Re: Tamiya bolt on reduction gear
 

Tnx Rimrock.

Well the first idea was to create something just by expanding what is already there. When you look at the Tamiya truck, and when you change all the stuff you ont really like, you end up just with a cabin, so why buy Tamiya in the first place?
I liked the 3speed from the hilux, first gear for crawling, and others for normal driving. But yes, 2 speed would be enough. I plan to develop such gearbox in the future.

Thing about this simple mod is, you use your stock out of the box tamiya truck, fit AWD GRU and front axle, and you have 10mm more in height, and AWD. GRU gives you probably slower 1st gear and more torque than Servonaut, and when you want to go faster, you have 2 extra gears, and it still is very fast in 3rd gear.

I think using 3speed with GRU changes everything. I am playing all mornign with AWD, and it is awsome. Before the truck wasnt able to climb 5mm bump unless you hit it fast. Now I can use it like a crawler, only the height of the front bumper limits where you can go with it. I guess I need to make offroad version of the front bumper :)

Re: Tamiya bolt on reduction gear
 

Standard GRU's will be ready to ship tomorrow. Please PM me if you want one.

Re: Tamiya bolt on reduction gear
 

I have to say that I totally agree with this statement.
I've had bone stock R620 Scania with the MFC III, and that combo was not really interesting for any "scale" play.

I've tried a 80T motor, but having so many windings with such tin wire, the motor simply had no power. I've boosted the MFC's output, run a 10T pinion... you name it. It just didn't had power to move.

Then I went with a good old Hobbywing Justock ESC & 21,5T motor. This setup had lots of power, lots of torque, decent low speed & torque resolution, but the problem was with lack of synch between the MFC's sounds & effects and the motion of the truck. And that was so obvious that it really had no sense to have MFC, specially for that price! At least in my books.

Then Doggy came out with his crazy idea. He started modelling the GRU and he sent me few pictures. I came to see him one day, and his unfinished truck that he used to run on 3S just felt so different. I asked him for one GRU and few hours later I had my tractor truck modded & pulling. Then my 3y.o. son came with an idea to make it a tipper truck, and since then we have been abusing the plastic 3D printed GRU with no success in breaking it.
The best thing is, all MFC functions are there. Sound is in synch with motion, and things do look SCALE.

Don’t get me wrong, I still want one made of metal, just cause I like it. But until that becomes available I’ll continue to use the plastic GRU, even on my next 6x6 or 8x6 project.

Re: Tamiya bolt on reduction gear
 

Ivan
I got the gru installed in the globe liner you need to make
a little room for the shift rod in the back cover. But so far
It looks great

Re: Tamiya bolt on reduction gear
 

Drilled a hole for the shift rod.. smooth gru now to see the pulling power
Way to go ivan!!!

Re: Tamiya bolt on reduction gear
 

Great to hear you got it! Thank you for the info about the hole, it seems that there are different versions of the tamiya gearbox, as on euro style trucks its right in the place. I will have to make it bigger so one size can fit all versions.

Re: Tamiya bolt on reduction gear
 

Just match the outer case to the hole in the inner case for the shift to pass through. Test drive later

Re: Tamiya bolt on reduction gear
 

I guess the outside contour doesnt match the bump on the gearbox case where the shift rod goes too?
This should be easy fix to make universal version to fit both types.

https://lh3.googleusercontent.com/Vi...Q=w764-h562-no

Re: Tamiya bolt on reduction gear
 

ivans 4:1 with 97 pounds on it

https://youtu.be/rLkZ433gmf4

106 pounds
https://youtu.be/odwRWeD11Y0

Re: Tamiya bolt on reduction gear
 

Great to see you fit it!

Its not 4:1, its 6,4:1 !

And i think the reason you wer not able to pull 106 pounds is in your motor! Try stronger motor, 55T doesnt have enough power, and now you need power to get the best results with GRU.

Its simple, you can find out how much GRU can pull when you brake it. Try stronger motor, 27T maybe, or 23T if you have. You will have to brake something under load. Trewq broke 2 driveshafts allready and something in the gearbox, but GRU is still in perfect condition.

If you want to test, try it, if you brake something on GRU, I will send you free replacement parts ;)

Re: Tamiya bolt on reduction gear
 

i'll swap out motor this week. also I have a different rear suspension in the peterbilt

Re: Tamiya bolt on reduction gear
 

I just unmuted the video, that sound, sounds like your gearbox dropped out of gear or you broke the GRU?

Re: Tamiya bolt on reduction gear
 

It pulled my younger 97 pound test load after the 106

Re: Tamiya bolt on reduction gear
 

That is the sound of the dogs skipping the selected gear within the Tamiya 3 speed.
My gearbox does that in 3rd gear when loaded. 1st and 2nd are good.

I am sure that I'll end up using metal gears within the Tamiya 3 speed for my next build :)

Re: Tamiya bolt on reduction gear
 

Well its just a matter of finding out whats the first weak point in the transmission so we can plan future upgrades.

Re: Tamiya bolt on reduction gear
 

I would like to see the slop in the slides go away

Re: Tamiya bolt on reduction gear
 

Mark I am sorry my english is not that good, so I dont really understand what you mean by that?

Re: Tamiya bolt on reduction gear
 

I assume that you are referring to the slop in the tamiya 3 speed gearbox, where the dogs and the actual gears latch?

Re: Tamiya bolt on reduction gear
 

It is not the Trans that’s the problem it is your bec. In first gear you’re not overloading the esc and the bec is able to keep the servo in position. In second which is center for the servo you won’t notice losing bec much. Now third is a different story when you pull a heavy load the esc losses its ability to put out full bec to the receiver. To test this run the truck with a load and if it seems like its slipping in third gear add a receiver pack to the receiver and try it again and I can guarantee the trans won’t drop out of gear.

Re: Tamiya bolt on reduction gear
 

Hmm, thanks for sharing this with us. I'd probably overlook this.
I'll run the HV esc then, and straight of the 2s batt.

To bad my main output shaft is broken. I'd test this straight away.

Re: Tamiya bolt on reduction gear
 

Just a quick update.
So far shifting servo is not an issue. Partly due to fantastic functions on my spectrum radio where I have reduced servo speed on the throttle channel to a very low percentage, so that the throttle does not go to 100% instantly. It takes a slow ramp up.
The result is a scale looking motion of the truck and a reduced motor/esc/battery load on the take off and breaking.

So, to get back to my third gear issue;
- when taking off with no cargo the third gear acts the same way as when the truck is loaded. I'd reckon that the engagement of the dogs for the third gear are not latching fully, and the same are damaged as well.
In this situation (due to my throttle signal conditioning) the load on the ESC'a BEC is not a problem. The voltage is being held stable.


Now, to touch the AWD GRU and the powered front axle;
- plastic front axle has proven the concept of simple add on FWD. it does make a world of change, and it certainly would be a game changer on my 6x4 Scania R620.
- my choice would always be a full metal axle.
- the 3 speed Tamiya gearbox does seem to be the weakest link on the AWD equipped unit. Mostly due to added load of the FWD, but that should not be a problem when all metal parts are used (metal AWD GRU, metal Front Axle, proper telescopic props hafts (not like the **** I've been making for the test purpose).
- the all opened differential truck with AWD does not get stuck easy. Totally feels like a crawler in an way. Really AWSOME fun to drive this thing around, if only it had a radio that could've been set up like my spectrum to limit the throttle and a steering speeds in order to make things look and feel real...
- the Tamiya steering system is even bigger **** with AWD. I am a strong believer that the hydraulic steering is a must(!) and I'll see if I can convince Doggy to add the hydraulic cylinder in the design files. I'll do the rest of R&D fabrication for this.

Re: Tamiya bolt on reduction gear
 

Just a couple of thoughts: The Tamiya gearbox is pretty much bullit proof if out together correctly. It has a bit of internal slack, but is very durable.
As for the steering, hydraulic steering would be a cool feature, but I think you will be more than happy with moving the servo between the frame rails. I normally use Hitec645MG servos for steering, and they are strong enough.

Re: Tamiya bolt on reduction gear
 

Hello
Look's good. I like it especially with disconnectable front bridge and option to leave battery on it's original place.
Shouldn't the gru be right under the top of the chassis line? The trailer will hit gru if you move the kingpin to correct position (about 10 mm backward from the middle axle, like for example Scania r620 has in real world).

Regards

Jukka

Re: Tamiya bolt on reduction gear
 

Just found this thread,, very interesting and inspiring. Printing technology is going to be more and more frequent and being used for more critical parts, in some cases the only way to make a part is to print it as no milling machines can get to cut areas, they are usually printed in metals then heat fused together. Pretty sick technology that some very intelligent folks have solved. I wonder how much cost would be to have them outsourced and printed in metal? But if proving to hold up in plastic then great, metals fail also. Those types of printer are still too expensive for the normal "hobbyist ".

Keep at it! You are definately putting a lot of time and effort into this hobby, I may not be into the trucks as much as equipment but I appreciate your dedication to this any advancement is awesome!! But I think you may have inflated rcp's head a bit with putting that logo in the part!! Lol!! Naaaa, man , keep up the good work!!!

Re: Tamiya bolt on reduction gear
 

Have there been more developments on this project? I'm very interested in the GRU along with front drive output! Looking to convert my King Hauler to a 6x6 and this looks to be perfect. :)

Thanks!
Tommy

Re: Tamiya bolt on reduction gear
 

Saddly no. I moved to another city, started working, and stil didnt setup my new hobby workshop. I hope to set it all up next month and continue the work ;)

Re: Tamiya bolt on reduction gear
 

Sad to know you haven't been able to work on it, but happy the work will continue soon!

Re: Tamiya bolt on reduction gear
 

Howdy,
I was wondering if you ever got the AWD GRU finished? It looks like what I need for my truck. Looks great. Keep up the good work. Thanks

Re: Tamiya bolt on reduction gear
 

Hi, I did one prototype and gave it to trewq for a few months to test it. He managed to brake something inside, and I still didnt get the time to disassemble it and see what went wrong. I believe something snaped as the truck had fixed drive shaft.
I will do my best to do some work on it soon, as my other projects are near finish now.

Re: Tamiya bolt on reduction gear
 

Now I wanna buy one of them fancy reduction thingies.

Re: Tamiya bolt on reduction gear
 

nice design!

Re: Tamiya bolt on reduction gear
 

I want to buy a reducer on the gearbox for a Tamiya truck. I live in Russia. In Russia, bad roads and heavy loads. We need a powerful reducer!

Doggy! Can you send two reducers to Russia?

Re: Tamiya bolt on reduction gear
 

I like the pricetag on this one!

Re: Tamiya bolt on reduction gear
 

I wish Photobutt would let us see the pics o fthe d@m thing, & how it's mounted! Do you still have that pic? If so would you consider mailing it to me?

Re: Tamiya bolt on reduction gear
 

Are you still making GRU..