Nitro RC conversion to brushless: Ofna Hyper 7 PBS

Converting nitro RC cars to brushless has become the craze lately, especially in larger scales, such as 1/8 buggies and monster trucks. I, for one, can not miss out on all this fun. For my brushless conversion, I have chosen an Ofna Hyper 7 PBS.

There are many reasons why conversion is attractive to hobbyists: you get the benefits of larger scale RC without the noise and smoke, the intense tuning requirements, expensive nitro fuel, and engine maintenance costs associated with it. I could also talk about the high efficiency and massive power brushless systems provide and other benefits as well, but that will be saved for another post.

So, going back to the buggy conversion topic...

Here is a list of the rest of the major components for the conversion:

• Castle Creations Mamba Max for ESC (Electronic Speed Controller) – 6 to 12 NiCad/NiMH or 2 to 3S LiPo , 100A continuous, PC programmable with built-in USB port
• Medusa 36-60-2200 for motor - 2200 RPM/V, 102A Feigao 9L for motor - 2731 RPM/V, 68A max
• Zippy 4S LiPo for battery - 14.8V, 5000mAh, 20C or 100A continuous Efuel 4S LiPo for battery - 14.8V, 5000mAh, 16C or 80A continuous
• Hobbywing UBEC-3A - 5.5V to 23V input, 5V or 6V output, 3A
• Kyosho center differential – 46T plastic spur, mod1
• Hardened pinion – 13T 15T, mod1
• Custom motor mount
• Custom battery tray/strap

For radio, the buggy has a Spektrum DX2.0, which uses 2.4GHz DSM and no crystals. Any radio will do actually and it doesn't really affect the conversion, but this one is nice.

Although the Mamba Max is listed to only accept up to 3S, it can actually handle 4S reliably. To do this, just disable the internal BEC. Adding a fan and one or more capacitors are also recommended but not required. The Mamba Max is an awesome ESC and PC programmable to boot. Currently, Castle Creations is offering a bigger ESC for 1/8 car/truck applications - the Mamba Monster Max.

The Feigao motor is far from the most efficient brushless motor, and yet it is still way more efficient than any brushed motor. In this configuration, it does get hot, but can't really complain much based on its good price. That is why, it has been replaced with the Medusa, which is more efficient and powerful. With the lower Kv (or RPM/V), the motor spins in its optimal range and provides more flexible gearing.

Despite being very crudely made, the battery holder with industrial grade Velcro between the battery and angled bracket, plus a Velcro strap, will not allow the LiPo pack to go anywhere. The battery didn’t budge at all even after the car did some flips and cartwheels. Still, I was not happy with it so I made a better one out of plastic container with foam inserts and Velcro. Now, the cell is safer as the tray forms an enclosure.

The weakest part of the conversion is the battery. I really wanted to get a better one because the system can easily demand from it more than it's max continuous amp rating of 80A ; however, at the time of the conversion, 20C or higher cells were expensive. Until a new LiPo pack is obtained, gearing any higher or putting bigger tires is not an option, so it was replaced by two Zippy 2S packs wired in series.

With this setup, the buggy has a top speed of more than 40mph or 65kph with a snappy acceleration. The runtime is not bad either at about 20 minutes of decent bashing. In addition, all of the electronics run cooler with the upgraded components.