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Another large scale Impreza project

Old 01-03-2010, 01:41 AM
  #26  
sam123
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Default RE: Another large scale Impreza project

Thats one nice looking rex [8D]
Old 01-03-2010, 09:25 AM
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Default RE: Another large scale Impreza project

Nice real car too!

For the pipe, if you have a tube bender it would be quite easy to fab a curved section that goes above the engine, leading to an expansion chamber...which can be "salvaged" from another pipe. If you're going to use steel, a basic arc-welder that will do the job isn't too expensive, and it's even cheaper if you have a friend close by with one

I just realized something about your carb though - it seems like it's a slide carb with a float bowl from the pics. Unless you mount the gas tank above the level of the float, it won't work properly. I had the exact same problem, so from a center of gravity and performance point of view, I went for an aftermarket tunable butterfly carb. It really does wake the engine up as well, so no regrets about that.

Enjoy the snow...
Old 01-03-2010, 11:45 AM
  #28  
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Default RE: Another large scale Impreza project


Hey Fabe thanks for the tip about the carb. I don't remember where, but Iremember I noticed on a home made projecta hosebetween the exhaust pipe and gas tank to pressurize the gas tanl. I also have this on all nitro models I have. I was thinking that this may be enough to pressurize the tank, but if it's not going to work I will try to find a replacement carb.

BTW, sorry for the noob question but what makes it a slide carb/float bowl ? (I guess a slide carb is like most nitro engines, a barrel that twists) I guess if I remove the filter and see a barrel it's a slide carb and if I see a butterfly I would be ok ? I will have a look, but from the pictures I saw online I think mine came with a butterfly carb from factory. I am still unsure if it is a 37 or 47 cc engine as they look identical and the site I bought it was sligthly confusing on this (zonemoto in montreal).

I did'nt notice you are from Quebec, I will probably have fun in the snow with the subie today Where are you in Quebec ? I'm in St-Georges (Beauce).




Old 01-03-2010, 12:33 PM
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Default RE: Another large scale Impreza project

Yeah, the tank pressure can be increased with a hose...you might have seen a pic from my build or someone else's, lol. I wasn't satisfied, however, because of the oily pressure line and inconsistent pressure. After playing around with that, and changint the jets and needles for tuning, I just bought an aftermarket carb since it's so much less hassle to tune.

Don't worry about the questions, that's what we're all here for! In your first set of pics, the engine has a slide carb, with a float bowl. Basically it looks like a cylinder under where the carb attaches to the air intake. In there sits fuel, but only fills up when a floating piece of plastic goes below a certain level. Gas then flows back into the bowl by gravity, which is why these pocket bikes have the gas tanks mounted above the engines. The slide is a cylinder with a cut portion of it that moves up and down when you pull/release the throttle to let more air (and fuel) into the engine. On the other hand, the buterfly carb is more like opening a door to let more fuel in, and creates a suction inside of it, so you can mount the gas tank anywhere. It is also less prone to leaking than the carb with a float bowl if the RC flips over.

If you can take the air filter off and look inside or take a closer pic of the carb we can tell you which it is.

I'm from laval - about 3 1/2 hours away. Have fun in the snow!
Old 01-03-2010, 02:53 PM
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Default RE: Another large scale Impreza project


I took a couple pics of the carburetor. Let me know what you think, I believe it is not the slide carb type after googling some pics of slide carbs.

But you are right the picture I posted in the first set of pics is this type. At first glance I thought it was the same engine as mine and posted the pic instead of taking anactual picture. I will edit it!

Here are the pictures of my carburetor I hope they are not too big




Old 01-03-2010, 03:46 PM
  #31  
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Default RE: Another large scale Impreza project

Hmm, I was not familiar with your carb, but it seems similar to [link=http://www.davesmotors.com/s.nl/c.885035/n.1/it.A/id.3735/.f]this one[/link]. Since it appears to have a diaphram reservoir with prime bulb, you shouldn't have problems with the gas tank afterall.
Old 01-03-2010, 04:42 PM
  #32  
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Default RE: Another large scale Impreza project


ORIGINAL: Fabe

Hmm, I was not familiar with your carb, but it seems similar to [link=http://www.davesmotors.com/s.nl/c.885035/n.1/it.A/id.3735/.f]this one[/link]. Since it appears to have a diaphram reservoir with prime bulb, you shouldn't have problems with the gas tank afterall.
It does look very much like mine. Glad to know it should work! Thanks for the help.

Do you know how I can be sure of the size of the engine ? Like if it is actually 37 or 47 or 49 cc ? To me they all look identical but I never had a chance to see other engines except internet pictures.

Edit: I am currently reading this, it looks like it have my answer at page 29, I will continue reading and compare with my engine. This is very interesting as it appears that chinese made engines are actually not 47cc, they are 40cc or sometimes 49 cc. See page 27 for details




http://bcpocketbikeracing.ca/media/P...ke_Secrets.pdf

Old 01-03-2010, 05:06 PM
  #33  
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Ok because we are all a bit lazy I extracted the interesting part about the difference between a 40cc and 49cc engine (which are usually all misleadingly advertised as 47cc). I just want to say this information is from http://bcpocketbikeracing.cait is not mine!

I thought others with custom home made project with similar engines would might find this info useful.

How To Figure Out Which Engine Is In Your Pocket Bike

How can you tell if your pocket bike has the 40cc or the 49cc engine in it?

Well there's 2 ways to tell:

1. By Looking

The first way to tell is to look at the 4 fins on the bottom of the cylinder

head. The bottom 4 cooling fins on the 40cc engine join right the way

around the cylinder head, with no break in between them. Whereas the

bottom 4 cooling fins on the 49cc engine stop at the corners and don’t go

all the way round.



Take a look at the picture of both the Cylinder heads below:



The cylinder head on the left is the 40cc engine - look where I’ve circled

the bottom 4 fins, you can see they are joined all the way round the

cylinder. The cylinder head on the right is the 49cc engine - look where



etc...
Old 01-03-2010, 05:10 PM
  #34  
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Default RE: Another large scale Impreza project

hello intresting work.

looks like a nice direction where your going with it.

i have a CAD build one off racing engine, with a lot of hand porting work also done,got it from germany.

best of luck with this.
Old 01-03-2010, 05:28 PM
  #35  
Fabe
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Default RE: Another large scale Impreza project

Nice find Frederik.

I have two engines over here, one on my project, and one waiting to be used. The engine cylinder looks like a cross between the two in the pic - I would say make the measurement to be certain. I did and it's a 44 mm x 33 mm, so about 49 cc. If you want to be certain for yours, just unbolt the cylinder and lift it up to be able to measure the bore and stroke. As an approximation, you don't even need to take the piston out of the cylinder, just turn the flywheel and measure how far up the piston goes from bottom.
Old 01-03-2010, 05:37 PM
  #36  
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Default RE: Another large scale Impreza project

Thanks dc2man !

Ok Fabe I will try this. Not really that it would be a problem that it is either 40 or 49 cc but it's always fun to know the truth !

I just found a second FG differential on ebay for my 4wd setup, it looks identical to my first one except it is alloy and the gear looks slightly narrower. Will post pics once it arrives here. I also got a couple large scale servos that should arrive at the same time.


Old 01-05-2010, 04:19 PM
  #37  
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Default RE: Another large scale Impreza project

Re: paint removal from plastic just thought I'd add that you can also use "odor free" EZ Off oven cleaner to remove several different kinds of paint including enamel from plastic (I've used it on styrene and ABS). Just have to be patient to let it soften the paint, then I've used an old toothbrush to remove the paint under running water, with a little dishwashing soap.

Cool project!
Old 01-07-2010, 09:23 PM
  #38  
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Thanks tomherb! I tried the softer stuffs first as I did not want to make the plastic brittle, I heard some stuff could slightly damage the plastic. I was lucky it worked the first time!

I did some other tests, this time with cardboard hahahah I placed 2 L shaped pieces, on on each side of the bottom of the chassis. Then I tried to find a way to brace the part that will hold the strut,when you think aboutitthis is where all the weight of the car will be.

and also thought of stiffening with rods and balljoints, but I figured I would be better with aluminium plates bolted as those would have resistance in more than 1 way (a rod with balljoints is strong only on pull and push, not sideways)



On the other side, I tried to find a way to hold with what woud be 3/16 inch aluminium pieces, with some folds to attach with the L pieces:



Some pics of the parts I have. After I bought the lathe, I tried to do an universal joint out of aluminium. It worked out good but I thing it would not hold very long as aluminium is pretty soft.

I have 2 types of balljoints. The big ones will mostly be on the front, and the other ones on the rear.


Here is what I did to the pulley. Will do the same to the other one.





Frederik

Old 01-07-2010, 09:31 PM
  #39  
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Default RE: Another large scale Impreza project

Sorry I did not rotate all the pics correctly. Should be better now.
Old 01-08-2010, 02:17 PM
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Default RE: Another large scale Impreza project

Very nice . I like it.

Have you a lathe ? You can make absorbs in 5 hours.You can not ? Why ? What do you need ?
Look at these .
Old 01-08-2010, 11:21 PM
  #41  
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Thank you VassilisG

I am missing some tools for the lathe (no boring tool and not much tools at all to machine inner part of a tube) and I dont know how to do treads yet. I should be able to make a tool to tread the outside of the tube, but not the inside.

On the design side, I am not quite sure where to put the oil seals in the shock body, and how to make them hold in place. did you just machinea groove, and then screw a cap over it to squeeze it slightly ?

Also I have to make a large diameter shock rod to make sure it can handle lots of side forces. I dont think the stock fg shafts would endure much side shocks. I guess I will have some testing to do to find a design. What metal did you use for the shock rod ? I guess I have to choose a corrosion resistant metal ? So that the shaft stays smooth (harsh surface would damage seals ?)

The best would be a complete strut with shock and spring, but maybe I will start with a simple telescopic strut (no shock) and put the fgshock separately,(attached to the lower arm)so I can concentrate more on the chassis and drive system.

All ideas are welcome! Let me know if you have concerns about parts of the design. I am still a bit afraid that the belt may not handle enough power, but I figured that the torque was divided between front and rear, and there is less weight on the front during acceleration so it should help Also the rear wheels are gear driven so only the front may suffer a belt problem..

Another concern I haveis the durability of the stock FG diff. I never drove an 1/5 scale car before and I have no idea what kind of power those diff can handle. I opened the diff and I see the gears are pretty large looks good quality.. butwhat do you think ? also the car will probably much heavier than a standard 1/5 car with this engine and all the crap I will bolt on the chassis hahahaha so that is more stress on all drive components.

Frederik
Old 01-09-2010, 02:04 AM
  #42  
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Default RE: Another large scale Impreza project

Build a rollcage and mount the struts to that. It will be strong and the weight is low.... and it will stiffed the chassis
Old 01-09-2010, 01:25 PM
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Default RE: Another large scale Impreza project


ORIGINAL: Frederik_b

Thank you VassilisG

I am missing some tools for the lathe (no boring tool and not much tools at all to machine inner part of a tube) and I dont know how to do treads yet. I should be able to make a tool to tread the outside of the tube, but not the inside.

On the design side, I am not quite sure where to put the oil seals in the shock body, and how to make them hold in place. did you just machine a groove, and then screw a cap over it to squeeze it slightly ?

Also I have to make a large diameter shock rod to make sure it can handle lots of side forces. I dont think the stock fg shafts would endure much side shocks. I guess I will have some testing to do to find a design. What metal did you use for the shock rod ? I guess I have to choose a corrosion resistant metal ? So that the shaft stays smooth (harsh surface would damage seals ?)

The best would be a complete strut with shock and spring, but maybe I will start with a simple telescopic strut (no shock) and put the fg shock separately,(attached to the lower arm) so I can concentrate more on the chassis and drive system.

All ideas are welcome! Let me know if you have concerns about parts of the design. I am still a bit afraid that the belt may not handle enough power, but I figured that the torque was divided between front and rear, and there is less weight on the front during acceleration so it should help Also the rear wheels are gear driven so only the front may suffer a belt problem..

Another concern I have is the durability of the stock FG diff. I never drove an 1/5 scale car before and I have no idea what kind of power those diff can handle. I opened the diff and I see the gears are pretty large looks good quality.. but what do you think ? also the car will probably much heavier than a standard 1/5 car with this engine and all the crap I will bolt on the chassis hahahaha so that is more stress on all drive components.

Frederik


Hallo Frederik ,
it is very difficult to me to explain ( ... my english ) but I would like help you , so I'll take a photo (tomorrow) from my absorbs ( Lotus 7 ) and everything will be clear.
Absorbs are tube aluminium ,14mm hole - 20mm outside ( ... it isn't necessary to drill ) .
Rods are steely (simple or inox).

Belts . I like theme but I never use because I don't accredit its endurance. All these i could found are from cars (valves moving) so I always use chain .How you put chain from one side to the other of your car ,...it is a problem ( small ).You can use acetal drivers and small gears to hold the line ( photo from Lotus again but ....when I 'll make it ).

FG diff ? I think that most of times there are problems from pins and axles , not from gears.



Old 01-09-2010, 01:57 PM
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Default RE: Another large scale Impreza project

It is most common that the plastic housing is throwing the towel in the diffs,get the alloy one,and the stainless steel sleeve,and you have a pretty strong lump of diff

VassilisG:how do you make the piston rods?What are they made from and how do you get them so smooth,like polished?
Old 01-09-2010, 02:49 PM
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Default RE: Another large scale Impreza project


ORIGINAL: Lars from Norway

It is most common that the plastic housing is throwing the towel in the diffs,get the alloy one,and the stainless steel sleeve,and you have a pretty strong lump of diff

VassilisG:how do you make the piston rods?What are they made from and how do you get them so smooth,like polished?

No 'like polished' Lars ,I polished them by metal polish paste .The material is face grinder , meddle steel but paste , made it like a mirror .
Old 01-09-2010, 03:40 PM
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Default RE: Another large scale Impreza project

VassilisG:

Your english is fine, I understand everything you say with no problem. English is not my first language either(its french).

I did nt think of using a tube, it will be much simpler like this. Thanks for the idea! Also that gives me some ideas about finding some kind of tube already designed to screw a cap or a plug in the end. That way I would not have to machine anything for the bottom of the strut (i dont have to have an attachment at the bottom as it is going to be screwed to the wheel hub).

Lars and VassilisG:

About the diff, I got an aluminium one (still not arrived) from ebay, and I already have another one of plastic. I will put the plastic one in front to start. Then if I find a second alu one I will replace the front one.

When you say the pins fails, are you talking about the pin on the driveshafts ? or the pins that hold the gears inside the diff ?

Thanks for your ideas and help. I will snap pics of the belts I plan to use to give you an idea of what it is. It looks pretty much like all the belts Isaw on 1/5 scale.

C.lyra:

About the rollcage, you mean building a cage based on the bottom plate ? Like some kind of hybrid between a tubular chassis and standard plate chassis?Because I dont have a welding machine so I cannot build a tube roll cage.

Thanks again all

Frederik
Old 01-09-2010, 04:09 PM
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Default RE: Another large scale Impreza project

It is the crosspin inside the diff,not the outdrives,but i guess this has something to do with the plastic housing as the pin allows itself to move due to the weakness in the plastic when putting a lot of power to it.Hmm,i barely understand what i just wrote

V.G:thank you for the info,maybe some day i have to undertake a similar project by making some shocks
Old 01-09-2010, 07:05 PM
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Default RE: Another large scale Impreza project


ORIGINAL: VassilisG


ORIGINAL: Lars from Norway

It is most common that the plastic housing is throwing the towel in the diffs,get the alloy one,and the stainless steel sleeve,and you have a pretty strong lump of diff

VassilisG:how do you make the piston rods?What are they made from and how do you get them so smooth,like polished?

No 'like polished' Lars ,I polished them by metal polish paste .The material is face grinder , meddle steel but paste , made it like a mirror .
VAssilisG: does polishing standard steel also make it more resistant to corrosion ?Because I am not sure I will be able to work stainless on my lathe with my current tools.

Lars: what is the stainless steel sleeve ?I never saw the interior of an alloy FG diff yet, I would guess the stainless steel sleeve would be between the housing and the pin itlseft acting like a bearing. Would it be possible to simply modify the plastic housing to put a bearing between the housing and the pin ?

Thanks,

Frederik
Old 01-10-2010, 11:45 AM
  #49  
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Default RE: Another large scale Impreza project

Have a look in my thread about the [link=http://www.rcuniverse.com/forum/m_9037920/anchors_9037920/mpage_1/key_/anchor/tm.htm#9037920]diff rebuild[/link],feel free to ask in the thread.The stainless steel sleeve is the outer casing of the diff,you see it as the most shiny parts in the pics.I think there will not be enough room to put bearings there if i understand you right.
Old 01-10-2010, 01:10 PM
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Default RE: Another large scale Impreza project

Maybe is a good idea to make a ' how to make absorbs for your rc car ' video ,step by step.

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