Cripple capacitor reversal.

[micro_Amps]

I have been doing some work on BCG booster cars and I have noticed that something strange happens to the range, but only sometimes.
I have been range testing the cars and then removing the cripple cap, and range testing again. Most of the cars respond by either improving or no change to the range achievable. In 2 of the last 4 cars the range dropped to 1 foot after removing the cripple cap, making the car useless. So I reinstalled the cripple cap and the range goes back to the original distance of about 10 to 12 feet (3 to 4 meters).
Anyone else seen anything like this?
:)uA

Edited by – micro_Amps on 06 July 2003 21:01:03

[GT-ahh]

u have to adjust/re calibrate the coil otherwise u wont get an increase in range

[micro_Amps]

Yes, thats the way I am checking the change in range, by walking away from the transmitter and adjusting the coil until I reach the maximum distance.
:)uA

[jamiekulhanek]

I think im guna try retuning one of my cars, the range is appauling, it only goes about 1 metre before stopping.

[GT-ahh]

well the cripple cap could be used as a filter (like that phat RF choke on playstation controllers) and not as a limiter like people assumed…

[jamiekulhanek]

You could be right, i have not studied the circuit, but is it part of an rf filter, is there a resistor connected to it??

[ph2t]

From where the “crip cap” is located on the RX pcb I beleive it is in parallel with the 100uF cap on the output stage of the 3V DCDC converter. Like what GT said is is prolly there to get rid of high freq interference.

From what I’ve read about DCDC converters usually a high value cap (in this case the 100uF eltrolytic cap, tha big black canister thingy :D) is use to filter any ripple on the output. The “crip cap” wouldn’t help this principle so it’s prolly there to counter RF interference.

Also, I’m having a bugger of a time in turning the ferrite core of the tuning inductor on the PCB. I melt the wax and then suck it up using solder sucker, but the pr1ck of a thing still won’t turn very easlily. I’m using a wooden “paddle-pop stick” cut and shapped to the ferrite core to be able to turn it but without much luck. Any suggestions fellas? Maybe melting the wax first isn’t a good thing ’cause it’s prolly melting futher into the thread and causing the ferrite core to stick, arggghhhh!:evil:

ph2t.

[micro_Amps]

Yeh ph2t, I think you are making trouble for your self by melting the wax first.
Just use something small and sharp to scrape it out, it usually comes away in one compact blob.
Dont bother using something non metallic to tune the coil, it doesnt make any difference if it is metallic or not in these cars. I use a small screwdriver filed down with the dremmel to about 1mm. After adjusting it, take the screwdriver away and test it. The only reason you need to use a non metallic adjuster is in sensitive amplified RF ciruits that woud be effected by the change in inductance of the screwdriver. Once its removed it as no influence.

:)uA

[ph2t]

Thanks dude, I’ll give it a whirl tongiht.

The reason why I ask is that I’ve managed to rip out the old 3V DCDC converter and replace with a 5V one. My goal is to increase the RX power and get a greater range. When I do this the RX is actually worse off. I get spasmodic reception at best. I gotta re-tune the inductor and test to confirm if the 5V boost to the RX stage is a feasible one.

ph2t.

[micro_Amps]

Ive been thinking about doing the same thing, but havent checked component compatibity yet. It should work, but as you say it will need to be retuned. Let us know how you go. It would be good to have 5v on the baord instead of the usual 3.3, it should boost the range heaps.
:)uA

[ph2t]

Look for the “New Dual Cell” thread under Bit Science at tinyrc.com for more info about DCDC converters.

ph2t.

[SurfmyStrat]

dude i had the exact same problem, after i removed the cap my range died to like 1 foot, then i just played around with it till it got to like 5 feet but it used to be around 12 feet.

[micro_Amps]

Yeh surfmystrat, thats exactly what I mean.
Were you able to solder it back on ??
If so was there any difference.??

Ph2t, I’ve seen that thread emerging, I think they are going to have problems with current supply using a DC-DC for motor power.
Intersting to see how things turn out though.
:)uA

[Prowler3]

My new RSXr has crippled range. Im an ametuer at this stuff. But the places that were meant to be connecteed byt the cripple cap where on the entire other side of the circuit board! It was a huge distance to be bridged by such a tiny thing

-I gave up!

[ph2t]

Prowler, post some pics of both sides of the PCB and we’ll see what we can do.

:smiley2:

ph2t.

[Admin]

Quote:

Thanks dude, I’ll give it a whirl tongiht.

The reason why I ask is that I’ve managed to rip out the old 3V DCDC converter and replace with a 5V one. My goal is to increase the RX power and get a greater range. When I do this the RX is actually worse off. I get spasmodic reception at best. I gotta re-tune the inductor and test to confirm if the 5V boost to the RX stage is a feasible one.

ph2t.

I applaud your adventurous nature. I’m not an RF designer, however, I dabble in the field a little. You don’t want to increase the power of your receiver, you want to increase it’s sensitivity. My guess is that the cripple cap is for the LC (inductor/capacitor) tank circuit that tunes the freq of the receiver. If they are using it to reduce the sensitivity, then they tune the receiver to max sensitivity for the transmitter after which they add a several pF of capacitance to slightly detune the receiver (thus reducing the sensitivity). I’m not sure what that has to do with the FCC, maybe they (FCC) feels it would act as a deterant to increasing the range. I have not seen the schematics for the receiver, so I could be way off here. Also, the part about the FCC, was something that I read about the cripple cap.

Having said that, coupled with what you are saying about a DCDC coverter. Well, maybe Cripple stands for the ripple reducing capacitor … I’ve seen the term Crip (a.k.a. ripple cap).

Could someone point me toward the schematic for the receiver? Is the black epoxy covering a die? I will need the datasheet for the receiver as well. I will analyze the diagram and make some suggestions or try some myself. Which IC on the PCB is the DCDC converter anyway?

Has anyone tried to change transistor Q2 (C945 EBC) with another transistor with a higher beta? Try the 2N3904 … becarefule about the pinout … the 2N3905 has a different configuration than EBC (Emitter/Base/Collector … I don’t have the data currently available). The higher beta will cause more current to flow from the collector to base … the inductor will produce larger voltage swings and thus more power. I hope some of this helps …

One last thing … does anyone know what kind of RF modulation is used and how the data is encoded?

Thanks.

[ph2t]

Wow, what a great first post. Here’s a link that should help your questions.

http://www.ausmicro.com/topic.asp?TOPIC_ID=254&FORUM_ID=9&CAT_ID=2&Topic_Title=RF+mod+%2D+more+controller+channels&Forum_Title=BCG+%2D+Technical

ph2t.

[Admin]

Quote:

Yeh surfmystrat, thats exactly what I mean.
Were you able to solder it back on ??
If so was there any difference.??

Ph2t, I’ve seen that thread emerging, I think they are going to have problems with current supply using a DC-DC for motor power.
Intersting to see how things turn out though.
:)uA

I did not notice much change in the distance w/ and w/o the Crip cap (ripple capacitor). When I have designed circuits in the past I use a large value tantalum capacitor and a 0.1uF monolithic cap or power supply bypass at the various ICs. You could think of the circuit behind the DCDC converter as another part of the circuit that needs to have the voltage held up, thus the large cap. Holding up the voltage is very important when the motor is switched on, where a lot of current draw happens. I know the tantalums have poor responses at higher freqs that is why you use the 0.1uF cap. The same is probably true for electrolytics. I cannot explain why the extra bypass cap (on rcvr PCB) improves performance, perhaps the addition of the longer antenna is where the gain is acheived. (Has anyone tried increaseing the antenna length without removing the cr-ap {cripple cap}.) This supports my nagging problem with removing the cap. My problem with the cap being put there to hamper performance, is WHY? … why would they want to reduce the performance of the receiver … it is the xmitter that is doing the most radiating. That is the most likely place to squelch the system radiation to conform to regulatory radiation limits. Hurting the rcvr only hurts sales.

I could be off-base, above. The only explaination I have for Crip hindering proper operation, is this … first, notice that the resistors have numbering printed on them (format xxy, where the value is xx times 10 raised to the y, i.e., 226 would be 22×10⁶ or 22Mohm). The capacitors have no numbering, in fact, the only way to tell a cap from an inductor is the reference designator silkscreened onto the PCB next to the part. When I first saw SMT caps I thought that the values were color coded, this is not the case; the colors have no bearing on the value (they vary from mfg. to mfg., and prolly from lot to lot.) Here’s the rub, the tech installing the ripple cap got them mixed up with other values (or supply gave them the wrong values.) Too small of a cap and some of the harmful EMI will not be smoothed out, too large and the supply can not … no wait a minute too large is not a problem. Crip is fairly large for a smt monolithic cap, that leaves a lot of room for other similar sized caps below that value. If someone (ph2t) has a bunch of the caps they removed measure the capacitance of the lot. It’s just a theory … it has holes … i.e., I haven’t seen anyone post that things got worse after removing the cap.

Re: DCDC converter for more voltage to motors. Increasing the voltage to the motors will increase the current, speed, etc. However, the trade off will be increase EMI/RFI when the motor or steering coils are switched on/off. Also, you are using some of your battery power in the conversion process. Look at the specs of your dcdc converter. Replacing the existing DCDC converter with one that has a higher efficiency value (nu, expressed in percent) would give more battery life. If you want to bump the efficiency of the motor driver circuits … check out MicroAmp’s page on the MosFET mod. Looks incredible, great job dude, … I will try it out after improving my range (what good is improved running time and speed if you have to stay within a few meters of the car … in fact, by making the car faster, you just decreased the amount of time the car is in range.)

You don’t get something from nothing … well until the universe stops expanding and entrophy goes to zero … after which it will start contracting and the universe will give our cars energy … but at that point we will die due to not being able to sink the heat. I’m not sure if the last part is true, see what a little knowledge will do? Ok, I just exceeded my philosphy quota for the year.

I wish I had as much to say during 11th grade writting class, I might have made a better grade.

regards,
bigAL

microAmp: Dude, I got my nickname shortly after starting high school where changing for gym was mandatory. Sorry about your nick … :smiley2:

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