How far can you push a £ 500 small electric car; Four years of Hacky Racer

Four years ago, when the idea of ​​an epidemic was something that only a few epidemiologists worried about, a team of British hardware hackers and robotic war enthusiasts came up with the idea. They will create their own small electric racing formula inspired by the American Power Racing series. Hacky Racers has become a rough version of its transatlantic cousin racing on mixed surfaces instead of tarmac, and as an inaugural meeting the first team of racers called for it to be tried at a cider farm in Somerset. Last weekend they returned to the same farm after being hampered by a racing epidemic four years after Hacky Racer development, and once again came to see how cars evolved at Hackade.

Perhaps you can have the most fun with five hundred quids

A busy hacky racer pit scene
A busy hacky racer pit scene

We’ve mentioned enough about Hacky Racer and Power Racing that many readers may be familiar with them, but again, the rules governing the series specify a maximum length and width of 1500 mm and 900 mm, with a 2-horsepower power limit appropriately enforced. . Fuse for rated voltage, and a £ 500 (approximately $ 600) budget limit. To keep pace with the power racing inspiration, many vehicles design creative bodywork, and the result is a field of cars where the maximum speed is 15 mph to 20 mph (about 30 km / h).

In 2018 those first Hacky Racer meetings had a mix of power plants. Mobility scooters were fast vehicles consisting of a few 24V DC transaxels, some DC power plants from golf bogies and 2 HP brushless auto rickshaw motors. Most chassis designs were changed from donor machines, and motor controllers were commodized to Chinese modules. It is interesting to see how the development formula has evolved over the years. Four years later the new machines all have custom chassis designs, the show had no mobility or golf-based DC motors, and rickshaw motors have been added by the alternative of converted cars. It is clear that most development is taking place in these last power plants, so it is worth taking a closer look.

Pushing the limit with the cheapest brushless motor of them all

We cover motor back conversion from alternators to early 2020 and from this we know that they require a DC bias for field winding as well as 3-phase AC from the motor controller. Experiments have shown that this winding requires between 2A and 5A depending on the alternator, but there are some interesting technical developments to handle this figure.

The back of this converted alternator has a dropper resistor for field widening.
The back of this converted alternator has a dropper resistor for field widening. It looks like a sack that encloses with a drawstring.

In a brushless motor the stator is a magnet, and it rotates in a case made by a set of coils spaced around it. Like most small brushless motors, rickshaw motors have a permanent magnet as their rotor, which works well but risks overheating. Alternators have an electromagnet with a set of brushes as a stator and these electromagnets form field coils. The more current there is in this coil, the more magnetic field there will be and thus the more torque the motor can generate. More magnetic field means more back EMF though, and since the motor controller must resist this back EMF there is a tradeoff that the higher the torque the lower the top speed. Interesting developments with these motors therefore come with variable field currents to select the desired combination of torque and top speed.

The easiest way to provide field current is to place a suitable resistor in series with the field coil and connect it directly to the battery. This seems to be the preferred route at the moment, a machine using a pair of relay-selected resistors for different motor torque through a button on the steering wheel. This first-generation field control is being replaced by active electronics, with one racer using a small DC motor controller to receive the coil and the other testing with a buck converter that will eventually map the field current for optimal torque at a certain speed.

It is then clear that the Hacky Racers are emphasizing the development of their formulas, and they are doing so by retaining the have-a-go character of the event. Motorsport is outraged by so-called checkbook racers, and in this case hacky racers join Longmawer Racing as an antidote to formulas that take themselves too seriously. Already the development of car alternatives as brushless motors has huge value for anyone experimenting with small-scale electric traction, so we look forward to further refining those techniques.

As we close this section it is worth mentioning the place hosted by the Hacky Racers because they have their hair down. North Down Orchard is a working Somerset cider farm with camping facilities and an excellent cider barn. Some of us at Hackaday are the masters of good quality real cedar, and we’ve sincerely enjoyed North Downs cider as a specially crafted example of the industry. We hope the Hacky Racers will reunite there, and we look forward to seeing the new technological advances they’ve made in the meantime.

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