My Yokomo YZ-834b Restoration

[Robbeman]

Hello,

I was so happy that I got an almost complete 834b / Dog fighter with tires, gears and chain in great condition. Unfortunately the pre-owner was obviously a full time smoker right in front of the shelve where the car was stored. After putting a wheel in the ultra sonic bath it immediately turned to coffee colour…but smell was totally different.

During disassembly I noticed several wrong assembled parts, I wonder that the car was ever running.

Here how it looks at the beginning

First disassembly and quick check on one wheel If I could get paint off and on roll bar if I can remove the nicotine (both worked)

Gearbox after full cleaning and correct assembly of the diff.

And here how it looks today. Still some work to do but it will be getting a nice orginal first release.

Original controller is on the way but still looking for a motor. I think I cannot afford a Yoko 05h so I am looking for a Graupner 05h. If somebody has one, let me know.

Also not clear what I will do with the body. It is badly painted and has a cut out at the side made for On/Off switch. Maybe need to go for a BlueGroove Repro.

[Dadio]

Beautiful , that's a very early specimen you have there judging by the gears with greenish tinge and moulded axles , later they changed to nylon for the gears then finally replaced the moulded axles with steel ones , very cool ! are you going to run it or display it ?

[Robbeman]

Hi, interesting to hear thet there were such running changes over the time.
It will be no runner bit for the shelve. The Yoko willbe will be equipped with a vintage RC (old Robbe system) that evrything is functional but will not fill the shocks or put any grease to the gears so it will need some extra work to get it run.
Only thing I will change compared to the orignal is the exchange of all sliding bearings to ball bearings. My hearts as an engineer is requiring that..
One additional information, I bought my Yokomo in Germany. So very likely that it was branded Graupner Dog Fighter as Yokomo distributed the 834b by Graupner in Germany (probably in Europe)

[Dadio]

As far as I've deduced the only difference between the Yokomo and Graupner other than the motor is the colour of the micro switch on the mechanical speed controller , the Yoke micro switch is black and the Graupner is grey but that may be something that changed over time rather than by manufacturer .
They are much smoother on the shelf with ball-bearings

[RC10resto]

Excellent cleanup and re-build.
And yes it looks like it was never run

[Dadio]

It's also got ball-bearings in the gearbox , that's not standard unless you already replaced them , it must have been at least lightly run or why change the speed controller and motor ?

[Robbeman]

When I got the Yoko the gearbox and axles were equipped with the factory sliding bearings. But I have exchanged them all after re-assemble. The picture of the gearbox was made after reassembly.
Regarding the controller I assume that the pre-owner burned the factory one and replaced it then with another MSC.
I assume that there was never another motor assembled. The 05h was not included in the original kit but only a recommended accessory. Could be that the pre-owner wanted to save money and bought the cheap Graupner Jumbo 550 Motor instead.
All that are only assumptions as there was no chance to ask for details about the history as the car came from a legacy.

Obviously the controller I bought is a yokomo as it has the black switch

[Robbeman]

First time again that the Yoko stands back on his own feet. Not fully assembled as some of the original Truss Pan Head to fasten the wheels were overrided ind the Philips head and need to be replaced.

But still looks good…

[Dadio]

That really is a lovely example , you got all the hard to find parts in mint condition on an early car , tires , wheels , top deck/chain guide ,even the shocks are not overly marked up from the adjusters .
Quite jealous really .

[Robbeman]

Almost there….

[Robbeman]

One question regarding the mechanical controller.
Can someone explain the function? Ist seems to me that forward can be regulated, but reverse is seems only full and between 0 and full the motor gets short cut, ist that kind of break?
Especially the large switch and why the drive battery is directly connected to the small switch and that directly to the receiver. Does such connection typically not require BEC?

[Robbeman]

By try and error with low voltage At least I could get forward regulated runniing and backward full.
Still no function on the small switch. I assume that this component is defect. I assume it is a diode.

[Dadio]

There is a BEC in the form of dropping diodes , under the switch is a dropping diode . I've never run mine with the mechanical Speedo so don't know the details exact function of it .

[bluewormx]

One question regarding the mechanical controller.
Can someone explain the function? Ist seems to me that forward can be regulated, but reverse is seems only full and between 0 and full the motor gets short cut, ist that kind of break?
Especially the large switch and why the drive battery is directly connected to the small switch and that directly to the receiver. Does such connection typically not require BEC?

Hi, Yes you are correct in all your assumptions, omitted is that the brakes are also proportional. You can see the "Forward Only schematic on page 60 of the original RC10 manual.
https://img2.associatedelectrics.com/pdf/cars_and_trucks/RC10/Original/rc10_manual.pdf

The reverse works as you stated full power. Basically the NC (normally closed) contact of the micro switch is connected to Battery negative and to the brake side of resistor. The NO (normally
open) contact is connected to Battery positive and to the forward part of the resistor. The COM. (common) contact is connected to the motor negative.

In forward operation: Negative reaches the motor across the NC and COM contact of microswitch, Positive reaches the motor across the wiper arm and the forward part of the resistor.

I reverse operation: The wiper arm engages the microswitch allowing the battery positive to be connected to the motor negative. The wiper arm also transmits battery negative across to the motor positive

attached to it.

Braking is achieved dynamically by shorting out the motor with the battery safetly disengaged using the shorter braking resistor.

And yes A BEC circuit may be missing, at that time two silicon diodes which typically have a 0.7 volt drop each where used as a very basic BEC. Battery nominal 7.2v two diodes (1N4006 or 1N4007) drop about 1.4v when in series, leaving a safe receiver voltage of 5.8v. Note these are nominal values a fully chrged 7.2v battery will have almost 8v but most receivers and servos will survive with a little over the nominal 6v.

[Robbeman]

Chassis work finished! At the end it turned out that I had a connection problem in the battery connector and no problem on the BEC diode at the controller. After that fixed all is running now. It would be a runner if you add grease to the gears and oil to the shocks.

My goal was to get it as original as possible. As I am from Germany the the car came from the German manufacturer I took a motor of that time (built by Yokomo and distributed by Graupner) but as I am a former Robbeman the rest of equipment of course need to be Robbe

No awaiting the new body from US.

Thanks for supporting me on this journey.

By the way, what would you estimate what it is worth now, assuming the clear body and wing present? I mean I will not sell it but would be nice to know.