. I did see bike odometers that were wireless (there's a transmitter mounted at the wheel and not connected by a wire to the display) and considered that the display could be warn on the wrist a bit like  a watch but this seemed more high-tech than necessary and I was dubious about how much power the wireless transmission would consume.

The bike computer market is mature - that means bike computers are a  mass produced product. Due to economies of scale this yields a significantly cheaper solution then going DIY and using a hobby microprocessor.

After much searching and comparing different cycle odometers I have settled on a five function one from Halfords. I figured it only costs 5 pounds and a small price to pay for experimentation. It measures speed, total distance and trip distance, plus it tells the time. Can't remember what the fifth function is....
Not sure if I'll order it or go there in person - probably travel there on my skareboard :). The next blog will cover the experimentation.

Distance anxiety

I've done more than 100 miles on my electric longboard now and the experience has been great. My travel distance on the skateboard for my commute to work is 2.5 miles each way. Sometimes longer when the weather is really hot and I choose a really picturesque path through the civic park.

I've tried the trip going many different ways and have learned which paths are the smoothest:- It's surprising how some tarmacked roads, although looking fairly smooth in appearance, give more judder than others.

Despite, knowing the board can do 4+ miles before needing a recharge, I was topping up the board battery power in the evening before work and during work. I never had a feel as to when the batteries would run out, as I wasn't monitoring my total distance for work or for play.

I've got into a regular pattern now with skateboarding to and from work. So now I only charge the board up at work :) However,  I do travel into the city centre on the board occasionally (just over 2 miles). One day on the way back I ran out of power. The board bleeped and then a two minutes later the power stopped!  I'm sure that beep should have given me more notice than that! - something I will have to monitor in future use. I was about a mile from home and had to lug that board all the way back. I did try free wheeling but fast concluded I needed more practice.

So I've been thinking about mounting a device on the skateboard to measure distance travelled. Knowing about the distance covered after each charge I can better forecast when the board needs a recharge.  Sure I could use an app on a smart phone to measure distance, but why not treat the board like a car  and have a permanent record associated to the vehicle.

A quick Google on the internet and a few attempts are evident. One manufacturer of conventional Skateboard use to make a board with built in odometer. Also a couple of hackers have made odometers for their boards. There's a nice "how to" on the instructables website. It uses the ubiquitous Arduino microprocessor, a magnet embedded on one of the skateboard wheels and a magnetic reed relay switch mounted close to the wheel on the skateboard truck. The Arduino microprocessor counts every time the magnet passes the reed relay  switch. Each pass of the magnet represents one revolution. Knowing the wheel diameter, the number of revolutions can be converted to distance. This is exactly how many commercial cycle odometer/computers work. I'd rather use something of the shelf than build from scratch myself. So I am currently investigating if a cycle computer could be re-purposed for measuring distance and speed on my longboard.

Curious onlookers on the boardwalk

On my commute back from work (train station) I have to go about 1/4 of a mile over a boardwalk. It always makes an incredible racket as the skateboard wheels bang against each plank of wood. The sound is almost like a machine gun with a slow fire rate. People always turn round to have a look. Yesterday afternoon, an oldish woman carrying two shopping bags appeared to freeze and just stare at me as I approached her. I gave her plenty of distance as I passed and she smiled and said an "an electric skateboard????" Yes! I cried, as I whizzed past her.

Volo-E to the rescue!

I've been in contact with Volo-E and they offered to swap the shell of my black controller for a white one. Here is the result:

Ok, still a gun shape but certainly looks less threatening than the black one.

Those black square patches are the Velcro patches that stick to the receiving patches under the skateboard. The controller conveniently goes there when you want to carry the board around.

Seem's not all eSkateboard manufacturers use a gun design for the controller

In terms of ergonomics the Volo-E gun fits the hand well and allows control of the longboard. However, in terms of the way it looks  I've heard a few comments now as I skate past various strangers such as "he's got a taser!" and "that looks like a gun". Whilst carrying my skateboard I've been stopped once already by the police and would rather not have that happen again.

I was curious if all electric skateboard manufacturers used a gun design for the controller. So I did a quick search on Google images. I've arranged the images of the controllers in order of desirability. Obviously the smaller and less gun like the better:

In a previous blog I talked about using  a 3D printer to make a new case design but concluded with the large PCB in the Volo-E gun controller there wasn't much scope to change the external design. In an ideal world the controller would be a bit like the Nintendo Wii Nunchuk. The products shown in the bottom images approach this. But I think that's only possible because they are not using conventional batteries but rather rechargeable battery packs which have a smaller profile allowing a tighter shape for holding inside the hand.

Found another review of the Volo-E Longboard

"TheBattersby" reviews the senior longboard (the same board as mine).  I see he has covered his Bluetooth controller in stickers to make it look less like a gun.

"TheBattersby" 's Electric Skateboard controller:

Hmm, won't be very easy to change the shape of the controller.... That printed circuit board is too big.... and the space inside the controller is pretty tight - not possible to saw off any bits to make the controller look less like a gun. Still saving up for my 3D printer so no early solution by making a new radically different shape housing is possible in the short term.