2022-12-13 EV SIG MEETING NOTES

AGENDA

  • Introductions by new attendees
  • What’s new in the EV world
  • Thoughts on Caterham’s plans for EV
  • Seven Conversions
  • AOB

ATTENDEES:

  • John, Mac, Ian, Paul, Simon (new), Dan, Andrew, John (new), Jonathan
  • Apologies: Stu

INTRO’S BY NEW ATTENDEES

  • John
    • Owns a '95 HPC and MG5 EV estate
    • Retired IT management
    • Has completed IMI EV maintenance course
    • Looked (looking) at setting up in business as EV specialist but unsure of economics at the moment
  • Simon
    • Day job is physics teacher
    • Also club membership sec and gen sec

REMEMBER: there's a reasonably active WhatsApp group that accompanies this SIG. Contact JM on ev@caterhamlotus7.club if you want to join that or this SIG.

WHAT’S NEW IN THE EV WORLD

  • Not really discussed

THOUGHTS ON CATERHAM’S PLANS

We had a fairly lengthy discussion about the comments made by Bob Laishley, Simon Lambert and David Ridley on the "An Evening with Caterham Cars" held on the previous evening (2022-12-12). Here's some of the discussion:

  • Bob said that any EV has to conform to the Caterham ethos (from the captioned transcript of the webinar):

... it has to be credible to the brand which is lightweight fun to drive, and simple and the core element of that is a track, day for me and you know if you got 1 h, session during the day of a track day 1 h in the morning, 1 h, in the afternoon, you want to be able to run for 20 min, have a cup of coffee or a tea, or a read a Book, and then get back out of the track and there were other 20, min so making a 7, that is capable of running wide open throttle for 20 min, charging in 15 min, and run again is a massive challenge for any OEM on the plane...

  • We discussed the fact that power supplies to the circuits are going to be a challenge (there's been a BlatChat thread about this too). And if you had 15 EV's all finishing a track session at the same time and wanting to charge at 150kW then the circuit would need a 2MW connection just for the charging. And it would only be used a few times a day for a few days a week (at best). The track's economics of this are a challenge and the resulting cost per kWh might be a little eye watering. Also discussed whether tracks could have large battery banks that mean lower supply to the circuit that can be charged over a 24 hour period and therefore not need instantaneous 2MW - certainly possible, but also expensive. Though perhaps such a battery could be "trucked" in for special EV meets - espeically as this EV track day industry builds. JM metioned that MSUK has recently announced an EV race series (possibly for 2023?)
    • Bob mentioned that a design consultancy had been commissioned to create some visualisations of what a non-Seven Caterham EV might look like
    • Simon mentioned that CC have an IRS test car that they've worked on.
  • We had a long-ish conversation about drag and the spreadsheet created by JM and shared on the EV WhatsApp (see below). The calculations are eerily close to what top speeds you might expect from a Seven. The frontal area and Cd figures used are guessed but seem to hold up and make the numbers work.

SEVEN CONVERSIONS

  • For newcomers JM mentioned there are a few EV conversion projects already underway. Sheffield Uni's AMRC is on their second iteration of their EV (and we're hoping their project manger to join us for one meeting), a French race training company has a couple of converted Sevens, there are a few Westfield conversions out there. JM is also aware of someone who wants to remain anonymous but is a long way through a conversion.
  • Lots of chat about motor placement options
  • Discussion about whether Seven EV is currently better suited as a hillclimb/sprint vehicle using a smaller battery and/or capacitor store. Led to a discussion about EVs holding records at events like Festival of Speed and McMurtry's fan assisted downforce car.
  • Paul asked if JM had had any more thoughts about hub mounted motors. Led to a discussion about Axial Flux motors from the likes of Yasa and Equipmake etc. Axial Flux motors have higher torque and potentially reach their best efficiency at lower RPM. JM mentioned that a Seven needs to achieve about 1800 RPM at the wheel to do 120mph (will vary depending on tyres/wheels etc). Making Axial Flux viable candidates for with hub mount or for a twin motor install where a diff would sit - needs linked motor controllers that take account of different wheel speeds when cornering and can provide LSD functionality.
  • Discussion about gearing of a conversion. Motors (especially radial flux motors) tend to run most efficiently at 10,000+ RPM and so need gear reduction to get down to 1800-2000 RPM needed at the wheel. Discussed relative merits of gear reduction at the motor, using existing gearbox (locked in one gear), diff gear reduction etc. Mac mentioned that it can be a challenge (and those attending the meeting know where Mac gets his data points from) to have a gearbox in the drive train and to use multiple gears. They tried it for a long time and couldn't get it to work. The main problem being the different intertia characteristics of an electric motor vs an ICE. You need a way of changing a motors speed to match the next gear ratio and having a smooth transition very quickly or put up with a slow gear change.

There's probably a lot more that I've forgotten or didn't make notes on. Please let me know if you attended and would like to have this post updated.

As mentioned above, here's a screen shot of the spreadsheet that calculates power needed to overcome drag at a given speed. If you'd like the source spreadsheet then please contact me.

The fairly simple math came form here. The figures for frontal area and Cd are guesses but seem to make sense from other discussions on these forums.

JM

Comments

We also discussed the need to actively manage regen braking to avoid vehicle instability in slippery conditions.