Electronic wireless shifting and passive RFID

[cribbit]

Why aren't passive RFID tags used in wireless electronic shifters? Compared to a normal battery + transmitter setup they're smaller, lighter, cheaper and last forever. It's not difficult to waterproof a normal setup but an RFID setup can be sealed trivially as there's no need to ever open it up.

Passive RFID is already used to great success in a lot of passive sensor reading areas.

[crankles]

you need a fairly decent electromagnetic pulse to induce the RF no?

[cribbit]

you need a fairly decent electromagnetic pulse to induce the RF no?

I've been trying to determine what the power draw is on the RFID reader that polls the tag. I know the polling rate can be plenty fast enough.

It should also be possible to have the tag only transmit a burst when a shift is made, allowing for a much lower power draw on the reader.

[Mark McM]

You'll have to explain what you are attempting to accomplish using passive RFID technology in a wireless shifting system. The inductive power transmission between the reader and the passive RFID is very inefficient - which is okay, because the passive RFID requires requires very little power. While using inductive power transmission in a wireless shifting system would eliminate the need of a battery at one end, it would greatly increase the size of the battery required at the other end.

Also keep in mind that the effective rage of inductive power transmission is highly dependent on the size of the transmitter's antennae coil - and you really don't have much room on a shifter or derailleur for a large antennae coil. The reason that the timing mats (used for race timing with passive RFID chips) are so large is not just so that they are hard for the racer's to miss, but also because they allow the use of very larger coil antennaes to get the required read range.

[cribbit]

You'll have to explain what you are attempting to accomplish using passive RFID technology in a wireless shifting system. The inductive power transmission between the reader and the passive RFID is very inefficient - which is okay, because the passive RFID requires requires very little power. While using inductive power transmission in a wireless shifting system would eliminate the need of a battery at one end, it would greatly increase the size of the battery required at the other end.

Also keep in mind that the effective rage of inductive power transmission is highly dependent on the size of the transmitter's antennae coil - and you really don't have much room on a shifter or derailleur for a large antennae coil. The reason that the timing mats (used for race timing with passive RFID chips) are so large is not just so that they are hard for the racer's to miss, but also because they allow the use of very larger coil antennaes to get the required read range.

I believe the amount of power used by the shifting motors is orders of magnitude bigger than that required to poll an RFID tag so it shouldn't be too big of an issue.

Transmission range and antennae size are much bigger questions to me. I'd also be worried about the frame and shifter body messing with transmission. Carbon frames should be fine, metal is more questionable.

One way to mitigate that is putting the receiver closer to the shifters, such as under the downtube. Basically as far forward as you can without being in anything that turns with steering.

While maintenance would be a bitch it would be kind of cool to see a bike where the receiver is inside the headtube or the front of the downtube, installed with the fork removed. And also potentially putting the front derailleur motor inside the seat tube.

[oldpotatoe]

I believe the amount of power used by the shifting motors is orders of magnitude bigger than that required to poll an RFID tag so it shouldn't be too big of an issue.

Transmission range and antennae size are much bigger questions to me. I'd also be worried about the frame and shifter body messing with transmission. Carbon frames should be fine, metal is more questionable.

One way to mitigate that is putting the receiver closer to the shifters, such as under the downtube. Basically as far forward as you can without being in anything that turns with steering.

While maintenance would be a bitch it would be kind of cool to see a bike where the receiver is inside the headtube or the front of the downtube, installed with the fork removed. And also potentially putting the front derailleur motor inside the seat tube.

Or hard wire it with really thin wires and put all including the battery inside the frame:)

Except for installation and setup, what problem does wireless solve, what question does it answer? On a mostly normal road bike?

Here we go...:eek:

[SoCalSteve]

Or hard wire it with really thin wires and put all including the battery inside the frame:)

Except for installation and setup, what problem does wireless solve, what question does it answer? On a mostly normal road bike?

Here we go...:eek:

Peter, I hope you are having a great weekend!

See what I did there...:banana:

[cribbit]

Or hard wire it with really thin wires and put all including the battery inside the frame:)

Except for installation and setup, what problem does wireless solve, what question does it answer? On a mostly normal road bike?

Here we go...:eek:

No wires to get in the way

No wires to break

No wires to worry about when disassembling

Can swap or move around shifters much more easily

Can completely seal against water more easily

That's comparing wireless electronic to wired electronic. Comparing all the way down to mechanical is a whole nother debate.

[Kontact]

I believe the amount of power used by the shifting motors is orders of magnitude bigger than that required to poll an RFID tag so it shouldn't be too big of an issue.

Transmission range and antennae size are much bigger questions to me. I'd also be worried about the frame and shifter body messing with transmission. Carbon frames should be fine, metal is more questionable.

One way to mitigate that is putting the receiver closer to the shifters, such as under the downtube. Basically as far forward as you can without being in anything that turns with steering.

While maintenance would be a bitch it would be kind of cool to see a bike where the receiver is inside the headtube or the front of the downtube, installed with the fork removed. And also potentially putting the front derailleur motor inside the seat tube.

I don't understand how passive anything is going to make shifting work more efficiently.

RFID is like a reflector designed to look a certain way on a radar scope. The reader is sending a signal that "powers" the RFID chip enough to make it produce a weak radio return signal that the reader can detect.

How is that process going to make an active shift system work better? Right now the shifter only sends a radio message to the derailleur when it calls for a shift. To use a passive system the derailleur would have to constantly ping the passive RFID equipped shifter to ask it if it made a change. That constant transmission and the fact that the output would have to be strong enough to light up the RFID in the shifter means that you derailleur battery would be draining constantly.

It is much more efficient to have the shifter produce the power for its own signal only as needed and the derailleur also sit dormant until a signal is received. It might take two batteries, but much less total power because both are sitting dormant 95% of the time.

[cribbit]

I don't understand how passive anything is going to make shifting work more efficiently.

RFID is like a reflector designed to look a certain way on a radar scope. The reader is sending a signal that "powers" the RFID chip enough to make it produce a weak radio return signal that the reader can detect.

How is that process going to make an active shift system work better? Right now the shifter only sends a radio message to the derailleur when it calls for a shift. To use a passive system the derailleur would have to constantly ping the passive RFID equipped shifter to ask it if it made a change. That constant transmission and the fact that the output would have to be strong enough to light up the RFID in the shifter means that you derailleur battery would be draining constantly.

It is much more efficient to have the shifter produce the power for its own signal only as needed and the derailleur also sit dormant until a signal is received. It might take two batteries, but much less total power because both are sitting dormant 95% of the time.

I believe it's possible to have the passive RFID only send a signal on a change in what it's sensing. Then you just need a good system that only sends polling (charging) signal when needed rather than continuously.

[Kontact]

I believe it's possible to have the passive RFID only send a signal on a change in what it's sensing. Then you just need a good system that only sends polling (charging) signal when needed rather than continuously.

How would the derailleur end know when to send a signal to check when the shifter has received an input? Passive RFID doesn't "send" anything, it is passive. What is sends is an echo of the ping the reader sent. Without that ping there is no output. If you want independent output, that takes a battery and it is not passive.

That isn't a technical question, at this point it is just a logic problem and a flow chart.

[Mark McM]

Ditto everything Kontact has said.

In order to avoid having batteries in the shifters, the OP has suggested a system where there is wiring up the downtube, with a large antennae loop for good signal range (and since the antennae loops are somewhat directionaly might even need two - one aimed at the right shifter, and one aimed at the left). These powered antennaes would have to poll the shifters continuously, producing a constant drain on the derailleur battery.

The alternative, as the SRAM eTap system has shown, is a simple, small, lightweight and inexpensive coin cell in each shifter. These batteries can last more than a year.

I know which system I'd choose.

[cribbit]

Ditto everything Kontact has said.

In order to avoid having batteries in the shifters, the OP has suggested a system where there is wiring up the downtube, with a large antennae loop for good signal range (and since the antennae loops are somewhat directionaly might even need two - one aimed at the right shifter, and one aimed at the left). These powered antennaes would have to poll the shifters continuously, producing a constant drain on the derailleur battery.

The alternative, as the SRAM eTap system has shown, is a simple, small, lightweight and inexpensive coin cell in each shifter. These batteries can last more than a year.

I know which system I'd choose.

That's the information I'm looking for! I'm trying to figure out what the issues with it are, because I'm assuming there are good reasons it isn't used.

[Kontact]

I guess I wasn't explaining myself clearly. Glad someone could for you.

[cribbit]

Next fun idea to have shot down - wireless internally geared disc brake rear hub, charged via regenerative braking.

Obvious downsides - maintenance will be tricky, but internally geared hubs are always like that.

Unclear how difficult it is to make regenerative braking, the battery, the gears and shifting all fit inside a hub.

Obvious upside - should take a long, long time until it needs maintenance. Can be made totally weatherproof.

Also, this allows for easy wireless braking. While obviously you want at least 1 of your brakes to be wired/hydraulic it makes more sense for that to be your front brake. With all the wireless aspects (receiver, battery) already in the hub it's easy to add braking. (and I think you would have to, in order to modulate regenerative and pad braking so that you can stop effectively)

[Mark McM]

Next fun idea to have shot down - wireless internally geared disc brake rear hub, charged via regenerative braking.

Obvious downsides - maintenance will be tricky, but internally geared hubs are always like that.

Unclear how difficult it is to make regenerative braking, the battery, the gears and shifting all fit inside a hub.

Obvious upside - should take a long, long time until it needs maintenance. Can be made totally weatherproof.

Also, this allows for easy wireless braking. While obviously you want at least 1 of your brakes to be wired/hydraulic it makes more sense for that to be your front brake. With all the wireless aspects (receiver, battery) already in the hub it's easy to add braking. (and I think you would have to, in order to modulate regenerative and pad braking so that you can stop effectively)


This again sounds like a more complicated solution than the problem warrants.

There is a lot of power that can potentially be harvested with regenerative braking. But it also requires a lot of sophisticated hardware to do it. The Copenhagen wheel does this for example, but it already has most of the components in place (in particular, the hub based motor/generator, plus the power electronics to run high currents through it).

The energy demands for electronic shifting are fairly small - a lithium battery that is a few cubic inches and that weighs a few ounces can power the shifting system for a year or more. Adding some type of regenerative power generator could increase the size, weight and cost of the power system many fold.

For the relative small power demands, I can think of a few power sources that may be simpler and easier than regenerative braking. For example, a small solar cell, which generates a continuous trickle charge, might be able to keep the derailleur battery topped off. Alternatively, perhaps a small kinetic generator, that converts shock and vibration energy into an electric current. Or, maybe the simplest of all - plugging the battery into a standard 5V USB charger for a few hours once a year.

[Kontact]

It would be much easier to generate electricity for the modest amount needed from a tiny dynamo than a huge braking generator. What are you going to do with all that extra electricity generated? Cars use it to accelerate.

Making devices that are many times more complicated just to avoid a battery doesn't make much sense. McM's solar cell is a better idea.