Off Road Electric Kick Scooter Build

[x88x]

Problem you'll run into there is that the cells will sag a bit (how much depends on what cells you get and how much current you pull), so they will drop below 3.6V during normal operation, even though they have not yet hit 90%DOD (Depth Of Discharge). You'll want your hard-cutoff at 3.0V, as that should be a last-ditch 'if I keep going on this, I will kill the batteries' cutoff. The soft cutoff I would put at probably 3.5V, as in my testing, my '20C' cells sagged ~0.1V at 40A (8C) draw. That cutoff will ramp back the current it's pulling, to decrease load on the cells, which will in turn raise the cell voltage.

Monitoring the full pack voltage should be fine for normal operation, but I would highly recommend getting a celllog (or something similar) for quickly and easily checking the individual cell voltages afterwards. You want to keep a particularly close eye on them for the first few cycles, and you want to check all pack before hooking them up to anything. Because of HobbyKing's less-than-stellar QC process (hey, they're dirt-cheap and mainly targeted at RC stuff, what do you expect?), expect about 10% of the packs to arrive with at least one cell either DOA (0V), or close to it. Also, if any of the pack you get are puffed at all, don't touch them, immediately file a claim with HobbyKing and carefully properly drain and recycle the cells (do the same for DOA or <2V cells, to be safe).

As a corollary to that, make sure you order ~10% more packs than you actually need.

CellLogs:
http://epbuddy.com/index.php?main_pa...products_id=27
http://epbuddy.com/index.php?main_pa...products_id=14

[Technochicken]

These are in stock for the first time in ages:

http://www.hobbyking.com/hobbyking/s...arehouse_.html

I'd be really pushing the voltage limits of these motors, so I might need to set a motor current limit lower than 100% if I used them in a 16s, 10ah configuration. I'm really tempted, as they are the best deal on hobbyking, in terms of watt hours per dollar.

*update*

Well, I went ahead and ordered 9 of those batteries (one extra in case of duds). More mechanical updates to be posted soon.

[x88x]

Holy crack, they have 1032 in stock! ...I may be getting some myself...just on principle...plus, I'm sure I could find a use for them...yeah...

[Technochicken]

Update time!

First off, I finished the carbon fiber/polycarbonate deck. I found some epoxy designed for plastics, that bonded the two extremely well. I drilled and tapped some holes directly into the old scooter deck, and screwed in the new deck with stainless countersunk hex screws, and installed the master power switch in a convenient location:

To maximize battery space, I mounted the motor controller to the gearbox, via some angle aluminum:

I wired the motors in series, using some large bullet connectors, and added screw terminal connectors to the first motor's positive and last motor's negative, to connect to the motor controller. I soldered a solid copper spacer to one (salvaged from a heatsink), so that I could connect the terminals parallel to the top of the controller:

I made a bracket that bolts to the underside of the platform out of some more angle aluminum, to mount the fuse holder to, as well as route the cables through:

While testing the suspension, I previously noticed that the 8mm stainless rod that is the pivot point of the rear swingarm flexes significantly under loads (e.g. me jumping up and down on it). To fix this, I drilled out all the holes to 1/2", and inserted a 1/2" stainless rod scavenged from an old scanner. I also had some 1/2" shaft collars lying around, so I added those to secure it:

That's if for now. The batteries are due to arrive on Tuesday. Then all I need to do is wire up the pack and build an enclosure for it.

[Technochicken]

Batteries arrived! I ordered one extra, but ended up not having a single dead cell in any of the packs, so I have an extra to mess around with. All the packs came charged to 3.85 volts per cell, +/- .01 V.

[x88x]

I would recommend running them through some heavy charge cycles before using them on the scooter. A car headlight is handy for such things. If you have something to monitor the cell voltage, do so. Cut it off when the first cell reaches 3.6V and see how far apart the cells are. This will help give you an indication of if you have any cells in danger of infant death (ie, puffing/etc after only a few cycles).

[Technochicken]

Lots of progress to share.

It's rideable! But first...

Batteries: after testing the batteries for duds (thanks for the suggestion x88x), I wired pairs of them in parallel, including the balance connectors:

Next, I worked on a battery case out of angle aluminum. Later on, I will cover the sides with some sort of plastic, like acrylic, but for now most sides are open. Rather than bolting the angle aluminum together, I decided to braze it, with the left over rods I used on the gearbox:

I made a front panel to cover the wire side out of a scrap of polycarbonate. It is attached by thumbscrews for easy access:

Here you go, a compilation of clips from my first test ride. Note: the video stutters at time because my camera fails, not because of your computer/youtube.



Summary:
I need a stronger spring on the chain tensioner. When I go over large bumps, it frequently throws the chain.
The brake works great.
Acceleration is great. I have to be really gentle on the throttle to stay on (as demonstrated at the start of the video)
I'm not sure what the top speed is, I would estimate in the mid 20's. It feels fast, and I wouldn't feel safe going much faster than the top speed. I'll do a proper speed test with GPS later.
The motors get quite hot after riding. The motor controller gets warm, and the battery pack doesn't seem to heat at all.

It's a blast to ride, even on roads.

[TLHarrell]

Looks like fun. I'm not riding it without riot gear and a crash helmet.

[x88x]

*watches the opening launch*

Heheh, yup, that's about what happened the first time I tried one of my scooters on lipo.

About what throttle level are you hitting in the video?

The motors are likely not intended for continuous use, thus the high temperatures. Do you have a temperature probe of some sort that would let you see how hot they get?

[Technochicken]

For most of the video, I'm barely touching the throttle. The only full throttle bit I caught on video was the very end.

The motors are fine for continuous use...at 12 V. Seems that 20-22V makes them a little unhappy. However, they didn't burn out, which is a good sign, and if they do, they are the cheapest component of the scooter. And no, I don't have a temperature probe. They have ferrite magnets though, so I don't really have to worry about destroying the permanent magnets.