8 ms·

> Oh, and make sure that your brakes are able to stop your 1000W+ motor if the throttle gets stuck wide open. This cannot be stressed enough. The amount of new

> Oh, and make sure that your brakes are able to stop your 1000W+ motor if the throttle gets stuck wide open. This cannot be stressed enough. The amount of new builds on ebike forums where people are building essentially electric motorcycles on bicycle frames with no upgrades to non-drivetrain components is scary. Even with my 500W motor (illegal here, but would be legal in the states, and puny compared to the stuff the article's author is talking about), I found myself wishing the brakes were more responsive. I upgraded the brake pads which made the ratio of stopping power to acceleration acceptable. Then after a year of using that, the aluminum stirrup that the brake noodle slides into bent enough for the noodle to pop out, putting my front brake out of service. This happened while I was applying braking power during a steep downhill descent going 35-40km/h, I lost control and fell off the bike. The stirrup wasn't designed to handle the braking forces I was applying to it with the new brake pads, so over time it bent outwards and eventually gave way. Don't neglect your brakes! After this I upgraded to mechanical disc brakes. EDIT: Regarding "if the throttle gets stuck wide open" - if you don't have motor safety cutoffs installed on your brakes, you should do so now. I've had my PAS controller get into a state where it decided to just apply power even with no movement on the pedals. Always have a cutoff switch! If you dislike the chinese ebrakes (and they do suck), there are inline wire sensors you can install to keep your existing brake handles, and it's also fairly simple to modify your existing handles with a reed switch.

phkahler 10y ago
Don't you guys have regenerative braking via the electric motor? From the sound of it, the motor controllers out there are rather primitive in this market. Thoughts?
- Neliquat 10y ago
  I expect it is a cost/benefit thing, where an ebike is already quite pricey, and equipped with a very reliable fallback.
- maxerickson 10y ago
  Towards the bicycle end of the spectrum you probably want it to be able to freewheel.
- Johnny555 10y ago
  There's not a whole lot of energy to recover -- most of the eBike's energy is spent fighting wind resistance, so there's not much left to recover when you're slowing to a stop at a stop sign. Long descents where there is significant energy to recover are not that common for most riders.
  - petre 10y ago
    Well you could just use the drive as an electromagnetic brake w/o necessarily recovering all power by diverting all or just a part of it to a load. Train engines do this.
    - Johnny555 10y ago
      Well you could, but it comes at a cost (in dollars, complexity and weight), and is likely not worth it since the bike still needs friction brakes. It's a different story with a 50 ton train where a 20 KW resistor bank is not a significant amount of weight, but adding a 500W resistor bank to a bike (since you need somewhere for energy to go when the battery is fully charged) is probably not going to be worth the weight and expense. Plus you need some sort of blending between regenerative and friction braking, so it's yet another thing that needs adjusted and maintained.
      - phkahler 10y ago
        Even a DC motor driven with an H-bridge can dump mechanical energy back into the battery. It's trivial.
  - phkahler 10y ago
    A stop should provide almost as much energy as starting back up again. How about an e-bike with a fixed gear? You get assist when starting, but pedal yourself at speed, regen to stop, and perhaps some option to charge the battery via the pedals that's up to the rider. The most unusual thing I ever saw in my EV days... We had a full Ford Focus Electric on a chassis dyno to debug some problems. After several hours of tuning and data collection we realized the car needed to be charged to get it back to our own facility. The dyno place had no high power chargers. So we set the dyno somewhere around 40mph, put the car in drive and left it. With no foot on the gas it would do a light regeneration at that speed. The strange part is that we sat around a table to analyze the days data about 5 feet from the car. We're at a table next to a car tied down and going 40mph and its almost dead silent charging via regen. Analysis done, car charged, untie it and off we went ;-)
- aaroninsf 10y ago
  My Bionx Xtracycle has regenerative breaking and it is as implied super-useful as a speed moderator here in SF when going downhill with a load (my two kids) would build up speed. It's firmware limited to 20 mph which _feels_ slow but is probably a sane compromise. We only hit that going down hill, and are far from the fastest cycle; but we average 12-15 mph on mild uphills and flats when conventional cycles usually average a few mph slower. I love my ebike, it makes a daily commute taking two kids to school then getting on to work feasible, regardless of weather or relative personal energy level.
WD-42 10y ago
You upgraded to mechanical disk brakes? What were you running before? V brakes? I wouldn't run anything less than hydrolic disks on something that fast. Preferably dual piston like the ones Sram are making now.
- gambiting 10y ago
  I've destroyed two sets of Avid Juicy 7 hydraulic disc brakes with upgraded pads just by mountain biking, and these are almost top tier of bicycle brakes. Can't imagine people are running electric bikes with a lot of power without matching it with appropriate braking system.
  - petre 10y ago
    I'd only use original pads and discs from the brake manufacturer. If you upgrade your brakes it's best to upgrade the whole system, not just the pads. Overbuilt components with more metal and more surface would normally dissipate heat better, reducing the prospect of brake failure. Also, mechanical brakes are easier to inspect, maintain and fix. You won't see if your DOT fluid absorbed humidity or you won't notice a leak until the brake fails, but you will certainly see a broken cable.
    - seanp2k2 10y ago
      If you're running a >30mph ebike, you probably want something larger than 160mm rotors and something heavier duty than XC disc brakes. I'd suggest some downhill gear, including DH forks, headset, bars, cranks, etc. Shimano has the Saint line: http://bike.shimano.com/content/sac-bike/en/home/components11/mountain/saint1/br-m820.html http://bike.shimano.com/content/sac-bike/en/home/components1... Hope makes some nice DH brakes: http://www.hopetech.com/product/tech-3-v4/ http://www.hopetech.com/product/tech-3-v4/ Avid has the Code: https://dirtmountainbike.com/bike-reviews/brakes-gears/avid-code-brakes.html https://dirtmountainbike.com/bike-reviews/brakes-gears/avid-... And other manufacturers also make calipers with >=4-piston calipers. Again for rotor size, 160mm is typically standard for XC, road bikes run 140mm usually, some "all mountain" bikes have 180mm fronts, and 200mm is typically seen only on DH/4x/trials/dirt jump bikes but likely what you want for a fast ebike. All that said, competition-level road bikes generally hold up fine at speeds up to 60mph (and the riders hit those speeds going down hills) and their brakes work fine. You obviously don't just mash them, and the rim surface they're clenching matters a lot, as do the pads, but the tech works well and has worked for the past 100 years. Weight distribution and even application of both brakes help a lot.
deleted 10y ago
[deleted]
7952 10y ago
Hydraulic disc brakes on mountainbikes are ridiculously effective.

phkahler 10y ago

Don't you guys have regenerative braking via the electric motor? From the sound of it, the motor controllers out there are rather primitive in this market. Thoughts?

Neliquat 10y ago
I expect it is a cost/benefit thing, where an ebike is already quite pricey, and equipped with a very reliable fallback.
maxerickson 10y ago
Towards the bicycle end of the spectrum you probably want it to be able to freewheel.
Johnny555 10y ago
There's not a whole lot of energy to recover -- most of the eBike's energy is spent fighting wind resistance, so there's not much left to recover when you're slowing to a stop at a stop sign. Long descents where there is significant energy to recover are not that common for most riders.
- petre 10y ago
  Well you could just use the drive as an electromagnetic brake w/o necessarily recovering all power by diverting all or just a part of it to a load. Train engines do this.
  - Johnny555 10y ago
    Well you could, but it comes at a cost (in dollars, complexity and weight), and is likely not worth it since the bike still needs friction brakes. It's a different story with a 50 ton train where a 20 KW resistor bank is not a significant amount of weight, but adding a 500W resistor bank to a bike (since you need somewhere for energy to go when the battery is fully charged) is probably not going to be worth the weight and expense. Plus you need some sort of blending between regenerative and friction braking, so it's yet another thing that needs adjusted and maintained.
    - phkahler 10y ago
      Even a DC motor driven with an H-bridge can dump mechanical energy back into the battery. It's trivial.
- phkahler 10y ago
  A stop should provide almost as much energy as starting back up again. How about an e-bike with a fixed gear? You get assist when starting, but pedal yourself at speed, regen to stop, and perhaps some option to charge the battery via the pedals that's up to the rider. The most unusual thing I ever saw in my EV days... We had a full Ford Focus Electric on a chassis dyno to debug some problems. After several hours of tuning and data collection we realized the car needed to be charged to get it back to our own facility. The dyno place had no high power chargers. So we set the dyno somewhere around 40mph, put the car in drive and left it. With no foot on the gas it would do a light regeneration at that speed. The strange part is that we sat around a table to analyze the days data about 5 feet from the car. We're at a table next to a car tied down and going 40mph and its almost dead silent charging via regen. Analysis done, car charged, untie it and off we went ;-)
aaroninsf 10y ago
My Bionx Xtracycle has regenerative breaking and it is as implied super-useful as a speed moderator here in SF when going downhill with a load (my two kids) would build up speed. It's firmware limited to 20 mph which _feels_ slow but is probably a sane compromise. We only hit that going down hill, and are far from the fastest cycle; but we average 12-15 mph on mild uphills and flats when conventional cycles usually average a few mph slower. I love my ebike, it makes a daily commute taking two kids to school then getting on to work feasible, regardless of weather or relative personal energy level.

WD-42 10y ago

You upgraded to mechanical disk brakes? What were you running before? V brakes? I wouldn't run anything less than hydrolic disks on something that fast. Preferably dual piston like the ones Sram are making now.

gambiting 10y ago
I've destroyed two sets of Avid Juicy 7 hydraulic disc brakes with upgraded pads just by mountain biking, and these are almost top tier of bicycle brakes. Can't imagine people are running electric bikes with a lot of power without matching it with appropriate braking system.
- petre 10y ago
  I'd only use original pads and discs from the brake manufacturer. If you upgrade your brakes it's best to upgrade the whole system, not just the pads. Overbuilt components with more metal and more surface would normally dissipate heat better, reducing the prospect of brake failure. Also, mechanical brakes are easier to inspect, maintain and fix. You won't see if your DOT fluid absorbed humidity or you won't notice a leak until the brake fails, but you will certainly see a broken cable.
  - seanp2k2 10y ago
    If you're running a >30mph ebike, you probably want something larger than 160mm rotors and something heavier duty than XC disc brakes. I'd suggest some downhill gear, including DH forks, headset, bars, cranks, etc. Shimano has the Saint line: http://bike.shimano.com/content/sac-bike/en/home/components11/mountain/saint1/br-m820.html http://bike.shimano.com/content/sac-bike/en/home/components1... Hope makes some nice DH brakes: http://www.hopetech.com/product/tech-3-v4/ http://www.hopetech.com/product/tech-3-v4/ Avid has the Code: https://dirtmountainbike.com/bike-reviews/brakes-gears/avid-code-brakes.html https://dirtmountainbike.com/bike-reviews/brakes-gears/avid-... And other manufacturers also make calipers with >=4-piston calipers. Again for rotor size, 160mm is typically standard for XC, road bikes run 140mm usually, some "all mountain" bikes have 180mm fronts, and 200mm is typically seen only on DH/4x/trials/dirt jump bikes but likely what you want for a fast ebike. All that said, competition-level road bikes generally hold up fine at speeds up to 60mph (and the riders hit those speeds going down hills) and their brakes work fine. You obviously don't just mash them, and the rim surface they're clenching matters a lot, as do the pads, but the tech works well and has worked for the past 100 years. Weight distribution and even application of both brakes help a lot.

deleted 10y ago

[deleted]

7952 10y ago

Hydraulic disc brakes on mountainbikes are ridiculously effective.