Really interesting interview

[codersarepeople]

I saw this really interesting interview with the founder of Grin Technologies, and thought it would really be interesting to people here.

 

Interestingly, at about 45 minutes, he points to an EUC he made and claims he made it at about the same time as Shane Chen. He also talks at length from about 10-35 minutes about some really interesting aspects of batteries. In another great video of his, he shows off his pedal-assist regular unicycle, which is really cool.

[Mono]

WOW, that's some deep, precise and honest information!

And a link to a nice motor simulator http://www.ebikes.ca/tools/simulator.html

6:11 The myth of voltage (building the "exact same" motor for different voltages, you won't be able to perceive a difference)

18:36 How to make a battery last longer

20:41 In short what makes the battery degrade faster: heat, .e.g from fast draining, and high voltage, .e.g from recharging it to 100% right away

23:03 For battery life, cycling 0%<->60% is better than cycling 20%<->80%

30:04 A Monowheel like self-balancing electric "skateboard" build in 2003, and an electric skateboard with weight sensors and hence no need of a remote control

45:58 a self-balancing seatless unicycle build in 2010

46:26 I love the patenting strategy: post the idea in the internet, build a working example of it, done.

1:20:06 Generative braking isn't quite relevant for energy balance but it saves wear on the brake pads extending their life by a factor 4-5

1:21:37 Geared motors are not less durable than direct drive, empirically

1:34:52 The impact of a front hub motor on steering: none, but why else we actually may not want a front hub motor. 

1:40:15 I am hoping that more people do embrace quantifying things, I couldn't agree more.

[codersarepeople]

I thought the myth of voltage was really interesting, especially given how much people seem to love the Gotway 84V machines over the KS 67V machines.

[lizardmech]

EUCs can't fit thick wire through the hub motor opening. You could make a low voltage EUC but you would have to make completely custom parts instead of borrowing existing ebike parts.

[Marty Backe]

2 hours ago, codersarepeople said:

I thought the myth of voltage was really interesting, especially given how much people seem to love the Gotway 84V machines over the KS 67V machines.

He did not say voltage is meaningless (a myth), just that it was meaningless in isolation. For our wheels higher voltage allows more power to be supplied to the motor without having to increase wire sizes. @Rehab1 can attest to the fact that there isn't much more room to grow in terms of feeding current to the motor. So if we want more powerful wheels it's only going to come with higher voltage systems.

It's an absolute fact that the 84v version of the same wheel is more powerful. That's why I just sold my 67v MSuper and bought the 84v version. And my 84v ACM is noticeably faster than my older 67v ACM.

I enjoyed the video.

[codersarepeople]

I suppose that could be remedied with thru-axle huh motors but at a high cost.

So as somebody who doesn't know much about this stuff, why is it okay to have higher voltage with the same thinnish wires? Did that not cause the connector/wire melting issues in the first batch of 84V gotways?

[Marty Backe]

35 minutes ago, codersarepeople said:

I suppose that could be remedied with thru-axle huh motors but at a high cost.

So as somebody who doesn't know much about this stuff, why is it okay to have higher voltage with the same thinnish wires? Did that not cause the connector/wire melting issues in the first batch of 84V gotways?

The connector/wire issues had nothing to do with the voltage level. The failures were caused by poor workmanship within Gotway. I think there have actually been more connector failures in 67v wheels than the 84v wheels. I personally witnessed a connector failure on a 67v ACM and a connector failure on a 84v MSuper. And I personally know the owner of a 67v MSuper who had a connector failure.

From an engineering perspective, if you are limited to thinner wires it's much better to run higher voltages. This may seem counter-intuitive unless you have a background in electronics. But this is just an aside, because all of the Gotway connector and wire failures had nothing to do with the voltage levels used within the wheel.

[Scatcat]

13 minutes ago, codersarepeople said:

I suppose that could be remedied with thru-axle huh motors but at a high cost.

So as somebody who doesn't know much about this stuff, why is it okay to have higher voltage with the same thinnish wires? Did that not cause the connector/wire melting issues in the first batch of 84V gotways?

Joule heating is the formula I^2 x R, where I is current and R is resistance. A thinner wire causes R to rise, given the same materials.

As you see, voltage is not part of the basic formula. But there is another formula (V1 - V2) x I that explains the same thing in other terms. In this case V1-V2 is voltage drop over a conductor and I is still current. Voltage drop is directly related to resistance, so a wire with high resistance creates proportionally higher voltage drop in that part of the circuit.

All the energy supplied is converted to some other form of energy. In our case it is either electromagnetism or heat. With high resistance wires, proportionally more of the energy is converted to heat. And the higher the current the more heat.

So if we want higher efficiency in a circuit with a certain resistance in the wires, a higher voltage will lose less of the energy to heat and leave more of the energy to electromagnetism which in turn becomes momentum in the motor.

So why is it a red herring in some cases?

Well, the difference between 67V and 72V is not really that much. You can probably compensate for the difference with better wires, either heavier gauge or a higher conductivity material.

Where the difference becomes crucial, is when motor power goes up beyond the physical constraints of current 67V systems. There is a limit to how heavy gauges we can use into the motor, since the wires goes through the axle and the hole can't be made bigger without weakening the axle. The solution would be to use a heavier axle, but that in turn would mean larger bearings and using non-standard parts/creating a new standard. That in itself would be very good, since axle-breakage is still a thing in EUCs. But it is also expensive and means more time in development and maybe even new production lines and new tooling.

The other way of supplying enough energy to the motor, is to up the voltage. We see 72V, 84V and even 92V-systems on the market or coming up - all of these try to solve the energy problem without adding more current, and thereby more heat. The problem with higher voltage systems, is that it heightens the risks of arching and electric shocks, which is why the standard UL2272 seem to have a limit on how many cells can be in series (does anyone know the actual limit?). So with higher voltage systems comes higher demands on the isolation of wires and connectors, the spacing on boards and so on. All to avoid outright short-circuits, as well as sparks and arching.

I think we will use higher voltages in the coming years, because it makes sense given the wattages we ask for. 1500W@~67V = ~22A, while 1500W@~126V = ~12A, and those numbers are for fully charged packs. When the voltage goes down the current needed goes up, and since the motor creates its own voltage as it rotates, the voltage is the absolute limit on torque in a given motor.

If I've made any mistakes in my description above, feel free to correct me. This is how I understand how things interact.

[Rehab1]

Great educational video!

At around 45 minutes into the video he talks about the battery 100Wh airline regulatory threshold for transporting battery packs.  He has designed a Lego Battery Stacking method creating a monolithic approach to satisfy these regulations. You can transport as many non connected packs you want using this method and then just reassemble the packs at your destination. 

Also using this monolithic pack method the BMS will not shut down the motor when there is one bad cell.

He also has a 15 meter battery drop zone to test the battery's integrity! Our EUC batteries would probably explode on impact!

 

[Rehab1]

5 hours ago, lizardmech said:

EUCs can't fit thick wire through the hub motor opening. You could make a low voltage EUC but you would have to make completely custom parts instead of borrowing existing ebike parts.

 

4 hours ago, Marty Backe said:

@Rehab1 can attest to the fact that there isn't much more room to grow in terms of feeding current to the motor. So if we want more powerful wheels it's only going to come with higher voltage systems.

The new GW motors are manufactured using 14awg wires compared to the previous 16awg. In order to fish larger 12awg wires through the conduit shaft would require machining a new larger axle with an increased bore diameter. 

[Scatcat]

18 minutes ago, Rehab1 said:

 

The new GW motors are manufactured using 14awg wires compared to the previous 16awg. In order to fish larger 12awg wires through the conduit shaft would require machining a new larger axle with an increased bore diameter. 

The current axles are too thin, it would be really really good if a new diameter adapted to the EUC would become a de-facto standard. Something like 26-30mm with ample space for heavy gauge wires, while still retaining enough strength to allow a 100% weight margin between maximum rider weight and what the axle can actually take.

This would mean shooting of curbs and even stairs would be less worrisome for the heavy rider.

[codersarepeople]

5 hours ago, Rehab1 said:

Also using this monolithic pack method the BMS will not shut down the motor when there is one bad cell.

He also has a 15 meter battery drop zone to test the battery's integrity! Our EUC batteries would probably explode on impact!

Unfortunately he says he's not interested in making any full evehicles just providing us with parts to do so. Can you imagine the quality (and I'm sure high cost) of an euc manufactured by him?

[US69]

7 hours ago, Rehab1 said:

ou can transport as many non connected packs you want using this method and then just reassemble the packs at your destination. 

Beside the 100(160wh) regulation there is another one that says, you are allowed to carrying max 2 (or3?) of these alltogether....

when i remember it correct the 14b was designed to carry it in hand baggage (without batteries) and you would have been allowed to carry 2 external batterie packs from 154wh.

 

Edit: And even if as max as we want....

90% of all airlines banned Eucs, hoverb., mini Segways from passenger plane in general. Even if they have no batterie anymore :-(

 

So visit Asia :-)

In Thailand or Singapur you can rent a euc for some small money with no problem :-)

[electric_vehicle_lover]

On 08/06/2017 at 5:34 AM, codersarepeople said:

I saw this really interesting interview with the founder of Grin Technologies, and thought it would really be interesting to people here.

Interestingly, at about 45 minutes, he points to an EUC he made and claims he made it at about the same time as Shane Chen. He also talks at length from about 10-35 minutes about some really interesting aspects of batteries. In another great video of his, he shows off his pedal-assist regular unicycle, which is really cool.

THANKS!! I want to make an EUC using EBike wheel just like that on the video -- many thanks!!

[Carlos E Rodriguez]

12 hours ago, Rehab1 said:

Great educational video!

At around 45 minutes into the video he talks about the battery 100Wh airline regulatory threshold for transporting battery packs.  He has designed a Lego Battery Stacking method creating a monolithic approach to satisfy these regulations. You can transport as many non connected packs you want using this method and then just reassemble the packs at your destination. 

Also using this monolithic pack method the BMS will not shut down the motor when there is one bad cell.

He also has a 15 meter battery drop zone to test the battery's integrity! Our EUC batteries would probably explode on impact!

 

that is crazy. the 18650 are not designed for severy impact. I mean they are better than the lipo bags. but still they are supposed to be protected and avoid shock. The thin lithium film will crack and lose capacity.

[Rehab1]

2 minutes ago, Carlos E Rodriguez said:

that is crazy. the 18650 are not designed for severy impact. I mean they are better than the lipo bags. but still they are supposed to be protected and avoid shock. The thin lithium film will crack and lose capacity.

I agree but he encapsulates the packs in fiberglass. It must be working as their building remains standing. 

 

[SeattleAbarth]

On 6/8/2017 at 11:02 PM, Marty Backe said:

He did not say voltage is meaningless (a myth), just that it was meaningless in isolation. For our wheels higher voltage allows more power to be supplied to the motor without having to increase wire sizes. @Rehab1 can attest to the fact that there isn't much more room to grow in terms of feeding current to the motor. So if we want more powerful wheels it's only going to come with higher voltage systems.

It's an absolute fact that the 84v version of the same wheel is more powerful. That's why I just sold my 67v MSuper and bought the 84v version. And my 84v ACM is noticeably faster than my older 67v ACM.

I enjoyed the video.

To add,

good site to just drop in some number calculations;
http://www.rapidtables.com/calc/electric/Volt_to_Amp_Calculator.htm

 

I've taken an Electronics course earlier in my years.  So the Higher Voltage does allow more amperage.  Which is the maximum draw rate based on how much wattage is being used.  forking a bit, this is why i recommend on the darkness bot app. to have a  chart column view of (wat/amp/volt) with speed & Warning temp on the chart as a nice to have.

If you are accelerating, and hit 500w, you will notice your battary voltage drop a bit in relation to the amp=draw being pulled from the battary.

What i find fundamentally interesting to performance test. Is, based on your 'usage'.  are you  redlining due to;

1. battary temp?
2. battary max amp = board max amp rating?
3. motor max wattage?

4. motor temp?
5. speed limit hit.

Or are you getting throttled/tiltback because a temp/amp sensor threshold was breached? (i'm assuming there are sensors for temp on the circuitry.. this may not be true for ALL EUC).


I won't go into the whole Ohms law drama, and stress on the finer details of gauge wire and resistance measurement.  But in re-inforce. the post, the Higher Voltage is the potential.
 

[Scatcat]

Basically, as long as we use thin wires higher volts is a better alternative to higher amps - it will create less issues with heat. As long as we're using lithium batteries, higher volts is a better alternative to higher amps - it will create less voltage sag in the batteries. Also, with higher volts, we can use cells with less CDR and higher energy density, since the max amp-draw will be less for the same power.

On the bad side:

Higher volts means higher risks for arching and higher demands on some components and the board in terms of engineering. There can be no millimeter gaps between leaders on the board. The same thing is true for condensation, where higher voltage means electricity have a higher tendency to arch small gaps created by dampness. That part should not be overstated though, as the difference is not between 67V and 267V, but between 67V and ≤92V.

[Mono]

On 6/20/2017 at 8:32 AM, Scatcat said:

As long as we're using lithium batteries, higher volts is a better alternative to higher amps - it will create less voltage sag in the batteries.

That seems to be in contradiction to what Justin is saying at 6:10.

Why would the same number of batteries when operated in parallel (low voltage) have a higher voltage sag than if connected in series (high voltage)? I would have thought that the relative voltage sag must be exactly the same.

On 6/20/2017 at 8:32 AM, Scatcat said:

Also, with higher volts, we can use cells with less CDR and higher energy density, since the max amp-draw will be less for the same power.

Same question: why is for a given output power the current in the single cells different if we compare the same number of batteries operated either in parallel (low voltage) or in series (high voltage)?

If I take 100 cells at 4V and want 400W power, I get:

• in parallel: 400W = 4V * 100A distributed over 100 cells is 1A per cell
• in series: 400W = 400V * 1A is 1A per cell.

[Scatcat]

4 hours ago, Mono said:

That seems to be in contradiction to what Justin is saying at 6:10.

Why would the same number of batteries when operated in parallel (low voltage) have a higher voltage sag than if connected in series (high voltage)? I would have thought that the relative voltage sag must be exactly the same.

Same question: why is for a given output power the current in the single cells different if we compare the same number of batteries operated either in parallel (low voltage) or in series (high voltage)?

If I take 100 cells at 4V and want 400W power, I get:

• in parallel: 400W = 4V * 100A distributed over 100 cells is 1A per cell
• in series: 400W = 400V * 1A is 1A per cell.

My bad, you are right. If we look at alternative configurations of exactly the same number of cells, the results are the same any which way. I blame not having drunk enough coffee that day...  

[qweiczz]

WOW, that's some deep, precise and honest information!

And a link to a nice motor simulator http://www.ebikes.ca/tools/simulator.html

6:11 The myth of voltage (building the "exact same" motor for different voltages, you won't be able to perceive a difference)

23:03 For battery life, cycling 0%<->60% is better than cycling 20%<->80%.

45:58 a self-balancing seatless unicycle build in 2010

46:26 I love the patenting strategy: post the idea in the internet, build a working example of it, done.

1:20:06 Generative braking isn't quite relevant for energy balance but it saves wear on the brake pads extending their life by a factor 4-5

1:21:37 Geared motors are not less durable than direct drive, empirically

1:34:52 The impact of a front hub motor on steering: none, but why else we actually may not want a front hub motor. 

1:40:15 I am hoping that more people do embrace quantifying things, I couldn't agree more.

[Seba]

Choosing right voltage for particular wheel is mainly a design decision, but as a general rule it is better to use higher voltages than higher currents.

For example let's say we have a wheel with 1000/2000 W cont/max motor power and we have a 18650 LG MJ1 cells having max discharge current at 10 A as per specs. So to keep current within battery specs we can use 16S4P battery pack with max discharge voltage limited to 3.13 V per cell (0 % level). Ok, but what with slightly more powerful wheel? Let's say we want to make a 1200 / 2400 W motor wheel. If we want to keep the same battery voltage, we have to use another 16 cells and add fifth string (16S5P) what will create some mass assymetry (3S left and 2S right) or will complicate EUC construction (two 2S and one 1S packs evenly distributed or one 5P placed over the wheel making the wheel "top heavy"). But there is better solution - add these 16 cells by 4 per string to create 20S4P battery. In this case we can achieve 2400 W load having perfectly symmetrical battery pack with 0 % voltage set slightly lower, to 3 volts per cell allowing for better capacity usage. So even if we have a two battery packs with same energy capacity, 20S4P is advantageous to 16S5P. Conduction/switching losses are current dependent. So by raising voltage we can lower losses in relation to power.

Of course higher voltage is beneficial to some extent only; when going higher and higher inital benefits will be cancelled by new problems - insulation problems, health hazards, legal requirements etc.

[eddiemoy]

I bought my first crystalyte conversion kit from ebike.ca over 10 years ago.  I also bought a bunch of their Ligo batteries last year after seeing him mention it in his interview.  You can put 3 Ligo batteries together to power your charger on the go.  LOL  Justin seems to have invented the modern EUC that we ride.  He custom built a motor assisted manual unicycle and went 25mph before he crashed.  He is an avid unicyclist.  Amazing guy!   

[Seba]

1 hour ago, eddiemoy said:

Justin seems to have invented the modern EUC that we ride. 

Wasn't Daniel Wood the first, or at least before Justin and Shane?

[eddiemoy]

2 hours ago, Seba said:

Wasn't Daniel Wood the first, or at least before Justin and Shane?

I mean the version we are riding, not the SBU which is a manual unicycle with a hub motor.