HappyGene

iTrader: (135)

Okeedoke, I don't mind buying a 1s controller, but I won't for this indoor season. Maybe next year. But I DO want to play around with my pan cars since PCRC put in that nice new carpet track AND since I like flying my old 12i down the street (hella fun and I'll have a post on that, later, too.) Also, I got some stump pulling 1s packs from a friend here on RCT that will work well in a T4 with a 4.5T to 6.5T motor. Yes, I have and use 2s, but this is fun, satisfies my curiosity and those little packs will even wedge into some Tamiya nicd tunnels.

I saw a little blurb about someone somewhere who either DID, or just surmised augmenting the drive and logic circuitries in a speedo by adding the missing voltage into the power switch lead.

So, I have tried and succeeded in doing that with a T-Sky speedo (google "jym73 tsky 120a" and you'll find it quick.) Bless this guy: he went to the trouble to figure out some other things about this esc that bump it up from an average device to a very good one. They are $20 bucks shipped, on average, and probably a solid 70-80 amp esc - 14g wires and a little lighter than the Venom Red 120 (the Atomik) that it appears to mimic and is actually a nice speedo, although it's BEC is only 5.4v in use.

I'm going to document this easily performed change and resulting near-instant change back to 2s on another 4 or 5 esc's. I welcome you to jump in with observations or your own experimentation.

Here's my overall quick change platform: I can attach nearly anything to anything else and grab it up with one hand if I need to reposition or relocate. The legs pinch up toward the angle and hold items similar to a c-clamp.

It's a corner (mitre) clamp for picture frames and quick-release zip ties from Harbor Freight. One could use rubber bands, but I found that to be frustrating when combining slippery plastic or painted items.

The end result was slower cooling fan since it's on battery voltage, speedo's BEC intact at 5v (will measure current, later) and full servo/motor operation. Now, the AC voltage across the AB phase at the motor was only 2.7v at full throttle, but my meter might actually be reading in peak-relax or RMS mode. It's cheap and I no longer have a scope to verify either way. But that 7.5T motor spins the old motor break-in fan fast enough to blow back small plastic parts. I'll put it in a truck, hopefully this weekend, and post the results.

Note that the variable speed operation of the cooling fan will be lost when plugging it into the receiver for power: it will simply be "on."

Here's the interesting part, to me: from presumed Eigen (google "Chapter 5 Series Parallel Circuits" for a brief overview) values based on looking where the battery wires traced into the controller board, I would've placed the leads from the little nicd pack +-+-, red to black, on the switch leads - an intuitive approach. I started that way, with some included resistance, and then quickly went to full voltage as it appeared to be a simple voltage opposition. If you're experimenting this way, I'd suggest using a 2s motor pack at first to determine the polarity so that the push-back voltage will be circuit-safe.

So, it works with the black(-) lead to the black-from-esc lead and the red(+) to the switch body. Look closely at the wiring to get a gist of this, which might be reversed on another brand of esc.


The extra battery pack is on the leads in the bottom of the pics. I'll have to measure current over a time period, but those little $1.50 180mah lipos might work for a full heat, that'd be cool! What you see in the larger pic is a little 250mah nicd pack from an OLD cordless phone, just larger than the receiver.

Now, what this means is that the speedo's drive is inverting right off the bat into idle like a typical audio amplifier, acting as an independent component within the speedo and should operate with any voltage that will activate the transistors, probably as little as 0.65v as long as the logic is powered up to say, "Yes, go." You might could run a car on a single D cell, if you wanted because the controller simply chops up and pulses the nearly full voltage. I'll verify that, too.

This could be great for gifting a repairable rc car to a younger child. The parents wouldn't have to buy chargers and special batteries. Pop in 2 or 3 AAA alkalines to run the radio for a loooooonng time and one or two carbon D's to run at less-than-break-neck speeds for quite awhile, then toss it into the closet and use it as a good behavior treat. No worries of any kind and less than $3 at a dollar store for a long play session.

You might ask, "Why not just use a bunch of AA's and not go to this trouble?" Well, one or two D cells won't provide enough power to break furniture or the chihuahua's legs and most inexpensive radio's don't have throttle dual rates. And you might not be able to find a high-enough-wind motor to be slow and fits the chassis. With this, shoe-goo on a plastic battery holder, change the power leads and you're good to go.

I'm going to solder up some JST connectors pretty & proper to replace this mess and then it'll be a simple plug in to change battery classes.

What's further interesting, is that I might find esc's that would allow 4-6s motor batteries with a voltage dropping component in the power lead. That will depend on the circuit surrounding the drive, but it's viable. Just think, a manufacturer might make 5000 units at a time with mostly changes in cases and code and not want to change the parts feed into wave or air soldering machines so...?

Geno B'do

HappyGene

iTrader: (135)

Okeedoke, here's another: the aforementioned Atomik Red 120a. End result: fan = full circuit voltage; additional battery inserted into white wire with (+) positive to switch and (-) negative to case.



Here is it closer:



That's not the clearest so, to be clear, the red & black wires aren't spliced. I only cut them to aid testing to see which of the wires acted like a source for any other pair through the switch.

That's a 4.5T 550 and it's going into a truck tomorrow with a little 250mah NiCad wired in for playing in the grass.

More to come,
Gene

HappyGene

iTrader: (135)

Okeedoke, I couldn't find my 5mm 48p pinions, so I tossed in a Tacon 6.5T - noisy as heck, but runs like a top. This old XXX (I think, no trough in the battery tray) is AWESOME and fun to run. I got this off RCT a few years ago and the guy set it up right, no doubt. If you recognize it, feel free to say hello The body is a southwest style red to yellow fade with gold intervals. I'll pic it, later.



The old phone nicd dropped out after half an amp of draw. It was fine at idle and trivial steering movement, but the pack's IR was just too high - these regular nxxx's do just fine, though. The murphy on this was that a shorty and a 3 cell nxxx WON'T fit into a standard tray - 3/32" too long!! The white spots around the rx pack are foam tape tabs to control the sliding back 'n' forth on the battery strap when I hit curbs & telephone poles



I was getting just about 30 seconds run time per esc cutoff and worried about the 1s packs, but the lvc was taking the extra nicd into account and shutting down. Did some testing to verify that because a light load fresh off the charger didn't pull the phone pack down much. I knew it was topped by the charge, but it had run fine in my test jig (under revision) and I needed to rule stuff out. I'm monitoring motor pack, BEC and the auxiliary pack and pulling extra control circuit current via the rx battery slot.



Then under mild servo action and later (no pic) with additional inserted load.

HappyGene

iTrader: (135)

Those little Asian volt meters are the bomb: $1.60 shipped and pretty accurate, although most won't read under 3.4 volts, reading 0 or just failing to display below that point. I've got some others that were $1.90 shipped that have a separate power wire and I'll try them, next.

Here's an easy way to make up some serial/parallel source/load insertions. Just hook or lightly twist the leads to hold together and hang them over the plug/jack, dab the flux and drop a small blob of solder onto it. No jig required and no cold joints. I'm moving less than 15 amps for this kind of testing so this'll do for a couple minutes at a time and it all plugs and unplugs easy cheesy.




I made a 2s to 1s jumper to mate with an external lvc alarm. Now, the buzzy ones won't buzz on just one cell, so I'd need to wire in the nicad on the jumper and keep it topped or just run a small lipo (my actual long term plan.)



But it will read out. Usually, the original battery (-) negative lead will actually be right-on-the-front-side, or left-on-the-back-side, so I had to follow the connection trail and put the new soldered lead properly, moving the 3rd (outer) 2s lead (1st cell positive) to the 2nd (middle) prong at the alarm end. I couldn't go by color on this stuff, not only for plug-reversal, but because the coloring scheme was not consistent on the leads I got.