Tamiya M4 105 Sherman

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Dayle Frame
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Re: Tamiya M4 105 Sherman

Post by Dayle Frame »

43rdRecceReg wrote:
Dayle Frame wrote:A quick update: I tried to measure the voltage on the CN3 pins while the MG was "firing". My VOM registered nothing. Of course, I don’t know if I was actually measuring 0.0VDC or my leads were too big to accurately perform the measurement. I also tried to measure the resistance of the LED. I used braided wire strands and inserted them into the LED’s pin holes. I measured 0 ohms.....I don’t know enough electronics to know if a functioning LED should have a resistance or not. But, again, maybe my measuring technique was faulty.

This is when I decided to buy a replacement MG LED. I found Tamiya part # 7255019 on eBay and purchased it. It’s supposed to arrive next week. At that point, I can check to see if the DMD is putting out the correct signal or if the original LED is at fault.

As to SoaG’s point, my LED is wired the same as 43ReeceReg’s working MG......orange wire on the right. Whether o connect the LED directly to the DMD or route it through the extension, they both behave the same.....noise but no light.

One of my previous jobs was to repair analytical instrumentation for chemistry labs. I learned how to diagnose problems that cropped on really complicated pieces of hardware. This is no different.....just smaller. It might be the board (DMD), the wiring or the LED.....I’ll get to the bottom of this one way or another.
Are you using the Futuba 4YWD 2.6G, Dayle? I had an issue lately with the cannon not firing or recoiling on my Panther. The firing trigger for that is: trim control fully up. and elevation toggle up (polar opposite of the MG method).
I discovered there's a certain speed technique needed on my 4YWD to get the change of mode from elevate to fire, to kick in. After two days of fitful attempts, I was in the same position that you're in, wondering which unit is the culprit. I found that by throwing the trim control forward quickly, the cannon would fire, the flash would illuminate, and the barrel would recoil. Eureka! In other words, the glitch probably lies in my left trim control, and has nothing to do with the tank. To be honest, I think it's very unlikely that Tamiya would wire the MG connector the wrong way round. Their quality control is excellent. At their prices- it should be!
I have configured my TX with all drive controls on the right stick, and all the turret functions (including MG and Cannon) on the left. If a real trim problem crops up, I could shift the functions over..but for now, I'm satisfied the tank itself is fine. I expect yours is too. Just try moving the trim control quickly aft, to see if that helps initiate firing. Perhaps the bottom trim control on that toggle could influence firing. Try experimenting. I did, and it paid off.
Again, there's nothing to lose in resetting the DMD.
With the LED cable removed from the DMD, You can test the LED with the Diode/Continuity tester section of your multimeter. The appropriate readings (good and bad) for your meter should come with its handbook, but should be something like this, but I expect you know all this:
http://en-us.fluke.com/training/trainin ... meter.html
I often use pin to pin coloured breadboard connector cables to connect units like the LED MG to my Multimeter, that way you get a good connection, and don't need three hands.
BUT..do look at transmitter issues first. That solved my problem (potentially much more expensive than your LED one :shifty: )
You bring up a very good point. I had not considered that the radio could a part of the issue.

I am using a 27MHz system leftover from when I bought a Tamiya KT back in 1991. Its a Futaba FP-T4NBL "Attack 4". The good news is that my my brother was so intrigued by my purchase that he went out and got one too. He lives in Durham, NC which is just an hour from AAF. He bought his radio from them at the same time (2.4GHz Futaba 4YF). If I can't solve this issue via the new LED, I can always borrow his radio and see if it changes the results. I'm sure he'll be coming up in the summer and so we can do battle with our critters in the back yard. I have a robotic lawn mower and I want to chase it around a bit.

On my rig, the tank movement is on the left stick. The right controls turret rotation (X axis), cannon angle (Y axis) and headlights (X trim). If I slide the right Y trim all the way down, it "fires" the MG.....if I slide it all the way up, it fires the cannon. The speed at which I move the trims seems to be irrelevant....only that they end up at the extreme end of their range.

Ad Lav....yes I did....at least I assume so as everything else works like its supposed to. I've reset the DMD a couple of times without any change in the tanks behavior.
Dayle
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Ad Lav
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Re: Tamiya M4 105 Sherman

Post by Ad Lav »

Try setting it up with the controls in the ‘tamiya’ way and see if the mg works.

Could just be a dud led.
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Dayle Frame
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Re: Tamiya M4 105 Sherman

Post by Dayle Frame »

We’ll the new MG LED arrived today and.....wait for it......it worked perfectly. I have to assume the original one was a dud. I now have to disassemble the MG in the hull so I can replace the LED.
Dayle
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Dayle Frame
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Location: DeWitt, MI (USA)

Re: Tamiya M4 105 Sherman

Post by Dayle Frame »

One last post to wrap up the details on the LED for the hull MG. I was able to separate the brass LED housing from the inside of the hull. The bad LED was attached and wouldn’t come out of the housing no matter what I tried. So I gave up on being Mr. Niceguy and took the assembly to the shop. I have a drill press there. I selected the correctly sized bit (3/32") and drilled out the LED. I used a dental pic to pick out the leftovers.

Back to the house to reassemble the new pieces.....and it’s all good. The MG lights up like it’s suppoed to and it’s waaaaay cool.

Last but not least, I decided to mount the on/off switch to the underside of top of the turret. This would allow me to use the loader’s hatch opening to turn the tank on and off. That is only practical if the switch’s wiring can be disconnected. To that end, I cut the wire leading to the switch and spliced in a micro connector from JST. Easy, cheesy.

Thanks again for all the help on the various hurdles.
Dayle
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