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  #1  
Old 03-16-2004, 03:27 AM
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4WD shaft mod + 180 motor mount

Finally got it done. A bit gruelling and I still think there are one or two issues to work out, but it seems to work. Mostly there is still a bit too much rolling friction for my taste (w/o motor installer, just the friction of rolling with the shaft). I think that it is mostly the shaft alignment/leveling. It's mounted using the front shaft mount and ball bearing, but in 3 places. Theres a hole by the ESC switch (which I had to move) that I mounted the middle shaft bearing at, and the I made a new hole at the end right where the rear diff is for the rear bearing.

After running around in my small kitchen, it runs REALLY well. The 180 (stock HPI) got warm, but I don't think near as hot as the standard mini-x 4WD motor would have gotten. I tried touching the fets and they seemed a little warm too, but I hadn't checked the before so I'm not sure if that was abnormal. I'm a bit worried about the ESC running the 180 with the rolling friction. It ran fine for my testing (5 min or so), but I'm not really sure how it will hold up over time. I also got a bit of glitching (seems to happen in my kitchen).

So I've got some questions:
1. Should the stock ESC be able to handle the 180, taking into consideration the extra resistance from the shaft rolling friction?
2. From the wiring, could the locations of the various wires be causing any of the glitching? (hasn't really been a problem in the past, but the motor location/wires are new. I had the antenna fully extended)
3. Are there any early warning signs of the ESC getting into trouble so I can hopefully save it if this configuration turns out to be too much for it to handle?
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  #2  
Old 03-16-2004, 03:28 AM
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driver side
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  #3  
Old 03-16-2004, 03:29 AM
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back that a-- up
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  #4  
Old 03-16-2004, 06:59 AM
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Re: 4WD shaft mod + 180 motor mount

First off, congratulations on succeeding where others have only talked! Try tweaking the tightness of the mounts (1/4 turn at a time) to see if you can get it smoother.
Quote:
Originally posted by cdog4w


So I've got some questions:
1. Should the stock ESC be able to handle the 180, taking into consideration the extra resistance from the shaft rolling friction?
the stock esc should handle any of your mods on their own, but you've got a combination of 4 or so mods that could fry it. Increased resistance, both from the shaft , and the bigger wheels (you are running OL tires, correct??), a bigger mod, and 6 cells with over 7 volts could well add up to a fried ESC.

Quote:

2. From the wiring, could the locations of the various wires be causing any of the glitching? (hasn't really been a problem in the past, but the motor location/wires are new. I had the antenna fully extended)
It's possible, I see motor has 3 caps, so not much interference there, you could twist the motor wires (like a pigtail, to cancel the noise out) and the servo/receiver wires.
Quote:

3. Are there any early warning signs of the ESC getting into trouble so I can hopefully save it if this configuration turns out to be too much for it to handle?
Try testing with the wheels spinning in the air (either lift it off the ground/ place it on a box, whatever works) run it for a while and see if the ESC gets hot really quickly, that glitching is not good news, I don't know if it's radio noise in the environment, or the cry of tortured stock electronics...

Keep the aerial wire well clear of the ESC and motor, if you've a tube, wrap it in tape for extra protection.

I'm sure there are plenty of boffins who can throw more light on this, well done again on a great Mod!!!
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Last edited by Cian; 03-16-2004 at 07:11 AM.
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  #5  
Old 03-16-2004, 10:21 AM
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Thanks for all the advice. For question three you said to run it in the air for a while to see if the fets get hot. How long do you think would comprise a good test? 5 min of straight full throttle?

Unforunately, if I loosen the shaft mounts too much, they wobble a bit, so I've got a finite amount of play. Hopefully the sweet spot is in that range though, it'll just take lots of screwing and rolling :P

Yes they are OL tires and that is a 6 cell that when fully charged gets up to just under 8V. What do you think of my chances with the stock 5 cell pack and the rest of these mods?

As for the interferance, I'll run a test outside today when I get home from work and hopefully figure out if its really a problem or just my kitchen.
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  #6  
Old 03-16-2004, 10:40 AM
mde mde is offline
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Nice work cdog,

That's what I was planning to do with my Mini-x but don't have time for as I'm 2 weeks away from the final exam in a night class I'm taking.

What did you use for a shaft? I was using a 2 mm bicycle spoke but it is slightly too big to fit the stock drive shaft bearing on.

Could you change the stock fets with larger ones or relays or some thing to rectify your concerns with the ESC?
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  #7  
Old 03-16-2004, 10:48 AM
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Quote:
Originally posted by cdog4w
Thanks for all the advice. For question three you said to run it in the air for a while to see if the fets get hot. How long do you think would comprise a good test? 5 min of straight full throttle?
Yeah, that should be more than enough. Watch it like a hawk though, just in case. If you're getting nothing, try for longer, like draining the batteries
Quote:

Unfortunately, if I loosen the shaft mounts too much, they wobble a bit, so I've got a finite amount of play. Hopefully the sweet spot is in that range though, it'll just take lots of screwing and rolling :P
Yup It's gonna be a real case of trial and error, I'd suggest starting with them all good and tight, then loosen each a 1/4 turn at a time, till you're happy..
Quote:

Yes they are OL tires and that is a 6 cell that when fully charged gets up to just under 8V. What do you think of my chances with the stock 5-cell pack and the rest of these mods?
Well yeah you're definitely improving your chances, I guess. I'd still bench test first, though.
Quote:

As for the interference, I'll run a test outside today when I get home from work and hopefully figure out if its really a problem or just my kitchen.
Hopefully that's all it is, all those appliances can create noise when they're plugged in...
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Last edited by Cian; 03-16-2004 at 10:54 AM.
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  #8  
Old 03-16-2004, 11:49 AM
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Thanks again Cian.

mde, good luck on that final. Ironically, my fiance having finals is what gave me the free time to do this :P As for the shaft, I'm using the shaft from the burned out mini-x 4WD motor. I stuck it in a vice and hammered the armature off (it was resting in the vice so that the armature was holding it up - the shaft was not viced in and was free to move while the armature was not). So its the perfect length and diameter. It shouldn't have warped either since I was only applying force along the length. BTW, I tried 2mm tube and the shaft from the motor is LARGER. Are you sure that spoke is 2mm? I think the diameter of my shaft is 2.5mm, maybe go check the forums for the inner diameter of the shaft bearing? Anyway, I ordered extra shaft mounts and shaft bearings from tiny and used the beige gears from the tamiya mini-4wd kit. I'd recommend getting some 2mm washers to shim the motor mount to ensure proper gear mesh. I can give more details if anyone is interested.

I found a place that sells mini-x fets (the 30100's) for $4 a pair. My question is what will this change the capability of my ESC to? Will it up my A handling by 50% or is it not a linear scale? Is A handling even the number I'd be worried about in this case? I've heard that the stock v2.0 mini-x ESC handles 8A, but I'm not sure if that was continuous or peak.

My other question was about installing the fets. There are three legs on each, and there are two empty spots on the ESC. I think 4 of the 6 holes look filled in, should I just hand drill those out (or use a needle, etc) to make room for the fet legs?

Thanks.
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  #9  
Old 03-16-2004, 07:24 PM
mde mde is offline
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Hi cdog,

I just checked some spokes, the are 2.00 mm and the armature from my Mini x is 1.98 mm .02 mm however is well beyond the +/-.005" accuracy of a good digital caliper like a Mitotoyo, mine is digital but it is a cheap piece of crap.

I can't measure the bearing ID because it is too small to do accurately with a caliper, a plug gauge is needed.

I hope some one can answer about the fets because I expect I'll be needing to add them to my car in the future.
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  #10  
Old 03-16-2004, 07:50 PM
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wacky. I'd swear the 4wd shaft is thicker than the 2mm rod I got at the hobby shop. No calipers here so I can't say for sure and holding it up to a ruler just won't work :P

Yea, so hopefully someone who has mucked with the fets will speak up.
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  #11  
Old 03-16-2004, 09:18 PM
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Just ran it outside, it was awesome :P I had 3 problems, but none of them were the motor or fets heating up. I ran it for about 10 min on my 6 cell with small stop intervals to right the car after a roll or to pop a tire back on track. No glitching either, apparently my kitchen is a sanctuary of electronics evil.

Problem one: traction rolls. dramatic, beautiful, traction rolls. Can anyone suggest suspension/diff settings to reduce this? I'm at a double disadvantage due to the high motor CG and the larger OL tires I'm running (almost nec. to run smooth(er) on this nasty asphalt). I'm currently running soft springs and slightly tight diffs.

Problem two: need to find a new way to keep OL tires on the rim. Edges kept popping off (mostly whenever I rolled). Right now I have some 3m foam tape inside that the OL tire fits over and its a pretty good fit.

Problem three: the most easily and already fixed, dropped the screw that connects my steering linkage to the servo.

Seriously though, it gets up to speed in no time and assuming you don't hit a hard turn at full speed, it runs very well with minimal rolling. On slightly smoother chunks of asphalt, I was able to spin out and of course do plenty of donuts. Such a shame its already dark or I'd head back out since I replaced the screw that brought me in.

I'm excited by the idea of being able to change my gear ratio at the motor instead of the diffs, and by shimming the motor mount up or down, it should be easy to ensure a good mesh as long as the gears can mesh. I think I want to go for higher speed since I apparently have plenty of torque now.
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  #12  
Old 03-16-2004, 10:23 PM
mde mde is offline
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I'm really glad to here that motor is working out well since it looks exactly like the one sitting on my desk beside the x.

2 of my suppliers have avariety of different shafts and axles I can use including some made of carbon. Once this course is over I can get to what's important.

Moding my X, finishing my RTTT and starting on my other TT projects. Actually about the only thing that will be Race Tin on the RTTT is the PCB and controller because I fried my Mini Z pcb:(
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  #13  
Old 03-16-2004, 11:02 PM
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RTTT? Carbon shaft would be cool too :P
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  #14  
Old 03-17-2004, 01:26 AM
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RTTT is what I call my Race Tin based Trials Truck. It will be a low speed 4wd version of an Overlander. Since we are doing another mini x order next week and I'm not that far into it yet it is likely to be more mini x than Race Tin.

The main focus is high manouverability. The steering system will have a ridiculous steering angle and of course in true TTTT form it will have good articulation but it will not be a tacky looking monster truck.

Wheels sticking out the sides will be another project.
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  #15  
Old 03-17-2004, 09:19 AM
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Re: 4WD shaft mod + 180 motor mount

Quote:
Originally posted by cdog4w
Finally got it done.
Nice!!!

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