Concept Discussion - Range finding for road biking.

Thread Starter

mcardoso

Joined May 19, 2020
116
Wife and I are amateur cyclists and are often drafting off of eachother to get some added speed. When drafting, it is important to stay within 0.5-3 bike lengths behind the other person otherwise you aren't really getting any benefit. As we get tired, it is not uncommon for one of us to accidentally "drop" the other and the person behind has a brutal time catching up.

While we were riding yesterday I was dreaming up a simple device that each of us would have on our handlebars that would have 3 LEDs. When the two devices are close (the person behind is right on your tail) the LED would be green, if they started to drift behind it would turn yellow, and if you dropped them and they were far away, it would be red. If the other receiver was not found, then the lights would be off.

I wanted to think about some ideas for what technology would be good for this purpose. Ideally it would be about the size of a speedometer and run on a large coin cell battery. It could be manually turned on at the beginning of the ride and only need to update maybe once per second. Minimum range would be 5' and maximum range of maybe 50'?

For the person in front, it can help them set a pace that doesn't kill the person behind them. For the person behind, it can be a little game to keep the light green.

Any thoughts on what sensor could do the range detection (thinking RF) and how to limit the power consumption so it lasts for a lot of rides?
 
Last edited:

wayneh

Joined Sep 9, 2010
16,398
Wife and I are amateur cyclists and are often drafting off of eachother to get some added speed. When drafting, it is important to stay within 0.5-3 bike lengths behind the other person otherwise you aren't really getting any benefit. As we get tired, it is not uncommon for one of us to "drop" the other and the person behind has a brutal time catching up.

While we were riding yesterday I was dreaming up a simple device that each of us would have on our handlebars that would have 3 LEDs. When the two devices are close (the person behind is right on your tail) the LED would be green, if they started to drift behind it would turn yellow, and if you dropped them and they were far away, it would be red. If the other receiver was not found, then the lights would be off.

I wanted to think about some ideas for what technology would be good for this purpose. Ideally it would be about the size of a speedometer and run on a large coin cell battery. It could be manually turned on at the beginning of the ride and only need to update maybe once per second. Minimum range would be 5' and maximum range of maybe 50'?

For the person in front, it can help them set a pace that doesn't kill the person behind them. For the person behind, it can be a little game to keep the light green.

Any thoughts on what sensor could do the range detection (thinking RF) and how to limit the power consumption so it lasts for a lot of rides?
Your description reminds me of a device my wife has in the garage to help her park. It detects the distance from the sensor to the car and indicates that with a 3-color LED. It resembles this one, and I suppose there are many competing products.
https://www.ebay.com/c/2254458678
https://www.homedepot.com/p/STKR-Ultra-Sonic-Garage-Parking-Sensor-00246/206130073

I think it uses an ultrasonic range finder and that's what I'd look at for your project.

Smartphones these days can also apply image analysis to measure distances. An iPhone can measure a sofa from across a room, for instance. I just don't see how you could make that work out though, even if you could find a cheap, used phone to use.
 

jpanhalt

Joined Jan 18, 2008
9,784
Rather than radar or sonar that depend on reflections, I would go the transponder route (sound or RF). Sound would be easier. Ultrasound with coded modulation for noise immunity would be sent by the leader, received and echoed by the trailer. Leader's display would show the distance. The advantage is that aiming would be less critical.

A simple horn on both might be much simpler. When the trailer gets too far behind, he would sound the horn to tell the leader to slow down.
 

Thread Starter

mcardoso

Joined May 19, 2020
116
Your description reminds me of a device my wife has in the garage to help her park. It detects the distance from the sensor to the car and indicates that with a 3-color LED. It resembles this one, and I suppose there are many competing products.
https://www.ebay.com/c/2254458678
https://www.homedepot.com/p/STKR-Ultra-Sonic-Garage-Parking-Sensor-00246/206130073

I think it uses an ultrasonic range finder and that's what I'd look at for your project.

Smartphones these days can also apply image analysis to measure distances. An iPhone can measure a sofa from across a room, for instance. I just don't see how you could make that work out though, even if you could find a cheap, used phone to use.
I like the concept of analog distance measurement from the sensor. It could either be a true analog signal or a serial connection. I don't know if ultrasonic would be the right sensor since it is so directional. The sensor would need to be mounted to the rear of the bike and would miss if the trailer moves off center (which you do in cross wind). I was hoping for an omni directional sensor that would be contained within the display device.

Would a radar module, such as this, do? It claims a range of 3-9m.
Honestly not sure what that module does :) If it is an on/off switch then that probably doesn't convey the info I need, but if it could do distance between the two modules then it might be perfect.

Rather than radar or sonar that depend on reflections, I would go the transponder route (sound or RF). Sound would be easier. Ultrasound with coded modulation for noise immunity would be sent by the leader, received and echoed by the trailer. Leader's display would show the distance. The advantage is that aiming would be less critical.

A simple horn on both might be much simpler. When the trailer gets too far behind, he would sound the horn to tell the leader to slow down.
I too agree with the transponder idea. Some sort of time of flight calculation.

The simple horn is what we currently do, but it makes a "slow the f*** down" sound. ;)
 

jpanhalt

Joined Jan 18, 2008
9,784
Of course, the speed of sound varies with atmospheric density. That is probably not much an issue unless you are biking at 12,000 feet. ;)
 

wayneh

Joined Sep 9, 2010
16,398
Now that you mention the beacon idea, can't modern Bluetooth estimate distance that way? Just use the signal strength. You might be able to use your smartphones with nothing more than a custom app.
 

MrSoftware

Joined Oct 29, 2013
1,824
I think I would give ultrasonic or radar a try. It's directional, but more like a flood light than a laser. Laser would be bad, too pin-point. Anything RF that works off of signal strength, as opposed to time, I think would be problematic. Small changes in antenna orientation can make big changes in signal strength. Time-of-flight for RF would be different, but I'm not sure what components are on the market right now to make that easy. So I would personally try ultrasonic; it's cheap and common, there are parts everywhere and worst case you put a few ultrasonic sensors together at slightly different angles and just listen to the one with the strongest signal. Here's a link to help with your search: https://www.sparkfun.com/products/639
 

MisterBill2

Joined Jan 23, 2018
6,358
When I ride with others I have always found it important to be aware of where the other bikes ar. This helps avoid bumping and crashing. And for drafting we kept our front tire just a very few inches from the back tire of the bike ahead. So focused attention was very important.
You could get a bike rear view mirror and glance at that frequently. Cheap, easy, and no battery to go dead.
 

MrSoftware

Joined Oct 29, 2013
1,824
Two pieces of rope with a flexible bar in between. Free ends tied to the bicycles.
Looking back on my childhood years, I can say without question that any sort of rope between bicycles (or motorcycles and bicycles, or motorcycles and skateboards, or motorcycles and stop signs, or anything with 2 wheels involved) is a very bad idea. The slightest mishap and someone has a rope wrapped around a tire. Side note: I do get what you're saying with the flexible bar, safer than loose rope, but any sort of connection between bikes with finite length is a potential problem.
 

atferrari

Joined Jan 6, 2004
4,020
I vaguely recall doing something like that as a kid but not the details. Adults focused on doing it right, could try something (previously signing a beefy contract with Assistcard).
 

Thread Starter

mcardoso

Joined May 19, 2020
116
Now that you mention the beacon idea, can't modern Bluetooth estimate distance that way? Just use the signal strength. You might be able to use your smartphones with nothing more than a custom app.
Very probably! Have no experience with writing apps, but you are probably correct. Omnidirectional distance measurement by signal strength.

I think I would give ultrasonic or radar a try. It's directional, but more like a flood light than a laser. Laser would be bad, too pin-point. Anything RF that works off of signal strength, as opposed to time, I think would be problematic. Small changes in antenna orientation can make big changes in signal strength. Time-of-flight for RF would be different, but I'm not sure what components are on the market right now to make that easy. So I would personally try ultrasonic; it's cheap and common, there are parts everywhere and worst case you put a few ultrasonic sensors together at slightly different angles and just listen to the one with the strongest signal. Here's a link to help with your search: https://www.sparkfun.com/products/639
I have quite a few of those sensors and I think they'd work well. I was hoping to avoid having to mount additional hardware on the bike, besides the display unit. Just more stuff that needs to be waterproof.

When I ride with others I have always found it important to be aware of where the other bikes ar. This helps avoid bumping and crashing. And for drafting we kept our front tire just a very few inches from the back tire of the bike ahead. So focused attention was very important.
You could get a bike rear view mirror and glance at that frequently. Cheap, easy, and no battery to go dead.
This is absolutely the right answer (and easiest!). I'm just being the silly engineer who wants to overdesign the solution. I agree with your first comments too. We are good at not rubbing tires, but I fall off the back sometimes and have a little pride thing not to shout out. My wife is in much better shape than me!

A rope connection between bikes in motion is a poor choice most of the time.
Operator awareness of the situation is the obvious solution.
Ouch!

Looking back on my childhood years, I can say without question that any sort of rope between bicycles (or motorcycles and bicycles, or motorcycles and skateboards, or motorcycles and stop signs, or anything with 2 wheels involved) is a very bad idea. The slightest mishap and someone has a rope wrapped around a tire. Side note: I do get what you're saying with the flexible bar, safer than loose rope, but any sort of connection between bikes with finite length is a potential problem.
LOL, I feel like there are many stories behind this comment!
 

drc_567

Joined Dec 29, 2008
855
The board shown here is said to detect objects up to 3 meters away. It would be necessary to interface with a microcontroller such as the Arduino ... an example is shown in the 'Arduino Workshop' by John Boxall.
distance sensor
 

Irving

Joined Jan 30, 2016
820
Ultrasonics work quite badly in the noisy field and the frontal area of a bike isn't great.

I've had quite a lot of success with sensor boards based on the STM VL53L1X time-of-flight sensor in the 1 - 3m range. Far more reliable than ultrasonics...
 

MisterBill2

Joined Jan 23, 2018
6,358
OK, now I am inspired to suggest that a relatively simple option will be a retro-reflective mode proximity sensor, similar to the common industrial versions used most often as beam-block photo-electric sensors. But in this case the reflector will be in the front of the bike towards the rear, and the sensor would be looking back from the leader bike. Detecting the presence of the follower would keep the green indicator illuminated, loss of detection will make it switch off. The main challenge will be in the width of the beam and it's return sensor patterns. In the industrial versions the beam is quite narrow, only 2 inches at several feet. So the radiator will need to be more like those used for security system beam break sensors. The good news is that those devices have been available for decades and so the technology is available in many locations.
 

Tonyr1084

Joined Sep 24, 2015
4,737
Rather than radar or sonar that depend on reflections, I would go the transponder route (sound or RF). Sound would be easier.
Isn't sonar "sound"?

The rope idea? I like it. Especially when I'm behind and I let the person up front tow me along. (JK)

I DO like the garage parking indicator idea (sound based). However, it's bouncing a sonar off the back of a large vehicle with basically a hard face, be it plastic or metal. A bike with its round profiles and the soft human body (extra soft with me) wouldn't be a good reflector.

Sorry, I can't come up with any good ideas. Can't even come up with a dumb one. Maybe a SWR meter (Standing Wave Reflection) like used when tuning a CB radio (or other transmitting device). But now you're carrying a transmitter and batteries. That idea doesn't EVEN rise to the level of "Dumb". But it will be interesting to watch this thread for solutions.
 

MrSoftware

Joined Oct 29, 2013
1,824
It is a case where RF time of flight would be a great solution, but I'm not sure if there are any RF ToF modules available to make the implementation practical.
 

MisterBill2

Joined Jan 23, 2018
6,358
The pulsed light beam system is a fully mature technology with many products available to purchase, and circuits available to copy. The leader wold have the device pointing behind their bike, the follower will only need a 3 inch retro-reflector pointing forward. The leader would have a green indicator that goes out when 6the distance becomes too far. Two units with different ranges could provide both green and yellow.
 
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