StevenTammen
1 µW
- Joined
- Jan 5, 2019
- Messages
- 4
For a while now I've had the idea of an exercise-focused EV that focuses on speed moderation as well as speed enhancement. This may seem somewhat strange, but I am going to attempt to explain below. (In a not-entirely-short but hopefully not-too-long exposition).
Speed and safety
All things being equal, going slower is safer. Impact forces will be less in a collision or fall, you will slide less far (and thus have to deal with fewer abrasion cycles), and you have more time to react to your environment (e.g., a child runs out in front of you).
Speed and situation
Matching traffic speeds is important when riding on roads that you share with cars. It is less dangerous to be going 10 mph slower than traffic than to be going 30 mph slower than traffic. Assuming you get to pick what roads you are on to some extent, going around 20-25 mph is probably sufficient for riding safely with car traffic (the trick is getting enough torque to do this up steep inclines). It is also important not to go very slow in bike lanes; forcing fast cyclists to pass you puts them at risk.
There are also some situations where going slowly is desirable. If you are on a paved nature trail or park trail that people take their kids and dogs on, going fast puts you and others at risk; the "best" speed for such trails is slow.
Speed generation
Electric vehicles have no problems generating speed. Particularly if you use something more powerful than a 250W DD hub motor.
Speed reduction
Here is where things get interesting. People using EVs for transportation typically want to preserve as much speed as they can, essentially only braking when necessary. However, when using EVs for exercise, it seems to me like lower speeds are superior in most cases that don't involve mixing with cars. Safety is one thing, but I find that I like to exercise most on paths, which often have pedestrian traffic on them, forcing lower speeds. Now, speaking from the perspective of someone who is moderately fit (rather than someone who is quite out of shape), it is difficult to get any sort of meaningful exercise while being forced to constantly check speed on such paths.
Another area that I find myself thinking about a lot is downhills. It is very hilly where I live, making any sort of exercise I do more akin to interval training than steady-state cardio. I huff and puff going up hills, but then zoom down them without being able to pedal since I'm already going quite fast. If I want to target my workout to be something like 30 minutes of 70% VO2 max, I can't, because I can never get consistent enough terrain to allow for steady output.
These two areas -- being able to exercise on paths that require low speeds, or just having having the option of exercising at lower speeds in general, and exercising while going down hills, are the main things I am interested in.
Options for speed reduction
Based on my research, the drag brakes of old, as used by tandems (among other tandem brake options) in the mountains, were typically drum brakes (in particular, the Arai drum brake, a part no longer in production, to my knowledge). The idea was to moderate speed using a big, heat-dissipating drum brake, so that rim brakes would not heat up on long descents and blow out tires.
Nowadays, a Tandem company called Santana has come out with a large-diameter disc brake that seems like it might be able to handle a lot of heat without fading, particularly if it only had to deal with the mass of a non-tandem bike and a single rider.
Additionally, DD hub motors can be used for regenerative braking, assuming motor controllers than can handle the amps and a BMS that keeps the battery cool enough. My understanding is that bigger hub motors are capable of more braking resistance (and winds and stator width can probably be optimized for maximum regeneration as well -- this stuff is beyond me at present). Quite a few people here on ES have mentioned that using regenerative braking saves brake pads a lot, particularly for cargo bikes.
Controlling speed reduction
It is my understanding that regenerative braking can be made progressive if you use a high-quality controller. I also know that the drum brakes of old typically used a form of "level selection" whereby a braking level was set so the captain wouldn't have to keep a brake lever compressed for miles on end.
What I want to be able to do, whether using friction brakes or regenerative braking, is to have a level selector in the manner of a gear shifter: level 1 for barely noticeable braking, and level 12 for basically locking the wheels. A completely analog selector would be even better - one that allowed for a full spectrum of braking levels rather than discrete options. It would probably be necessary to set different braking levels for the front and rear, since front brakes tend to dominate, and rear wheel(s) slip more as weight shifts forward
Questions
Alright, sorry for the length. Now that I've gotten through all the background, here are specific questions I have:
I think that's enough to start! Any other thoughts people have would also be appreciated.
---------------------------------------------------------------
In case you want to read even more, here's some additional information:
Speed and safety
All things being equal, going slower is safer. Impact forces will be less in a collision or fall, you will slide less far (and thus have to deal with fewer abrasion cycles), and you have more time to react to your environment (e.g., a child runs out in front of you).
Speed and situation
Matching traffic speeds is important when riding on roads that you share with cars. It is less dangerous to be going 10 mph slower than traffic than to be going 30 mph slower than traffic. Assuming you get to pick what roads you are on to some extent, going around 20-25 mph is probably sufficient for riding safely with car traffic (the trick is getting enough torque to do this up steep inclines). It is also important not to go very slow in bike lanes; forcing fast cyclists to pass you puts them at risk.
There are also some situations where going slowly is desirable. If you are on a paved nature trail or park trail that people take their kids and dogs on, going fast puts you and others at risk; the "best" speed for such trails is slow.
Speed generation
Electric vehicles have no problems generating speed. Particularly if you use something more powerful than a 250W DD hub motor.
Speed reduction
Here is where things get interesting. People using EVs for transportation typically want to preserve as much speed as they can, essentially only braking when necessary. However, when using EVs for exercise, it seems to me like lower speeds are superior in most cases that don't involve mixing with cars. Safety is one thing, but I find that I like to exercise most on paths, which often have pedestrian traffic on them, forcing lower speeds. Now, speaking from the perspective of someone who is moderately fit (rather than someone who is quite out of shape), it is difficult to get any sort of meaningful exercise while being forced to constantly check speed on such paths.
Another area that I find myself thinking about a lot is downhills. It is very hilly where I live, making any sort of exercise I do more akin to interval training than steady-state cardio. I huff and puff going up hills, but then zoom down them without being able to pedal since I'm already going quite fast. If I want to target my workout to be something like 30 minutes of 70% VO2 max, I can't, because I can never get consistent enough terrain to allow for steady output.
These two areas -- being able to exercise on paths that require low speeds, or just having having the option of exercising at lower speeds in general, and exercising while going down hills, are the main things I am interested in.
Options for speed reduction
Based on my research, the drag brakes of old, as used by tandems (among other tandem brake options) in the mountains, were typically drum brakes (in particular, the Arai drum brake, a part no longer in production, to my knowledge). The idea was to moderate speed using a big, heat-dissipating drum brake, so that rim brakes would not heat up on long descents and blow out tires.
Nowadays, a Tandem company called Santana has come out with a large-diameter disc brake that seems like it might be able to handle a lot of heat without fading, particularly if it only had to deal with the mass of a non-tandem bike and a single rider.
Additionally, DD hub motors can be used for regenerative braking, assuming motor controllers than can handle the amps and a BMS that keeps the battery cool enough. My understanding is that bigger hub motors are capable of more braking resistance (and winds and stator width can probably be optimized for maximum regeneration as well -- this stuff is beyond me at present). Quite a few people here on ES have mentioned that using regenerative braking saves brake pads a lot, particularly for cargo bikes.
Controlling speed reduction
It is my understanding that regenerative braking can be made progressive if you use a high-quality controller. I also know that the drum brakes of old typically used a form of "level selection" whereby a braking level was set so the captain wouldn't have to keep a brake lever compressed for miles on end.
What I want to be able to do, whether using friction brakes or regenerative braking, is to have a level selector in the manner of a gear shifter: level 1 for barely noticeable braking, and level 12 for basically locking the wheels. A completely analog selector would be even better - one that allowed for a full spectrum of braking levels rather than discrete options. It would probably be necessary to set different braking levels for the front and rear, since front brakes tend to dominate, and rear wheel(s) slip more as weight shifts forward
Questions
Alright, sorry for the length. Now that I've gotten through all the background, here are specific questions I have:
- My understanding of traction is that braking eats up some amount of available traction. Does this mean that riding around with drag brakes always engaged is actually leaving you with less traction than you would otherwise have? (I can see this being a big problem with the front wheel).
- Silly question -- can you even pedal while you are braking? This whole concept revolves around being able to continue to pedal with drag brakes engaged. (I would test this myself except I don't currently own any bikes to test with).
- Would running two of the large tandem disc brakes be sufficient for limiting speed on pedal-power alone on flats?
- How about the same setup when pedaling at full bore going down a 15% incline, say? The brakes would obviously heat up a lot, but given a single rider's mass, would they fade out if this was kept up for minutes on end? Would air-cooling keep up with the heat generation?
- How about two big DD hub motors (like the Crystalyte H35) on the flats -- would they be able to sufficiently limit speed?
- How about these same hub motors pedaling while going down a 15% incline?
- How about a combination of the large DD hub motors and large disc brakes? I think the disc brakes would have more problems with cooling right up against the hub motors, but could the combination handle full speed reduction?
I think that's enough to start! Any other thoughts people have would also be appreciated.
---------------------------------------------------------------
In case you want to read even more, here's some additional information:
- I am aware that many things can be done to slow things down without activating brakes. I am already planning on running fat tires at low-ish PSI on whatever EV I settle on, and am currently leaning towards modifying an Elliptigo for reasons outlined in this blog post of mine. The standing position on the Elliptigo is very much un-aerodynamic, which will help moderate speeds especially for downhills (air resistance being proportional to the square of velocity). You can always just put more watts through motors if you need the speed to mix with traffic, assuming you are running with high quality battery packs that have good energy density.
- The weight shifting when braking is an interesting subpoint that may be relevant after some of my initial questions get answered. Upright bikes have most of their weight on the back wheel, which is why it is usually best to put the motors there (either mid-drive through the drivetrain or via a rear hub motor): the back wheel doesn't slip nearly as easily. When braking heavily, however, weight shifts forward onto the front wheel, meaning that front brakes have much more of an impact than rear brakes.
- I have also thought about using a derailleur to disconnect the chain from the drivetrain when you don't want your pedaling to contribute to your speed. There would need to be some other form of resistance to pedal against ( a flywheel perhaps?), and this is also more fiddly than using progressive resistance since it is binary, and you would have to shift a lot to maintain a level speed (or just use hub motors for vehicle speed, and this other thing for exercise). I would be interested to hear if this would be possible though, since I've never heard of anything like it.