School of Watts Part 1: The Power to Propel Bicycles

Подписаться 29 тыс.

Просмотров 8 тыс.

50% 1

This is part 1 of a 3 part educational series we're producing all about WATTS as it applies to the world of electric bicycles.
There is copious misinformation about how much power is needed to push bikes around a city, about how much power electric motors can produce, and about how this entangles with legislation. We're doing our bit to set the record straight for those wanting to be properly educated on this topic, and hopefully inform regulators on how to make more sensible ebike regulations going forward.
In this first section we go in-depth about the actual power needed to move electric bikes and other PEV's on the roads, not just on flat ground but with hills, headwinds, and tailwinds.
0:00 - Introduction
0:30 - Familiarity with Watts
1:26 - Human Power Generator
2:00 - 4 Places Power Flows
4:08 - Flat Ground Power Curve
5:08 - Effects of Rolling Friction
5:50 - Effects of Bike Aerodynamics
6:30 - Effect of Winds
9:18 - Effect of Hills
11:07 - Effect of Vehicle Weight
12:35 - Summary of Bike Trip

Наука

Опубликовано:

15 июл 2024

Ссылка:

Скачать:

Готовим ссылку...

Добавить в:

Мой плейлист

Посмотреть позже

Комментарии : 76

@AaronHendu 8 месяцев назад

This type of discussion makes me less insecure about my 120lb weight lol. Being as thin a telephone pole has aero benefits, rolling resistance, etc. I can also leg press over 600lbs, so I am not super weak or anythint. My first ebike was only 250w and it could get me up the steepest road hills in my escarpment town. Upgraded though cause I didnt like mid drive so much and switched to hubs. It is awesome! So quiet and smooth, no gear changing necessary...she just rips. And absolutely no issues with anything, just attached tk the bike and start riding. It just works. I was able to build my hub motor wheels all by myself with no prior experience, right down to measuring the hubs and ordering the correct length spokes first shot, and it was all just from Grin Tech discussion and tutorials. I had little confidence, but it went so well now I feel like a pro lol. Will be building all my own bike wheels now! I even managed to true my first wheel in only a few minutes with no stand or anything, just a spare bike fork. Honestly, Grin Tech is the reason I felt able to convert my 2010 Trek 3700 into an ebike way better than any of the cheap ones that are still far more expensive. My whole setup wasnt much more than $500, including the bike. Constant compliments and people offering to buy it for far more than I paid. I was run over by a car years ago and havent been fully able to bike like I used to and ebikes gave me a new lease on the hobby I love so much.

@snowstrobe 8 месяцев назад

Is hub better because it is more direct?

@carlsisk2177 8 месяцев назад

❤

@sammiller6631 8 месяцев назад

leg press over 600 pounds?! Wow. I guess you never skip leg day.

@MarkSpohr 8 месяцев назад

Finally, someone who understands electricity! It's amazing the number of people who don't understand Watts.

@SimonBrowneNZ 8 месяцев назад

Thanks Justin. Beautifully explained and illustrated.

@Cowardlyduck 8 месяцев назад

Thank you. This is the sort of quantitative evidence based analysis that should inform ebike restrictions globally rather than the current arbitrary limits thought of by some bureaucrat who probably doesn't even ride a bike.

@GrinTechnologies 8 месяцев назад

Actually is even worse, most of the original power and speed based regulations were lobbied from within the pro cycling community, who felt that an ebike should be modeled after a human power bike, with all the flaws that entails. Like going super slow up hills, and super fast downhills, limited in cargo capacity, and being at the merci of winds. None of that makes cycling safer on the roads, or more practical and appealing.

@seanyounk1 6 дней назад

Looking forward to Part 2. Thanks.

@engineer9528 8 месяцев назад

So much needed theory for bike world, clearly and simply explained. Thank you Justin and GRIN Tech team!

@b.griffin317 8 месяцев назад

Thanks Justin! Looking forward to pt 2.

@solarEbike 8 месяцев назад

Another excellent video. Thank you for continuing to produce high-quality educational content like this.

@solarEbike 8 месяцев назад

13:15 1698 watts “absorbing power” due to wind drag during 60 KPH downhill: as much as I love bombing down a nice, long hill, I set my regenerative braking to limit downhill speeds to 30 KPH when touring in order to minimize these losses and maximize my regen

@AlbertPhan 8 месяцев назад

Thank you Justin! I forget how powerful the grin motor calculator is. It's fun to play with!

@johndate1776 8 месяцев назад

So thankful for this, guys!

@JonPrevost 8 месяцев назад

I had to double take on the formula. Yes, POWER, v cubed, force, v squared. This always makes me squint. Then I think of velomobiles and am still blown (pun intended) away by their efficiency.

@lufknuht5960 2 месяца назад

Great start, now where are PARTS 2 & 3 ???

@serdarozdemirkan8428 8 месяцев назад

Thanks very much for this very informative video. Looking forward to next...

@SkyGizmmo 8 месяцев назад

What a great job presenting! Looking forward to next.

@snowstrobe 8 месяцев назад

That was just so informative, even my simple brain was able to follow along. Thank you!

@solomon__ejay 8 месяцев назад

Hey Justin, on the next part, Please Mention the effects of drafting (slipstreaming) behind large and small vehicles. I'm curious to know what performance gains are associated with these advantages.

@GrinTechnologies 8 месяцев назад

That's a much trickier thing to be analytic about and model, but basically it's the same thing as having a small or modest tailwind. The degree depends on how big the leading vehicle is and how closely you follow. The next part is all about motor power, so no more mention of air flow except as it pertains to convective motor cooling.

@solomon__ejay 8 месяцев назад

@@GrinTechnologies Thanks Justin. This is truly valuable content you're putting out there. I, for one, found the section on the hills particularly interesting. This is because I live in Rwanda(aka The Land of a Thousand hills) and i'm designing a mid-drive ebike with the perfect specs to tackle this challenging terrain. If you'd like to know more about my progress, I'd be more than happy to share them with you.

@JohnRushworth 8 месяцев назад

Excellent. You have articulated so very well, that which I know and understand but cannot come close to your educational abilities. I have enjoyed your website and the simulations for some years. Many thanks from Scotland. Looking forward to your next two videos in the series. I’m on my 3rd pedal assist mid drive electric bike. Currently a 2015 Moustache full suspension MTB with many upgrades. Original Bosch CX motor. Works great for an out of puff pensioner like me. Assist opens up new vistas for my age and health!

@thomasdufaux 5 месяцев назад

Great video! Although I'm missing something fundamental (but maybe it was planned for the follow up videos). So all the stuff about maintaining speed (cruising) is very well explained, e.g. that vehicle weight has no effect on "air drag, which is the main force of power needed when you're talking about riding a bike on flat ground". But what I'm missing here is how much power you need to *accelerate* up to your cruising speed, and that you need more power if you want to 1) accelerate faster and 2) accelerate more weight. Anyways, can't wait the follow up video that will convince us all why regen makes so much sense, especially on slower vehicles.

@GrinTechnologies 5 месяцев назад

Super good question. I deliberately left out the acceleration power since it has no bearing on the net energy consumption and didn't want to further complicate the equations with transients. Power for acceleration is simply p = m v a. So take your speed (in m/s), the vehicle mass (in kg), and your acceleration (m/s/s), multiply them all together and that is how many watts of power is going into changing your kinetic energy

@GrinTechnologies 5 месяцев назад

With regen, the acceleration term is negative and so you get negative watts, the power of your kinetic energy returning to the battery system.

@strepto42 8 месяцев назад

Awesome vid, clearly presented, thanks!

@greensavant2573 8 месяцев назад

EXCELLENT!!!

@r.williams8349 8 месяцев назад

Excellent video thank you!

@ridefast0 3 месяца назад

Great presentation, useful data, thanks. Justin: "1250W is way more than any human can sustain". Tour de France winner: "Hold my beer ... "

@GrinTechnologies 2 месяца назад

Lance Armstrong could not sustain 500 watts for even 30 minutes in his most doped up state. The average power output of leading riders on the tour-de-france is in the realm of 250-300 watts. The word "sustain" is subjective but was intended to mean for a duration of at least 10's of minutes. The power output a human can do in a very short sprint is different (and impressive!)

@ridefast0 2 месяца назад

@@GrinTechnologies All agreed - and certain road, track and BMX cyclists are reported to have exceeded 2000 watts for a few seconds! And even I can get above 1500W for a few seconds - the time is heat limited - using my CYC Photon mid-drive eBike motor on a 48V battery.

@Zachrzan 8 месяцев назад

very informative, can’t wait for the next episode

@asuury 8 месяцев назад

Awesome Video!

@methods-SE 8 месяцев назад

I haven't even watched yet and I agree.

@methods-SE 8 месяцев назад

I watched the video in full, it was very informing. Thank you sir.

@antonantona 8 месяцев назад

Thanks for this very educational video 🙏

@EugeneShamshurin 8 месяцев назад

That's why I love physics, and explains how my BionX feels like riding with a tailwind!

@GrinTechnologies 8 месяцев назад

I used to say it felt like the hand of God was pushing me along, but a tailwind is just as apt!

@matejorsag6515 8 месяцев назад

Wonderful explanation, thanks! Greetings from Czech Republic ;)

@nc3826 8 месяцев назад

This was just Whatt we needed.

@quantumfx2677 8 месяцев назад

The biggest concern I've have had with hub motors is hills and stressing & wearing out the motor. Also dealing with big drops in speed so learning to pick the right hub motor with enough power is very important if you have to deal with lots of hills.

@GrinTechnologies 8 месяцев назад

If your are worried about stress and wear on the bike climbing hills, then the suitably torquey hub motor is usually what you want. Stress and wear happens to your drivetrain and brakes which is exacerbated by a mid-motor, and greatly reduced with a hub drive. But as you say, you need to get a hub motor that is sized to your needs (weight and grade hill) and then you can fly up the hills. An undersized hub is underwhelming.

@scottwilliams6257 8 месяцев назад

Strainuous, hard and slow could also explain the age of the rider and the equipment being used. Then when you throw a hill in front of it, might be somewhere off the charts.

@maximumchargeEV 8 месяцев назад

Thank you for this video! I recently made a video saying that to calculate an ebikes top speed with ok accuracy, you have to go both ways on a relatively flat runway to negate some of the gravity and wind forces acting on the ebike. Sharing!

@GrinTechnologies 8 месяцев назад

That's not exactly calculating your top speed, that's called measuring your top speed! But yeah an easy way to partially negate some environmental factors. You should also do it both sitting upright and in a crouched tuck position.

@maximumchargeEV 8 месяцев назад

@GrinTechnologies oh yeah that's true!

@Chris-bn1bn 14 часов назад

I guess your not going to discuss gear multiplication & the effect on energy consumption. I'm sure tons of people would want to know what's roughly ideal for given uphill scenarios, yes weight too. Tire diameter, etc.

@rishi-m 8 месяцев назад

Folks, was the Ligo 10X abandoned? I had this idea of using specific power cells for a similar purpose, would love to discuss it with y'all if the project is still underway. If it was abandoned, can I use a similar idea non-commercially or have you folks patented the format/application?

@andrewwhite8638 4 дня назад

Very nice. Is part 2 going to talk about how long it takes to burn out geared hub motors under various conditions?

@GrinTechnologies 2 дня назад

That will be part of it, geared or DD, just understanding the full map of power output vs rpm vs time for different motor models and what determines those things, and how dumb it is to try and characterize that with a single "rated watts" number.

8 месяцев назад

Best example to be an engineer: Justin!

@JohnRushworth 8 месяцев назад

In the motor power I’m looking forward to you going through the serial and individual component efficiency of the system from battery through controller to motor and how the graph of that varies with current drawn, rpm etc. I’ve tried having this discussion with Bosch mid drive motor tech guys because their app seems to display power taken from the battery not the actual power added for assistance, which is all very misleading. In fact the app which shows assist vs ride split is pretty meaningless although their human input power is pretty good.

@GrinTechnologies 8 месяцев назад

ru-vid.comdxJe_gygRGU?si=PFwBySpMw-CR2L2V The next video will be purely about power capabilities of motors in isolation, not really the other parts of the system. See the video above if you want an in depth treatment of motor and system efficiency.

@fredtatch1572 8 месяцев назад

Nice job Justin. This video would be great information for policy makers in creating the new regulation standards.? What regulations make sense to you for watt limits?

@yvan2563 8 месяцев назад

Limiting watts in e-bike makes no sense as we've seen in this video. Im my opinion the laws and limits for e-bikes should only apply to maximum speeds and where we're allowed to ride. For example, in my small town some of the bike paths have high grade inclines where even a 2000W motor would struggle to drive a rider uphill. If we want a cleaner and more fun future, we have to take fully loaded cargo bikes into account, because for a cargo bike going uphill, 500W or 750W is not even half of the energy needed. Edit: motor gearing will, of course, change the torque power of the bike. I can't wait for the next videos.

@snowstrobe 8 месяцев назад

@@yvan2563 Exactly. The only thing necessary is speed limits on paths where children or other vulnerable bike users are present.

@GrinTechnologies 8 месяцев назад

That'll be the subject of part 3. But fundamentally yes, power should not enter the regulatory framework at all. Speed and mass are the only things that affect relative road safety, and acceleration limits (to like 0.1 or 0.2g) can very easily and effectively address any concerns about systems being unsafe for inexperienced riders to handle, without any compromise in the ability to climb hills.

@nettoyageadriance 8 месяцев назад

GRIN... Ebike aliens from a future better universe. So much knowledge 😮

@hishamalsuqi1683 7 месяцев назад

great presentation , i would like to know what is the program which you are using in the simulation to get the result and the curves ?

@GrinTechnologies 7 месяцев назад

A slightly tweaked version of this: ebikes.ca/tools/simulator.html Just set your throttle to like 5% so that it doesn't entre the equation and hide the motor related curves via the radio buttons on the top of the graph.

@hishamalsuqi1683 7 месяцев назад

@@GrinTechnologies thx a lot ...if you excuse me I would like to ask you a favour ..I am a senior student from Palestine I am building an e-bike with the regenerative braking system as a senior project for the university , and I have watched a lot of your videos that show your huge understanding to this field and exquisite explanations for this topic and I know the thing is too big to be explained on a RU-vid comment..but I wanna your help , in giving me notes website, tutorials, published paper and anything you believe it could help us and give us insights to do things in a better way .. I know it is a lot to ask .. But thanks any way for your help

@hambernat6444 6 месяцев назад

As far I know your schema is wrong, frontal air drag caused by high pressure is different air drag flowing along your body. It's not cubic. It's between square and cubic. What about rotational mass and drivetrain efficiency?

@GrinTechnologies 6 месяцев назад

Rotational mass has no effect at all on the steady state power needed to move a bike at a given speed, and is a weird and misguided obsession by people who talk about bicycle power. And yes the cubic relation between air drag and power is an approximation for turbulent flow, but is pretty darn close. Errors from this are much less than uncertainty in the CdA approximation so it's rather splitting hairs to do a higher order model of that. The same goes for rolling drag, it's not exactly constant (some speed dependancy exists), but accounting for that in a complicated model would change anything about the result.

@sunoncream1118 3 месяца назад

wath is the calculator used?

@GrinTechnologies 3 месяца назад

That's all done using our motor simulator web app ebikes.ca/tools/simulator.html

@STAR-RADIANCE 8 месяцев назад

I would never ride my bike through Watts! 😳

@dparryd 3 месяца назад

How do I find part 2❔🤞

@GrinTechnologies 3 месяца назад

Not yet filmed :-(, but still in the plans for upcoming video projects

@FarrisBarakat 2 месяца назад

Part 2 please!

@russellwilson5246 8 месяцев назад

are you sure dobbling the wind resistance caused 8 times the force?...i thaught it was 4 times.

@GrinTechnologies 8 месяцев назад

You'll notice we are careful to say 8 times the power, not 8 times the force. Power is force times speed, so if force to air drag increases at the square of your speed, then power increases at the cube.

@russellwilson5246 8 месяцев назад

you say at 2.39 "air resistance has a property that it increases with the cube of your bicycle speed" that is very interesting as i thaught it was mass times velocity squared that determined force. looks like i may not fully understand why drag creates a cube ...i guess with drag the force is in front and behind the object creating a force on the object higher than the frontal drag force alone. I need to up my considerations of drag..thanks for the education.

@GrinTechnologies 8 месяцев назад

@@russellwilson5246 The drag force increases with the square of speed, hence the drag power increases with the cube of speed. In a similar way, rolling friction force is independent of speed, while the power to overcome rolling drag increases linearly with speed. In this video everything is in the context of power (ie watts), so when I mention rolling and air friction quantitatively it's about the power needed to overcome them and not the force needed to overcome them.