Throwing Money At My Problems

[Mrowka 493]

Build a Fox they said! It'll be fun, they said!

So I did. Bought a mostly complete Fox, with new bearings all around and a rebuilt transmission. Just needed electronics, body and rear tires and wheels. Even had an original build manual.

Should be easy, amirite?

TRIGGER WARNING - long post.

I got the missing parts together and an Hobbywing brushless ESC and 17.5T motor. Snagged a driver doll to boot.

Putting the pieces together was a pain, because I couldn't think of a decent place to mount the ESC and still get airflow. After much agonizing and more overthinking, I saw that people usually put the ESC in the electronics compartment, so there it went.

The other problem was that I couldn't figure out how to route the motor cables. Even if I used the hole that the battery cables were supposed to come out of, I'd have to enlarge that hole to fit the battery cables, the three 12 AWG motor cables, the antenna and switch wiring.

Not to mention, the results look sloppy and ugly, and all that wire adds weight and costs power.

Finally, it dawned on me that I could use the hole and routing that was intended for the switch. I would have to extend the cables some, but that was going to happen, regardless, unless I moved the ESC to the rear where the wing was supposed to go (and extended the battery cables). Of course, I also needed a longer sensor cable.

So in everything went. 

The problem was that I could not get the pinion to mesh properly. Any power and the transmission screamed like the kinds of noises I hear every time I ask an attractive girl for a date. 

And getting the motor screws in was a nightmare. Getting both screws in took hours of fumbling, and once both screws were in, the transmission was either locked up or noisy.

Nothing I could do would get the gear to mesh. No lubricant seems to help (and I know from experience when lubricant is futile). I am mostly a newbie when it comes to cars, but I've built and repaired dozens of helicopters and managed to get all of them to fly and not make obscene noises.

I brought the car to a friend who knows more about these things than I do. He suggested that the motor is simply too powerful for the transmission. I could try and reduce power, rebuild the transmission with heavier duty components, or just find a silvercan and comparable ESC and enjoy the car the way it was intended.

Admittedly, my friend's experience is with modern buggies. He is a very smart guy, a genius with electronics and probably somewhere on the spectrum, but his idea of fun is putting a 4S in a car designed for a 2S.

I had another project for the brushless, so I got a cheap ARRMA brushed motor and another HW brushed ESC. The motor cable came broken, but I was going to have to solder in a new one anyway. Needless to say, my first attempt was a fraction too short.

Reinstalled everything, with the same result. The transmission was either locked up or howling like a banshee and clicking and jumping teeth. Nothing in between. Screws still impossible to get aligned into the motor holes.

Then it occurred to me that I might try reading the manual. People have successfully built tens of thousands of Foxes and most of them probably read the manual. Why couldn't I do that?

The manual had all kinds of useful information about the motor plate and how it was positioned, depending on the number of teeth in the pinion. An ingenious setup, but it didn't help much. Still lots of clicking and clacking and less pleasant noises. Still can't get the screws in, at least not without a ton of wrestling.

So I got some more parts and tried rebuilding the transmission, thinking that maybe it made noises because I had probably broken something. Nothing was obviously wrong, and when everything went back together, the results were no different. Same with another motor I had around (maybe the screw holes were out of alignment? Maybe not.)

Then I try switching gears. Any 32p 14-18 tooth gear ought to work, but I am really at my wits' end. How can something so simple be this difficult?!?

I take the only gear I have that I know for a fact is genuine Tamiya, an 18T, and I can barely get it to fit at all. In part because it's bigger than the others, in part because, I noticed that, even with the gear as far down the shaft as it will go, the notch in the motor shaft means that the gear is hitting the end of the transmission opposite the motor.

And it was then that sweet music came to my aid...

I take some studs (so I don't have to wrestle with both screws and washers) and 3mm washers to act as spacers between the transmission and the motor. The washers effectively move the motor shaft away from the far end of the transmission, so I get clearance. I fasten using nuts and washers (to spread out the clamping force) at the other end. Naturally, I don't have any of this hardware on hand, so that means a trip to the LHS. Joy.

TA DAH! Pinion meshes perfectly, no noise, no clicking, no grinding. I had to disassemble everything to get the body back on, but that's no big deal.

There's only one problem. The 3mm nuts are so big that the cover on the transmission opposite the motor won't fit. 

For now, I put a piece of clear tape where the cover is supposed to be. It's a piece of redneck engineering worthy of my trailer park relatives, but it works for now.

I suppose I could grind the nuts down until everything fits, but I really don't want to mess with something that finally finally works.

[Kayak 50]

Could you have flipped the pinion gear around on the shaft.... so the set screw would still be on the flat portion... but the 'gear' would move closer to the motor?  Sometimes... that's all it takes to get the clearance... so long as it makes good contact with the spur gear.  I have found that some of the new motors are considerably longer where the bearing/ bushing area is... and I have to 'flip' the pinion to get a decent fit.

[mtbkym01 4008]

This sounds extremely unusual, post up a series of pics to illustrate what is going on here, the Fox is one of the most reliable cars Tamiya has ever released (let’s face it, most of them are anyway)

[Mrowka 493]

10 hours ago, Kayak said:

Could you have flipped the pinion gear around on the shaft.... so the set screw would still be on the flat portion... but the 'gear' would move closer to the motor?  Sometimes... that's all it takes to get the clearance... so long as it makes good contact with the spur gear.  I have found that some of the new motors are considerably longer where the bearing/ bushing area is... and I have to 'flip' the pinion to get a decent fit.

Honestly, I had not thought of that.

[Mrowka 493]

7 hours ago, mtbkym01 said:

This sounds extremely unusual, post up a series of pics to illustrate what is going on here, the Fox is one of the most reliable cars Tamiya has ever released (let’s face it, most of them are anyway)

I didn't photograph my build progress, but the problem wasn't reliability - it was fitment, along with my own incompetence. I am attaching some photos of the finished results, including the redneck engineering that got the job done.

FOR THE RECORD: I do not blame the seller, not do I blame Tamiya for fitment issues using non-Tamiya parts.

[Mrowka 493]

Redneck engineering Exhibit A.

[Mrowka 493]

I would upload exhibit B but the forum isn't letting me do so.