Mid motor car question

[SteveK]

Good stuff guys, how about the wheelbase on mid motor cars. How does this affect the handling? Should this car be a bit longer or narrower than regular?

I started working on it this week and will probable have something to show in the next 2 weeks or so. It is going to be more of an old school design (no comp for the modern ones like the S2 and X-6) but it might be able to keep up. I might be close to an Tekin conversion but nicer, IMO.

This is a pic of the design process. I am planning to use some hobby shelf part so I can repeat the car and I am making some custom parts like chassis and towers.

A longer wheelbase will make the car more stable. A mid-motor setup will make the steering much more responsive. It's a tradeoff; stretch the wheelbase so it handles more like a stock car and you might as well just leave it alone. You change the weight distribution to change the handling, so you'll probably want to keep it close to the stock wheelbase and see how it handles.

See if you can design in a set of holes for a slightly longer wheelbase, so you'll be able to play with it.

[Mr. ED]

how do you plan your front kick-up?
I would stretch the wheelbase to near legal limit if your track is low grip. For me the best benefit on the midmotor is how it jumps.
If I want livelier cars I shorten them.

[m_vice]

The front and the rear bulkheads are Traxxas, so the front already has the kick-up and with a top plate on I’ll be solid. I am adding a nice sit/bumper on it to make it smooth underneath ( I will make surer to start a new thread when the car is done with detail shots). The trick with the front bulkhead will be to play with different front steering hubs, like using the B3 to make it shorter. The bulkhead is longer than a 10T and shorter than a regular RC10 so we will see because I want to use modern B4 wheels. I think it is going to work out ok.

My question about the wheelbase I base on me trying to use a straight stick battery pack. If I max the wheelbase and play with the front steering servo I might be able to make it happen. If not I will have to mount it sideways or divide it in (2) 3cell packs.

I usually measure 10 times and cut once so I studying all the possibilities. The first car will probable be very prototype and I planning to get some new material if it works out and make a final version to keep the proto parts as spares.

Thanks for the comments. Any more opinions on the wheelbase will be very appreciated.

[Mr. ED]

Some ways to give yourself a little more space on the center of the chassis:
- use a low-profile servo or stand the servo up
- use a rack steering system , not swingarms (one of the oval brands makes 2 types)
- use swept-back front suspension arms so the front bulkhead can sit further forward and move the steering as close to the bulkhead as possible

[m_vice]

Ok, this is a test for fit. Everything looks good but it is going to have to sit for some time because I am waiting for material. I will start a new thread when I get all the parts made. Not sure where to start it, maybe under Vintage Non-RC10 Section / Other Makes/Models? We might need a new section for custom cars.

[Mr. ED]

Have you considered turning the battery configuration 90° That way they are a little more centered.

Just continue the threat here; it's nice to have all info and the history on 1 project in the same place.

[m_vice]

Yes, I actually have a bit of a different final design on the chassis with the battery that way. I will keep posting as the project move along.
Thanks for the comments.

[m_vice]

Ok, not a lot of progress to show but this is the status now. cut some partial parts and adapted an inverted B4 motor plate that would allow me to use the gear cover and it lets me slide the batteries a bit more to the rear.

I will add a top plate from the front to the middle of the chassis and some bracing from the tranny to the center of the chassis. I think I’ll have a nice rigid chassis.

More on this next time.

[markt311]

What's the wheelbase at on your prototype? It looks like it would be easy to tie some turnbuckles from the top of the trans down to the chassis in front of the batteries. It wouldn't be the prettiest thing but it would allow torsional flex while keeping the chassis ridgid front to back.

Looks really good so far.

[cmain]

I can't recommend the 4 gear setup enough it makes a huge difference. I converted a RC10GT with a 3 gear and it would unload the tires on exit of the corners but once I put a 4 gear in it hooked up just like a t4 would but still turns like mad. I love my mid motor monstrosity: D

To see what the motor is doing with a 3 gear take the motor out of the car and hold it in your hand then peg the throttle. Now imagine all that torque lifting the rear of the car as you try to take off it is not good. With a 4 gear it is the opposite all the torque is going back to the rear wheels adding traction.

There is a short vid of my truck at this link
http://www.oople.com/forums/showthread.php?t=32894

[m_vice]

I think I've seen your truck in the oopel forum. Very cool. I am thinking of getting a GT tranny and making one like that.

Ok, correct me if I am wrong. Adding the 4th gear will make me flip the motor plate making the motor rotate the same direction I have now.
With the set up like I have it now the motor rotates to the back giving the traction, like a X6 with the extra gear.

'm I missing something? LMK thank for the attention.

[scr8p]

your not the only one that must be missing something. i don't understand how the motor being installed from the right would be better than from the left with a mid motor configuration.

but, i've always been a few fries short of a happy meal.

[markt311]

hold a motor in your hand with the endbell to the left like a conventional setup and hit the gas, it wants to rotate to the rear. Hold the motor with the endbell to right and do the same thing, it wants to take off towards the front.

That same force is either pushing the rear of the car down creating more rear traction, or (to the right) trying to lift the rear end. By adding the fourth gear and keeping the endbell facing the left you are using the motor as a mechanical advantage by pushing down the rear of the car under acceleration, creating more rear traction.

It's all explained pretty well by Chazz and Paul Sinclair on XFactory's website

www.xfactoryrc.com

[scr8p]

hold a motor in your hand with the endbell to the left like a conventional setup and hit the gas, it wants to rotate to the rear. Hold the motor with the endbell to right and do the same thing, it wants to take off towards the front.

That same force is either pushing the rear of the car down creating more rear traction, or (to the right) trying to lift the rear end. By adding the fourth gear and keeping the endbell facing the left you are using the motor as a mechanical advantage by pushing down the rear of the car under acceleration, creating more rear traction.

i know how a motor rotates. which is why i can't seem to wrap my head around why they (x-factory) would add a 4th gear to the trans in order to have the endbell on the right side of the car. especially if the whole goal in the design is to create more rear traction.

[markt311]

http://www.xfactoryrc.com/rc/Images/TechImages/ChassisDetails_02-big.jpg

You're confused, they added the 4th gear to keep the motor on the left, like a conventional rear motor car