Piranha or Electric Eel

Electric Formula Libre

Piranha or Electric Eel

The car in question is, as I write this, just a collection of steel tubes stitched together sitting in my workshop and that’s it. It was purchased in 2010 by Daryl Watt of New South Wales and is a Melbourne-built Piranha hill climber of 1990-ish vintage with an extensive career doing short runs up the various inclined tracks around the country by the five or so previous owners. Daryl’s usual and very successful racer is a road-registered Westfield with a Toyota 20 valve silvertop, but he decided to get a bit more serious and buy a dedicated hill climber car. For most of its life it had a Suzuki GSX1100 motorbike engine in it, but after a catastrophic failure a replacement in the form of a Suzuki Hayabusa 1300 of about 175hp was fitted, though the installation had not been completed by the time Daryl bought the car.

As it sat, the car was not too far from being a runner; it just needed the wiring to be sorted out, a diff fitted, some plumbing, an exhaust system, and the usual list of fiddly things you have to do to make a racing car suitable for inspection by the scruitineers. So Daryl set about getting the parts need to make all that happen: A Haltec 500 ECU, a viscous LSD from a Mazda MX-5, and a deeper wet-sump for the Hayabusa, so it could keep the oil flowing under the violent forces a hill climber car generates during the 11/10th’s run the faster drivers always seem to do.

After a few months work the new diff had been fitted with a big motorbike sprocket to suit the chain that the Hayabusa engine uses and a steel cradle to hold the grease-lubricated diff unit in place. The wiring was done with the help of one of Daryl’s local friends and Daryl had fitted the new sump to the big bike engine. This is about where I came into the story, as Daryl had also purchased a Haltec Racepack dash and didn’t have the welding skills or equipment to make the little tabs that are needed to hold the display unit in place, nor the bracketry for the brakes lines and exhaust and so on. I was down his way, near Grafton, when a group of us had got together to destroy the World’s Ugliest Car™ near there and he wanted to show me the car. I agreed that I could do those fiddly jobs for him. All he had to do was to bring it up to my workshop on the Gold Coast. So since he arrived with a nearly-complete car, but it’s now a completely bare chassis, you may ask, “How the heck did that happen?”

Happy days – the Piranha when it was complete.

Happy days – the Piranha when it was complete.

Well, Daryl arrived here in May this year with the car and all the parts on the back of his trailer. I made it pretty clear that I have a heap of work to do for myself (Fraser, Mallock Mk31, Saidor 166S, etc.) so I’d have to fit it in between all those and I don’t work quickly anyway. He wasn’t in a rush so it all looked pretty convenient. First step was to remove the suspension, then the wiring, then the engine / gearbox. That left a bare but sheeted chassis and it was very obvious that although the car would physically be able to run around a hillclimb track, it was in a fairly sad state.

The alloy panelling had obviously seen a lot of hard work and at an absolute minimum I would have to replace the panel on the floor under the driver’s feet. That would ensure that Daryl wouldn’t be able to see the ground rushing past during a run, and I felt that would be a positive move. Daryl also provided a suitable battery and a Calsonic radiator off some other UK-based machine that I’d have to figure out where to fit. Because the car only typically runs for thirty seconds or so at a time, I had planned to mount the radiator horizontally behind the driver’s seat and have some ducting to pass some air through it during a run. I decided that the temperatures would (probably) stay in the acceptable range, because of the short full-power time – even with poor ducting.

I dug around on that internet thing and found a motorbike wrecker / parts company that sells motorbike oil / water heat exchangers and had also planned to fit one of those to help get the oil temperature up before a run. I’d have to fabricate a tiny two or three litre fuel tank, that small because that’s all you need for one run up a hill.

As all this was coming together, however, I looked more and more at the alloy panelwork on the car and decided (with Daryl’s approval) to do a complete re-skin as it was just an unacceptable mess. Gouges, dents, cracks ….. So after drilling out what felt like a few thousand rivets the chassis was back to bare tubes.

The story doesn’t get any better unfortunately, as it was clear that every time the car had been rebuilt, the old rivet holes weren’t filled-in with fresh metal and a new hole was drilled a little further along. Whilst this might make for a nice light chassis it also makes for one with a torsional stiffness not a lot better than spaghetti. This also wasn’t helped by the fact that the Piranha chassis is, I’m sorry to say, really not very good. At all. It’s fairly conventional with four tubes forming the four main longitudinal chassis tubes, and a number of vertical and horizontal tubes to form a three-dimensional structure, but as far as diagonals to form triangles to give those square sections strength – there’s just two in the main chassis and that’s one per side where the driver sits. Go forwards or backwards from there and the main chassis itself has nearly zero triangulation.

The roll-over hoop does have a pair of bars that go back and there’s another bit of bracing at the front but overall I’m pretty sure I could make the chassis twist noticeably with my bare hands. And it gets better – It didn’t seem to sit nice and flat on the build table, so a quick look along the lower chassis tubes showed that from about the start of where the engine would sit, the tubes actually bend downwards so the rear of the car is a good 25 mm lower than the front. You might think that’s the result of repairs from an accident, but some measurements showed that the top tubes are nice and flat (no, they’re not, I’ll get to that soon) and that the rearmost vertical tubes that tie the top and bottom chassis tubes together are that 25 mm longer. So for some reason that I can’t figure out, the car is meant to have a curved floor but it’s curved downwards instead of upwards so the airflow has no chance of making any aerodynamic downforce.

More careful measurements showed that the left-rear corner is also down a further 6 mm from the flat plane of the top tubes, no doubt due to old crash damage.

After digging about the deepest hole I could for myself with it, it was time to start fixing it and improving it where needed. First off was welding up a seemingly never-ending supply of old rivet holes. That took a couple of weeks of part-time work and I estimate it used-up about fifteen metres of 0.8 mm welding filler wire and a fair chunk of a G-sized argon bottle.
From the years of abuse, the lower-front chassis tubes were badly dented from hitting the ground and also looked like Swiss cheese from all the re-panelling. The two vertical tubes at the front only had four rivets in each to hold the alloy panel on, yet the tubes had over fifteen holes each. The vertical tubes could be repaired with TIG welding to fill the numerous holes, but the lower horizontal tubes were too far gone so they had to be cut out and replaced.

The other thing that will be done is the lower chassis tubes, the ones that bend down instead of up, will be also cut away and new ones fitted but with the rearmost end being level with the lower-rear suspension inner pivot and so be a good 100 mm higher than it is now thus allowing the fitting of a floor that can curve up usefully to make downforce. More diagonals will also be added along the chassis and also a pair of tubes that go from the roll hoop to the front smaller hoop, that’ll make it a lot stiffer and also safer for the driver but a bit more difficult to get in and out. The tubes going back from the roll hoop will be extended and moved back to also make the chassis stiffer. It was also around that period when Daryl had an urge to buy yet another car, the UK-built Force, powered by a 1600 cc Hayabusa and is very, very fast. So while he raced that I would be under no pressure to finish the Piranha.

This is about where Daryl wandered in one day and changed everything yet again.

“Bill, I’ve got a crazy idea.”

Daryl’s a real country boy so I braced myself. “I want to convert the car to be completely electric.”

Well I wasn’t expecting that and this is where it gets more difficult for me because as far as electrics go, anything much more difficult than changing the battery in the TV remote has me stumped. Well maybe not quite that bad, but not too far off it.

“Sure, we can do that, great idea!”

As it turns out there’s a fair few performance electric cars around and some are remarkably quick as well, with a fair bit of information about it all on the internet. Some furious searching initially showed a very fast drag car in the UK and much to our surprise the electric motor they are using came from a milk float. Again, we didn’t expect that. More research, mainly with the help of a popular Electronic Vehicle (EV) forum we found that a very popular motor can be found in many forklifts. They vary in size with the common ones being 8”, 9”, or 11” diameter with a corresponding reduction in maximum RPM. The one that seems to be the way to go is the 9” one as that has the best balance between rpm and weight. They’re about 60 kg and the 11” motor is over 100 kg, though has a lot more torque but a much lower maximum RPM. The 9” motor runs to 7,000 RPM without too much trouble and with modifications will rev harder again.

On the subject of electric motors we are picking the one that effectively makes the least power for its weight. That would seem to be the worst way to go but the reasons are these – An AC motor makes far more torque for the same weight motor. The problem is getting one at a reasonable price and a suitable controller also at a reasonable price. The two units together have you parting with upwards of $20,000 and that’s way out of the budget. There are existing suitable production AC motors from a couple of the recent group of hybrid cars, such as the 111 kW Holden Volt unit and the 147 kW unit from the Lexus GS450h, but they still require a very expensive controller and quite a lot of expert fiddling. A bit of research on the various hybrid motors surprised me as most of them are only around the 60 kW mark, including ones that you would think have a lot more such as the big VW Touareg hybrid which again only has an electric motor also of about 60 kW. So it’s difficult to both obtain a decent AC motor and also get one for a reasonable price and also an AC controller for a reasonable price. It’s much the same story for brushless DC motors so plain brushed DC it is then.

That brings the cost down a fair bit as after doing a bit more research it seemed to be possible to buy a used 9” forklift motor for as little as $100. That does vary depending on the going rate for copper of course but in good times the forklift repair shops nearly give them away. I know this because I visited the repair shop nearest me and I was a week or two late; they’d just sold their pile of used parts and spares to a scrap metal recycler so they had nothing. So the plan is to get at least three 9” motors as Daryl and I figure we’ll probably blow one or more up as we muck around trying to get the most power out of it. The aftermarket DC controller scene seems to have plenty of choices and the favoured one at the moment is a Soliton 1 unit. We don’t need any fancy things like regenerative braking or the like, just a simple box that passes plenty of power to the motor is enough. There’s an optional throttle pedal assembly for them, which we will fit to the car, and I’ll also fit a new brake pedal assembly that sticks out the front a lot more than the original Piranha one did as Daryl has kindly asked me if I want to drive the car as well. Well yes I do! I’m a bit on the tall side so instead of cutting the chassis in half to extend it so I fit, I’ll just add more metalwork to the front for crash protection. There’ll only be the brake and accelerator pedals, of course as the car will have no clutch or gearbox.

Bodywork stripped off, showing the ‘innards’. It looks good, but hides the wear and tear of the years it has raced.

Bodywork stripped off, showing the ‘innards’. It looks good, but hides the wear and tear of the years it has raced.

To control it all, I believe we will be able to tailor the output of the Soliton controller so that the torque output of the motor doesn’t do the usual linear-like decrease that electric motors typically have. Another trick the EV people do to get more top-end power is to advance the brushes, just like spark advance on a petrol engine or maybe a touch of Honda V-TEC action. I haven’t seen one of the 9” motors yet but I will be investigating the possibility of making the brushes have variable timing with revs, so that the motor produces maximum torque at all times. The dashboard is also going to be quite a lot more simple and clear than a petrol-powered car as it won’t have one. There’s no pressures or temperatures to monitor and the RPM is what it is, we can look at the data logging later to check that the gearing is correct. It doesn’t need to be warmed-up before a run either, just check the battery charge and go.

Further stripped, the basic tub with the old skin on it was full of creases and dents.

Further stripped, the basic tub with the old skin on it was full of creases and dents.

On the EV forum one of the more knowledgeable chaps wrote that the “batteries are the engine and the motor is the gearbox”. That’s a bit different to a petrol-powered car of course, and it does make us focus on the batteries. The best batteries available right now are the lithium-polymer type that is commonly used in model aircraft and they have their own terminology that describes the performance of each battery pack. The battery pack we are looking at is called a 10S 65 – 130C 5000mah unit. What all that means is the ‘10s’ says it has ten 3.7 volt batteries inside it so the pack produces 37 volts. It’s 5,000mah and the 65 – 130C thing isn’t anything to do with temperature, it’s how many amps the pack can produce and in this case it’ll sustain sixty-five times 5 amps or 325 amps at 37 volts, with a burst rating of one hundred and thirty times 5 amps or a mighty 650 amps output. Each pack (from www.hobbyking.com) is a little over US$200 and so not cheap but we shouldn’t need too many of them. Some rough numbers show that six packs would be enough to get the 70 volts + 1,000 amps we need as a minimum, and that we should get enough runs out of those six packs to complete the average day at the hill climb track. But we can of course recharge them if there’s a handy power point somewhere. They won’t take up a lot of space either, at only 300 mm x 50 mm x 50 mm in size each. Worst case is that we have to build two complete battery pack units that we can slot into the car (six batteries together only weigh about nine kilograms) and swap them over between runs. It’s also quite easy to add more batteries to the pack unit to get more grunt if need be.

Not much in the way of triangulation in the rear end!

Not much in the way of triangulation in the rear end!

To finish the story, we also looked at twin smaller motors, one for each rear wheel. However, there’s then the problem of finding a controller that can work both motors as we need to. But it’s also mechanically easier to just have the one motor and with that single motor also much easier to change the gearing to suit each track as the big motorbike sprocket on the diff splits in two so it can be changed without having to pull anything apart. We also looked at making it 4WD, using four even smaller motors, but packaging up the front is quite difficult and if we went to hub-type motors that substantially hurts the unsprung weight. With the aerodynamics, the car originally had big side-pods that are not going back on, and a big pair of wings for each end that are going back on. There’s no need to duct air to the radiator but the big electric motor will need some cooling air as they apparently get quite toasty after a run. So maybe a hand-held cooling fan for when it sits in the pits as well. Another benefit of the electric propulsion system is that unlike a naturally aspirated engine it won’t lose power when raced at places like Bathurst, which with the ~600 metre elevation makes a non-boosted engine lose about 8% power. The other upside to making the rear part of the car go upwards instead of downwards is that the removable floor from Daryl’s other car, the Force, will fit. It’s very light and helps make a big part of the total downforce but with little drag. Speaking of Bathurst, the hill climb cars run there from the end of Mountain Straight to up near Skyline and the fastest ones do it in about 36 seconds. The faster bike-engined cars do it in about 42 seconds so still quite fast and to put that in perspective the V8 Supercars take about 44 seconds to do that same distance, however that’s during a flying laps and the hill climb cars do those times from a standing start.

Since I might be driving it, I thought I’d see if I fit. Um ... not really. The pedals will have to be right at the front of the chassis.

Since I might be driving it, I thought I’d see if I fit. Um … not really. The pedals will have to be right at the front of the chassis.

So that’s how the intent to weld on a few simple brackets ended up with the car completely stripped and ending up a bare chassis with a plan to make the car fully electric. It’ll be running in the Formula Libre class and so have some good competition but it’s likely to be the only totally silent racing car there and for some time to come. There’s very little budget for it right now as well so it’s not going to be together until at least the end of next year, but as progress happens I’ll write about it here. The car should be pretty fast though, courtesy of the very flat torque output and no gear changes at all, and we will keep working on it until it is one of the fastest cars. We aren’t building it to come second. The last thing to add, which will help it to be one of the fastest cars, is the addition of the last Watt: Daryl Watt.

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