Lightweight standup-scooter sanity check

Hi All,

I have been lurking ES for a while now, but finally decided to join and am thinking of getting a portable scooter build going. The background is basically that I have ridden close to 1000 km on my [commercially available] electric kick scooter, and while it is a quite reliable work horse it is rather heavy to carry (11 kg) and is not really a blast to ride neither is it really comfortable.
Checking what the new electric longboards can achieve as well as doing some rough calculations, it seems pretty feasible to DIY something that is an improvement. However, I have not found something really lightweight when checking the other build threads so I like to run this with you guys before pressing the button.

So my design goals is something like:
Weight: 7-8 kg
Max speed: 30 km/h
Range: 15 km
Other: 7-8 inch air tires

How do I plan to achieve this then?
Batteries: 11s1p 26650 cells. There are 3500mA cells with 20 A continuous discharge, so that should be more than enough.
Motor: I’m assuming that the best weight vs torque ratio comes from RC style outrunners with belt drive. Perhaps Alien drive 6354 (60 kV); for a max speed of around 30 km/h it should need a 1:2.5 reduction ratio at 11s.
Controller choice seems to be pretty obvious; the VESC.

So my questions are:
1. Does this seem like a reasonable starting point?
2. About the motor choice, is there a point in choosing higher kV and larger reduction on the belt?
3. How is the general reliability of outrunners for this kind of application? Varies with price like everything else? Any recommendations?

BRs

HI
Best place to start looking is to look at the builds done by the member on here- search for "Beetbocks"
He has the most wicked small and powerful scooter builds.

7-8kgs and 15kms don't mix the battery's will be half that weight alone.

I see one first flaw in your BOM, instead of your 11s1P 26650 battery which will only give you 161Wh max for 800 gr, I suggest 10S2P 18650 LG HG2 which will give you 250Wh for 860Gr.

Assuming 10Wh = 1km (conservative, you can do more if you don't bash) that's 25km of range. You also ease discharge and life cycles of your batteries (you only want 20A discharge you get the double) , you can make it flatter. You remain in better limits for the VESC - and get more options if you want to change for a more plug and play solution.

You need to find a very lightweight frame for your scooter and inflated tires will likely eat away your battery faster than PU wheels. This or try to adapt 125mm dual density inline skate wheels?

Get the largest motor you can get, it will help once again.

Prob' babbled already on ES, BUT, my first "ebike" was a standup kick scooter (w/"extra kick" via 2x 12V 10Ah batts and a motor... and maybe a controller). After thousands of urban miles, my about only complaint was the lack of cargo space/ storage. So, I was left to hang bags "up high" on the handlebars (where weight "not the best"). Alternative approach:
https://endless-sphere.com/forums/viewtopic.php?f=35&t=19001

Hi guys, thanks for the replies and suggestions!

WeeChumlee said:

..search for "Beetbocks"

Click to expand...

yeah i know, his builds are awesome. I like how he evolved them for each iteration. Only thing I dont like is chain drive.

Vanarian said:

I see one first flaw in your BOM, instead of your 11s1P 26650 battery which will only give you 161Wh max for 800 gr, I suggest 10S2P 18650 LG HG2 which will give you 250Wh for 860Gr.

Assuming 10Wh = 1km (conservative, you can do more if you don't bash) that's 25km of range. You also ease discharge and life cycles of your batteries (you only want 20A discharge you get the double) , you can make it flatter. You remain in better limits for the VESC - and get more options if you want to change for a more plug and play solution.

You need to find a very lightweight frame for your scooter and inflated tires will likely eat away your battery faster than PU wheels. This or try to adapt 125mm dual density inline skate wheels?

Get the largest motor you can get, it will help once again.

Click to expand...

Agree, 18650 are indeed more developed, but I had an idea to place as much batteries in the steerer tube, and then the 26650 format fits better. But it is a quite distinct difference in power density and max current, hmmm I need to think about this again! By the way, I avarage 8,5 Wh/km at 25 km/h with my current scooter, so very accurrate estimation.

Not so convinced about solid wheels, I have to deal with cobblestones on a daily basis. And properly inflated tires have lower rolling resistance for the same amount of damping and grip. It will be more of a sourcing issue, to find good small air tires...

LockH said:

So, I was left to hang bags "up high" on the handlebars....

Click to expand...

I have a nice dakine backpack I use for skiing. Can it avoid swinging then, it is fine for scooter use!

north said:

Hi guys, thanks for the replies and suggestions!

[...]
Agree, 18650 are indeed more developed, but I had an idea to place as much batteries in the steerer tube, and then the 26650 format fits better. But it is a quite distinct difference in power density and max current, hmmm I need to think about this again! By the way, I avarage 8,5 Wh/km at 25 km/h with my current scooter, so very accurrate estimation.

Not so convinced about solid wheels, I have to deal with cobblestones on a daily basis. And properly inflated tires have lower rolling resistance for the same amount of damping and grip. It will be more of a sourcing issue, to find good small air tires...

Click to expand...

You're welcome! If I can suggest something else, you'll have a more enjoyable ride if you can make a flat pack under your frame because steering will be lighter ; also a tip from a biker, you don't want a "heavy fork" because you will understeer when you gain some speed.

True solid wheels are more fit for asphalt type road, if you go through "not so road" path inflated tires are better. But it does indeed takes more energy from the motor because of more deformation and less slipping coeff.

I want to see that build! :wink:

Yeah I need at least something to cushion those cobblestones, feels like my teeth are about to rattle out of my skull... Not so nice to ride on, but I guess it has been so since before the horse was invented.
Anyway, good to have some feedback from different angles!

But about the motor kV, is there any benefit to go for a higher kV and more reduction at the belt? I can probably fit around 1:7 reduction and have a 170 kV motor. My initial idea was to avoid too small motor pulley to reduce belt wear, but I'm not sure it is relevant and most other builds seems to use higher kV motors.
Or it is more the motor size that matters than the kV?

Forget about running a high RPM outrunner and a beltdrive. It takes up too much space and becomes a big weak link.
Given your moderate top speed goals, weight goals and everything you said.. I would go with a hub motor.

Know those "hoverboards" everyone was crazy about last year? one of those hub motors used as your rear wheel would work excellent for you.. clean, no noise, etc.
pair it with a proper ESC like the VESC or Phaserunner and you will have the drive part down easy.

You may have to go to an aluminum frame to meet your weight goals.

as far as the batteries go, I would go lipo, but I also know it well and respect the danger it presents. If you can go lipo, it will be much lighter and the battery can either be physically smaller, or give a longer range. If you dont, thats cool too, with LiFePo4 your range and weight goals are still doable.

are you looking for something as slim as a razor scooter or wide like a goped?

I was under the impression that hub motors are pretty heavy for their performance. The one I have in my current scooter (E-Twow) feels like 2 kg or something (just guessing from holding it), and that's my starting point for improvement. I thought about geared hub motors to keep the weight down, but then they introduce another weak point that is harder to service then a belt.

By the way, over here we are about 1 year after you guys, these "hoverboards" are the craze right now here

For the frame I though about using a wood or carbon skate deck and aluminium wheel attachments. Not sure how to deal with the fork and headset yet though, might harvest something from a scrap bike or so. We'll see, this will be a long-term project. Definitely carbon tubes for steerer tube and handlebars (yes I'm aware of radio, electrical and health characteristics of working with carbon fibre).

I have been building some multicopters with lipos, so yeah weight/power ratio is good but I'm kind of tired of sitting on charging watch. When it comes to LiFePO4 chemistry, I was tempted by the quick charge ability of the A123 cells (12 minutes to 80% !) but felt that power density is too low. Li-ion cells seems the most reasonable tradeoff, or what do you think? I have not worked with Li-ion cells before, but it seems they are considered more safe than LiPo packs, correct?

I'm aiming for something slim as a razor... Basically "Beetbocks" smaller scooters are what I'm trying to achieve, just doing it myself.