Choosing efficient motor + battery combination

[SaladFish]

Hello,

I want to efficiently discharge a <384 watt battery pack through a single stage gear reduction mid drive motor propelling an e-bike weighing 120kg as far as possible in 1 hour (no pedaling).

This is for an efficiency competition. http://www.hunterevfestival.net/evprize.html

In a previous thread of mine it was determined that Samsung INR18650-29E Li-ion batteries from Nkon are the cheapest batteries in the world so I will be using them.

Samsung INR18650-29E Li-ion
Configuration: 7p, 5s
Volts: 25.9
Amps: 14.5 amp
Capacity: 375.55 watt hour
Weight: 1.68kg

I want to know how to find an affordable efficient motor for this application. I have considered RC motors but just as with ebike motors there are many to choose from and I wouldn't know where to start.

I'd prefer something user friendly with a little computer to enable me to accurately determine the power being drawn so I can effectively ration the power over the hour and optimize the gearing ratio through testing.

Further more I'd like to be able to change between all on button and throttle for race/road use. Also I'd like a 200 watt mode to comply with legislation so I can fight the police in court should they decide my ebike is an unregistered, uninsured motorcycle.

I hope you can help me find an efficient motor and battery combination, thanks.

 

[cwah]

Would be interested too...
Is your 1h straight long road.. or hilly? Start and stop? Will help decide

 

[SaladFish]

Would be interested too...
Is your 1h straight long road.. or hilly? Start and stop? Will help decide

Corners and small hill.
https://www.youtube.com/watch?v=mPzzj6yulhs

 

[Miles]

What do you mean by

a single stage gear reduction mid drive motor

 

[SaladFish]

What do you mean by

a single stage gear reduction mid drive motor

The motor has a small sprocket and the rear wheel axle has a big sprocket.

Like this.
https://www.youtube.com/watch?v=0AVaR7jzYjo

 

[Miles]

Ok. Thanks. I'd call that a 2 stage reduction to the rear wheel (in the video).

Wheel diameter? What reduction ratio, in total?

 

[SaladFish]

Ok. Thanks. I'd call that a 2 stage reduction to the rear wheel (in the video).

Wheel diameter? What reduction ratio, in total?

Wheel size will be 700c, I have not determined sprocket sizes since I need to find out what motor to use. I am aware some BLDC motors are above 90% that would be quite an advantage against someone using a 80% efficient motor.

 

[Miles]

I have not determined sprocket sizes since I need to find out what motor to use.

It's good to to have an approximate ratio in mind, in order to work out the size of motor required.

 

[Miles]

Speed is around 35-40 kph. Right?

What is your CdA?

 

[SaladFish]

Speed is around 35-40 kph. Right?

What is your CdA?

I ran some numbers I should be able to get above 45km per hour on the straight on 350 watt.

CdA might be around 1-1.5 CdA. Depends how good the fairing is. There are a bunch of rules that make it challenging and uncomfortable for the unfortunate rider lol.

If I can find a motor and battery pack at least as good as my competitors I should stand a good chance if I don't make a big mistake.

 

[Miles]

I ran some numbers I should be able to get above 45km per hour on the straight on 350 watt.

CdA might be around 1-1.5 CdA. Depends how good the fairing is.

Something doesn't add up there.... Where does your 1-1.5 figure come from?

If I can find a motor and battery pack at least as good as my competitors I should stand a good chance if I don't make a big mistake.

This is the competition: https://endless-sphere.com/forums/viewtopic.php?f=30&t=76018

 

[SaladFish]

Something doesn't add up there.... Where does your 1-1.5 figure come from?

That's the secret sauce (fairing).

If I can find a motor and battery pack at least as good as my competitors I should stand a good chance if I don't make a big mistake.

This is the competition: https://endless-sphere.com/forums/viewtopic.php?f=30&t=76018 [/quote]

I had a look at what they have put up. Looks like they have some bright ideas.

 

[Miles]

Something doesn't add up there.... Where does your 1-1.5 figure come from?

That's the secret sauce (fairing).

I'm saying the figure is far too high!

 

[SaladFish]

Something doesn't add up there.... Where does your 1-1.5 figure come from?

That's the secret sauce (fairing).

I'm saying the figure is far too high!

Haha I think so too, there are some dastardly rules that I am trying work within.

 

[Miles]

You need a CdA of around 0.25 to achieve 45 kph with 350 Watts (output)

 

[SaladFish]

You need a CdA of around 0.25 to achieve 45 kph with 350 Watts (output)

Whoops I just realised I put the decimal point in the wrong place.

0.1 - 0.15 CdA.

 

[Miles]

That's better

 

[Miles]

Something like this, then...

 

[SaladFish]

Something like this, then...

Yep, something like that.

 

[Miles]

How about using a single stage 5M toothed belt reduction?

 

[CoulombMotorsport]

Hi SaladFish,

We've competed in this competition for the past 3 years flying all the way over from Western Australia. Last year we came 3rd in the race and set the Pole Lap.

Check out our bike build on Facebook if you like. We won't be competing this year so happy to help you.

It's a hard competition to win, every year the weather does something different and the riding is actually quite difficult as all the school kids with little track experience tend to cut you off.

Here is our parts list for last year's bike:
- Turnigy Rotomax 50cc motor
- Castle Creations 160HVF
- Manson Solar Panel Monitor with external 100A 50mV shunt resistor (right next to the battery)
- Custom 37V 10aH LiPo battery pack. 20 x 3.7 V 5aH pouch cells (10S 2P)
- A Gigavac Minitactor (next to the battery pack for minimal wire length)
- A 9mm wide 5mm pitch pulley from RS Components on a custom adapter plate to the rotomax which went via a belt to a modified Golden Eagle Bike Engines (GEBE) driven pulley on the rear 26" wheel.
- The bike can be viewed on our FB page (link below) and is a highly modified frame (pretty much 95% custom fabricated) with a handmade polystyrene fairing covered in 2 layers of self applied Carbon fibre (no vacuum bag).

Hope this helps.

In order to win, I would've asked for a less windy day haha and also gone for a 2kW motor rather than the rotomax (around 5kW). You require about 1200 Watts to go up the killer hill at Newcastle in race trim and 2000Watts in qualifying.

James,

Coulomb Motorsport

 

[Miles]

Following on from James' set-up of last year. Here are a few references:
https://endless-sphere.com/forums/viewtopic.php?f=28&t=23764
https://endless-sphere.com/forums/viewtopic.php?f=28&t=10635
https://endless-sphere.com/forums/viewtopic.php?f=28&t=9172

 

[CoulombMotorsport]

Had a quick read of the Lightcycle Thread and I agree with the belt slip issue.

One of the biggest problems is getting the right reduction for the track.

In 2013, we had a DC motor with a fixed reduction (i forget what it was but it got up to 40 kph on the flat....). That got us 2nd or 3rd in qualifying but we suffered in the race, lasting only 48 minutes of the hour.
In 2014, we returned with a 750W geared 36V DC motor, the MY1020, coupled with an 8 speed in hub nexus 8 gearbox. This was great if a little inefficient and took us to 3rd in the race.
In 2015, the bike handled really well and I think if we'd kept an even pace we would have won. As we travel from Perth, Western Australia and have to assemble the bike on race day at 5 AM in Sydney before driving up to the race in a hired van, we don't get to see much of the track and so spent half the race working out how efficient the bike was......

I wouldn't recommend helping the reduction by reducing your voltage as your wire losses will be higher, but I would recommend getting a motor such as the Turnigy 9235 which is around 100 kV and run it with a 16mm wide 5mm width HTD belt or a chain with a reduction of 9:1.

Our bike from memory used a 24T drive pulley with the 148 GEBE driven pulley. I'll hae to check but I know that we blew everyone out of the water last year when we clocked 72 kph down the main straight on our fastest lap. You really need to gear for 55 kph top speed.

Anyways I hope you benefit from my help (you wouldn't believe how much money I've put into my team over the past few years developing our bikes and cars.......)

 

[Miles]

Mention of the GEBE pulley reminded me of something I tried a few years ago. !00t 8M belt used as a tyre on a 100t Strida MkII pulley, to convert it to "160t" 5M toothless operation

 

[SaladFish]

Hi SaladFish,

We've competed in this competition for the past 3 years flying all the way over from Western Australia. Last year we came 3rd in the race and set the Pole Lap.

Check out our bike build on Facebook if you like. We won't be competing this year so happy to help you.

It's a hard competition to win, every year the weather does something different and the riding is actually quite difficult as all the school kids with little track experience tend to cut you off.

Here is our parts list for last year's bike:
- Turnigy Rotomax 50cc motor
- Castle Creations 160HVF
- Manson Solar Panel Monitor with external 100A 50mV shunt resistor (right next to the battery)
- Custom 37V 10aH LiPo battery pack. 20 x 3.7 V 5aH pouch cells (10S 2P)
- A Gigavac Minitactor (next to the battery pack for minimal wire length)
- A 9mm wide 5mm pitch pulley from RS Components on a custom adapter plate to the rotomax which went via a belt to a modified Golden Eagle Bike Engines (GEBE) driven pulley on the rear 26" wheel.
- The bike can be viewed on our FB page (link below) and is a highly modified frame (pretty much 95% custom fabricated) with a handmade polystyrene fairing covered in 2 layers of self applied Carbon fibre (no vacuum bag).

Hope this helps.

In order to win, I would've asked for a less windy day haha and also gone for a 2kW motor rather than the rotomax (around 5kW). You require about 1200 Watts to go up the killer hill at Newcastle in race trim and 2000Watts in qualifying.

James,

Coulomb Motorsport

I had a look at the facebook page, bike looks pretty cool.

It would be great to get some insight from someone that has done the competition, they won't even allow testing on the course due to insurance only covering go karts.

1200 watts is quite a lot and 2000 watts is also quite a lot. Lipo batteries are not allowed in custom battery packs so I was thinking of using these batteries since they easily reach 381 watts but only have 2.86 c rating (10a). So max 1089.66 watt not including inefficiencies.

LG INR18650MJ1 3500mAh (10A)
http://www.nkon.nl/sk/k/Specification%20INR18650MJ1%2022.08.2014.pdf

I see you were using a pulse and glide technique to make sure the motor's rpm remained in the optimal range. I was thinking of using some sort of constant amp draw button and save a little bit of power for the final sprint to be accessed with a throttle to secure the fastest lap once everyone had been lapped. If the hill lowers the motor's rpm too much this may be an inefficient strategy.

Did you find it difficult to maintain speed around the tight corners and moving targets (children). It is hard to imagine what speed can be maintained based on my motorcycle experience which is a lot different to a bicycle.