RCMC Lansu 3 channel 2.4 radio problem

[braq]

measure between the two outside pins. If it is connected to the circuit it might give a disorted reading (namely of other components). You may clip one outside leg of the pot and resolder again (but you wanted to replace it, right, so it actually helps towards desoldering it)

cheers

braq

[sgl]

Thanks Braq,
Yes I want to replace and the reading just didn't seem right. I'll clip the lead, after alI if I can't do that I shouldn't have opened it up in the first place. I hadn't considered that possibitity that the other components could alter the readings. Once again apreciate the help.
sgl

[sgl]

I metered after isolating and values did come up 1.79K ohm so once again not what I expected. I now wonder if it is also due to dame from me working it over? I wonder of I should go with a 2.5K ohm unit , but as always I am open to suggestions.
Thanks You
sgl

RCMC
MRC-pro

[braq]

any imprints on the pot itself, how does the other pot meter out?

[Charlie-III]

Originally Posted by sgl

I metered after isolating and values did come up 1.79K ohm so once again not what I expected. I now wonder if it is also due to dame from me working it over? I wonder of I should go with a 2.5K ohm unit , but as always I am open to suggestions.
Thanks You
sgl

RCMC
MRC-pro

I'm wondering if it's a 2K pot with a wide tolerance.

[sgl]

Hello,
I'll meter the throttle pot as well, there are no markings on the pot. I am not familiar with wide tolerance pots? I was leaning towards me some how damaging it but not certain how realistic that is. I imagine is there a possibility of manufacturing tolerance shift depending on the source and quality assurance.
Thank you
sgl

RCMC
Losi MRC-Pro

[Charlie-III]

Pots (variable resistors) & fixed resistors have various tolerances. The tighter the tolerance, usually the greater the cost. Most of the time, they make a batch, then test to see the range. Depending on the measured value, they sort them out to:

+/- 20%
+/- 10%
+/- 5%
+/- 1%

So, a 2000ohm (2.0K ohm) pot at 10% could be ~1800 - 2200ohm.

[sgl]

Charlie-III,
That makes lots of sense to me. 20% is huge but then if they check 1 in 1000 or 1 on 10,000 or 100,000 I could see one coming in below spec and with use drifting below usable values. Now I guess it's a hunt for one I can fit on the unit. I really appreciate all the help you and Barq given me on this project. I'll keep posting as I go along till it's complete. For a relatively inexpensive purchase I have certainly learned a great deal from it.
sgl

RCMC
MRC-Pro

[sgl]

I disassembled the pot ( 3 tangs holding it together ) and found the conduction material, on the inner contact ring , had been worn away by the contacts. The outer contact arias ( 2 contact arcs ) appear have fine scratches fine where the finger contacts meet the surface. Looks like it may have been poor PCB fab processes as all the contact surfaces look marginal. I'm thinking a new pot will make all the diference in the world.
sgl

[sgl]

Yes, there is an imprint on the pot. It is Cherkfah the k is in highly stylized script as is the h the "h" looks like a Hyundai logo turned sideways and the "K" the upper vertical arm is further up the upright so that it dose not meet the lower arm and the lower arm is flared as it meets the upright. I realize a picture would be ideal but no matter which lens I use ( I haven't a macro ) the resolution is poor.
sgl

[sgl]

Hello;
First in regard to the markings CHERKFAH, I am wondering of the K and H-are bracketing the F and A as the are so stylized and there actually calling out traditional (old) marking code for F and A ( linear, antilog )?
I am having difficulty finding a POT, I a'm wondering if I have to stick to the Carbon ( Carbon comp on Phenolic resin ) original style. I am having a difficult finding the single gang with ( with dual gang characteristics ), with center off in the 2 k range with a 270 ° rotation. I would think the Conductive Plastic would work but not sure about the Wire Wound units? So far the only POT even similar are all Log ( audio ) in the five K range, I have even taken to metering out the pots in some old Airtronics AM radio as well as a Hitec FM radio with no luck. Any suggestions?
Thanks for the help.
sgl

[braq]

Hi sql,

imprint was more meant into regards of the value being imprinted

Anyway, I don't know if it is mounted sideways or upright, but here is one of many to choose from
PDB12-H4251-202BF Bourns | Mouser


Check if the pin diameter more or less fits with the existing one (can turn it down or add tubing, but there are enough out there to get the right one in the first place)

Did the 2nd pot meter out to the same value as well?

A picture would help a lot

....and two more things
- very very likely it is not logarythmic (you'd create this characeteristic within the Tx, called expo)
- if you were to use a 5K type pot, most likely it will work (just when the resistance exceeds 2K measured from the mid pin it will not result in a difference on the Rx side anymore)

cheers

braq

[sgl]

Braq;
The throttle pot metered out at 1.60 , which was near the first reading I had for the steering pot (1.65) I thought tere was a problem with my readings , either technique or meter ( I replaced the battery ) ( double checked method) readings still seemed off. I was looking for something near 5k or at least near a whole number 1K, 2K etc. I was just uncomfortable with a reading in the middle. The pot you sent a picture of is simular as the Lansu is upright as well. I was as able to find single gang (1k , 5k ) same physical measurements, shaft 3.42 sjaft hght 8mm , shaft screw dia 6mm - body dia13mm body hght 5mm, over all hght 20mm. But not double gang with only three feet, center off no. I had even considered a double gang stacked soldiering the center post together, but with the left and right lead on seperat gangs. I hadn't thought of using a 5k, but I imagine 280° or greater would possibly provide a enough usable contact aria. Is the one pictured double gang center off? I apreciate all the help thank you very much.
sgl

RCMC 1/24 Sumo
Losi MRC-Pro

[braq]

Hi,

there is no reason to go with exessively other values than the ones in the circuit originally. Linear, the axis can easily be cut but it comes in handy if the diameter is the same and nice when the pins line up the same way.
I took my Lanzu apart and get the same readings, around 1.7K.
Seems there are so many more choices in 2K, so that would by my choice and pick one that comes close in dimensions and not too exotic (aka expensive). While you are ordering anyway, might check out their selection of LEDs if you are into lights on the rig,

cheers

braq

[Charlie-III]

sgl..........While I've never metered my own steering post, I sorta think you're over-thinking this. In general, these pots have a swipe of a resistive material (it makes up the stationary part of the pot, it goes up in value/resistance as you travel along it length with one probe fixed to an end) and a wiper. The circuit design will allow "~x ohms = '0'". As you add/subtract resistance it drives the circuit in a direction. This means as you go above ~1/2 (or ~.85Kohms "+") the steering goes one way, as you go less than ~1/2 (or ~.85Kohms) the steering goes the other way.
I find it hard to think the designer made a pot that is "0"ohms at midpoint.

Does this make sense?

What you may have is a bad spot in the swipe/arc and get a funky reading around the midpoint of the arc leading you to believe it's 2 separate circuits.

If everyone is getting 1.6K-1.7Kohms on the swipe/arc, then get a pot with the same dimensions and a similar resistance and swap it in & test it out. The steering trim should allow for the minor variations in the total resistance.

[sgl]

Charlie-III;
What you have described is an interesting concept, although is seems to me there would be a discrete circuit to interpret and produce the directional signal, more expense . Unfortunately it really is a rotary dual gang single turn pot in the 16mm standard panel mount. I opened the pot and found that the etching on the phenolic resin base had a 6.5mm center circle then a complete .24mm clear aria ( no carbon matrix )encircling that and on either side a small arcs 2mm thick covering some where between 90° and 100°s. it looks like a circle surrounded by a c and backward c ( ® ) like this only the center solid ( ® ). There are 5 contacts 2 on the center circle and three on the outer, the two center contacts scraped a three mm arc from the carbon matrix on the phenolic base. The outer contacts have already nearly worn through both outer arcs.
I purposely made the explanation as simplistic as I could just for clarity, It's apparent you have a pretty good foundation in electronics as well as having put a lot of thought to my situation, thank you for the continued support. I will try again for some pictures.
sgl

RCMC 1/24 Sumo
Losi MRC-Pro

[sgl]

Braq;
Thanks for metering out your unit, it's nice to know it meters out the same. I do have a tendency to get caught up in the values, everything I have done has required clear attention to results values given. The site for the potentiometers was helpful and I have ordered five inexpensive units to try.
Thanks agian.
sgl

RCMC 1/24 Sumo
Losi MRC-Pro

[Charlie-III]

Hmmm....interesting, yes, I understand your explanation.

Almost makes me want to open a couple of my TX's to see what they have in them.

[sgl]

I looked inside old Cox/Sanwa am radio and it's pot was in the high 3k oh
bracket. Next was a Hitec 5 channel FM and it was consistently just under 5k ohms. I ordered up a few different pots from Mouser, to see if something will work. I'll place wires on the board until it's all sorted out.
sgl
RCMC 1/24 Sumo
Losi MRC-Pro

[braq]

cool,

keep us updated on your experiments,

cheers

braq