How far can you push a small £500 electric car; four years of hacky racer

Four years ago when the idea of ​​a pandemic was something that only worried a few epidemiologists, a group of British hardware hackers and robot warfare enthusiasts came up with an idea. they will take inspiration from american Power Racing Series To build your own little electric racing formula. hacky racers Racing on mixed surfaces instead of tarmac became a rough version of its transatlantic cousin, and as an inaugural meeting the first group of racers convened at a cider farm in Somerset to try it. Last weekend they were back at the same farm after four years of Hacky Racer development in which racing was disrupted by the pandemic, and Hackaday came once again to see how the cars developed.

Probably the most fun you can have with five hundred quid

" data-medium-file="https://hackaday.com/wp-content/uploads/2022/06/hacky-pit-scene.jpg?w=363" data-large-file="https://hackaday.com/wp-content/uploads/2022/06/hacky-pit-scene.jpg?w=568" loading="lazy" class="wp-image-540590 size-medium" src="https://hackaday.com/wp-content/uploads/2022/06/hacky-pit-scene.jpg?w=363" alt="A busy hacky racer pit scene" width="363" height="400" srcset="https://hackaday.com/wp-content/uploads/2022/06/hacky-pit-scene.jpg 1000w, https://hackaday.com/wp-content/uploads/2022/06/hacky-pit-scene.jpg?resize=227,250 227w, https://hackaday.com/wp-content/uploads/2022/06/hacky-pit-scene.jpg?resize=363,400 363w, https://hackaday.com/wp-content/uploads/2022/06/hacky-pit-scene.jpg?resize=568,625 568w" sizes="(max-width: 363px) 100vw, 363px"/>

A busy hacky racer pit scene

We've mentioned hacky racers and power racing enough that many readers may be familiar with them, but in short, the rules governing the chain specify a maximum length and width of 1500mm and 900mm, enforced by the appropriate 2-horsepower. Power limits the fuses to the planned voltage, and a £500 (approximately $600) budget limit. Many vehicles design creative bodywork with power racing inspiration in mind, and the result is a field of cars with top speeds between 15 mph and 20 mph (about 30 km/h).

Those first hacky racer meetings in 2018 had a mix of power plants. Some 24 V DC transaxles from mobility scooters, some DC power plants from golf buggies, and 2 hp brushless auto rickshaws were fast vehicles with motors. Most of the chassis designs were modified from donor machines, and the motor controller Chinese modules were commoditized. Thus it is interesting to see how some years of development have developed the formula. Four years later the all-new machines have custom chassis designs, there were no Mobility or Golf-based DC motors on show, and the rickshaw motors have been joined by converted car alternators. It is clear that it is in these last power plants that the most development is taking place, so it is worth taking a closer look.

Pushing the limits with the most affordable brushless motor of them all

we covered converting alternator to motor Early 2020, and from this we know that they require DC bias for their field winding as well as 3-phase AC from the motor controller. Experiments have shown that this winding requires between about 2A and 5A, depending on the alternator, but it is in managing this figure that some of the most interesting technological developments lie.

" data-medium-file="https://hackaday.com/wp-content/uploads/2022/06/hacky-alternator-field-dropper.jpg?w=300" data-large-file="https://hackaday.com/wp-content/uploads/2022/06/hacky-alternator-field-dropper.jpg?w=469" loading="lazy" class="wp-image-540593 size-medium" src="https://hackaday.com/wp-content/uploads/2022/06/hacky-alternator-field-dropper.jpg?w=300" alt="Behind this converted alternator can be seen dropper resistors for field width." width="300" height="400" srcset="https://hackaday.com/wp-content/uploads/2022/06/hacky-alternator-field-dropper.jpg 1000w, https://hackaday.com/wp-content/uploads/2022/06/hacky-alternator-field-dropper.jpg?resize=188,250 188w, https://hackaday.com/wp-content/uploads/2022/06/hacky-alternator-field-dropper.jpg?resize=300,400 300w, https://hackaday.com/wp-content/uploads/2022/06/hacky-alternator-field-dropper.jpg?resize=469,625 469w" sizes="(max-width: 300px) 100vw, 300px"/>

Behind this converted alternator can be seen dropper resistors for field width. Looks like a little grass was picked up during the last race.

The stator in a brushless motor is a magnet, and it rotates in a field created by a set of coils spread around it. Rickshaw motors, like most small brushless motors, have a permanent magnet as the rotor, which works well but is prone to overheating. The alternator has an electromagnet with a set of brushes as the stator, and this electromagnet forms the field coil. The more current this coil carries, the greater the magnetic field, and thus the more torque the motor can produce. More magnetic field also means more emf, and since the motor controller must counteract this back emf, there is a tradeoff that when the current is high for more torque the top speed is lower. Hence interesting developments with these motors come with variable area to select the desired combination of torque and top speed.

The simplest method of providing field current is by placing a suitable resistor in series with the field coil and connecting it directly to the battery. This appears to be the preferred route at the moment, in which a machine switches in and out using a pair of relay-selected resistors for different motor torques via a button on the steering wheel. This first generation of field control is being replaced by active electronics, in which one uses a small DC motor controller to power the racer coil and the other uses a buck converter that will eventually run at a particular speed. Will map the field current to the best torque.

It is then clear that Hacky Racers are pushing to develop their formula, and that they are doing so, while maintaining the has-a-go character of the event, to their credit. Motorsport is discouraged by so-called checkbook racers, and hacky racers get involved in this regard. Mower Racing As the antidote to formulas who take themselves too seriously. Meanwhile the development of car alternators in the form of brushless motors has huge value for anyone experimenting with small-scale electric traction, so we look forward to further refinements of those technologies.

As we close this piece, it's worth mentioning the venue that hosted hacky racers as they let their hair down. north down garden There is a working Somerset Cider Farm with camping facilities and an excellent cider barn. Some of us here on Hackaday Connoisseurs of good quality genuine cider, and we wholeheartedly enjoyed North Down Cider as a particularly well-crafted example of the art. We hope hacky racers call there again, and we look forward to bringing you all the new technological advances they've made in the intervening time.