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Tamiya DMD and CH.1 - 4/23/2012 6:02 AM   
CountChocula



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Status: offline 		Hello all,

Between being too busy and under the weather, I've been slow in getting back to my Rolls Royce AC project. Today however, I was able to mount the DMD (I'm using M51 Sherman electronics DMD/MFU and will post on my actual AC thread) and ran into a couple of issues/problems when doing some simple tests. First of all, I was unaware that the DMD won't even respond unless you have the CH. 1 (rudder) coming off the DMD plugged into the receiver. The problem is, I don't want to use CH. 1 from the DMD as I'm using my own servo for steering. With my 250 Half Track, I remember early on in testing, I was able to leave CH. 1 off of the receiver and it worked. For some reason, I can't seem to get away with it now. I'm also trying out a new Dx6i radio that I'm new with so maybe the problem could lie there as well perhaps. For testing purposes to see it run, I just plugged CH.1 into an available random slot temporarily to get it to work and I can run the chassis using CH. 2 (throttle) and my servo. I'm not sure how to get around this at the moment, but CH.1 has to go at some point since I'll need those other slots on the receiver!

Another problem I ran into, is that I can push the throttle forward and see the double green lights and the vehicle moves foward fine. If I pull the stick down (I'm using the right stick for steering and throttle btw) slowly, I notice right off, the DMD is showing me red lights but it will move slowly in reverse as expected. The problem is if I give it full reverse, the DMD just shuts down or simply stops. I can turn it off/on again then I'm running again.

I'm not sure if anyone has any thoughts about the two problems I'm having, but I appreciate any feedback you may have. I'm not using (or plugging in) CH.3 or CH.4 at this point as this is just a simply driving test using CH.2 and my servo.

Thx all,

Dave

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RE: Tamiya DMD and CH.1 - 4/23/2012 6:24 AM   
thecommander


 

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Status: offline 		Try using a Y-connector to the DMD & Servo. This way both get the command signals and you can run set-up. Before I do anything "exotic" I set a tank up normally than do all my tests to ensure all is 100%. Then I'll move on to the "exotic" and custom configurations. I believe strongly in the KISS principle.
Good luck, Bob

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RE: Tamiya DMD and CH.1 - 4/23/2012 12:48 PM   
ausf



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Status: online 		I read somewhere about issues with 2.4 aircraft radios and the DMD units, but I'm not sure what it was or if it's been resolved.

I second Bob with the Y-connector. I tap in and off of Rx wires all the time. Squidward's head on my Tiger is just Y-ed off the turret channel on the Tx.

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RE: Tamiya DMD and CH.1 - 4/23/2012 5:33 PM   
Darryl Usher


 

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Status: offline 		I use 2.4 in all my tamiya tanks, no problems.
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RE: Tamiya DMD and CH.1 - 4/23/2012 5:37 PM   
CountChocula



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Status: offline 		Thanks for the info, unfortunately, I can't use a Y splitter on this project as I can't have the power changing on the two motors. I'm using a solid axle through both gearboxes to get a positive track affect. I use a Y splitter on my HT as I need the tracks to assist in steering. In this case, I can't have one motor slow or even a super spin effect to take place. I always need both gearboxes to always maintain the same power forward and reverse.

I may switch back to my old FM radio for now for testing so I can eliminate the radio as a cause to my dmd quitting.

Thx again all.

Dave

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RE: Tamiya DMD and CH.1 - 4/23/2012 5:54 PM   
Pershing.Driver


 

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Status: offline 		the red lights are caused by an overload (pulling too many amps for the function) since you have a DX6i adjust the End Point Adjustment downward from 100% to say 90% and retest.... I ran into the same issue when I upgraded the turret rotation motor in my Leo 1 and that solved the issue nicely.

Also either channel 1 or 2 (I cannot remember which) must be connected or else the dmd will not turn on (because the receiver will not have power). but it can be connected to any socket on your receiver so put it in the gear or flap or even the battery socket on the receiver.

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RE: Tamiya DMD and CH.1 - 4/23/2012 6:10 PM   
CountChocula



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Status: offline 		Ah... Thx Pershing Driver! I will do as you suggest with the radio and adjust the end points. I'm still learning the radio so this is good. I think CH.1 is the required one I'm afraid. I didn't know it was the power connector for the Rx so this all makes more sense now.

Thanks again!

Dave

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RE: Tamiya DMD and CH.1 - 4/23/2012 7:00 PM   
Jeff489


 

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Status: offline 		The "Rudd." channel on the DMD is the one that powers up the DMD.  Specifically, the white (signal) wire.  As mentioned in previous posts, you can plug it into any channel on the RX.


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RE: Tamiya DMD and CH.1 - 4/23/2012 7:34 PM   
CountChocula



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Status: offline 		Thx Jeff,

I'll plug it into the batt slot or some other one that won't interfere with CH.3 or CH.4 coming off the dmd.

What I don't get, is why I get the double red lights right off if I move the stick down to go in reverse. I mean you barely move it off center and they're red. I tried resetting the dmd and moving the sticks to the extents etc.

I havent had a chance to try what Pershing suggested yet. Sorry I missed you guys Sat. Slowly but surely getting past this!

Dave

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RE: Tamiya DMD and CH.1 - 4/23/2012 8:25 PM   
kclank



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quote:

ORIGINAL: CountChocula

Thanks for the info, unfortunately, I can't use a Y splitter on this project as I can't have the power changing on the two motors. I'm using a solid axle through both gearboxes to get a positive track affect. I use a Y splitter on my HT as I need the tracks to assist in steering. In this case, I can't have one motor slow or even a super spin effect to take place. I always need both gearboxes to always maintain the same power forward and reverse.

I may switch back to my old FM radio for now for testing so I can eliminate the radio as a cause to my dmd quitting.

Thx again all.

Dave


Cut the signal wire from the DMD. That way you will have power. using a "y" splitter should complete the connections you want. as for the radio i use 2,1,3,4 for my 2.4 spectrum radios instead of the more common 1,2,3,4 for FM and AM radios. you could also get power to the DMD by hooking up your rudder straight from the battery, thru a switch, if required. As far as the fwd/rev functions the only thoughts i have are: 1. reprogram the dmd using more abbreviated throttle movements during programming. 2. is there anything else on the throttle signal wire that might be stealing power, and check that there is no mechanical drag or interference on the motors or tracks (like a track pin sticking out that catches in reverse.

hope this helps.


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RE: Tamiya DMD and CH.1 - 4/23/2012 11:24 PM   
Jeff489


 

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Status: offline 		Dave,

We all missed you Sat..  There were several new faces and some new tanks.

I'd suggest following up on what Ken suggested regarding the motors.  Check for obstructions.  Try isolating the motor assembly by connecting the Rolls drive motor directly to a battery.  Run it in the vehicle, in both forward and then reverse.  If it runs ok, this will eliminate the motor and drive train as a potential problem. 

If the DMD goes red immediately (when the stick is pusshed off center), the endpoint adjustment likely won't work as the throttle stick seems to be overloading the DMD before it gets anywhere close 90% of full deflection.  Pershingdriver is right about the  two red lights in the DMD.  Two red lights indicate either a short circuit in the DMD or an overload/overheat situation.  Based on past experience, I know the Tamiya DMD puts out about 30 amps per motor.  That should be more than enough to push that little gearbox in the Rolls and strip gears in the transmission if there is any obstruction.  I've seen a Tamiya transmission go into a full stall without triggering the overload on the DMD.  Two red lights without any appriciale load sounds fishy to me, and it may be indicative of a defective DMD. 

To further diagnose it, I'd suggest pulling the MF/DMD out of the Rolls.  Pull out the MF/DMD in the T34, and install the Rolls MF/DMD into the T-34, (where you know the drive train works fine).  Just use the rx in the T34 for the initial test.  Next, do a run test on the T-34 (with the Rolls MF/DMD installed) in forward and reverse.  If it works fine, then try subbing out the Rolls rx with the T34's rx, and then try another run test.  The idea is to find out if it's a problem with the chassis on the Rolls with the Rolls MF/DMD electronics package, or with the rx.  Swapping it out should be a dead giveaway. 

 If the Rolls MF/DMD combo doesn't work in the T34, try dropping the T-34's MF/DMD combo into the Rolls and run testing. 

J.


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RE: Tamiya DMD and CH.1 - 4/23/2012 11:34 PM   
rampa203


 

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Status: offline 		I'm sure this is a stupid question, but why are you using a DMD? Why not use a cheap chinese brushed esc which you can get on ebay for $11 including shipping. I know there is something I'm missing however.

Russ

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RE: Tamiya DMD and CH.1 - 4/24/2012 4:18 AM   
CountChocula



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Status: offline 		Well all, again, thanks for all the advice you have given me so far.

I put CH.1 into the 'aux' slot on the "orange" rx and that seems to have done the trick. The receiver has power and it doesn't interfere with any needed functions.

kclank, I checked for any obvious obstructions and couldn't/can't find any. Since this is for my armored car, there is no tracks/drag involved this time and the double wheels are mounted directly on the output shafts of the gearboxes. I have the rear lifted off the table so the wheels can spin free for testing.

Jeff, I did as you suggested and hooked the DMD up to my T-34 gearboxes. I still get the red lights at around 10-20% of stick, but I can run it at full throttle with the red lights and it runs without cutting out. In the opposite direction, I get double green lights and it can run at full throttle as well. I can't believe It runs foward/reverse at full throttle with the stock T-34 gearboxes, but craps out on 2 FA-130's! It bugs me though that I can't seem to get those red lights green no matter what I try using the radio and setting the adjustments. Again, I'm a greenhorn with the DX6i but I'm learning as I go and I have all the other functions set up and working properly as far as I can tell.

I will pull the motors and replace them with two spare 130's that I have. All of them should be able to handle up to 9v but who knows. I'm using one of my HT's 7.4 LiPo packs for testing for now. I don't sense any binding or anything interfering with the gearboxes but maybe the solid shaft running through them is a bad idea. Since no two motors are alike, my guess is one may be working harder than the other turning a common shaft and this too could be a factor perhaps. Although I did loosen one of the set screws so they could run independently from each other and the lights are still red.

I will pull the DMD from the T-34 as well (It's the older Sherman type w/Pershing mfu) and run it with the Rolls gearboxes and see what happens.

My biggest fear is a bad DMD... I hear Tamiya will replace/fix them, but will they if you cut the Tamiha plug and bullet connectors in place of something else? It's brand new other than that. =)

rampa203, not a stupid question at all... trust me... there are times i wish i could go that route! However, I'm wanting my Rolls to be a battler on the field so I opted to with the the Tamiya DMD/MFU.

Thanks again all... truly appreciate all the comments and suggestions,

Dave

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RE: Tamiya DMD and CH.1 - 4/24/2012 5:06 AM   
Jeff489


 

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Status: offline 		Dave,

If the T34 DMD/MF unit works in the Rolls, then it sounds as if you've got a bad DMD.  Tamiya should likely replace (even withtout the plugs).

If the T34 DMD/MF doesn't work, you may have a problem with back EMF increasing your current load on the 140 motors.  The back EMF would increase the current draw significantly.  This would also show up as two "red" lights on the DMD due to the high current draw (DMD would think it's a short circuit).  Try doing some searching on "back EMF" in DC motor applications.  I am guessing that the motors in your T34 have something on the motors to eliminate back EMF.

Jeff.  


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RE: Tamiya DMD and CH.1 - 4/24/2012 6:32 AM   
CountChocula



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Status: offline 		Jeff,

I did some testing and tried the new dmd (T-08) in the T-34. I get the same red lights, but it works fine full throttle foward, and all green in reverse and at full throttle. I then hooked the T-34's dmd to the Rolls and I get the same lights and it fails still like the newer dmd. So my guess is this isn't a dmd issue at all really. When I hooked up my T-34 back with it's original dmd. I noticed that it always has red lights moving foward as well but it works fine. Is this a Sherman dmd thing or what? LOL

This got me thinking about current draw perhaps and that the smaller motors simply can't handle what the dmd is pushing out. So for kicks, I disconnected one of my small motors (basically half of the gearbox), and hooked the dmd leads into a stock Mato Sherman gearbox. I believe they run a 380 motor but I could be wrong. Anyhow, with the sherman gearbox tethered with with the other side of my small gearbox containing the 130, it runs perfectly fine! Both motors work great in tandem and I still get the red lights going foward (just getting used to that now), but I can run flat out both directions and I can also quickly accerlerate (by flicking the stick) and it doesn't kill the dmd (If i flick the throttle stick quickly in any direction foward or reverse using both my 130 motors, the dmd quits working).

So i set the "Travel Adj" to 85% on the elevation since I'm using that side for throttle (as Pershing.Driver suggested). This seems to work for a few minutes, but the dmd still ends up dying after about 3 to 5 minutes of driving around on the floor. The motors aren't hot and neither is the dmd that I can tell. I'll just keep backing off the Travel Adj until I can find a number it likes, this or I'll have to find something else in terms of motor size that works.

I'm still dinking with it and still may change the motors out with others and see if that helps. I'm still hoping to get away with these smaller modified 130's if I can as I like these smaller gearboxes.

Oh... I also tried changing radio's/rx's to see if that played into this or not... it doesn't. In fact, the DX6i seems to work alot nicer with it. Can't wait to change my HT and T-34 over to it as well.

Thx again... I'll keep playing with it and see what I learn. As much frustration as this has been, it's been a learning experience. It's been also nice to see my chassis (with v3 of my home made suspension and steering) actually move across the floor. I'm quite pleased with it so far.

Dave

P.S. Honestly, I don't know what I'm doing! Just trying different things, taking notes, then trying something else! LOL =)



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RE: Tamiya DMD and CH.1 - 4/24/2012 7:15 AM   
tomhugill


 

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Status: offline 		 Red lights on the dmd don't indicate a fault they indicate reverse. I've just tested my panther and KT both show red in reverse.......

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RE: Tamiya DMD and CH.1 - 4/24/2012 8:54 PM   
Jeff489


 

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quote:

Red lights on the dmd don't indicate a fault they indicate reverse.
This is true.  In contrast, flashing red lights are not normal, and indicate a fault.   Tom makes a valid point, and to redirect back onto the OP's topic, I believe the OP is talking about solid red lights, which most notably would be normal operation.

Dave, it is a relief that the DMD/MF are not defective.  

I suggest running both motors separately with the 380s to see if they both will work like the first test. 

If nothing else, I would try a couple of these diodes.  They're cheap, and might work. 


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RE: Tamiya DMD and CH.1 - 4/24/2012 9:44 PM   
kclank



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quote:

ORIGINAL: CountChocula

Well all, again, thanks for all the advice you have given me so far.

I put CH.1 into the 'aux' slot on the ''orange'' rx and that seems to have done the trick. The receiver has power and it doesn't interfere with any needed functions.

kclank, I checked for any obvious obstructions and couldn't/can't find any. Since this is for my armored car, there is no tracks/drag involved this time and the double wheels are mounted directly on the output shafts of the gearboxes. I have the rear lifted off the table so the wheels can spin free for testing.

Jeff, I did as you suggested and hooked the DMD up to my T-34 gearboxes. I still get the red lights at around 10-20% of stick, but I can run it at full throttle with the red lights and it runs without cutting out. In the opposite direction, I get double green lights and it can run at full throttle as well. I can't believe It runs foward/reverse at full throttle with the stock T-34 gearboxes, but craps out on 2 FA-130's! It bugs me though that I can't seem to get those red lights green no matter what I try using the radio and setting the adjustments. Again, I'm a greenhorn with the DX6i but I'm learning as I go and I have all the other functions set up and working properly as far as I can tell.

I will pull the motors and replace them with two spare 130's that I have. All of them should be able to handle up to 9v but who knows. I'm using one of my HT's 7.4 LiPo packs for testing for now. I don't sense any binding or anything interfering with the gearboxes but maybe the solid shaft running through them is a bad idea. Since no two motors are alike, my guess is one may be working harder than the other turning a common shaft and this too could be a factor perhaps. Although I did loosen one of the set screws so they could run independently from each other and the lights are still red.

I will pull the DMD from the T-34 as well (It's the older Sherman type w/Pershing mfu) and run it with the Rolls gearboxes and see what happens.

My biggest fear is a bad DMD... I hear Tamiya will replace/fix them, but will they if you cut the Tamiha plug and bullet connectors in place of something else? It's brand new other than that. =)

rampa203, not a stupid question at all... trust me... there are times i wish i could go that route! However, I'm wanting my Rolls to be a battler on the field so I opted to with the the Tamiya DMD/MFU.

Thanks again all... truly appreciate all the comments and suggestions,

Dave


If push comes to shove solder the stock connectors back on, including the tam. power plug. there should be no issues if that stuff is there for tamiya to test with. they just don't like having to use patch cords or test leads to check out the dmd's. i have always had good fortune with them and i have sent 2-4 dmds back over the years. one acquaintance of mine did get refused because he did not send it back with the tamiya style power plug. make it easy for them and they will accommodate you i am sure.


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KT,T1, JPIV, Pnthr F, Stug III, JPntr, T34-85, SU85, SU76i, SU100, KV1, KV85, JT, JP-2, Elefant,T55, SU152, IS-2

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