HobbyKing Red Brick 70A ESC (Opto)

From Hobbyking's website specifications:

Max Amps: 70A
Ubec: Nil
Cells: 2~7s Lipoly
Size: 84mm x 14mm 40mm
Weight: 64g (Inc Wires)
Fig 1:

Fig 1 shows the RB70A(OPTO), its shrink cover and top aluminium plate removed.

Note that there is no opto-isolator on the servo input, Hobbyking's description as an OPTO ESC is a fraud.

The ESC is supplied with leads but no connectors.

The ESC was found to have a hardware fault, the 4k7 resistor from the servo S lead to the MCU was intermittent, a result of poor quality soldering. The hot melt glue and resistor were removed and a new resistor soldered in place. This intermittent operation would have resulted in a crash in a flying application.

The pin connections on this ESC are different to those in SimonK rb70.hex, though they are the same as rb50.hex. This board contains a digit "2" etched into the PCB just below the top FET driver, this may denote a revision level of the board from the original RB70A.

 The top aluminium plate which has been removed has a thin synthetic insulation later to prevent contact with the battery leads and motor terminals. In my view, the sharp corners of that plate could cut through the insulation and short circuit the batter or motor leads, and since the battery is unfused, it represents a fire risk. In the ESC which I received, that insulation was rolled under at the motor end and the end 4mm of the plate was bare over the motor terminals. This appears to have been done deliberately to contact the FET drivers. The plate appears to have no real purpose in the non-BEC (OPTO) version, the FET drivers did not get hot in operation, so it will be left out when the ESC is re-wrapped.

The ESC is low cost, has a well implemented bank of FETs and heatsink, the top plate is questionable, and aside from the fault, construction quality was mediocre with most components poorly aligned (a sign of worn machinery and incorrect soldering cycle).

Stock firmware

The ESC was bench tested with the stock FW on a Hobbyking 4822-690Kv motor on 4S and a 1045SF propeller. The motor speed sluggish in response, the speed at high speed varied with cyclic surging. Measurement of the drive waveform showed 30°pp timing jitter.

The stock FW was unsuitable for flying with the 4822-690Kv.

SimonK firmware

SimonK RB70A was loaded and was clearly incompatible with the ESC.

A check of pin connections revealed that this ESC had pin connnections like that of the SimonK RB50A configuration. The RB50A configuration was used as is, and the motor tested with and without COMP_PWM again 4S and 1045SF propeller.

The motor performed faultlessly, rapid response, no hesitation or surging.

The same timing jitter test was performed and 2°pp timing jitter was measured.


The RB60A(OPTO) is a basic ESC without integral BEC, and it does NOT have an opto-isolator interface.

The PCB appears to be a second revision of the original RB70A.

 The stock firmware worked poorly and was unsuitable for flying the tested motor.

The ESC uses common Atmega8 TQFP32 hardware that is readily flashed with third party firmware. The tgy (SimonK) rb50a.hex firmware delivered excellent low speed operation, more rapid response and no indication of sync loss under rapid throttle changes.

No warranty

Advice (or a warning) to those who might try to replace the firmware on an ESC. Most FW comes with no warranty, and typically the OEM firmware is read protected so you cannot save and restore it. In most cases, changing the firmware may terminate any seller's warranty.

In making hardware or firmware modifications, you may damage the ESC, or the model may fail and cause consequential damage.

The author gives no warranty and makes no representations about the suitability of this technique or any particular products for the end user, or the accuracy of the article content, they must inform themselves and make their own judgment aware that there are risks. If you are not competent to do these things, don't do them!


The article should not be seen as a recommendation or endorsement of any products.

In fact the product had an electronic fault, and even when that was fixed, it was not suited to the Hobbyking 4822-690Kv because of surging speed at higher rpm. The problem was not referred to Hobbyking as a result of previous experience.

The products shown in this article are from Hobbyking who manufacture products under a range of brand names, possibly creating an illusion of competition. Their products tend to be low in cost and low in quality, products are not good value when you have to throw a proportion of them in the rubbish because the cost of returning them exceeds the value of the replacement which is only available after excessive delay, many follow ups and haggling. If you see the claim [o]ther stores will force you to ship the product back to China in full retail packaging every time! Hobbyking's warranty service is professional, fair and fast, don't believe it, it doesn't work that way in my experience... I get better service from most eBay sellers!



Version Date Description
1.01 30/11/2013 Initial.

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