Mindsensors MTRMX-Nx issues

[mattallen37]

There are a few things that really bother be about both the MTRMX-Nx, and the lack of warning about hooking it up wrong. I may be the only one that has these issues (maybe it is my fault).

Is there no way to get a 100% PWM duty cycle? My O-Scope isn't working, so I can't test the actual duty, but I know for a fact I cannot get a 100% PWM duty cycle. This is a huge issue to me, as it can only supply 600ma to begin with. Both of these factors make for really poor motor performance.

Another issue that I believe is very real, is that you can only connect the RCX wires in two of four positions (actually, 4 of 8). Due to the PCB and RCX connector design, it will cause a short if the wire is connected wrong. Again, am I just looking at it wrong? I don't think it is just me. I tried for a while to get RCX motors to work with the controller, and finally after a while, I got results. Not what I was looking for though; it was the smell of hot electronics. I had connected my wires the way three of four are connected on the mindsensors product page, and it had caused short circuits. Thankfully, I smelled it before the magic blue smoke was released (I suppose they are probably thermally protected, but still). I contacted mindsensors about it, and was politely told I was wrong. Am I wrong, or is it really an issue that has been overlooked and denied?

Long story short, I would rate the MTRMX-Nx at about 4/10, with a mindsensors products average of 7+ (of the mindsensors products I own).

[doc222]

I have had two of these for many years now. In projects of note I used 1 in "sloth X-4" it powered the four gripping hands. Also have used it in many pneumatics pojects to just flick switches.

Issues:

The main issue is/was power lose through the divice. This lose is not all lost, you get heat. Power in and out is about a 15+-% lose (just a guess but close). I measured back then the input power compared top power out and had at least 2v drop. Thats alot with say Nicds that only have 7.2 to start so now the motors run on 5.5 or so. To over come this you have two choices more power, or more gear reduction so the motors will complete what task given. Or over volt it so you get 9v out. In my test(NEVER DO THIS AT HOME< EVER) witha 12v power in, I would get just wee bit over 9 to the motors and they sounded sweet. BUt thats alot of voltage and in a few minutes the Mofs got rather hot, not so hot they burned up but I had no loads against the motor too. Back then I though that perhaps a few memory cooling fins glued on with heat compound like artic silver. Over all this issue was not a big deal or a deal breaker.

Be very sure to hook the power to the mx with care to watch polarity( you know that though:)


Last issue I never seen? I have hooked them up every direction possible(even bottom or top mounted) and the only thing it will do is change direction of motor. since it is DC and not ac it should be fine no matter how its connected. I have tried every motor on these too. From the older RCX to buggy motors, nxt motors and PF even a few home made lego motors I made back in the dark ages(that was before Tomas Edision invented power)


Over all these mx's filled a gap that we aflos had back in the early days. The New NXTmmx has none of these issues that i could tell in power. since it uses the phone like pluge it only can hook up one way. I have shorted a gang of 4 NXTmx's before in X2 once. The wires that feed them that run to the battery pack, one wire pulled from the NXTMX and shorted to the other wire, well you know that blueish greenish blackish smoke you talked about, yea and it stinks too. Even my wife said," smells like you fried it. I though so too, FEAR ran through my heart. Did I just burn out 4 nxtmmx's!!!!! oh nooooooo. Naaa just melted the supply wire , but it looked bad there for a second. with tons of smoke coming from X2, it looked bad real bad.


So what are you running with a RCX mx?



Doc, "frying wires"

[mattallen37]

Yes, mine works fine for really light duty applications.

Even getting it to output a full 9v, it still suffers from a lack of duty cycle. Even setting the speed to 0xFF, the output would be like setting the power to less than 100%.

Look at the PCB traces, it connects to all four contacts. Two are one polarity, and two are for the other. The issue, is that all four sides of each contact can make contact with the male wire connectors. So if it gets turned by 90 degrees, well, you can see what I mean. The female side of lego connectors only have contacts on one of 4 sides, so no risk of shorting.

I am not using it for anything now, but I only use it for RCX motors or lamps (sirens don't work, they need a 100% PWM duty cycle to work).