Tamiya bolt on reduction gear

[Doggy]

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

[Doggy]

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

[trewq]

Originally Posted by Doggy

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

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.

[bigford]

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

[bigford]

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

[Doggy]

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.

[bigford]

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

[Doggy]

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.

[bigford]

ivans 4:1 with 97 pounds on it

https://youtu.be/rLkZ433gmf4

106 pounds
https://youtu.be/odwRWeD11Y0

[Doggy]

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

[bigford]

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

[Doggy]

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

[bigford]

It pulled my younger 97 pound test load after the 106

[trewq]

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

[Doggy]

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

[bigford]

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

[Doggy]

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

[trewq]

Originally Posted by bigford

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

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

[fhhhstix]

Originally Posted by trewq

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

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.

[trewq]

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.