4x6 semi truck tech talk

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trewq
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4x6 semi truck tech talk

Postby trewq » Thu Oct 08, 2015 9:40 pm

Gents,

I am trying to find some input on the Mickey Thompson 1.7 Baja ATZ Scale Tires Commercial 1/14 Semi Truck Lorry Tyres.

In short, I've ordered the Scania 4x6 wheel drive kit and I am looking to drive it off the flat concrete (well not literally off road, but yes I'd take it to the garden) and I am looking for any extra grip that is possible to achieve.
Having experienced RC rock crawling I looked at the RC4WD to see what they have to offer in this sector, and there they were; Mickey Thompson 1.7 Baja ATZ Scale Tires Commercial 1/14 Semi Truck Lorry Tyres :D

I was hoping to see what experience you guys have with these tires. Any comparison with the original ones that tamiya is selling would be great! I can see that these are a bit pricey, but is it worth the cash?

The power setup that I plan to run is Hobbyking Xerun 21,5T sensored motor & Justock ESC combo running on 2s initially and possibly switching to 3s to gain more towing power. I also plan to slow down the throttle response so that the rig does accelerate and brake slow, just like the real one. There will still be loads of torque available, just the delta speed will be limited to make it look like the real scale model.

Looking forward to see your inputs!

Cheers

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astecme
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Re: 4x6 semi truck tech talk

Postby astecme » Fri Oct 09, 2015 9:26 am

You will be well overpowered with that set up. Our preferred motor carson poison only gives 6000 rpm on 7.2 volts. you will have well over twice that. Pulling power requires lower kv through the gearbox.

trewq
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Re: 4x6 semi truck tech talk

Postby trewq » Fri Oct 09, 2015 11:10 pm

Evening Astecme,
my primary reason for the separate setup is the fact that there are quite few posts of MFUs dying mysteriously. And we are not talking about cheap parts now.
So I have taken the known route: sensored BLDC.

I've been running the same setup (21,5T + Justock + spectrum 4 ch receiver) on my RC4WD Gelande 2 D90 scale crawler and it has worked great!
21,5T motor, stock pinion, 3S, trough the R3 (2 speed) gearbox, stock transfer case, stock diff, Throttle limited to 35%, with a dash larger DC mud tires - and it did run perfect! So, as there is really only a limited writeup on durability of MFC-03 with 60T or 80T motors I have moved to a field I am familiar with.

I am aware of the fact that there are better motors for my choice, but you can not beat the versatility of the BLDC motor once it is equipped with the sensors. If I do notice any issues I'll promptly report it here.

I will compile an excel sheet to compare all the drive train, gearbox, tire size and the motor / battery combo. Give me some time to complete this. I am quite occupied trough the day so I am lagging with this bit a little.

Thanks for your input!
Cheers

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astecme
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Re: 4x6 semi truck tech talk

Postby astecme » Sun Oct 11, 2015 10:23 am

The MFU 3 does seem to be prone to issues but I have not seen many. I have seen one where the BEC gave up with a fair few lights attached and one with an iffy brake light that mysteriously fixed itself.

I personally do not use MFU's but do use carson 55 turn and Snowpanther 50 turn motors on std road trucks - My recovery truck has a Servonaut style motor gearbox running at 100 rpm on its output. It has plenty of speed for the course. Your 21.5 is I guess equivalent to a brushed 27 turn with none of the problems. So still too fast IMO.

trewq
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Re: 4x6 semi truck tech talk

Postby trewq » Sun Oct 11, 2015 12:34 pm

Good day Astecme,

I'll need to run these two motors to compare the shaft speed when loaded. Un fortunately I haven't got a trailer to load the motors and see the outcome with load on them. But I do have plans to build one when time permits.

As from what you are saying, the next mod to plan could be to rewind the 21,5T xerun motor to something more applicable I'll run it stock first to see how it goes before I strip its copper guts out. The HW Justock ESC spec sheet does not specify max motor turn that we should run so this might be a trial and error kind of thing. I'll definitely refresh this page with more info once I get the rolling truck with an engine in it.

Thanks for your input!
Oh, BTW, you have got one very interesting web store! I should have registered here before buying the whole kit.

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astecme
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Re: 4x6 semi truck tech talk

Postby astecme » Mon Oct 12, 2015 8:20 am

Trewq

thanks, and yes - spent a lot of time finding bits but it does help that the area Tamiya salesman is only a 100 yards away.

Allan

trewq
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Re: 4x6 semi truck tech talk

Postby trewq » Tue Oct 27, 2015 1:15 pm

Allan,
Just to confirm, the 21,5T motor is to fast for my taste.
I'll be modifying that sucker and I'll let you guys know the outcome. :)

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Re: 4x6 semi truck tech talk

Postby trewq » Sat Oct 31, 2015 1:32 pm

I always like to see nice machines in a forest or in some muddy terrain. I somehow tough that my r620 would fit in occasional visits to my back yard but on the first occasion both left and right wings were torn off due to very low ride height... So I tough that this issue had to be fixed...

http://i1122.photobucket.com/albums/l52 ... fgijka.jpg

trewq
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Re: 4x6 semi truck tech talk

Postby trewq » Sat Oct 31, 2015 2:35 pm

It looks really tall on these tiny tires.
Image

The problem now is the drive shaft...
Image
I'll try to make this one a little bit longer, but it won't fix the problem as now I'd need the telescopic shaft...

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TamiyaKen
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Re: 4x6 semi truck tech talk

Postby TamiyaKen » Sat Oct 31, 2015 8:02 pm

You could cut off the bottom of the mudguards then you wouldn't need such a steep angle. ;) The flexing of the suspension is not that large, so as long as it doesn't bump the wheel tops, you should be ok.

Cheers,

ken

trewq
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Re: 4x6 semi truck tech talk

Postby trewq » Sat Oct 31, 2015 11:30 pm

Sorry Ken,
I do not understand what mud guard are you referring to?

The original kit has too long bolts and screws which are getting in contact with the chassis before the axle can get in contact with the rubber bump stops. I've addressed that and the chassis does have much better flex now.

I've been cutting some wood in the back yard and that needs to be transported sow how now. I really need this semi to work in mud soon :)

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TamiyaKen
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Re: 4x6 semi truck tech talk

Postby TamiyaKen » Sun Nov 01, 2015 10:22 am

Hi trewq,

Glad the screws helped with your problems. The mudguards are the curved bits of plastic going around and over the top the real wheels. I did think that maybe these were 'grounding' when on rough terrain and felt that by reducing their overhang, would prevent hitting uneven ground.

An interesting challenge, out of the ordinary. :AG watching with amazement.

Ken

trewq
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Re: 4x6 semi truck tech talk

Postby trewq » Sun Nov 01, 2015 9:47 pm

Good day Ken,

Oh no, the mud guards never came in contact with the wheels, that was fine from the box, even after the nylock issue was solved.
I want to achieve contact of both axles with the terrain and that could be done only by raising the ride height. This will also aid in getting better approach angle on the front as the front bumper is really low...

Now, I am planning to add front powered axle. Do you have any suggestions? I was hoping for an axle that would have the same differential ratio as the forward one to avoid spending money for the whole set. Any advice would be appreciated.

Thanks Ken ;)



TamiyaKen wrote:Hi trewq,

Glad the screws helped with your problems. The mudguards are the curved bits of plastic going around and over the top the real wheels. I did think that maybe these were 'grounding' when on rough terrain and felt that by reducing their overhang, would prevent hitting uneven ground.

An interesting challenge, out of the ordinary. :AG watching with amazement.

Ken

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TamiyaKen
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Re: 4x6 semi truck tech talk

Postby TamiyaKen » Mon Nov 02, 2015 9:36 am

I am not familiar with front powered axles that would also have to steer, as they are out of the 'remit' of Tamiya trucks.

A bit of research on the Web might be needed here. A lot of good gear is produced in Germany if you want to have a look there.

Cheers

ken

trewq
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Re: 4x6 semi truck tech talk

Postby trewq » Wed Jan 27, 2016 11:33 pm

It's been a while since I have been here.
So far I have ordered the famous 80T brushed motor from rc4wd and I really wanted to see what is all the buzz around it being a MCU killer!

So I have rigged up my oscilloscope to the stock Tamiya motor that I think is 27T, and my regulated bench power supply got set to 7,4V.

What I have observed is that there was quite some RF noise generated on the motor. Even tho the motor has internal ceramic capacitor to mitigate this RF junk, it seems like this was not really effective.
But the peak voltage generated at the motor's side was not that high in amplitude, so I have just ignored taking a peak to peak voltage reading.

Now, with 80t motor the situation was not really that good.
The rc4wd motor also has internal ceramic capacitor, but the RF voltage generated at the motor was something worth taking a note.
My scope has detected a peak of over 50V being generated on the motor. Now that makes perfect sense, as the poor MFU is probably not designed to cope with that It's not that good.

So, I've rigged up an filter that is now located in between the MFU and the MFU killer ( well, that will be the 80t motor) and I've started some tests.

With the MFU set to stock throttle adjustment, and the radio being at the full throttle, the RF voltage generated on the motor was peaking to 57V. The second channel of the scope was hooked up to the output of the MFU, and that one was reading 17,2V of the same RF peak signal that was ment to kill the MFU.

From all these tests, I think I could safely say that the MFU was not designed to run high turn motors without added protection of a specially designed RF filter.

If you find interest in buying one RF filter, I could run the numbers for a small production run and give you some heads up on this topic.

Now, what motors are you folks running in your Tamiya rigs which are ment to pull some load, beside being show models only.
The above declassified MFU killer is not really a powerful solution for someone who wants to pull a trailer loaded with sand or similar load.
I'd really appreciate your input, as right now I am more thinking on going to the Brushless 21,5T motor and adding another reduction stage somewhere...

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astecme
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Re: 4x6 semi truck tech talk

Postby astecme » Fri Jan 29, 2016 11:15 am

I have not heard of the MFU killer one BUT I would expect that you will get worse effects at half throttle. What you are seeing currently at full throttle is the effects of commutation. At half throttle you can add back emf which will be far worse.

RC4WD use the snow panther motors (branded) and actually same brand as the 35 t that comes with the truck. Experience tells me that the lower turn motors are in general far more harmful ( from racing days and manufacture of ESC's). Tamiya Electronics are robust and I would expect internal protection in the form of a super fast schottky diode and/or a zener ( not as fast).

Having said all that it is much much better to kill noise at source and again experience shows that the caps provided are almost always insufficient. I would recommend a 0.47uf high voltage ceramic across the motor and a 0.1uf from each terminal to the case. (Some race ESC's recommend up to 47uf electrolytic cap and a diode (preferably schottky) but they only turn one way!


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