Aussie EV Autocross Special
- Thread starter galderdi
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stan.distortion
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Great project and thread, subbed. Good luck with it, very interested in how it's working out in the hillclimbs.
stan.distortion said:
Thanks for the support and interest.
Hillclimbs are super competitive and I'm not competitive at that level yet. I am a little under powered, my handling still isn't quite right and my brakes are unbalanced. I am consistently placing mid field. I am happy but not satisfied. I know I can do better by tweaking my suspension and increasing my brakes. Then I can go into corners with more confidence and I am sure I will pick up a few seconds. Edit: Plus to be outright competitive requires investment in Avon hill climb tyres. I am not serious enough to justify that jump in budget.
My last event was a club level bitumen khanacross. It was wet which amplifies the weaknesses I mentioned. The All wheel drive cars had the advantage. But despite a couple of major penalties resulting from my struggles in the weather I still managed 7th outright (also 1st in class but that is a hollow victory as I was the only one in my class). If it had been dry it would have suited me much more.
My next outing is a static EV display on Aug 10 at the Ipswich Rail Museum.
My next competitive event is another club level bitumen khanacross on Aug 17. I am hoping to have the brake situation solved by then so I have high hopes for a solid result.
Here are a couple of pics from Noosa early June.
stan.distortion
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Did you look into torque limiting/traction control? Makes the case for 4 independent motors and controllers, a leapfrog ahead of infernal combustion 4x4. The WRC cars are an example, the damn things can almost do ballet thanks to their traction control systems but they're limited to operating brakes and clutches on a conventional drivetrain, they can't have one side charging the batteries while the other side pushes around the corner.
EDIT: Electronic gear changes could be a winner too, they've got a bad reputation but that stems from cutting edge tech, F1 and WRC. Smacking a syncro box from one gear to the next at about the right time would be a lot simpler than millisecond changes with a dog box.
EDIT: Electronic gear changes could be a winner too, they've got a bad reputation but that stems from cutting edge tech, F1 and WRC. Smacking a syncro box from one gear to the next at about the right time would be a lot simpler than millisecond changes with a dog box.
All electronic driver aides are banned in my sport unless it was a feature delivered standard in the car through mass production. I built my car in 10 months on very limited budget. One of the reasons I was able to do that was because I opted for simplicity. I do have torque vectoring, but it is manual through my samurai sword handle. It has two master cylinders. If I push it forward it sends more torque to the left wheel. If I pull it back it sends more torque to the right wheel.stan.distortion said:
I also have passive rear steer (active rear steering is banned). I have infinite adjustment from neutral to aggressive rear steer by winding a bolt up or down to introduce rear bump steer. It works well but it is not good to have it too aggressive for any speeds over about 50kmph.
Gear changes aren't too much of an issue. I launch in 1st (only because it is fun) and then change straight to 3rd or 4th depending on the course. Then it stays in that gear for the rest of the run. I could launch in 3rd and it wouldn't impact my times. But launching in 3rd is boring and it makes me look slow to the spectators.
stan.distortion
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Cheers for the reply and sorry for the terse post, was rather drunk at the time and thinking out loud. Also read through kiwiev's Sonic thread earlier (hot damn, I'd sleep with that car!), dual motors on that one and had a mish mash of thoughts on the possibilities. Not sure how the "standard car" points in the rules would apply to yours but makes sense to keep the traction gizmos out of the sport, could quick turn into "he who pays, wins".
How come you went for and aft with the independent brakes? Seems counter-intuitive, impressive to see what folks can do with them in mud plugging (sporting trials) but there doesn't seem to be one "right" way of doing them, all kinds of variations in use. And had you considered going direct drive (no gearbox) or would that leave you short on higher speed events? From what I gather DC motors pretty much need the gearbox for road speeds, would've thought variable commutator timing could widen out the rpm range but don't seem to see it used much.
Thanks again for documenting everything so well, great read and really helpful for seeing the kind of pitfalls that can come up
How come you went for and aft with the independent brakes? Seems counter-intuitive, impressive to see what folks can do with them in mud plugging (sporting trials) but there doesn't seem to be one "right" way of doing them, all kinds of variations in use. And had you considered going direct drive (no gearbox) or would that leave you short on higher speed events? From what I gather DC motors pretty much need the gearbox for road speeds, would've thought variable commutator timing could widen out the rpm range but don't seem to see it used much.
Thanks again for documenting everything so well, great read and really helpful for seeing the kind of pitfalls that can come up
stan.distortion said:Cheers for the reply and sorry for the terse post, was rather drunk at the time and thinking out loud. Also read through kiwiev's Sonic thread earlier (hot damn, I'd sleep with that car!), dual motors on that one and had a mish mash of thoughts on the possibilities. Not sure how the "standard car" points in the rules would apply to yours but makes sense to keep the traction gizmos out of the sport, could quick turn into "he who pays, wins".
How come you went for and aft with the independent brakes? Seems counter-intuitive, impressive to see what folks can do with them in mud plugging (sporting trials) but there doesn't seem to be one "right" way of doing them, all kinds of variations in use. And had you considered going direct drive (no gearbox) or would that leave you short on higher speed events? From what I gather DC motors pretty much need the gearbox for road speeds, would've thought variable commutator timing could widen out the rpm range but don't seem to see it used much.
Thanks again for documenting everything so well, great read and really helpful for seeing the kind of pitfalls that can come up
Hmmm I hadn't even considered your post terse. No biggy.
When you say for and aft I assume you are referring to the for and aft movement of the handle? So in the first incarnation of the car I had the same handle with a single master cylinder applied equally to both rear wheels. It was intended to operate in the same way as a traditional hand brake to brake the rear end lose and swing the rear end around tight corners. But with all the weight on the back wheels I could barely get it to do anything. I had seen and driven cars with "fiddle" brakes where they had multiple brake pedals operating the brake sides independently. I likes parts of the idea. But I have large feet and found it difficult to ensure I was selecting the correct pedal for each situation. Also those cars were dedicated to lower speed motorsport where a mistake would not result in a catastrophic accident. My car is used for a wider range of motorsport and a mistake like that at highish speeds could easily kill me. So a re-design of the handbrake seemed like a good variation of the idea. The handbrake is operated by my left hand. I chose the forward direction to turn right and the backward direction to turn left because in both directions the right and left arms move in basically the same direction. The idea is to make it easier for my brain to handle. The idea works quite well and I have proven I can now throw the car around a hair pin where I would have not had any chance before. However the brake capacity in the rear is still a problem and I really have to use all my strength to get it to work. So I am hopeful the rear brake upgrade will help on this front also. (Sorry for the long winded explanation)
The gearbox decision is a no brainer for me. But I acknowledge it isn't so clear cut for other situations. If I were building a car for other purposes I would face a different set of considerations. But in my situation the following were my main considerations.
1. I was building the car from front wheel drive parts and needed a diff, so the gearbox provides the diff.
2. As I compete in a wide variety of motorsport having a gearbox allows me to select gearing that is optimal for the particular event/course.
3. Launching in 1st is the best part of my car. I wouldn't give that up for anything.
4. I have a DC motor and I compete in motorkhana. DC motors need the brushes advanced to rev higher without arcing. motorkhana requires occasional sections reversing at speed. The alternative mean I would need to implement electric reverse rather than mechanical reverse using the gearbox. This alternative would force me to leave the brush timing in the neutral position because if I didn't the brush timing would become retarded when applying the electric reverse. So for motorkhana I think a gearbox is the way to go.
It's not so much the top speed that is the consideration. I haven't even used fifth gear in anger. So fourth is the equivalent of direct drive to the diff anyway. So if the brush timing is advanced it can handle the speeds direct drive with my diff ratio.
The three biggest challenges I would quote to anyone playing in the same space are:
- Chassis design is a way tougher challenge than building the Electric drive train.
- Striking the right compromise between weight and power is tough with current technology. If budget were no issue and you were building a car dedicated to lets say hill climb, then you would end up with a larger, higher powered car like the VW Pike Peak monster. But budget is an issue for me and so is size and weight. Yes I could build a more powerful version but then it would need more batteries = more weight = more size = bigger tyres = less agility = more cost etc etc. It isn't what I was setting out to achieve. I am trying to prove EVs can compete in grass roots motorsport on a grass roots budget.
- Lack of noise is the other thing that I quite often talk about. It isn't a big deal from a competitor point of view. But a big part of the motorsport experience from a spectator point of view is the roar and rumble that comes from a powerful combustion engine. We can deny it all we like but for EVs to become a real option at all levels of motorsport we will need to somehow fill that void.
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