Today I worked on some speed calcs for various battery packs and it has some interesting results that make me question which batteries to buy. I had originaly planned around 2ea 200KV motor and 2ea 6S packs, but with HK out of stock on most motors and the new SK3 motors not being released (until now..dooh) I gave up waiting and bought an Aeolian 6354-250 KV motor which now has me dealing with more RPM per volt then I had planned. But I am unsure if that is not a good thing in some way.
I ran the calcs with various battery packs and gear ratios and it looks like I can go with one less cell then I had planned and possibly even 2, but I am unsure if that is a good idea as my EE knowledge is limited and usualy based on propellors for R/C aircraft so unsure what the pros and cons will be on my board. Anyhow I have room for a 70 tooth rear sprocket and I can get motor sprockets in ranges from 11 to 15. I can even bump up the rear a little as well but probably no more than 5 teeth due to diameter constraints.
Anyhow what I found is as follows. These are just voltage to ratio to RPM to MPH and I am unsure what amount of losses to add to this equation... I was thinking of taking the resultant MPH and figuring 80%, but unsure... Below is 100% no losses figured. These also figure in raw 6S/5S/4S voltages and do not take into account that freshly charged packs read more then nominal either...
At 6S (22.2) with a 70/12 sprocket (5.833 ratio) I get a rear wheel speed of 25.47 MPH
At 5S (18.5) with a 70/12 (5.833 Ratio) I get a rear wheel speed of 21.23 MPH
At 4S (14.80) with a 70/15 (4.667) ratio I get a rear wheel speed of 21.23 MPH (same as 5S at above ratio)
So my question is what will I gain or lose by choosing to go with 5S over 6S? And if I can get the same speed at 4S why would I choose 5S?
I plan to start with 1 pack for each motor at 5000 MAh and then at a later date buy another set and run them in Parallel. However if I go 4S I can afford to just buy all 4 packs at once. Buying the batteies is an investment which has me leaning toward the 5S or 6S since I would hate to buy the 4S only to find I do need the added voltage. I am using the HK 150 amp R/C Car speed controlls rated for 6S that also have the hall imput connector.
Now about me, I am big at 6'4" and 235lbs so curious if higer voltage at a larger ratio is better then lower voltage at a smaller ratio.
Can those in the know explain what the tradeoffs are for higher or lower voltage with ratios that bring the overall speeds down to close to each other? SInce I will be standing on this thing 25mph seems like max I would be comfoprtable ever going and even then I would limit the throttle travel anyhow. And if I plan to limit the travel anyhow, why bother and just use lower voltage instead and more throttle travel... Oh my I am confused...