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Old 03-12-2005, 03:22 PM   #1
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Default Power Cap and ESC

I have been having problems with glitching ever since swapping to a digital servo with my Futaba MC800C in an XRay T1R. I read some people were having problems due to the 5.8v output instead of 6v and they fixed it by installing a power cap either through the receiver or the ESC. I have a JR XS3 with the RS300 receiver. Servo is JR too DS8417.

I bought and installed the Novak 4700uf power cap and havent had a chance to try it on the track yet but it did glitch ONCE in the driveway. But no more when trying full throttle takeoffs and turns. This is with a 19T C2.

I installed the cap by way of a servo lead through the battery input on the receiver. Since space is at a premium on the T1R chassis I was trying to think of some other ways to route the cap. Currently I have it servo taped onto the top of the servo.
If I solder the cap directly to the posts of the ESC can I just tape it on to the top of the case of the ESC opposite side of the setup button?
Think the receiver moved to the top of the servo would cause more problems? I could then run the antenna through some fuel tubing to cross under or over the center brace to the antennae holder.
I am just looking for ways to fix this without having to cut the leads on the cap too short and then having to buy another one if it doesnt work. Any other ideas or suggestions?
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Old 03-14-2005, 04:43 AM   #2
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The easiest solution is propably to solder thin wires to the cap, the other to the ESC. Then you can pretty much put the cap anywhere there is room.

It seems that digital servos are very likely to cause some glitching. Has anyone tried adding a choke, like used to come with FET servos to try to eliminate the glitching.
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Old 03-14-2005, 04:10 PM   #3
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the cap is more effective when it is closer to the esc. you want the wires from the esc to cap as short as you possibly can
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Old 03-14-2005, 04:25 PM   #4
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Since you are using the Novak Cap through the receiver and not the ESC I am not sure what affect it will have to solve or worsen your problem, but I can tell you that the Novak Cap WILL NOT work correctly when hooked up directly to the Futaba ESC. The Futaba is a rebadged LRP ESC. The FETs that are used by LRP ESC are not the same as those used in Novak ESC's. Since FET's open and close at specific timing and the cap you use should be made to work with that timing. Since the FET's on LRP ESC's open and close at different rates than on Novak ESC's the Novak Cap will not work with an LRP ESC.

I had a similar problem witth my QC2 and the Worlds kit solved it. My recommendation would be to buy either the LRP or Futaba World's kit and use the large capaciter hooked up directly to the ESC.
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Old 03-15-2005, 01:13 PM   #5
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I'm a little confused by the question and responses.

It seems to me that CAPs are used on the reciever when you have too much draw from the servo and/or accessories attached, and the esc is not providing enough power to keep the correct voltage to the electronics, causing glitches. Isn't that what new92 is trying to solve?

To me, this isn't direct battery voltage, rather what the ESC provides through the interface cable, and ESCs have different ratings on what they supply to the reciever, unlike what they accept from the battery.

Caps on the ESC smooth out power fluctuations directly from the battery, which could also cause the same symptom, but not to the same degree. I'm under the impression they are most used to provide intial punch, with a secondary use to avoid major voltage drops.

I know some of the Spektrum users solved issues with the reciever/servo drawing too much power (causing resets), by adding a CAP hooked up to the reciever itself. I've also seen others use the same setup with normal recievers to avoid glitching.

So, if you have glitching issues, wouldn't it be best to hook the CAP straight to the reciever, thus smoothing out the delivery of the interface voltage?

Mike
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Old 03-15-2005, 01:49 PM   #6
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Quote:
Originally posted by SCML
I'm a little confused by the question and responses.

It seems to me that CAPs are used on the reciever when you have too much draw from the servo and/or accessories attached, and the esc is not providing enough power to keep the correct voltage to the electronics, causing glitches. Isn't that what new92 is trying to solve?

To me, this isn't direct battery voltage, rather what the ESC provides through the interface cable, and ESCs have different ratings on what they supply to the reciever, unlike what they accept from the battery.

Caps on the ESC smooth out power fluctuations directly from the battery, which could also cause the same symptom, but not to the same degree. I'm under the impression they are most used to provide intial punch, with a secondary use to avoid major voltage drops.

I know some of the Spektrum users solved issues with the reciever/servo drawing too much power (causing resets), by adding a CAP hooked up to the reciever itself. I've also seen others use the same setup with normal recievers to avoid glitching.

So, if you have glitching issues, wouldn't it be best to hook the CAP straight to the reciever, thus smoothing out the delivery of the interface voltage?

Mike
I have never hooked a cap to a receiver. The problem I was having that lead to glitching and also caused my AMB personal transonder to not record every lap was a power drain. This drain was caused by the motor sucking up so much of that battery when i was on throttle, that it was pulling juice away from the receiver, causing minor glitching and pulling juice away from the transpoder so it would at times not record all the laps.

By using the large cap in the World's kit, I was able to have the added benefits of using a cap on the ESC but it also allowed me to store extra juice so it is there when the receiver and transponder need it.

After the installation, I had no more problems and everything worked flawlessly!
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Old 03-15-2005, 02:15 PM   #7
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The CAP on the receiver will help with glitching due to power loss. On regular (not Spektrum) receivers, though I am not sure it makes a huge difference, as far as glitching goes. In those circumstances, mostly you will see a slower response time (servo transit speed) with lower voltages.

Installing a CAP on the ESC usually helps provide more punch, and helps the ESC run cooler. Cooler you say. Why yes. By helping to limit voltage depression on hard acceleration, the ESC doesn't need to pass as many AMPS to provide the Wattage the motor is asking for. Voltage times Amps= watts. To figure this divide the motor wattage (stock and 19 up to around 180 watts) by the available voltage to get Amps. Realize that when you punch it, the voltage is going to drop across the battery, to say 6.8 (not to sure on that)
180/6.8=26.5 amps run the same equasion at 6.0 volts (going dead) and you get 30 amps. So you can see higher voltage decreased the amps running through the ESC.


koabich :

I am not sure your description about the effect on caps in relation to different ESC is completly accurate. Any electrolytic capacitor in the right voltage and micro-pharad rating will work. The switching speeds of these ESC's are so high as it is, the switching doesn't really come into play. What your getting at is differences in ESR, but I think you might be over the top on that. The Novak cap is just basically a radio shack capacitory with a sticker on it.
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Old 03-15-2005, 05:51 PM   #8
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Quote:
Originally posted by SCML
I'm a little confused by the question and responses.

It seems to me that CAPs are used on the reciever when you have too much draw from the servo and/or accessories attached, and the esc is not providing enough power to keep the correct voltage to the electronics, causing glitches. Isn't that what new92 is trying to solve?

To me, this isn't direct battery voltage, rather what the ESC provides through the interface cable, and ESCs have different ratings on what they supply to the reciever, unlike what they accept from the battery.

Caps on the ESC smooth out power fluctuations directly from the battery, which could also cause the same symptom, but not to the same degree. I'm under the impression they are most used to provide intial punch, with a secondary use to avoid major voltage drops.

I know some of the Spektrum users solved issues with the reciever/servo drawing too much power (causing resets), by adding a CAP hooked up to the reciever itself. I've also seen others use the same setup with normal recievers to avoid glitching.

So, if you have glitching issues, wouldn't it be best to hook the CAP straight to the reciever, thus smoothing out the delivery of the interface voltage?

Mike
Exactly what i was thinking. I currently have the cap wired to the receiver by way of soldered to a servo lead then plugged into the batt slot on the receiver. I have not been back to the track due to weather and stuff but have been up and down the driveway a few times. It SEEMED to cut out the glitch I would get when rocking the wheels back and forth with the radio. Which I suspected was the servo pulling too much juice. The only ties it would glitch the one time I raced it on the track with the new servo was coming off of a sweeper onto the back straight and off of a hairpin onto the front straight. About the only 2 spots on the track where you are wide open throttle. Well, actually I thought I heard the motor "cutting in and out" a couple of times down the back straight.

I previously could set the car on the ground and rock the wheels back and forth really fast and after a few seconds the car would jump forward about 6 inches. Like justa quick quarter throttle stab. Then I kept watching and it seemed like instead of throttle sometimes the brake light on the ESC would come on. Since I put the cap on the jump has happened ONCE. I then ran a few quick bursts up and down the driveway and it went away when I would rock the wheels again. Does the cap need an initial "jolt" to fill up with energy? If so, then that might explain the one time glitch that goes away after supplying some power.

I am going to shorten the wires from the cap to the receiver as short as possible and see how that works. I just left them long till I could figure out if it worked and then decide on a mounting spot.

Thanks for all of the tips and keep the ideas coming if you think of anything else.
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