Area Representative Purplemeanie Posted February 8 Area Representative Share Posted February 8 Hi all, unfortunately I can't make this month's SIG meeting next Tuesday. So in lieu of that meeting, here's an update on the project with a few images. I'm also in the process of writing a piece for March's Lowflying that I should hopefully get written before the deadline later this month. As those of you that attended last month's meeting will remember, I've now started to make significant progress with my project. I've been sidelined a little by trying to get two "explainer" videos published to YouTube, but they're very close to being finished now and should go live in the next couple of weeks. The first gives an "explainer" on what forms of electricity are used in an EV (DC and AC) while the second goes into what components I'll be needing in my project. They're meant to be resources that novices can look at to understand what's in an EV, and that I can keep referring back to. Hopefully they'll be useful to anyone wanting to know a bit more of the behind the scenes. Link to a short YouTube video showing how a motor works... this is part of the second video. As for project updates... The big change is that I've decided to explore more fully the idea of a twin rear motor configuration for the car. Each will be a smaller motor of around 120kW, mated to a small 6:1 epicyclic gearbox to reduce the ~12,000rpm of the motors down to ~2,000rpm needed at the wheels. This has the advantage of removing prop-shaft and differential while also improving packaging - meaning I can have more space for batteries up front. See image below... The second big change is that I'm planning to use a high-power DC-to-DC converter that will sit between the battery pack and the twin inverters. This means I can de-couple the voltage of the pack from the voltage required for the motor. One of the critical conundrums of an EV project is to be able to get enough voltage supplied to the motor without significantly increasing the size of the battery pack to accommodate that voltage. A high-power DC-to-DC converter will allow a low pack voltage of say 250V but still drive the motor at 400V. This gives me much more flexibility on the battery options up front. See image below... Finally in big ticket items, I've finalised on how I'll do all the electronics control of the car now. I'm going fully CANbus for the control interfaces and removing the standard gauges to be replaced by an electronic dash. I appreciate that some may baulk at the idea of an electronic dash, but for my "prototype" car I need a much higher density of debug information on a screen. And this should allow me to do that. Another benefit of going completely CAN, is that I can use a Power Delivery Module. This will replace my current fuse box (that would have needed rewiring anyway) and replaces it with 32 programmable "soft" fuses. I expected to have been "blowing" a lot of fuses if they are standard fuses, so having a soft-resettable fusing system will be a big bonus. The PDM can also do a lot of logic functions for me and seems to be a big win-win for the design of the car. It also means there's a lot less wiring to do. Image of AIM dash and switches below... This last CANbus decision has also meant I can replace more of the wiring in the car. This isn't perhaps ideal, I'd have rather keep the current loom as "stock" as possible, but the reality is that an awful lot of it will change anyway and I might as well go all on with it. A consequence of this is that I'll be replacing the wiring to the lights at each corner with a CANbus driven lighting system (of my own design). Prototype board shown below... And finally, finally, I've been diverted a little by a project to determine actual rear suspension travel. I need to know how much suspension travel I'll need so I can get a good handle on the rise/drop angles of the rear suspension - I'll need new half-shafts with the twin motor arrangement. So... me being the type to dive in with a way over engineered solution, I've created a way of "instrumenting" suspension travel using a RP2040 processor and some data-logging prototype boards. See image below and link to YouTube short. The processor samples a distance measurement 30 times a second and records it to an SD-card. The distance is taken using a laser based Time-of-Flight sensor which I attach to the frame of my 420R above the De-dion "ears". As the ears move up and down I record their travel. More info on my results in further reports. Here's an image of the "Suspension Logger", link to video below it... As well as the electronics to capture suspension position, I've also modelled, and printed, a "widget" to attach the T-of-F sensor to the frame of my 420. The processor and data logger sit in the boot of the car (in the dry) and the sensor clips onto the frame in the wheel arch. This arrangement isn't meant to be permanent. And in fact even "temporary" is stretching its use. It will be attached for a few minutes to gather suspension travel information - if I wanted it attached for any longer, and for all weather, then I'd have done something more robust. But this should get me to the data I need. Link to suspension logger video: That's all for now. If you have any questions then please shoot them my way. John 1 Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted February 8 Member Share Posted February 8 3 minutes ago, Purplemeanie said: Each will be a smaller motor of around 120kW, mated to a small 6:1 epicyclic gearbox to reduce the ~12,000rpm of the motors down to ~2,000rpm needed at the wheels. If there's going to be a mechanical reduction gearbox could you use a design where the output isn't inline with the input? That could reduce the angulation of the drive shaft. Jonathan Link to comment Share on other sites More sharing options...
Area Representative Purplemeanie Posted February 8 Author Area Representative Share Posted February 8 1 minute ago, Jonathan Kay said: If there's going to be a mechanical reduction gearbox could you use a design where the output isn't inline with the input? That could reduce the angulation of the drive shaft. Jonathan Hi Jonathan, yes, I’d thought about that, and others have suggested things like belts etc. However, an epicyclic gearbox is the perfect solution. They’re small, light, can run in both directions and can deal with the power. The downside is that their complexity increases cost… and I’ll need a custom box designed. But I’ve got a couple of companies giving me what look like reasonable quotes for a design and supply. So, all in all it’s my currently preferred option. Link to comment Share on other sites More sharing options...
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