How does regenerative braking factor into a system where just the engine has been replaced by a motor?
Obviously it wouldn't work with a slushbox, but are there going to be weak points driving the motor from the wheels, on downhill parts, to put power back in the battery?
Numbers vary, but regenerative braking can extend range a fair bit (60%ish)
Regen works awesome on the #1 style EV conversion. On the street it just feels like engine braking in 2nd gear ish and you can come all the way to a stop, except it works at any speed. On my truck I have the OEM t-case and in low range the regen is extremely strong. I can adjust it between 3 settings and usually only use the 3rd for extreme downhill descents (going down to Hell's Gate and Wipe Out Hill etc) but use the other 2 settings depending on trail conditions.
One weird thing that you hit on is that the electric motor is working against the forward motion, whereas the tranny/engine are just putting a load on it. The regen is speed dependent and the computer controlled inverter has a feedback loop to maintain/accelerate/decelerate depending on what your throttle foot is doing. So for instance when going down really steep sand dunes in Sand Hollow in max regen with foot off the throttle, the tires would "skip" and kind of overslow then speed up then overslow again, similar to ABS. It's actually really hard to steer when it does this so I either get on the throttle ever so slightly or turn down regen if I need to steer.
Regen is worth like 10% on point-to-point range, but where it really comes in handy is going up and down in elevation. That's probably where you got the 60% number. So for instance if you go x amount of distance regen helps 10% but if you go x amount of distance and climb a mountain in the middle then regen can give you maybe 60% more range.
I have a lunchbox locker in the rear it seems to work normal.
What dictates the "ideal" configuration? Is it a simple matter of packaging and quickness of fabrication?
In the case of a 4wd, does the electric motor need all the axle and transmission gearing? My general understanding is there isn't a min RPM for the electric motor nor is there an 'off idle lag'.
My interest is potential conversion on an old Civic without a drivetrain.
Yes, electric motors definitely need gearing. Teslas, LEAFs, Rivian, etc all EVs have reduction gears. Usually the total reduction is 7:1 to 11:1 depending on the application.
Contrary to popular opinion, modern AC electric motors do not give full torque at 0RPM. They need to ramp up the RPM in order to put down the torque. Usually they are software limited. My truck will not give me full power till about 1000 RPM then it ramps up, all controlled by the inverter's logic. At low RPM in order to make lots of torque you need tons and tons of amps. All good except if there is an obstruction aka the motor is "stalled" then it will fry in a split-second, cook the magnets, etc. So at low RPMs they are limited. Gear reduction lowers the load and raises the RPM, both help out. Just like in a gas powered truck.
If you watch the Hummer EV or Rivian doing rock crawling you will see they struggle. They start to climb up the rock and then come to a stop and stall out so the driver gets more on the throttle and they either lurch up or spin the tires or just fail and can't climb it. Not elegant. TFL Trucks youtube channel has a couple good videos of the Hummer and Rivian in Moab and other trails where they really struggle to do what pretty much any 4x4 from the last 40 years could do.
They tested a Tesla Model Y and it was really apparent that just because it can do 0-60 in 3 seconds or whatever, it really can't climb over a small rock.
The only way around that is with reduction gearing. For my truck I run about 11:1 in high range and 26.5:1 in low range (that's total reduction from motor to the axles). The Rivian is 12:1 permanently and the Hummer is 13:1 front 10:1 rear permanently. Rivian patented an EV specific low-range transfer case earlier this year so they finally figured this out.
