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View Full Version : Got my mini-x! A few criticisms/?'s...


Bravin Neff
12-07-2002, 12:40 PM
Great little car!! Pretty quick, and the engineering involved is mostly sound. Here are some initial observations and criticisms, to aid in improving it:

1. Changing the front caster causes a tiny interference between the front knuckle and the lower front a-arm. This is minor, and could easily be modified for the proper clearance. I noticed this interference only occured on one of the arms, not on the other, and is just the result of tiny tolerances stacking.

2. Changing the front caster causes the steering arm to be a little out of wack with the steering servo. The stock position works fine, but in the alternate caster setup, it is not as effective.

3. In my opinion, the steering setup is the weakest design of this car, and it would be cool to devise some kind of tiny turnbuckle/ball-cup arrangement, though the parts would have to be so small it is hard to imagine finding the appropriate parts that would actually work. The stock steering does work well, though, and it tracks neutrally. The steering is quick and accurate. And the straight steering connector arm has enough flexibilty so as to appear to cause no interference with the front suspension's ability to work.

4. The diff-units on my car have a noticable amount of out-of-concentricity, or "run-out," between the outdrives and the spur gear. Consequently, since the outdrives are immobile, hard-located between their bearings, the spur gear will not spin a perfectly circular path, but will follow an eccentric and elliptical path instead. Fortunately the gear mesh has enough clearance to all but compensate for this. Technically, all gears have a degree of this, and can be ignored if sufficiently small. With these diffs, it is visually noticeable. The real reason I care about this on this car: you need to be able to turn one wheel, watching the opposite spin backwards, in order to adjust the diff. Usually this works fine, but if you do this when the spur gear's eccentricity catches itself on the high spot of it's rotation, the friction becomes too great and will catch causing the opposite wheel to turn WITH the wheel you are turning, and you will cause the motor to spin instead. It causes me to wonder how effective the diffs can be, as this run-out is tantamount to making the diff alternate between soft-stiff-soft-stiff during its rotational motion. I have NOT disassembled the diff yet, so it may just be a case where the parts need to be realigned. At any rate, for a car so small, I realize I am nitpicking here. Really, it's splitting hairs, and it appears to have no obvious effect on the car's performance when I drive it. The diffs do work as advertised, and I am amazed a car of this size has ball diffs at all.

5. Part fitment. I was amazed at how well most of the tiny parts fit together. I was expecting more slop, particularly between the a-arms and their tiny hinge pins. If you are familiar with how injection molding works, you know that it is not perfect, and no where close to a competent machining process. On my car, the clearance between the hinge-holes in the a-arms, the holes in the chassis, and the hinge pins seems to be as good as one could reasonably desire. If you could enlarge this car to, say, 1/10th or 1/8th scale, the fitment here would probably be better than any other car out there.

6. On the other hand, the clearance between the uprights and the wheel bearings is too great, as is the clearance between the axles and the bearings. It causes an unnecessary amount of slop in the parts. This seems to be something that would be easy to improve.

7. The stock suspension springs are too stiff, as I suspected by reading other's comments. I bought the optional spring set and installed the softest ones. They work well, and seem to provide a good load ratio to the car's weight. I ran the car on my shaggy carpet, and it has creases in it large enough that would normally cause a car this small to bounce around. The suspension soaks the bumps fine. This tiny suspension really is quite effective. But do put the soft springs in.


***
Please do not take my comments as disparaging. My aim only is to draw attention to the car's potential shortcomings, in the interest of improving the car, or helping others, or having someone prove me wrong and help ME understand better. This car is fantastic, really, and it causes one to wish it were perfect, given the fact so much engineering was devoted to such a small car. I would have killed for something like this when I was a kid, and it's still very cool as an adult. Now on to some questions I have for everyone...

1. I could not get the esc to setup properly, and I tried dozens of times. The directions claim that, after the red light stays on and the green light goes out, to pull the trigger all the way full-throttle until the green goes on and the red goes off. Then move the throttle full reverse until the motor beginss spinning in reverse. This never worked for me, and the car only seemed to run well after I turned it off and just turned it back on, without attempting to set it up. Even then, reverse never really works well (full forward works fine, but it just sputters in reverse, and very slowly). I tried every combination of throttle-channel reversing, messing with the throttle trim, and so on. I am suspecting that the radio I'm using (I'm using an AM airtronics blazer temporarily) is just not compatible with the receiver, as I notice people are having good luck with Futaba's and those Perfex ones that come with mini-z's. What do you all think? Is the red light supposed to come on during full forward throttle, which mine does, or is the green supposed to, as I would have expected? Perhaps the esc is accidentally wired backwards to the motor (I can't tell, since the motor doesn't have any marks to distinguish between + and -)?

2. After 3 batteries, I burnt out the motor. I noticed it got very hot, but just ignored it as nobody seemed to have any problem with this. There is an enormous amount of clearance between the long side of the armature and the motor's bushing, but I figured this was just sound engineering as the motor easily could bind if the alignment was not perfect (which it can't be, given the fact the shaft is so long). What do you all think about this?

Thanks for your time,
Bravin Neff

Russ
12-07-2002, 07:48 PM
Just making sure of one thing kinda... What did you do to adjust the caster on the car?

My car came with the diffs too tight too (grab a wheel & the whole drivetrain spins). If you look inside there are screws to loosten or tighten the diffs. Play with that a little & you can set em up so they aren't slipping, but they are smooth as mayonaise.

Bravin Neff
12-07-2002, 09:23 PM
Just making sure of one thing kinda... What did you do to adjust the caster on the car?

The lower front a-arms can be flipped, meaning it is mounted upside down. This changes the caster. Thus, there are only two caster angles available: the stock arrangement and this flipped one. I guess I'm not a hundred percent sure this is supposed to be an option at all, but I don't see why it wouldn't be. The hinge portion of this lower a-arm is symmetrical, so flipping it has no affect on how it swings on the hinge pin. Even the suspension spring mounts the same.

My car came with the diffs too tight too (grab a wheel & the whole drivetrain spins). If you look inside there are screws to loosten or tighten the diffs. Play with that a little & you can set em up so they aren't slipping, but they are smooth as mayonaise.

Yes, I've adjusted the diffs. The adjusment works very well, too, except that it doesn't affect the elliptical motion I spoke of, if that's what you have in mind.

Anyway, it's a fantastic car just the same. Unbelievable how feature-ful it is for this size! I checked out all the other cars... mini-z, kawada, abc, and so on, and while they all seem to have nice features, this one just takes the cake.

Incidentally, I managed to put together a proper pivot-ball steering system on the car -- and relatively easily, too -- after visiting a lhs and using some tiny rc airplane parts, and following some queus I've seen that others have done elsewhere on the web. It tightens things up nicely, and appears to have zero bumpsteer. I'll try to post some pics fairly soon!

I've also discovered a way to tighten up the chassis, involving the motor mount and the front diff mounts. If you look, there is clearance between the esc and servo, above the motor shaft, for a small piece of carbon fiber to stretch between these mounts. I'm going to fashion one in hope of solving the front broken-gear problem, which I've already experienced after one day!

I love this thing, though. Amazing.

Regards,
Bravin Neff

Russ
12-08-2002, 09:28 AM
K, you actually did it the right way LOL I hear people talk about "look at the caster my car has" and the unscrewed the bottom ball joint for the wheel hub & I'm all like, hey man, that is camber ;)

Thanks alot for the huge review man, enjoyed reading it!

Bravin Neff
12-09-2002, 10:52 PM
By the way, here's those photos I mentioned.

Bravin Neff
12-09-2002, 10:55 PM
And another one...

Here's a teaser... I'm also working on the mother of all mini-x modifications, one that anyone should be able to perform, and one that I believe any mini-x owner will not want to be without. But before I can finish, I need some help. Can anyone direct me to some sources where I can find gears that have an I.D. appropriate for these 130 sized motors? I'm particularly looking for ANYTHING between 20 and 60 teeth. Do such gears exist?

Please help!
Regards,
Bravin

dtmracer
12-30-2002, 01:12 AM
hey, good job on the steering. you asked about gears for the 130 motors. tamiya mini 4wd plastic gears work great. but they dont make them up to 60 though. they might make them up to 30 max to my knowledge. 60 would seem way to big for these little buggers. o and you mentioned excessive play in the wheels of the car. i noticed this also and there a a very easy way to fix this for about 2 bucks. go to your local hobby shop where they sell 1/10 rc parts and buy a "motor shim kit". these are super thin and super precise washers. i put one on each rear wheel behind the little wheel pin. and for the front, one on the inside and one on the outside, behind the pin. this takes out a ton of play. hope this helps

Bravin Neff
12-30-2002, 02:17 PM
hey, good job on the steering. you asked about gears for the 130 motors. tamiya mini 4wd plastic gears work great.

I've read about these, but haven't found any on the net. Can you direct me to where I might find some?

o and you mentioned excessive play in the wheels of the car. i noticed this also and there a a very easy way to fix this for about 2 bucks. go to your local hobby shop where they sell 1/10 rc parts and buy a "motor shim kit". these are super thin and super precise washers. i put one on each rear wheel behind the little wheel pin. and for the front, one on the inside and one on the outside, behind the pin. this takes out a ton of play.

Good idea. I did something similar, it helped a lot. The thing runs much more predicatably now.

Regards,
Bravin Neff

dtmracer
12-30-2002, 03:43 PM
i get my mini 4wd gears at ultimate hobbies in orange california. i know that you can order over the phone. their phone number is (714) 921-0424.

Bravin Neff
12-31-2002, 06:54 PM
Cool, man! Thanks for the info.

Regards,
Bravin