I have an electric remote control car which has an electronic speed limit of 40km/h. After putting new wheels (which are around half the circumference) onto it, the effective speed limit is now 20km/h.

How can the pulse from the three wire speed sensor be changed so that the real speed limit is 40km/h with the smaller circumference tires?

Update: From Russell's answer is seems that a 4013 Dual D Flip Flop CMOS IC will be able to do the job?

Would one like this one work: https://www.jaycar.com.au/4013-dual-d-flip-flop-cmos-ic/p/ZC4013?

The sensor connectors look like this: enter image description here

From looking at the spec sheet for HEF4013B (which I believe is the same product as linked above?), would the following diagram be correct? enter image description here

Lastly, are the two connectors standard connectors which can be purchased, and if so what terms should I search for?

  • \$\begingroup\$ This questions is so vague. Eg what motor specifically? \$\endgroup\$ – Bradman175 Jan 31 '17 at 3:55
  • \$\begingroup\$ @Bradman175 Apologies, I am a complete EE noob. Can you elaborate on what you mean what kind of motor? The battery is a 36V battery Lithium Ion battery, so I assume the motor would be 36V too. The speed sensor is plugged into other circuitry so I was hoping to put a small frequency conversion circuit between the sensor and where it plugs in? \$\endgroup\$ – Greg Jan 31 '17 at 4:01
  • \$\begingroup\$ Twice the motor RPM will require twice the voltage, for a start, unless you feel like rewinding the motor. \$\endgroup\$ – Brian Drummond Jan 31 '17 at 13:19
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    \$\begingroup\$ The Jaycar cat ZC4013 CMOS DualD Flipflop will probably work OK - possibly with some extra minor "glue". Jaycar have been lazy and sloppy (they are often better than this) - they do NOT say what the actual part is and there are several choices , and the picture is of some other IC. Here is a typical data sheet MC14013B . The original 4013 family were all 15 or 20V rated (some CMOS families are not) and will wok over a wide range of voltages. The 4013 has a "fairly whimpy" drive capability but will probably work OK. \$\endgroup\$ – Russell McMahon Feb 1 '17 at 13:30
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    \$\begingroup\$ Did you see my added diagram and comments? \$\endgroup\$ – Russell McMahon Feb 2 '17 at 1:58

Note that by limiting speed to 40 kph with half diameter wheels you are achieving twice the motor RPM as previously. This may be acceptable or a problem depending on the application.

If the digital speed signal is of sufficient magnitude (which it probably is) you can probably add a divide by two "flip flop" to produce one output pulse for every two in. I say "probably" as it is possible but not overly likely that the following circuitry needs a series of short pulses rather than a half frequency square wave. This too can be accomplished if necessary.
Two flipflop toggle' divide by 2 arrangements are shown below.

Removal of every 2nd pulse can be achieved by eg having a flipflop toggle circuit as shown below and passing the signal through an eg AND gate with the gate enabled when a FF output is high and disabled when it is low. This has the advantage of preserving the pulse width of the signal.



In both cases Vout is a square wave which changes either from low to high or high to low on active transition of the clock signal. (I will not detail what that means specifically at this stage - clocks can be arranged to be +ve edge or -ve edge triggered or in some cases level triggered.)

A "D flipflop" will provide divide by two functionality when connected as shown below

enter image description here

The above diagram is from this webpage which also provides a good introductory tutorial into digital divide by N circuits and covers use of both D and JK fipflops.
Also covered here - same organisation.


A JK flipflop ahieves divide by 2 when connected as shown here

enter image description here

From here

eg MC14013B & friends:

enter image description here

  • \$\begingroup\$ I've updated my post to include a specific part and a circuit diagram. Could you please confirm if it is correct? \$\endgroup\$ – Greg Jan 31 '17 at 13:44

If you're talking about a brushless ESC, then you'll have 8 wires coming out of it in total: 3 thick ones that go to the motor, 2 thick ones connected directly to the battery (or a switch), and then 3 thin ones, generally red, black, and yellow.

If this is what you see, then there's no speed sensor, which makes everything relatively simple, as you could use an arduino or the like and read the incoming "servo" signal and essentially double it, and then send it to the ESC.Brushless esc If what you have is different, then unless you give pictures or more thorough descriptions, then I can't really do much. Note that doing this won't help if your motor is already at it's maximum rpm, and the only way to go faster would be to put larger diameter wheels or change out the motor and put one with a higher max rpm. It's quite possible that your car is physically limited to 40kmh rather than electronically.

  • \$\begingroup\$ It's definitely a brushless motor and the speed is measured using a magnetic sensor. That is, one of the wheel axles has a disk with a magnet attached to the disk. As the wheel spins, so does the disk and the magnet. The sensor which is next to the disk has a cable coming out of it which looks like this: imgur.com/a/FCAtN. Those are the correct colours too. \$\endgroup\$ – Greg Jan 31 '17 at 4:57

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