Category Archives: Technical

Generators on the wheels

One of the reasons we built Trev was to get people thinking about the energy they use for mobility. Most people appreciate that using tonnes of machinery to transport a 75 kg person uses a lot more energy than necessary. But some people get a little too inspired: Why don’t you put generators on the wheels?

Generators on the wheels is not a bad idea. The electric motors used in most electric and hybrid cars can act as motors converting electrical power to mechanical power, or as generators converting mechanical power to electrical power. Working as a generator, the motor can convert the kinetic (movement) energy of the car into electrical energy, and this energy can be used to partly recharge the battery. But converting the kinetic energy of the car to electrical energy slows the car. It is called regenerative braking, and the braking force that can be achieved is about the same as the driving force that can be achieved by converting electricity to motion.

Regenerative braking cannot convert all of the kinetic energy of the car into electrical energy—some of the energy is dissipated by resistance forces in the tyres and bearings and by aerodynamic drag, and some is dissipated as heat in the motor/generator and in the electronic controllers. But some of the kinetic energy can be converted to electricity and stored for later use—which is better than occurs with normal friction braking, where all of the kinetic energy is dissipated and none of it can be recovered.

But the proponents of generators on the wheels often want to go beyond regenerative braking to generate electricity without slowing the car. Not necessarily perpetual motion, where the generators generate more than enough electricity to power the motors, but enough to reduce the power required from the battery.

It doesn’t work—at least, not in our universe.

To see why it doesn’t work, try writing power values in each of the empty boxes in the diagram below. Suppose the car is travelling on a flat road at constant speed, so the power values are not changing. The total power into the motor must be the same as the total power out of the motor, and the total power into the generator must be the same as the total power out of the generator. It is like Power Sodoku—everything has to add up.

Instructions:

  1. Write in the power required for propulsion. This is the power required to overcome rolling resistance and aerodynamic drag. Trev uses about 4000 W at 70-80 km/h.
  2. Write in the motor losses. Losses in an electric drive system are about 10% of the propulsion power.
  3. Write in how much power will be transferred from the motor to the generator, and generator losses (about 10% of the power into the generator).
  4. Calculate the ‘battery out’ power and the ‘battery in’ power.

The total energy from the battery is (battery out – battery in). What do you have to do to minimise (battery out – battery in)?

Lessons learnt

On 20 July we gave a presentation on lessons learnt to the Adelaide Branch of the Australian Electric Vehicle Association:

Lessons learnt

More video from Berlin

Trev has just arrived by ship in Vancouver, and should hopefully clear customs tomorrow. The next leg of Zero Race starts on Friday.

In the meantime, here is some more video of Trev in Berlin, being repaired and being driven.

Trev being repaired in Berlin

Trev, the remote control car

Zero Race is moving across Europe at a challenging pace—see the Zero Race blog for details. We have had no time to replace our temporary suspension fix with a permanent repair, or to fix the communications problems in the battery management system. So while the rest of the race is in Brussels, we have moved ahead to Sven’s workshop in Berlin to give us a few days to fix these problems before rejoining the event when the other teams arrive on Tuesday. (Sven is the main rider of Team Vectrix, and one of our benefactors. He has also booked to drive Trev between Moscow and Shanghai, so is keen to have the car running reliably.)

Trev in the Berlin workshop

Trev in the Berlin workshop

Communications between the crew in Europe and the rest of the team in Adelaide is improving. In fact, last night we achieved a major breakthrough in remote automotive diagnosis:

Peter, in Adelaide, hooted the horn, in Berlin.

Here is how we did it. The horn button in Trev, along with all the other driver buttons and controls, is connected to a microcontroller under the dash. When the horn button is pressed, the microcontroller sends a ‘horn on’ message to the rest of the car via the Controller Area Network (CAN) bus—a pair of communications wires which connects all of the electrical devices in the car. Another microcontroller, the front right lighting controller, receives this message and turns on the horn. When the driver releases the horn button, the driver controls box sends a ‘horn off’ message and the front right lighting controller turns off the horn. Easy. Connections are made in software, and there are no large looms of wires running around the car.

The CAN protocols automatically handle message priorities and arbitration between devices wanting to send messages at the same time.

Any device can listen in on the communications. To diagnose problems, we connect a netbook computer to the car and log the CAN messages. But we can also put messages on the CAN bus from the netbook. Last night, Nick had the netbook connected to the car, and Peter (in Adelaide) was operating the netbook via the internet using TeamViewer software.

Hooting—via wireless modem, internet, Android phone, netbook computer and CAN bus—was inevitable.

Technical difficulties…

We have experienced a few technical difficulties over the past few days. Most frustrating have been problems establishing reliable communications between the crew in Switzerland and the rest of the team back in Australia. Getting a good data plan is not easy if you are only going to be in a country for a few days. But the information and photos started flowing today (thanks Keith!), and we have started a gallery.

Nick on the start line, Geneva, looking for an Australian socket

We have also had some problems with the car:

  • Moisture in the battery box caused communication problems in the battery management system. This did not stop the car from driving, but Nick and Jason put in long hours in the two days leading up to the start of the race trying to fix the problem. The crew will pick up replacement parts in Brussels.
  • There was some damage to the lower suspension mounts in transit. With the help of the Zerotracer team, the crew has overcome the problem by running reinforcing beams across the underside of the car. Meanwhile, the team back in Australia has worked out a permanent repair.
  • The installation of the GPS tracker in our car has not been reliable; consequently, our location on the Zero Race web site has been missing or delayed. This should be fixed soon.

The crew is working very hard—Zero Race events, driving between cities, and maintaining the car. Mic joined the crew yesterday, and provided some welcome respite. But they are in good spirits, and getting an enthusiastic response to the car wherever they go. We will post some of their stories and photographs over the next few days.

Trev. It’s registered.

A milestone for the logistics team

The logistics team have completed their first major challenge, successfully importing our new batteries from Korea to the Team Trev workshop in Adelaide.

With no experience importing goods (especially dangerous and expensive goods!), we relied on the experts. We thank Chris Sergeant and Ben Poprawski from Customs Agency Services and Chris Donnelly from Donnellys Insurance Brokers for their great service in organising many aspects of the task and providing us with quick advice.

The arrival of the batteries was cause to stop and celebrate the progress of the team in preparing for Zero Race which starts in Geneva on 15 August, 2010.

If you look closely at the photo, you can see that work is still continuing on the car. Coordinating the arrival of the batteries is only one of the tasks which must be done to ensure that Trev will be ready for Zero Race in time. The technical team is working very hard and putting in an enormous effort.

Outside the workshop, there are still many logistical jobs to complete, including organising insurance, car registration, freighting the car to Europe, driver uniforms, driver rosters, visas, travel, and so on. If you want to help, contact us through the website.