# (Video Inside!) First Build | \$40 Deck and Trucks | 190kv Turnigy SK3 | Custom Aluminum Mount | 8s3p 18650 Li-Ion Battery | VESC 4.12

Hey everyone, I’ve finally finished my first build after browsing these forums regularly for the past 4 months. I don’t have any pictures, but I made a video instead. Let me know what you think:

7 Likes

Do you get any voltage sag?

What pulley set do you use?

15T/36T, 255mm 5M HTD belt, it can be found here:

http://www.ebay.com/itm/DIY-Electric-Skateboard-ABEC-Flywheel-Pulley-Kit-15mm-Wide-Belts-/182618936000?hash=item2a84efd2c0%3Ag%3AjxsAAOSwjvJZP6e6

1 Like

Nice video, good to see it’s possible to solder those batteries. Do watch you joints, some looked to me a bit brittle and ‘cold’. Bit scary with the metal box tho.

But it’s nice to see you made almost everything yourself.

Very nice first build!

I actually insulated the bottom of where the vesc was sitting to make sure nothing would short, I was worried about this too.

Voltage sag is relatively small, but still significant with my specific pack because of the internal resistance of the cells.

Every cell has ~20milliohms IR which will be the cause of the power dissipation and voltage sag. Total power at the terminals of the pack is

``````   P = IV - I^2*R
``````

where I^2*R is the loss dissipated as heat due to internal resistance. Since we’re only drawing 60A maximum,

`````` I^2*R = (60)^2*(.020*8 cells in series) = 576 watts
``````

and then at the terminals, ideal power is:

``````3.7V*8 cells in series * 60A = 1.776 kW
``````

so we can set up a ratio to find voltage sag and actual power:

``````1776W/29.6V = (1776W-576W)/x volts -> x = 20V
``````

so we’re getting a voltage sag of approx

``````29.6V - 20V = 9.6V
``````

at maximum current draw, and voltage sag will decrease exponentially from P = I^2*R as the ESC draws less current

All calculations aside, it accelerates quick enough, and although voltage sag is an unfortunate characteristic of non-ideal voltage sources, we can still draw more current to account for power loss as long as it’s not above 60A

1 Like