Tamiya QD "technical review"

[korreka 53]

 Tamiya QD Super Sabre "technical review"

The Tamiya QD series (1/14 scale) are advanced toy grade cars that were many people's entry into the world of RC cars.

The transmitter electronics have the OKI L9362 encoder integrated circuit and the encoded output is on pin 9.
 There are two internal potentiometers for steering and propulsion adjustment. The transmitter has channel 1 
as throttle and channel 2 as steering (in reverse of a hobby-grade transmitter).

PPM signal on pin 9 of the OKI L9362 i.c.

The circuit diagram of the transmitter:

This buggy was powered by 8 AA batteries. I have removed the battery terminals to insert a 
9.6V NiCd (Ni-MH) battery.

To disassemble, you remove the body (3 screws) and an electronics cover (4 screws) on the car.

The car circuit board

The power supply connector is soldered as seen in the picture. There are two holes to adjust the 
neutral of the steering and throttle on the circuit board.

 

The electronic board has the OKI L9367 integrated circuit; pin 16 is the input signal coming 
from the receiver and on this pin you can see the amplified PPM signal. This one is the diagram:

 

The 27Mhz receiver, demodulator and intermediate frequency filters is very similar to 
the diagram shown in the OKI L9362 datasheets:

And the signals are these:

The rear wheels have a 6mm hex axle; the hexagon can be pulled out: it is inserted into
the splined shaft. The shaft is 4mm diameter and the nut is M3.

To remove the gearbox, first remove the shock absorbers from the brackets.
Remove the motor cover and then remove the motor. The gearbox is held by 4 screws on its bracket.

The 280 motor has an 8 tooth 0.6M pinion. Its specification is 17000 rpm (not load) at 7.2V (0.32A) or 22,600 rpm at 9.6V; It matches the RC-280SA-2865 motor specifications. To access the inside of the gearbox, 3 screws are removed:

The gearbox has two speeds:
slow speed: 1: 16.3 ratio  (40/8 * 49/15).
fast speed: 1: 10.2 ratio  (40/8 * 43/21)..

The speed with the 67mm diameter wheels would be around 21 or 22 Km/h.

This car has front independent suspension with friction dampers (spring only) 
without any additional anti-rebound system. The rigid rear suspension was inherited
from another Tamiya buggies (Hornet, Grasshopper).

Spare tires are hard to find; If we want to change the rear wheel for a standard 12 mm 
hexagon wheel, we can do it with a 4mm hexagonal adapter (with grub screws):

Wheel axle detail.

The Super Sabre in action (Badiola RC photographer):

These thread is in spanish lang. in 
https://reparar-cochesrc.blogspot.com/2015/12/reparar-antena-de-emisora-tamiya-qd.html

[Mouc-RC 915]

Nice article, lots of details

Not sure if your pictures are only related to the Super Sabre, but with the Sabre (and the Thundershot (46001 & 46002)), you should have the "No-led" transmitter. And as far as I know from my experiences, the "early" No-led radio is fully proportional in steering, but "2-speeds" only in throttle. 2nd gen. transmitters (starting with 46003 Thunder Dragon QD) have kind of a "6-steps" forward throttle (this is what I "hear" at least).

Here are mine, the "On position" is indicated via a red sticker that the switch hides or not :)

[korreka 53]

My Super Saber car has a transmitter with LED.

The car is fully proportional throttle; The electronics have OKI L9362 and L9367 circuits with 2 fully proportional channels; Believe me, I'm an electronic technician.

I have seen other 80's RC cars with L9367 circuit and 2-speeds throttle but on the circuit board, they had relays and a power resistor to drive 540 motors.
In the 80s, a relay was cheaper than a power Mosfet transistor.

 

It is possible that the "early" QD cars were sold only in the USA and UK and the "second generation" was sold worldwide.

[wolfdogstinkus 2063]

Great post. Very informative. Massively under-rated buggies.

[kinxkinx 1]

As I have time, I'm back to my QD project (or two). My children are 8 and 6, the same age I was when I had this car, looong time ago...

I have four QD (46001 and 46002), I couldn't resist the temptation to buy a lot of 3 used cars. Each facing issues with motor control. One moves only forward, another simply 'vibrates,' and the third seems to lack power. I have four transmitters that are in good working order, so the problem is not there.

As many people encounter similar problems, I'd like to adress them, without a hudge upgrade, and try to find what's wrong in the PCB. I am confident that, Korreka, you may have some answers or clues. Which components might have failed? Is it more likely the transistors of the ESC part—Q11 to Q16 in the scheme—or the OKI? And how can I test this?"

Many thanks if you guys have some clues

 

 

[Mouc-RC 915]

I've seen this lot for sale also, and admit that I had some hesitation... ;)

Don't know if it helps, but I've got some QDs also and I can say that the first gen transmitters (with a red sticker hidden by the switch when "OFF") are a bit flimsy, compared to 2nd gen ones (the ones with the red LED when "ON" ). If you have a second generation transmitter available, you may try it with the appropriate crystal, and the problems you describe above may disappear.

You could also try some di-electric cleaner spray on first gen transmitters potentiometers, but it helps for one or two weeks only :/

Good luck!

[kinxkinx 1]

Thanks for your response Mouc-RC, but as I tested with many transmitters (four, first gen. I guess), I'm quite confident that the problem is not the transmiter. (the problems are specific to the car, not to the transmitters). It must be a problem on the PCB of the cars, so, likely the transitors of the esc part.

[korreka 53]

On 1/22/2024 at 10:43 PM, kinxkinx said:

I am confident that, Korreka, you may have some answers or clues. Which components might have failed? Is it more likely the transistors of the ESC part—Q11 to Q16 in the scheme—or the OKI? And how can I test this?"

Hi,
Before replacing motor transistors, you should check many things; You should have a multimeter at least (if you have an oscilloscope, the better).
* Clean  rust and sulfate on the battery terminals, cables, soldering points, etc. with oil or vinegar.
* check the antenna and the soldering point (cuts or cracks on the board)
* Check the continuity of the battery and switch cables with the multimeter; The sulfate corrodes the copper inside the insulator.
* You can test the car with the original transmitter or with a 27 Mhz hobby transmitter and appropriate frequency band (steering and throttle are swapped)

* Check the quartz crystal socket and plate (cuts or fractures) and crystal pins for movement; change the quartz crystals for others to see if it works.
* Turn on the transmitter and the car and check the voltages on the switch (12/9.6V, orange and blue wires), pins 8 and 11 (6V), pin 12 (2.3V).
* On pin 16 you can signal the transmitter if the receiving stage works well.
* there are two trimmers (throttle and steering neutrals); Turn the trimmers a little because sometimes it gets dusty; If you have electronics cleaner, use it.
* on pins 9 and 10, the forward and backward signals are output to the transistors; They can be seen on the oscilloscope (https://www.youtube.com/watch?v=muKW6eYPamE). With the multimeter and the throttle lever at 100%, the voltage would be about 4V.
* Check the motor connected directly to a battery.



 

[Mouc-RC 915]

Don't know if it helps, but

On the left: First Gen QD Buggy, on the right, Second Gen.

As far as I know and have seen online:
46003 to 46019 use same electronic (second gen)
I guess that early 46001 & 46002 use first gen electronic, and maybe were then updated with 2nd gen if production run long enough. "RC Everyday" on Youtube has a ThunderShot 46001 which seems to have a 2nd gen electronic gear.

[kinxkinx 1]

Thanks Korreka. The last time I saw an oscillocsope was not in this century. But I'm gonna try to test everything! Many things seem fine to me (the transmitter, quartz, antenna), but anyway, they deserve a chek up.

And thanks Mouc RC. The 4 qd I have are all first gen (with the specific transmitter without LED). It's written on the box (in French) that there are just 2 speeds forward and one backward. Don't know if that impacts the electronic on the car.

From this side of the PCB, difficult to say if there are many différences.  I'll take some photographs when I'll open them.

 

 

[Mouc-RC 915]

You're welcome. I'm pretty sure that PCB "1" power output is much lower than PCB "2", but I haven't measured this yet. Mainly because this involves de-soldering motor wires & solder them again. One day...

But clearly on the track, my 46002 Super Sabre is much slower than my Avante 2001 (46010)

 

 

 

 

 

 

 

[Nikko85 4388]

Another differences is that the later models can take bearings, the rear gearbox can fully take bearings, as can the front wheels. This makes them a little easier to work on. I believe the pinion is also slightly different - although the spur and diff units are the same.

This is a great resource, I've got a few in which I put modern electronics. I run a 370 motor in a couple which gives lots of speed for the size, using the 8 x AA batteries, but I've also dropped in a 2030 brushless on occasion. 

These are mine:

Only the thunder dragon has a stock body - the from right to left it's a 1/16 slash, WPL D12, MN45, Thunder Dragon and QD beetle (moved from the MT to the buggy).

 

 

[kinxkinx 1]

4 minutes ago, Mouc-RC said:

But clearly on the track, my 46002 Super Sabre is much slower than my Avante 2001 (46010)

Did you try to switch transmitters? I haven't open the car yet, but it may be fully proportionnal regardless the version (as Korreka suggest). It's clear that first gen receiver only has 3 speeds, see the pictures : (slow forward, fast forward, and backward). Otherwise, they look quite similar (obviously, the same oki L9362). That dosen't make any sense to have less power in the first gen !

 

 

[Mouc-RC 915]

56 minutes ago, Nikko85 said:

[...] Another differences is that the later models can take bearings, the rear gearbox can fully take bearings, as can the front wheels. This makes them a little easier to work on. I believe the pinion is also slightly different - although the spur and diff units are the same. [...]

Good to know, thanks! I knew for the front wheels, but haven't open gearboxes yet

55 minutes ago, kinxkinx said:

[...] Did you try to switch transmitters? [...]

For sure I did. 2nd gen transmitters can drive 1st gen inboard electronics.

I only use 2nd gen transmitters, 2 steps throttle is a no-go for me.

55 minutes ago, kinxkinx said:

[...] That dosen't make any sense to have less power in the first gen ! [...]

I wouldn't say that. Starting 46004 Midnight Pumpkin, there's some big wheels... Much more power needed. Then it could be production rationalization reasons that may have dictated to use a single type of electronics. Also, 1st gen transmitters are truly flimsy, quality wise; 2nd gen is tough as nails I found.

[kinxkinx 1]

I opened the car, but haven't tested electronisc yet. So far, what I can say is that the circuit board is very similar to 2nd gen. (see the picture). Why did Tamiya changed it? mystère et boule de gomme.  The most visible difference is the shape of the h-bridge radiator.

The motor doesn't look exactly the same.  That can explain the lack of power, or maybe it's just because of the mechanics (bearing?). As both versions must have the same voltage...  Anyway, confirming your idea, Mouc, the seller told met that the thundershot lacks of power (compared to his Avante 2000)

 

 

[Mouc-RC 915]

You have the 1st gen electronics. My feeling is that neither the motor or the transmission bearings are involved in the lack of power (but I cannot confirm yet).

For the sake of documentation, here are the:

Early electronics (box-art info):

Later electronics (also used in QD Monster Trucks from the nineties):

And once again thank you Nikko85, had the QD boxes under my nose, and never seen the "gearbox differences" before

Edited January 27, 2024 by Mouc-RC
Bigger images

[korreka 53]

18 hours ago, kinxkinx said:

 

I don't have any first generation buggies. The second generation transmitter uses a potentiometer on the throttle trigger and sends the standard PPM signal and each pulse varies between 1 and 2 msec; a hobby transmitter of  27Mhz (80-90`s years) uses the same signal.

It is possible that the first generation transmitter uses a switch on the throttle trigger  and fixed resistors and the pulse is not in the 1-2 msec range.

An old motor with worn brushes is slow and has no power. The motor  280 of the second generation buggy has 17000 rpm (no load) at 7.2V;  It may be the RC-280SA-2865 motor. There are similar motors with these specifications on Aliexpress or eBay.

Also check and clean the battery terminals; Sulfate and oxide do not allow the current to drive well.

 

[Mouc-RC 915]

Finally no surprise that my Super Sabre is much slower than my Avante 2001. I just measured the output voltage on motor wires, motors unplugged & fresh sets of 8 AAs in both cars, full throttle on a gen. 2 transmitter:

- 6.30 volts for the Sabre (gen. 1)
- 12.00 volts for the Avante (gen. 2)

Now the question is: What voltage should theoretically deliver the generation 1 PCB?

For the record, motors look exactly the same except the output shaft which exceeds the pinion for the Avante 2001's one. Which is also a bit faster than Super Sabre's one (couldn't measure anything, my old "Made in Japan" optical tachometer stops @9999 rpm)

[kinxkinx 1]

12 hours ago, Mouc-RC said:

 

- 6.30 volts for the Sabre (gen. 1)
- 12.00 volts for the Avante (gen. 2)

 

That's kind of strange! Full powered, the voltage must be the voltage of the battery pack (that's what the h-bridge must do...) So, no more than 9.6v. Did you check the voltage at the battery's output?

 

16 hours ago, korreka said:

It is possible that the first generation transmitter uses a switch on the throttle trigger 

 

 

That's it! the trigger is basicaly a switch (with 3 or 4 positions). But to be honest, I don't understand everything. Your schemes don't fit what I see in your previous youtube video

[kinxkinx 1]

 (couldn't measure anything, my old "Made in Japan" optical tachometer stops @9999 rpm) : If you have perfect ear, 10000 RPM => 166 Hz ==> E (rpm is multiplicated by 1.05946 per semitone).

[Mouc-RC 915]

I didn't use 1.2 volts batteries, but 8x 1.5 volts double-As (also LR6), thus 12 volts.

What is a H-bridge (sorry I'm blind in electronics)? Is there one included in the first gen. PCB? Can a H-bridge have a failure?

Edit: I learned a bit for myself about "H-bridges". Ok it's mainly used to drive electric power to the motor & reverse the rotation direction. But as far as I understood, the voltage at the entry of the bridge is the voltage you finally have on motor wires, when full throttle at least. So the voltage difference between gen. 1 & 2 may happen "upstream" on the PCB, which would explain the final voltage on motor wires...???

[kinxkinx 1]

note: I'm note used to the rules of this forum (even if "Nemo jus ignorare censetur") shall we start a new topic about this problems ? Anyway, I don't know how to move posts.

I've tested many things Korreka adressed.

Electric tension on the PCB's good, I mesure 10/11V bettween + and -.

* Turn on the transmitter and the car and check the voltages on the switch (12/9.6V, orange and blue wires), pins 8 and 11 (6V), pin 12 (2.3V).

==> I tested 2 cars : OK (one is 6.2V on the 8/11 pins, is that good enough?)

* on pins 9 and 10, the forward and backward signals are output to the transistors; They can be seen on the oscilloscope (https://www.youtube.com/watch?v=muKW6eYPamE). With the multimeter and the throttle lever at 100%, the voltage would be about 4V.

==> On both cars, the voltage is arround 2V when trigger at 100%, move a bit when I turn the trimmers, but not to 4V. So, I deduct the command is always around 50% on fast position. Less in slow position. (off topic, I must find a way to control signal with my PC or rapsberry, an oscilloscope is too expensive). That's confirmed by the voltage on motor poles. Arround 6V (To answer your question, Mooc, the lower voltage is due to the h-bridge that acts like a switch cutting power about 50% of the time)

* Check the motor connected directly to a battery.

==> I hadnt' time to do so but I suspect the motors to be worn out... The cars move very slowly with 6V

 other strange problems :

On the second car, the signals from pin 9 and 10 are 2V (on 9 forward, and 10 backward). But the motor don't turn (forward) each time i pull the trigger ==> h-bridge problem?

I mesured a low signal on 9 and 10 pin on one car (arround .1v)

The electronics are very ticklish. Each time I touch it with a screwdriver or with a pole of the multimeter, the car trembles.

To conclued  :

==> You were right, Korreka, that's not a transistors/h-bridge problem.

==> There is a problem of signal from pins 9 (and 10?). 2V when I expect 4V. On both of my cars, and on Mouc's one... Can we deduce they've been built like that or that it's an usual failure?

==> may be a problem of motors.

 

TO BE CONTINUED

Edit : see above but this deduction are false ==> resistance problem explain everything. Exept that the 9 and 10 pins give 2V

Edited January 31, 2024 by kinxkinx
Some mistakes in my deductions

[Mouc-RC 915]

When I did some tests the other day, I swapped motors between 3 cars (Super Sabre, Avante 2001, Midnight Pumpkin). They all sound the same on both types of controller (just a bit of a bit slower for Super Sabre's one). No motor problem on my cars, pretty sure.

Personally I found gen.1 & gen.2 PCBs have appox. same sensibility to undesirable radio perturbations, but the gen.1 transmitter is way more glitchy than gen.2

[kinxkinx 1]

I had a moment of clarity and tested the voltage between poles of the PCB (battery output). It decreases when the motor turns, equal the motor voltage when the trigger is at 100% and decreases (with the motor voltage) when the motor is loaded. I'm not an electornician but it must be a resistance (rust or sulfate?).

That's the problem when you try to diagnose rather than cure... But that explains many things.

I'll start again at the beggining (As Korreka suggest : clean first! )

[korreka 53]

Hi,

First of all, when measuring voltages you must have the motor running. So the battery current is high,  you can see if there is a suspicious voltage drop in the wires, solders, switch, and even the battery itself that is weak. Remove the rear wheels or put the buggy with the wheels on the air to do this.

 

* If you want to measure the maximum no-load speed of the motor (RPM), use an "audio spectrum analysis" App. I use Spectroid app. Measure the first pulse in Hz and multiply it by 60 seconds. The motor must be outside the gearbox. Video: https://www.youtube.com/watch?v=_Y93yM2kLog


 

 

 * An H-bridge is a circuit of 4 transistors (2 NPN type and 2 PNP type in the Tamiya QD) to allow the change of direction of rotation. In one direction of rotation, only one NPN and one PNP transistor are activated. Active transistors work in saturation mode: the voltage between emitter and collector is 0.5 - 0.6V. That is, if you have 12V power between emitters, in the motor at maximum speed there are:

12V - 0.6 - 0.6 = 10.8V. This test is done with the motor connected.

 

 

* On pins 8 and 11 of the L9367 circuit there should be about 6V (circuit supply voltage). On the electronic board there is a voltage reducer (circuit with Zener diode) for this.

*  On pins 9 - forward (or 10 backward) of the L9367 circuit there should be about 4V at full throttle. It is a pulsed PWM signal visible with an oscilloscope. This signal activates and biases the H-bridge transistors. The signal information is in the duty cycle, not in the voltage. I recorded this video in a Nikko proportional control car: https://www.youtube.com/watch?v=muKW6eYPamE

 

I believe that the 1st gen transmitter pulses are shorter or longer than the 2nd gen transmitter. Then, the buggy waits to receive the original pulses. Try turning the throttle neutral trimmer on the buggy board in case it corrects it.

 

* With Ni-CD or Ni-MH batteries,  you achieve better results in a Tamiya QD because they have a higher maximum current discharge than an AA alkaline battery. Alkaline batteries have a higher internal resistance and if the motor requires a lot of current during acceleration, the voltage drops a lot. The best Ni-MH AA batteries are Eneloop brand, widely used in powerful flashlights. They say that Ikea's  Ni-mh AA batteries are "white label" Eneloop. Li-ion (3S) can also be used if they fit in the battery box.

 

*  I assume you belong to the "Tamiya Quick Drive" group on Facebook. You can ask there if anyone has used a first generation buggy with a second generation transmitter.

 

 * A low-cost oscilloscope (20Khz) can be made with an old laptop through the sound card. Don't do it with a new laptop in case you damage the sound card. With 20Khz of bandwidth it is enough to see the signals of the PWM speed control pulses and the PPM of the transmitter. It is easier to configure the sound card with W98 or XP. The test leads are self-made with resistors to achieve an attenuation of 1:10 or 1:20 because the line input of the sound card supports 1 Vpp. This oscilloscope only allows you to see pulses or alternating signals; DC voltages cannot be seen. See this: https://reparar-cochesrc.blogspot.com/2016/01/osciloscopio-traves-de-tarjeta-de-sonido.html