Build a 5/6ch pistol Tx for $120

[clockworks]

Originally Posted by Racer4Life

Great write-up. This is awesome.

I could never pull this off without burning myself, or loosing my temper and throwing it accross the room.

Believe me, I've felt like giving up a couple of times!



The servo jitter problem seems to be caused by the RF stage modulating the supply to the main board (specifically, to the A-D encoder chip). Disabling the RF board cures the jitter. I guess that's why they fitted 2 separate regulators on the original PCB.

The reason I didn't spot this problem earlier is because I was testing it with cheap analogue servos, but my rig has digital servos. The analogue servos have a wide "deadband", so don't respond to the slight position change caused by the power fluctuation.

Looks like I'll have to go back to using the regulators, which means using 8 cells, unless I can use a 2s Lipo (or maybe 6 AA cells). Not sure if that will give me enough voltage headroom to let the regulators work.

[meao]

Originally Posted by clockworks

I connected the radio to my crawler for the first time today. All the controls work as expected, but I get jitter on all the servos. Not a huge amount, but enough to be annoying.
It also shows up on the PC software - the bars on the graphical display jump around very slightly. I don't remember seeing this when I started the build.

I'll need to look into this. May be a bad Tx, or it might be related to the 4-cell mod (removing the voltage regulators means that the RF module is no longer isolated from the rest of the Tx - might be modulating the 5v rail).

I don't think that it's a design or wiring problem, as my DX6i-based Tx doesn't have any problems.

Have you noticed any problems like this, Carlos?

I dont understand what does "jitter" mean, but I think you are saying something like "glitching"
I never noticed something like that. Do you remember the video where I show the car with 3 servos and a "servoswitch"(for a led)?. There you can see that I haven't any of this problems.

I dont think that is a wiring problem. Would be a problem with the software?. Do you "click" -Get User- button everytime you make a change in the software?(before making any change). If you dont make this, the software would become "crazy".

[clockworks]

"Servo Jitter" is like glitching, but it's continuous. The servos move side to side by small amounts all the time.

I posted on the RC Groups Tx thread. It's a common problem with the 4-cell mod - is your 4-cell conversion working properly?

[meao]

Yes, it works perfect.
I'll take a look to this in my new build, cause I'm building a new one with the 4-cell mod.

If I can, I'll take a video this night to show you.

[clockworks]

I've had some replies on RC Groups. It doesn't affect all radios, so maybe I'm just unlucky.

A fix has been suggested - remove the regulators and replace them with 100uH radial inductors (chokes in a small can, like a transistor package).
mis_b, who designed the LED warning circuit, emailed me saying that the inductors fixed his jitter problem.

I've ordered some inductors, and will post the results when they arrive.

In the meantime, I've started to fit a steering multi-switch to my KO/DX6i conversion.
I'm also looking for a multi-colour LED voltage circuit that I can build and fit to the KO.

[meao]

[clockworks]

I tried removing the regulators and bypass wires, replacing them with 100uH inductors. It made no difference to the jittering.

I think that I'll try refitting the regulators and using 6 cells.

[clockworks]

I've refitted the regulators and tried 8 cells. Also tried a 2s LiPo. I still get the jittering servos problem.
Looks like the Tx has gone faulty on me:-(

[meao]

but,.....
...when you made the first test, still having the electronic into the "air case" you didnt notice that problem, do you?

[clockworks]

No, it worked fine when I first got the Tx. I tested it thoroughly before starting the mods.
I'm going to strip everything back to it's original state (remove all the mods) and see what happens.

[clockworks]

I've removed all the mods. I've got an 8 cell back connected directly to the PCB, and a single pot connected to channel 1. I still get the jittering.

The Tx is definitely faulty, so I need to either give up, or get another Tx and try again:-(

[meao]

Today I've received the LiPo voltmeter I'm going to install to check the battery voltage. So, in a few days I'll finish the build with "multisteering switch" & "4cell mod". Then I'll tell you what happens.

I havent noticed jittering till now.

Cheers.

[meao]

Hi Steve, finally, I could install the LiPo voltmeter:

http://www.youtube.com/watch?v=HCNRquQKxF4

Cheers.

[clockworks]

Looks good. Can you set the voltmeter to just display the total voltage, or does it always cycle like that?

Are you using a 2s LiPo with the "4-cell mod"?

[meao]

I buyed this voltmeter because it was suposed to read 1 LiPo cell, but when I tested it, it didn't.
It always cycle, so I decided to connect it to the 4AA the same way a LiPo works. So, the first read(Nº1), gives the volt range for the first couple of cells, and the second read is for the other 2cells. And finally, we can read the total voltage.

I know it's not so pretty as we want, but it works fine

Note: I'm using 4AA cells.

[clockworks]

OK - I guessed that was what you'd done, as the voltage readings are a bit low for LiPo. I wonder if you can stop it cycling? somewhere on the circuit there will be a timer that makes the display step through the different displays. You could disconnect the timer and cycle through the displays with a switch.

Do you have a link for where you bought the voltmeter? If it's cheap, I'll buy one and try modifying it.

I've bought some airplane Rx battery monitors from Hong Kong: http://cgi.ebay.co.uk/ws/eBayISAPI.d...#ht_2265wt_941

My plan is to replace the 7 LEDs with 7 3x5mm rectangular LEDs glued together to make a "bar graph" type readout that I can fit through the case of my KO/DX6i Tx.

Is the 4-cell Tx working OK with a crawler - with no servo jitter?

[meao]

There are a lot of this voltmeter. Search "LiPo Voltmeter" on Ebay or similar and you'll have it. It cost me 7€ shipped.

I havent tested it yet with the 2.2, just with the PC, and it looks like it work fine.

[clockworks]

I've ordered a voltmeter - 4 Euros delivered! http://cgi.ebay.co.uk/ws/eBayISAPI.d...ht_1694wt_1167

Is this the same as yours?

Let me know when you've tried your Tx with a crawler. If it works OK, I'll buy another Turborix and try again.

[meao]

No, it's different. This looks working better, cause it can read only one cell.

I'm buying one now.

[meao]

Testing the TX 4-cell mod:

-PC:
http://www.youtube.com/watch?v=AoCc1...layer_embedded

-2.2(El Cucaracho):
http://www.youtube.com/watch?v=gjTdZ...layer_embedded

Cheers.

No jitter with analogic servos