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  #1  
Old 06-13-2003, 09:40 PM
WillS WillS is offline
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Lightbulb Carbon Fiber Chassis

So far Im workin on a chasis design. and all the parts and part number through local big dealers (Tower hobbies,omnimodels mainly) on what to use. On the motor mount IM not sure if I can get that seperate or if a modified dtm x4 will work. so far conversion ( minus chassis) is under 20$. Great deal if I might add. On my version of the chassis Im lookin at tc3 style (haha I loved that car, but hey racing motorcycles is more fun than lil cars ) and on the chassis cuttin Im havin question..... unsure on how much flex I should have in the chassis and stuff like that. So Im lookin for ideas on cutouts in the chassis. Also should I set the batteries low in the chassis to allow for lower cg? should I make the motor sit lower too? LOL these are all problems Im lookin at. right now on batteries I have located some .67x1.14 1000ma 1.2. Im lookin to run 4 side by side style on the left side of the frame. Currently runnin stock receiver and a lrp quantum with reverse (small and dependable so far- Always LRP when I run r/c). so any ideas you have (If you can in english please) email me on question or pics of the drawings so far for chassis design. email Me



Will post a pic later of template on chassis. hopefully I can cut these bad boys out in mass on my friends laser machine for cheap costs
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Old 06-13-2003, 11:50 PM
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Cool, WillS! Yes, sink the cells and motor as much as possible, but don't short them out on the CF! Keep us posted on this!
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Old 06-14-2003, 11:01 AM
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motors?

ok ok came across the idea of throwin in a elite mod orion rs4 micro motor in it. Should I make 2 version chassis or just use the big motors or just the mini-z motors........
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Old 06-14-2003, 08:38 PM
WillS WillS is offline
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Batteries

Ok so far I picked up the batteries (Thanks to those gurus at Batteries Plus Link for info ) I decided to do a 4 cell (part number nt100afh) 1000mah 1.2 batteries hehe. long runtime yeaaaaaaaaa. Ok so now I need to go with motor idea to figure out HOW much room I will need. Come on guys makin me do too much thinking, havent done this much thinking since I had to run the first Atlas ym-34 in northern california.
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Old 06-14-2003, 08:39 PM
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3series takumi 3series takumi is offline
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just make 2

go for both, i cant wait to see either on of them. especially tc3 style! make sure you leave some instructions
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Old 06-14-2003, 09:01 PM
WillS WillS is offline
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instructions

Instructions? uh what are those? LMAO Might work on making some instructions but come on its simple :P all I would need to really do is put the part numbers and order them up, question on the suspension ( easy for me hard for you) was just gunna put it on a belt sander and grind off the old chassis. but I dont think everyone has access to a belt sander 2 chassis I shall hopefully there is room in the micro rs4 for everything Mini-z motor is plenty of room..... updates later...................
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  #7  
Old 06-15-2003, 04:32 AM
Hooters Driver Hooters Driver is offline
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These are some of my thoughts on building a custom mini-x chassis:

Since the mini-x has 4 wheel independent suspension the chassis should be as stiff as possible. You want the suspension to do the work, not the chassis.

Another reason for building a stiff chassis is due to the long motor shaft. In my opinion, chassis flex is one of the reasons the stock mini-x motor runs so hot.

The other reason the motor runs hot is due to the front dog bones binding up. This problem definitely should be addressed if you want maximum performance from your mini-x. I've worked on this quite a lot and it's a very fine line between free rotation throughout the entire supension travel and having the dog bones falling out.

In my opinion, the whole purpose of building a custom cf chassis is to save weight. With that in mind it seems to me that running 1000 MAH batteries would be counter-productive. To save weight one thing you might consider is running lithium-ion or lithium-poly batteries. That way you get the high MAH rating and still keep the weight down. The challenge with lithium batteries is finding a large MAH battery narrow enough to fit between the motor shaft and the body.

Since batteries are the heaviest component on the car they should definitely be placed as low as possible. If you run out of room and have to stack components then the receiver should be the first thing to go up top, next would be the speed control. If at all possible the batteries and motor should be the lowest components on the car.

Another weight consideration is where you place the heavy components. I race circle-track cars and we practice the rule of the 3 Ls during car construction - low, light, & left. Unless you run your mini-x on an oval the left may not apply to your car but you should still consider your track when building the car. If you run counter-clockwise (more left hand turns) the heavy components (batteries and motor) should be on the left side of the chassis. If you run clockwise the arrangement should be just the opposite.

One final thing to consider is the motor. Because its shaft is placed parallel to the centerline of the car, the torque of the motor causes the car to be loose when turning right and tight when turning left. If you use shaft drive like the dtm it will allow you to mount the motor perpendicular to the cars centerline (similar to a mini-z) which will eliminate this bad handling characteristic. Depending on which direction you spin the motor it can also affect weight transfer which can help tune the car for your track.

I hope you find some of these tips helpful or at least thought provoking. Good luck on your custom mini-x.

Last edited by Hooters Driver; 06-15-2003 at 07:41 PM.
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  #8  
Old 06-15-2003, 09:07 AM
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Here's a car made like you want by another user

http://www.tinyrc.com/forums/showthr...&threadid=6484
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  #9  
Old 06-15-2003, 03:01 PM
WillS WillS is offline
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battery/motor placement

Ok your points are taken, but after reviewing all the 4wd cars out there, batteries are all on one side. But as far as I can see its the only way to get a good amount of power for the battery/motor placement that way. I am kinda wierry (?sp) on soldering/charging li-ion batteries but I will lookin to that.

On motor placement, now I havent seen steering problems on the tamiya or tc3. And not not really sure how I could place it any other way without a whole lot of machining.

*added info.... ok ok on batteries I will work on some cell phone or flat cell battery. It still will remain on one side. Also lookin at a suspension setup. not springs more like the shocks. but I will need to machine some shock towers (oh god its gettin complicated). ok I decided chassis thickness with me 1 - 1.5mm and I decided to make a top plate (damn it with this complication) oh well lol should make for some better competition for the micro rs4s hehehe smaller, lighter and faster (hopefully)


oh yeah I need the size/quanity on the screws ( I hate phillips heads for the life of me when they are this small ) Im lookin to get some allen head screws.
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Last edited by WillS; 06-15-2003 at 06:34 PM.
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  #10  
Old 06-15-2003, 06:43 PM
Hooters Driver Hooters Driver is offline
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I think the batteries should all be on one side but which side depends on the layout of your track.

I have done a lot of research on charging lithium batteries. The two major concerns with lithium batteries are that you don't charge them above 4.2 volts per cell and that you don't exceed a charge rate greater than 1 time their MAH rating (e.g. don't charge a 1020 MAH lithium battery faster than 1020 MA). Because of those two factors they are a little more tricky to charge but if you use a good quality charger specifically designed for lithium batteries you shouldn't have any problems.

If you use lithium-poly they come in a soft case which will vent in the event of overcharging instead of blowing up. That is the same way that NIMHs are designed, therefore the li-polys should be almost as safe as the nimhs.

With a li-poly you can get two 1020 MAH batteries for about $20. The pair will produce 7.2 volts and only weigh approximately 41 grams.

Two more important things to consider when choosing batteries: increasing voltage will increase the power output of the motor, increasing the MAH rating will increase the run time of the car.

Here is a comparison chart between nimh, li-ion, and li-poly batteries:


Battery  # of Cells  Voltage    Weight  MAH Rating
nimh       &nbs p;   4    &nbsp ;    4.8   &nbs p;     50 gms       &nbsp ;750
nimh       &nbs p;   6    &nbsp ;    7.2   &nbs p;     75 gms       &nbsp ;750
li-ion       &nbsp ;   2          7.2   &nbsp ;     52 gms      1020
li-poly       &nbs p; 2      &nbsp ;  7.2     &nbs p;   27 gms       &nbsp ;660
li-poly       &nbs p; 2      &nbsp ;  7.2     &nbs p;   41 gms      1020




Now on to the motor problems. I have never driven either of the cars you mention but I have driven a futaba 1/20 scale indy car (it also has a longitudally mounted engine) and it suffered from the same problem as the mini-x. If you look back through the mini-x archives you will find a past discussion of the loose/tight condition I have described.

You can correct this problem with chassis tuning but it is difficult to get equal left and right hand cornering when you are fighting the motor (handling will change significantly depending on whether or you are on or off the gas). It makes much more sense performance wise to use the torque of the motor to increase rather than decrease traction.

I realize it is difficult and would require more fabrication to fit the motor on the chassis when lined up that way (probably impossible with a 180 motor) but a perpendicular motor placement should allow for a better handling car.



Re: Added info

1.0 mm will probably be thick enough if you reinforce it with a top plate. I am currently using .030" (.762 mm) cf for a mini-z/mini-x hybrid project I am working on. It is very thin and flexes a great deal but this car has a solid rear axle so I am using the chassis flex as my rear suspension. On a past project I used .060" cf (1.52 mm) and it had absolutely no flex in it.

Last edited by Hooters Driver; 06-15-2003 at 07:27 PM.
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  #11  
Old 06-15-2003, 09:39 PM
WillS WillS is offline
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Ok on batteries. I happen to open up my lil cell phone and to my surprise eh 3.6 li ion. noticing in the design by uoi he has 2 3.6 600mah li ion stacked ontop of each other.

motors....... well Im sticking only with a mini-z motor. but I located a mount inorder to mount and easily change motors. Will be purchasing these parts and giving reviews on the parts and specs on how they fit in the chassis.
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  #12  
Old 06-16-2003, 01:47 AM
Hooters Driver Hooters Driver is offline
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I am currently running a pair of 1020 mah li-ion batteries stacked on the mini-zx project I previously mentioned. I purchased those before discovering the li-poly batteries. I got them off of ebay as a pair of cell phone batteries for $4.20 each plus shipping. I removed them from their plastic case to save weight, removed the overload protection circuit (you may want to leave this on just to be safe but most r/c lithium chargers are designed to charge without this circuit), and then soldered them together to make up the pack.

In my opinion li-poly is the better choice. I just purchased 4 of those to play with in different projects I am working on.

This is the cheapest source I have found for li-poly cells:

Bishop Power Products

Last edited by Hooters Driver; 06-16-2003 at 01:57 AM.
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  #13  
Old 06-20-2003, 03:31 AM
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Quote:
Originally posted by Hooters Driver

In my opinion li-poly is the better choice. I just purchased 4 of those to play with in different projects I am working on.

This is the cheapest source I have found for li-poly cells:

Bishop Power Products
How long the run time u have with that Li-Poly?
Thank you.
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  #14  
Old 06-20-2003, 12:30 PM
WillS WillS is offline
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Oh time for fun to begin

OK OK good news parts are in though further thinking carbon fiber and am band freq arent a good idea I decided to go with 1mm fiberglassed resin plastic similar to that other guy with the blue chassis. The gears I bought look like they will work marvelously.

Tower hobbies part numbers:
(2) tamw1832 - gear set
(2) tamw1936 - gear set
(2) tamw5285 - gear set
ok ok I bought 2 of each due to the fact each is a different sized gear mmmmm different gear ratios. Only used on gear outta the bags though will place the gear size when I count them up.

Currently workin on top plate and how to lighten up the chassis. batteries I have located for 28$ + shipping (1020ma 7.2v 1.5oz) ASSEMBLED through Hooters link. Thanks bro.

Currently lookin at this motor plate i picked up I believe it should work well. Will see when I have it all mounted

Will post pics of how it looks on the stock (stripped to hell) chassis for the drivetrain (if I dont make a top plate I could see massive bindin in the shaft if any flex is involved)

Still lookin into to shock ideas. Any help on sizes would be great.
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  #15  
Old 06-20-2003, 06:16 PM
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3series takumi 3series takumi is offline
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just to add a note about the handling and the motor. the rotation blah blah of the motor isnt enough to change the handling too much and can be easily adjusted by turning the droops screws. i had the problem of spinning out in one direction and not in the other, a turn or two on the droops screw of the rear suspension fixed it and it now handles perfectly in both direction even with non-smooth throttle input around the corner. hope that helps

oh and also mounting the motor to the side of the drive like the tc3 counters the effect cause you have the motor spinning in one direction and the long shaft in another (just thought i should add that
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