kdraun

Hey there

I have bought some servoes and they have a MPX 3 Pin Servo plug. Is it possible to connect these to a, lets say, Tamiya /hitec, whatever connector. and use them together with a Tamiya reciever.

Thanks in advance
Stoffer

Gary Retterbush

Yes, as long as you get the wires correct. A servo needs "plus", "minus" and "signal". Each company uses a different color code and even different plugs. MPX uses red for plus, black for minus and yellow for signal. There are even adpater cables made if you don't like to solder.

kdraun

Thanks

I will take a look at that - soldering is not a problem - solder is my middlename... :-) - I just need to buy the plugs then.

I am going to use it for a computercontrolled servo controller - take a look at it - it can control 16 servos at the same time - expandable to up 128.
http://www.pololu.com

/stoffer

rorywquin

Gary

Wouldn't his transmitter also have to be able to send the correct pulse length ??? I think that if the MPX servo has the standard pulse then the wires are red, brown & orange?

Please correct me if I am wrong!

Gary Retterbush

Those are the colors Graupner/JR uses but they are still plus, minus and signal. The wire color has absolutely nothing to do with it other than to signify which wire is which. Robbe/Futaba uses red, black and white while Simprop uses red, blue and black (watch out here as black is signal and blue is minus). Airtronics changed connectors (wire position in connector) and that muddied the water for lots of folks. But, if you put the right wire function to the right servo input, it works.

The pulse width for neutral varies a slight amount between some companies but that is really no big deal. It just means that the very first time you power up that servo the center point will move a slight amount. Move the output arm one tooth position and away you go. Or, if you have a good computer radio it will allow you to change the neutral pulse width point.

Some where out there there is a nice data sheet that shows almost all the wiring set ups in use today but I don't know the URL. Sorry.

Hope that helps.

HarryC

My Feedback: (1)

I think rory is right. If the servo has a Multiplex plug instead of JR plug it will not work entirely correctly. The centre will be offset but also it will only rotate about 3/4 of the amount that it should at full travel. A computer Tx could be made to work with it by altering the centre and massively increasing the travel, otherwise with a standard radio it doesn't seem worth the hassle. You could move the arm round the splines to artificially correct the centre but you would still be left with much reduced travel.

harry

kdraun

Thanks for all the help.

My "transmitter" is not an odinary radio-transmitter, but a Computer-controlled servo controller. I can define the pulselength, so that's not a problem!

you can take a look at it at
http://www.pololu.com

Fly gliders in 1:1 ..... :-)

/Stoffer

Gary Retterbush

Hmmm, I have been using many different servo brands with my MPX radios for years and have never had a problem. Just to check, I just hooked up a Graupner servo, a Simprop servo, a Futaba servo, a Dymond servo and a MPX servo. They all had full travel. Only the center is moved a small amount and that can be corrected with servo centering. The total travel was not reduced on any I tried. Harry, how about doing a check on your end and let me know what happened.

EDITED:
A quick check shows it is one tooth on the servo output arm or about 12% if one uses servo centering (MPX 4000). It makes absolutely no difference what plug is used as long as the wires are electrically correct. It is the pulse width that counts (1.5 to 1.6 is what is usually used as center).

BTW, most servos can be moved well beyond the 100% travel points. Now if you wanted to use more than what would be 100% travel (say 125%) it might be possible to run into a limit at the end. Never been there, never done that!

rorywquin

Hi Gary

I do know that MPX supply servos with yellow, black and red wires or orange, brown and red wires - I am no expert but I always understood that this was to differentiate between the mpx (yellow black red ) pluse width and the others (orange brown red).

I have noted that it makes a difference which type I select on my tx but, have not had a proper examination, of the effects, as you have - I always select what "I beleive" is correct according to the wire colours!


Regards

HarryC

My Feedback: (1)

A multiplex servo with multiplex plug (not an mpx servo with JR plug) expects a signal of 2.15ms at one end. A JR servo to travel the same distance expects 1.9ms (a japanese Tx at 100% travel is 1.1 or 1.9ms). JR Tx allow a max of 150% which is 2.1ms, but a true Mpx servo will not reach max normal travel until 2.15ms.

The % travel are calculated on the time from centre to end, in the case of the Jap Tx normal 100% is 0.4ms (1.9-1.5 or 1.5-1.1). Mpx normal 100% is 0.55ms. Turn a JR Tx up to 150% and you get 1.5*0.4=0.6ms. For an Mpx to drive a jap servo the travel is 0.4/0.55=.7272, or 72 to 73%. For a Jap Tx to drive a true Mpx servo is 0.55/0.4=1.375 or 138% but that is if centres have been corrected. If the centre is not corrected then the Mpx servo at max normal travel is 2.15ms-1.5ms = 0.65ms. 0.65/0.4=162% which the jap Tx can not deliver.

I did extensive testing of the 3030 and 4000 against Jap Tx using JR591 servos fitted with a massive balsa arm and marker. First marks were made using Jap Tx. Then use 3030 and 4000. The adjustments required to Mpx were to move the centre by minus9% (which equates to 1.5-1.6ms/1.1ms full travel), and then reduce travel to 72% or 73%. That way the servo centred and reached the same end points as with a Jap Tx. I then switched the 4000 to its "other" timing. That shifted the centre but still left the travel at 0.55ms either side of centre, it does not adjust the travel to Jap standards, so the 4000 with "other" timing still needed to be set to 72% travel to match the Jap Tx. With the Jap Tx at 150%, the Mpx was at 109% (0.6ms/0.55ms). At about 1% more, the Jap servo hit its mechanical end stop. I then had some correspondence with Mike Shellim of the rc-soar website and his oscilloscope measurements confirmed the timing signals being generated by the Tx matched my observations of the travels of the servo, so we have the data both from observing the time of the Tx pulses, and from observing the movement of the servo, both are in agreement.

Using a Jap servo with an Mpx Tx, after correcting the centre you should not use more than 109% travel or most servos hit the end. I turned up the mixer limit to 109% in my master memory so that even if I forget and try to use more in the servo screens I can not overdrive the servo. I don't think it damages a modern servo, but it stops moving before you reach the end of the control stick travel, which is of no use to you especially if the servo on the opposite aileron is going to the shorter end of the timing signal and has sufficient movement left to go all the way, you get unintended differential. There is no real harm done in leaving the Mpx tx at 100% with a Jap servo, but once you start going above the 72% point the rotary motion of the servo is strating to really move the pushrod sideways instead of along its length and the top 1/4 of your movement is progressively being wasted.

harry

kdraun

My servos is Red-Black-Yellow in that order.

Their name is MPX Nano-servo nr.65000

/stoffer

Gary Retterbush

Okay!! I finally realized what you mean when you say a servo with a MPX (or whatever plug). You mean one that is timed for one standard or the other. I am especially dense today, sorry. MPX is one of the few that makes servos timed for different rigs.

Harry, you are correct as usual. Thanks for the detailed info.

I still suspect that most people would never know the difference if it wasn't spelled out as Harry has done.

HarryC

My Feedback: (1)

The effect is most obvious if you use an Mpx Tx to take over an existing model which was set up for Japanese Tx. Then you can see centres have shifted and that travel is much more than before.

If you set up a new model with an Mpx Tx you might not notice because you will be setting the linkages for that particular servo travel. But the servo travel remains larger than normal so at the end of stick travel you are getting a diminished control response, almost like a reversed exponential, which is why I discourage leaving travel at 100% when using non-Mpx servos. With the 3030's ability to go well beyond 109% you also risk getting well beyond the servo's mechanical limits if you regard 100% as the norm instead of 72%. For instance you might be tweaking the throttle movement, I start at 72% and have plenty space to increase if I need to. If you start at 100% then you only have 9% left, and because the servo's motion is already mostly sideways at that level, you have to make massive increases in the % to get a tiny movement of the pushrod, hence the very high probability of hitting the mechanical end stop. Also as the motion becomes more sideways, any slop in the linkage takes on a huge % of available motion, the servo can rotate quite some way and the slop takes the motion so the pushrod barely moves which does not give you accurate control. Add in the possibility that you have further offset the centre to make a mechanical linkage align the way you need, and end stops can easily be hit before you have moved the stick all the way. I had a lot of problem with this on my TwinJet when I tried to increase travel to hot it up.

Harry