Custom MRC X Chassis Suggestions Please.

[makakoa808]

Here is my custom made MRC X Chassis.
Still very much a prototype I'd like to make it better any suggestions would help.
Currently it allows 3 postiions for mounting the shocks..
Not sure what the Benefits would be on the diffrent postiions it only raises it a little higher.
But I'm guessing the angle of the shock also makes a diffrences.
(Sorry I just started crawling dont know all the details of making a better crawler yet.. lol)
Ive also added a lower body mount option again it's not much lower...
but any lower and the body starts hitting the chassis.
Again this is very much a prototype.. Any suggestions to make it better
would be much appreciated..

Here are some pics below.

MRC X Chassis with Stock chassis in the middle


MRC X Chassis Shocks Mounted on Last Hole


MRC X Chassis Shocks Mounted on First Hole


MRC X Chassis Shocks Mounted on First Hole Angle View


MRC X Chassis With Body

[TAT76]

Good work man. I can't tell you anything about the angles yet as I'm new to but think the shocks should be mounted on the inside for better performance. Also make some small spacers so the shocks are at an angle like stock. Maybe make some cross braces for support.

[engineerjoe]

Looks good for a first try.
it looks like you just copied the stock geometry and added more shock positions.

My suggestions:

1. make multiple upper link positions (a little lower would be good, this will add anti-squat)

2. make it look a little different. Reverse engineering (copying) is looked down upon. Yes the "X" thing is cool but doesn't add any functionality to the design.

3. Add a hole(s) up near the top where people can put a cross brace and add a crossmember and some vertical body posts.

Did you do this in CAD? How were the plates cut out?
if you did it in CAD I would suggest that you make some mock axles and links and start playing with the design on the computer. A little tweak can make a huge difference on how a rig performs

Edit: moving the shocks to the outer positions will make it have less flex, but the shocks will have a better mechanical advantage (higher effective springrate and damping)

[makakoa808]

Thanks for the input it's much appreciated..
So having the option of setting your shocks vertical is not worth anything..? It's better to have the shocks at an angle..

I do X-pect some major changes to the MRC X Chassis. this first one was
made mainly to make sure everything matches, screw and mounting holes.

Can you explain with a little more detail why the Y link should be mounted lower on the chassis?

I'm not using CAD I'm using Corel Draw. And I take it to a CNC shop to cut.

[makakoa808]

Ok so here is an updated design.. any thoughts..
I call it the X3 chassis.. because it has 3 options
where to connect the Y link, the shocks and body mount.

[engineerjoe]

Originally Posted by makakoa808

Thanks for the input it's much appreciated..
So having the option of setting your shocks vertical is not worth anything..? It's better to have the shocks at an angle..

I do X-pect some major changes to the MRC X Chassis. this first one was
made mainly to make sure everything matches, screw and mounting holes.

Can you explain with a little more detail why the Y link should be mounted lower on the chassis?

I'm not using CAD I'm using Corel Draw. And I take it to a CNC shop to cut.

Well, having the shocks CAN be a benefit, it really depends on what the drivers preferences are.

mounting the Y-link a little lower will increase the amount of anti-squat in the suspension geometry. Basically it will keep the chassis level when torque is applied at the tire patch.

Originally Posted by makakoa808

Ok so here is an updated design.. any thoughts..
I call it the X3 chassis.. because it has 3 options
where to connect the Y link, the shocks and body mount.

It looks good, but the holes for adjustment are too far apart. only small adjustments from stock are really needed to make the MRC run very good. The holes you have on this one will move the shock and Y-link too much.

[engineerjoe]

Try something like this:
Notice the curved lines are changed to straight edges (just for looks)
The holes are far enough away to change the characteristics of the chassis but not too much that you can't tune it in to what you want.

[makakoa808]

Originally Posted by engineerjoe

Try something like this:
Notice the curved lines are changed to straight edges (just for looks)
The holes are far enough away to change the characteristics of the chassis but not too much that you can't tune it in to what you want.

Cool apreciate the drafted image... hmmm looks like it's time to redo the design... Ability to finetune got it... Thanks for the advice..

[makakoa808]

I'll have to tackle the 4 link connection later.. but here is my new chassis design.

[makakoa808]

Any one got pics of a MRC 4 link setup?
I know I can do a search but if anyone is willing to post will save me some time...

[punkuup5150]

that biohazard chassis looks awsome! i would almost add some more material to the shock mounts and add a second row of mounting holes and also the top links could allways use a second row of mounting holes. looks good more ajustability is allways better

[picklewagon]

That x-3 chassis seems dangerous. I'd crash into a judge and cut him bad for calling my rollbacks as reverses!

[RCMFMaxxMan]

good start! I think what you will benefit the most from is just getting some prototypes cut out and actually testing them. Also figuring out first hand how moving a shock position or a link position really effects the handling of a crawler.

One piece of advice that i will offer (and i don't know if it is correct but it is my personal preference and as a science minded guy, i feel like this should be the way all chassis are)...
I like when changing a mount position will ONLY effect one variable. In science when conducting an experiment, to have complete control, you should never alter more than one variable at a time. So on that note, For the MRC, their is only one option for mounting shocks and links on the axles. And the way your chassis mounts are set-up (and a lot of mounts on after market chassis are this way actually), is that the mounting points are at all different distances from the axles mounting point. They will always be all different distances as long as the mounting points change in a straight line formation. This means that more than the geometry will change when making adjustments. For example, as you mount the shock further in the chassis, your geometry will change (good, that's what you want to happen), but your ride height will also change because the shock is mounting deeper (bad, for one because then you are messing with two variables at a time and you should really only change one variable at a time to dial in your performance, and two because if you feel the need to change the ride height, you can do so by other means dedicated to changing ride height, such as changing shocks or adding spacers to your current shocks). For the links, changing mounting position will change geometry (good) but will also change the caster (pinion angle basically but more technically and equally important, it is the angle of the steering block when look straight at the face of the wheel) because mounting the upper link further down effectively pulls the axle in but only at the top so it is actually rotating down and bringing the pinion angle down (bad).

For both these issues, there are two solutions:
1. everytime you mount your shocks or links to a different hole, you change the length of the shocks or links to compensate for loss or gain. This could get very labor intensive if you change your mounting positions often or at least a few times to dial in your rig. It could also get spendy if you end up needing to purchase longer shocks or links to maintain the current dimensions.
2. When designing the chassis, design it so that changing mounting positions will only alter the geometry. to do this it is very simple and to me it takes out some of the guess work on mount positions. In your cad program, locate the mounts on the axles. draw a line that is the VIRTUAL length of the shocks or links when viewed from the side. (when viewing from the side, a line that is parallel to your eyes, it appears to be the real length. But notice as one end of the line gets further away or closer to you, it appears shorter (talking 2 dimensional here). This shorter length is the virtual length. It is important and hard to understand why without getting hands on or just being very geometrically minded.) Anyways, the virtual length is easy to find in CAD by drawing an isometric drawing (a top view of the links transfering to a side view.) Next take these lines that represent shocks and links and "mount" them to the "axle" in CAD. Always keep them there and just rotate them slightly and mark each point as the top of the "shock" or end of the "link" changes. These are viable points for mounts. You will end up with arcs (one for the shock and one for the link) with the centers at the axle mounts and the virtual lengths of the shocks and links being the radii for these arcs. You should only have one arc per shock or link. You can also get close to this method by placing mounts along a tangent of these arcs (some designs do this) and you will minimize other variable changes. But while you are in CAD, you might as well just draw out the arc and ensure that your axle will remain in it's original position throughout changing mounting points. Now this is all considering you neglect how the shocks will change behavior as their angles change :P haha but that would get into some intense calculating that i don't know about and probably wouldn't offer very much if any improvement.

So that was long winded but it is a concept that is very helpful to me and i think it should be helpful to you if you can make sense of my ramblings. haha. So much of this stuff is visual and hard to explain in just words. good luck! i'll watch your progress and chime in when i can.

EDIT: one more thing. consider weak points such as near holes. For small holes like for 4mm or 3mm or 2mm or whatever size screws, i generally try to make a ring of material around the whole that is equal to the radius of the hole. For autocad, it's easy. Just draw the mounting points, offset all the mounting points with a distance equal to the radius, connect the tangents of these circles around the mounting points, trim circles, fillet corners, cut out unnecessary material and voila!
Also braces between the tops of the two plates is important (as stated by someone previously). The stock skid is not very rigid and the plates will flex too much.

[makakoa808]

Ok how does this look..?
The shock mounts can be lowered or raised to desired height.

The screw that mounts the shocks will also serve as a brace, going
across to the other side plate.

Having the shock mount holes at an angle helps with not changing the
ride height but I does still change a little. My concern with the shock
mounts angled up is that it will require you to cut holes in the body.

I know the design is very diffrent from whats out there... But the
beauty of this design is being able chance out the shock mounts

As you see in the image there is a straight and an angled option.
Maybe in the future have one with a 4 link option...

Any thoughts??

[engineerjoe]

looks like a great setup to start learning about chassis designs. Play with the link/shock positions snd find out what works better in different situations.

I like to think of the chassis as one big bracket that holds everything in place so it can work correctly.

[RCMFMaxxMan]

lookin better and better each time It is kind of a long the lines of the Losi Comp Crawler's chassis which has mounts like your but they pivot rather than move up and down. I don't think you should worry too much about the chassis ending up too tall. It looks pretty safe to me. Also, people will drill body mounting holes appropriately if they decide to use your chassis. And if they are using the stock body with the stock mounting holes, from looking at your body mount points, even on the lowest one, the body should clear the shock mounts just fine! The stock body has about an inch of clearance from the chassis. Although if you are concerned about it but still want the shock mounts angled, you could design the chassis for using shorter shocks. A lot of people are seeing improvements from shorter shocks anyway. But I think the adjustable shocks mounts is a good way to go. I don't believe there is an after market chassis out there with this option for any axle. This actually even crossed my mind when i was designing my chassis but i opted for less parts and screws. I'd say cut one of these out and test out every mount option and from there you can probably determine if some of the extremes are too extreme (like no one would really need them) and then you can reduce some of the holes to make it simpler. But having this many options for testing will probably be good for you, especially since you are just getting started in chassis design. You will be able to test a LOT of different shock geometries and get familiar with what adjustment does what and what works and what doesn't. happy testing

[Biggons]

I like the Losi logo, but watch out, it's a trademark logo. The latest design looks like it has plenty of adjustment, I'm just not sure about making the TVP's multiple pieces. Looking good though

[makakoa808]

I appreciate all the input... It is kind of a complicated design along the lines of having 3 parts... Which I'm not really loving.. but it's diffrent from whats out there and thats kind of what I was going for..

Thanks again for everyones input.. will be cutting and posting pics soon.

[makakoa808]

Ok got my MRC X Chassis, here are some pics.. I got it at the most extreme setting.. The highest high and lowest low possible with this X chassis.

[Mr. Ed]

I like the belly dragger How's it drive? I'd love to give you some advice but the guys that are helping ya are much more quailifiied. I do know this your MLST2 stuff is great ( wish I had some, but to broke for right now:-( ) and I'm sure this will go good. are you planning 4 link front and rear plates? or are you wanting just the tvp's to be your focus?