Let's Make Robots!

"Pedometer" for roller skates?

So as I mentioned a few months ago, I'm currently training to join a local roller derby team. I am, for lack of a better word, quite out of shape. I can only afford to go skating once a week, and want to make sure I am getting the most of my sessions.

I've seen pedometers for runners, and even small GPS units for skaters going outside, but what if you're inside?

I'm a quad skate snob, and will use my indoor skates for INDOOR ONLY. However, I really want a way to track how far I've gone during my sessions. Even the knowledge that I'm going a wee bit farther every time would be exciting. I get disheartened easily and want something to keep me going.

I'll first post pictures of my skates to get creative juices flowing, then spout off my own ideas:



OK. So I'm thinking one idea would be to paint on the inside of one wheel and use an encoder, but I'm not sure how high I need the proc to count.

The top two pictures show where ideal proc placement would be between the shoe and plate. I want it in a place that is easy to get boots on, and won't hurt me if I fall, because I WILL fall.

Waterproofing isn't a big deal, but if it works out well, I'd like to eventually make a waterproof version for when I can afford a second pair for outdoor use.


Any thoughts guys?

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First of all: Kudos on the meters! Especially when measuring footwear!

The optical wheel encoder is indeed the obvious choice, so I will makeone less obvious. Measure the exercise, not the distance.

Of course there is all kinds of ready made training meters that will monitor heartbeats. But how about measuring how often and how hard your foot pushes against the floor. I suggest a piezo pressure sensor in between the toe of the shoe and the wheel plate. The voltage generated with each push will tell you how hard your leg is working. And how often.


How about putting a resistive strain gauge onto the underside rubber mech.

I assume the rubber Mech. flexes with your sportive skating style.

ooh, that's a cool idea!

It might be a good idea to do both. I'm not sure if it would register though. the bottoms of skate shoes are quite tough. I might just have to buy a pressure sensor just to see.

Why not put a small tab off to the side of one of the wheels and have a PIC count how many times the tab triggeres a sensor. If you know the circumference of the wheel multiply that by the number of revolutions. Or as someone else said find out how far around the track is and count how many times you go around. It isn't exact, but it is free.

EDIT: I forgot to think about hwo the wheels continue turning when you pick up your foot and how when skating you cover some of the same ground twice. If you want precise this will make it a bit more difficult unless you find out your average stride and count how many times you put your foot down. This would count distance the same way hikers and orientiering people do it over vast distances in remote locations.

yeah, I'm not too worried about exact amounts. But maybe with Rik's idea. When the pressure sensor is active that's when it counts rotations.

The only thing there is I'd have to have one on each boot to count total distance. Hmm...

I think starting dirt simple may be best. You could start with an off the shelf pedometer. From the pic, it should fit in the gap between the bottom of the boot and the frame. It already has a nice counter, display, and reset. It should be simple to bypass the defult input and trigger the counter with a microswitch. Then there are two simple options for counting.

1. you could put a small bump on the wheel(small epoxy lump maybe?), and mount a microswitch so that it is triggered by the bump. I think that this may be a bit too much for the microswitch since the rpms of the wheel will be pretty high.

2. Again with the microswitch, but drag a small feeler, so that the switch is triggered when your foot is lifted.

You could try this for $10 or less in parts, and just take a look at the data. Do a fixed number of laps and look at the count, then try again. I imagine that you will find a relatively consistent number of counts per lap. I know that this is not the exact solution you are looking for, but it should give you some useful result, and it is cheap.

Very cheap idea! I like!

Quite simple to compared to the others.

Now I'm tempted to go buy a pedometer just to hack it and see what I can do.

Thats assuming that you only move with your feet on the floor. Depending on how you skate your feet are off the ground half the time when not coasting. That distance needs to be calculated somehow.
And that's the stumbling block I come accross every time I try to figure this problem out! I would say my feet are off the ground about 1/3 of the time. There are quite a few moves that involve both feet on the ground.

So each rollerskate has to know when the other one is off the ground, which means they have to communicate. You could create one unit that only sense on/off ground and the number of rotations of the weels and send it (or only send rotations when the skate is on the ground) to the other unit, which takes the data from unit one and the data from itself and calculates the distance. Since the distance between the two skates are relatively small, I don't think the radio transmitters will be very large. It might work.

Sparkfun has some radio modules http://www.sparkfun.com/commerce/categories.php?c=79. Some of them seems to take up too much space for your application and some of them are out of stock, but it might be worth taking a look at.