Chris's ChtiCat Racer

[McG 6969]

Hello to everybody,

It’s been a while since the Bella Ballerina build blog, but here we are again. ‘We’, as Gaston, my preferred assistant is still ‘helping’ in La Grotte.

Maybe a quick word of explanation regarding the ‘ChtiCat’ original name before someone starts to wonder about my potential dyslexia.

The word ‘chti’ originated during WW1 when French soldiers were calling their North-French (Picardie, Pas-de-Calais) - or South-West Belgian - colleagues the ‘chtis’ as, in their dialect, they were pronouncing the ‘s’ as a soft ‘ch’ or ‘sj’. For example, when they say “Chti mi”, it means “C’était moi” or translated: “It was me”.

Some years later and up to nowadays, a genuine ‘Chti’ community arose with pride of being what they represent, with even a few French funny movies dedicated to their local dialect.

Now concerning the ‘Cat’ in the name, that seems to remain a well preserved mystery…

The ChtiCat Racer was designed in early 2016 by Christophe Malapel, aka ‘ChtiPanda’ - what’s in a name? - a passionate RC-citizen from Lille in the North of France and soon hundreds of them were competing indoor all over the country.

Very probably the ease of build combined with a cheap powertrain are key to the success of the ChtiCat.

Guixmodel in France made a kit for the ChtiCat Racer - laser cut or CNC routed? - in EPP (30 Kg/cubic m) including a ply motor mount and a carbon ‘front bumper’. I don’t know the reason of the EPP choice, but it might be even cheaper to source. EPP is quite lighter/softer than Depron, so only one thickness - apparently a bit more than 6mm - is used in the kit.

I will be using Christophe’s original plan (+/-?) in my build.

(to be continued very soon)

Hakuna matata

Chris

BRU - BE / CTR ChtiCat Control

 

Edited By McG 6969 on 22/10/2017 18:23:04

[Andy G.]

Hi Chris, good to see you and of course Gaston posting another thread! The Cat looks an interesting beast. Any details on the kit, price, supplier etc ?

[TigerOC]

EPP is more rubbery than other foams and therefore bounces as opposed to breaking. Hence its use in indoor air frames with very hard surfaces. Requires more support than other foams because its so floppy.

Rob

[McG 6969]

Thank you for commenting, Andy.

The EPP kit from Guixmodel.fr costs €20,- with a ply motor mount, a 6mm carbon fiber ‘bumper’ strip and some basic hardware to connect the rudder servo. Here is a link, but of course the site is in French only.

Guixmodel also proposes a powertrain kit with IBM 2204 1400KV motor, an Ipeak 10A ESC, a SG90 servo and a GWS 7035 slowfly prop at the cost of €35,50. No idea of the postage charges though.

The choice of motor & ESC is dictated by the race regulations to keep it as cheap as possible. So a 2204 motor (mostly IBM or RCTimer) must be used with a maximum 10A ESC. There are simply two racing classes being either with 2S or 3S battery. The prop diameter and pitch remain free.

As I have it laying around, I will use a XXD 2212 / 1400KV motor (€4,80!) with a 15-20A ESC and 8x4,3 prop, on 2S to start with.

Hope this helps.

Hakuna matata

Chris

BRU - BE / CTR Kit Control

[McG 6969]

Thank you as well, Rob.

Well, your arguments do explain Guixmodel's choice then.

Altough the large majority of the builds seem to stick with the original plan of using Depron but they seem to have adopted the ply motor mount and the carbon front 'bumper'.

Hakuna matata

Chris

BRU - BE / CTR EPP Control

[McG 6969]

Hi again,

I thought I would serve some French 'apéritif' tonight.

You'll find the free appetizer here.

Those are the two first Chticat Racers built and 'driven' by Christophe & his friend Seb. Motor 2204, 10A ESC on 2S 800 mAh. And it seems that 3S is a lot faster! Enjoy...

Hakuna matata & yes, you can "watch and drink"...

Chris

BRU - BE / CTR YT Control

[McG 6969]

Hello again everybody,

I downloaded and printed the plans which is straight forward - at least the printing - as it is just a few sheets in A4 format.

All the bits and pieces are grouped per sheet and only one part (the sides of the pod) are 2 sheets to be sticked together.

When build, the ChtiCat’s overall length is 430mm with a width of 208mm.

All the parts are to be cut in 6mm Depron except for the two parts with the dotted lines (pic above) which are 3mm foam.

In fact, it uses some kind of ‘suction’ with a built-in venturi section in the pod, a bit comparable to the ground effect created by Colin Chapman with his revolutionary Lotus 79 having its first victory at the Belgian GP in Zolder…  

If somebody is interested to have a go, the plans can be found here on Christophe’s forum. Just scroll down the page and click the word ‘Plans’ in red. You might have to register to the forum though.

If Molière’s native language gives you some dizziness, just send me a PM with a mail address and I’ll be pleased to send you the .pdf.

Hakuna matata

Chris

BRU - BE / CTR Chapman Control

 

Edited By McG 6969 on 24/10/2017 18:24:02

[john stones 1 - Moderator]

Posted by McG 6969 on 23/10/2017 18:09:48:

Hi again,

I thought I would serve some French 'apéritif' tonight.

You'll find the free appetizer here.

Those are the two first Chticat Racers built and 'driven' by Christophe & his friend Seb. Motor 2204, 10A ESC on 2S 800 mAh. And it seems that 3S is a lot faster! Enjoy...

Hakuna matata & yes, you can "watch and drink"...

Chris

BRU - BE / CTR YT Control

[Stephen Jones]

A indoor Hover Car ,

Unfortunately our indoor flying venue does not allow any ground base models or Helicopters .

But i shall be watching your build .

Steve

[McG 6969]

Thank you both, gents.

Too bad that your indoor hall is banning rotor & crawling 'thingies', Stephen.

But you can play with the ChtiCat outdoors as well. Some are using parking lots, shopping mall's empty parkings on sunday or even RC-cars drift tracks. The flatter the better, of course. But you don't need an enormous area.

Instead of using soft 'skids' like felt or Velcro for indoors, they use carbon fiber strips or plastic packing straps (like used on palettes) glued to the pontoons.

Hakuna matata

Chris

BRU - BE / CTR Ban Control

[McG 6969]

Hi out there,

I made a start at cutting some foam. I used the pin method to transfer the drawings to the Depron as they are real easy - mostly straight - parts.

I really don’t possess Simon’s or Tony’s skills, so I started prudently with the 6mm parts.

Sorry, but I forgot to include the fin & rudder to the picture.

Next were the parts for the motor mount, including the 2mm birch ply reinforcement and the fuselage deck - Depron 3mm – to be scored later.

Next is my first ‘amendment’ to Christophe’s original plan. As explained earlier, the existing kit is made out of EPP, but quite a number of buyers complained about the fact that the 6mm thick ‘thrust fairing’ at the front is forcing against the sides of the pod making it impossible to build straight sides without having to bevel it heavily, which is apparently not a joy to achieve with EPP. The thinner the better, I thought. So I went for an even ‘thinner’ version of the original 3mm foam by using a piece of acetate from an overhead projector. No need for scoring, extra thin & even stronger than foam.

… or am I wrong with this step/decision? …

Hakuna matata

Chris

BRU - BE / CTR Cutting Control

[AndyD]

they look like real fun,shame I don't have any place to use them unless they work on short grass.

[McG 6969]

Hi Andy,

Yes, they look like real fun on all the videos I've seen.

No idea though if they work on "short grass"? I'm afraid not as there must be some 'suction' effect between the skids and the underground. Worth a try though, it's cheap enough, doesn't it?

But even a tarmac piece of ground or an outdoors basketball playground is great to have some fun. Just add the right type of underneath 'skids' to the ChtiCat.

Hakuna matata

Chris

BRU - BE / CTR Grass Control

[Max Z]

Hi Chris,

Thanks for bringing this to our attention, I love it. I have the same problem as Andy and Stephen though, no immediate place to run it. I would have to join a club which has facilities for indoor flying and running these machines.

I am seriously thinking of building one myself, I do have some depron (imitation) laying around. I do not see the need to cut al these tabs and slots though, with a bit of careful assembly I think you can do without those.

I can see your problem with the front intake, and polyester overhead sheet may be a good alternative there. But 3 mm depron glued to the front-bottom part of the skirt would give that more rigidity, which you would need when bumping into things.

May be we'll meet on the track oneday....

Max.

[Iris Vlieghe]

Posted by McG 6969 on 25/10/2017 18:47:48:

"...As explained earlier, the existing kit is made out of EPP, but quite a number of buyers complained about the fact that the 6mm thick ‘thrust fairing’ at the front is forcing against the sides of the pod making it impossible to build straight sides without having to bevel it heavily, which is apparently not a joy to achieve with EPP. The thinner the better, I thought..."

The thinner, the better? Honey, I ran out of oxygen after reading that sentence before 'the thinner' one. Sometimes less is more! The shorter the sentence, the less blue I am going to get while reading it out loud. Nice 'thingy' anyway! Can't wait to see the final result.

Lot(h)s of love, I

BRU - BE / Oxygen Control

[John Robertson 3]

Nothing wrong with long, well constructed sentences, wiv comma's' an' fings innit not?

[Iris Vlieghe]

Posted by John Robertson 3 on 25/10/2017 23:20:28:

Nothing wrong with long, well constructed sentences, wiv comma's' an' fings innit not?

A well placed full stop from time to time can do miracles.

Have a good one!

- Iris

BRU - BE / Grammar Control

[Max Z]

Hi Chris,

Just for fun, I am building a virtual 3D model of the Chticat in Rhinoceros, also to see the construction details and how I could simplify that when I leave all those tabs and slots off. Then I came across this: by copying the small size overview drawing and measuring it up, i noted that the top is slanted some 3.5 degrees backward. Looking at the unrolled shape of the motor fairing, the forward-bottom corner has an angle of 90.5 degrees. This would mean that the firewall is slanting 3 degrees backward, and the motor would be pointing upwards by that angle. However, when I look at the pictures on the internet, the firewall is vertical. Is there anything mentioned in Christophe's description about this? I can read and understand the French forum thread, but knowing what to search for is something else.

Max.

[McG 6969]

Hi Max,

It seems that you got yourself convinced than.

Did you use the pic that I posted in my album? If you want I can post a larger one.

I don't have any CAD software but after reading your post, I rotated the large pic against a grid in Photoshop and you're totally right regarding the degrees > -3,5° for the 'body' deck & + 0,5° at the motor mount which should give an upthrust of 3°. And, yes, looking at different pics, I thought the motor mount was vertical as well. But then camera angles can often be misleading. I'll have another look at some pics.

I've been reading Christophe's blog on his forum several times & everything else I could find about the ChtiCat, but never saw anything about up- or downthrust. Starting to scratch my head now...

What do you think about that 'upthrust'?

Hakuna matata

Chris

BRU - BE / CTR Upthrust Control

[McG 6969]

@ John Robertson 3 > personally, I wouldn't want to start a 'war' with Iris.

During a former career,The LotH was a teacher way back in Texas (*). She used to have and 'drill' a majority of tex-mex teenagers in her classrooms (*). In future Texan history books even Genghis Khan might be described as a 'mild' conqueror (*).

(*) = a 'full stop'...

Hakuna matata

Chris

BRU - BE / CTR History Control

[Max Z]

Posted by McG 6969 on 26/10/2017 11:28:20:

It seems that you got yourself convinced than.

Not necessarily...

Re upthrust: the propeller will create a downward moment. Whether that needs to be balanced will be dependent on the pressure distribution under the skirt and the position of the centre of gravity. Giving the prop some upthrust or downthrust may help to balance that, but I have no experience with hovercraft design so I don't know.

re matching the inlet piece to the side panels, here is a picture of my cad design:

Although the representation of the inlet is not accurate ( I kept it simple, with more effort it would have been possible to represent the folded sheet construction accurately), it is clear that you will need to add some near-triangular pieces at the top end corners.

Max.

[McG 6969]

Hi Max,

I'm convinced you will be tempted to build one (or more?).

Also being quite a bit envious regarding your CAD skills.

Concerning the front 'thrust fairing', visualizing your drawing now, I can understand that the guys that bought the 6mm EPP kit were complaining about its thickness.

I'm more and more convinced about my acetate fairing. Intention is to fix it with thin double sided tape sticking it flat at the front but also flat against both sides of the pontoon. I might just have to alter the dimensions a little. Simples.

I've been looking at some others pics in relation with the 'upthrust'.

If you have a look at the Red Bull one, the yellow side edge compared to the white motor mount seem to indicate the presence of an angle. The position of the cross mount (vertical line) gives me the same impression. Anyhow, playing with a few washers is part of the fun, I guess.

I left a message/question at the 'Aeromodelisme.com' forum about it. Just hoping somebody answers now.

Hakuna matata

Chris

BRU - BE / CTR Washers Control

[Steven S]

Hi Chris - looks like a fun project. Is there a recommended C of G, and where is the recommended battery location?

[McG 6969]

Hello Steven,

Nice to have you visiting.

During my research about the ChtiCat, I never noted a mention of CoG. I suppose it should be a little after the rear end of the thrust fairing as that's the spot where the ground effect is created. But that's only a guess.

Regarding the Lipo, the trapeze-sized hole is where the battery goes in. My intention is to have the ESC flat on the top deck inside the fuse just behind the firewall with cooling holes in the latter.

Battery should come on top of it on a Depron tray. Receiver at the back on one of the internal fuse walls, next to the rudder servo. The fuse deck isn't an enormous cavern really, so I'm just 'projecting' for now.

By the way, do you still have that Vicomte/Baron project in mind? Or is it in the 'back of the queue' position?

I will be starting my Vicomte 1916 somewhere during november. Looking forward to it, really.

Hakuna matata

Chris

BRU - BE / CTR Vicomte Control

[Don Fry]

A slightly used example. When it hits a wall, or another slider, it flexes, and the prop takes a chunk. They are incredibly fast, and the aerodynamics only work with loads of power on. No power, no control. I am cognating the repair process.