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Coupe de France de Robotique - Eurobot

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3D printed compressed air tank

In order to perform the funny action for Eurobot 2016, we considered a pneumatic umbrella and needed to have a reservoir of compressed air in our robot.

The tank would need to sustain prolonged operation at 4 bar and the pneumatic system as a whole would have to be airtight enough so that a funny action triggered 60 minutes after refilling the tank would still be successful.

Idea doubled by opportunity

3D printing allows for fast prototyping at low costs and super low iteration cycle times. Once you get used to printing parts and you have to test a new idea, you just end up doing it without a second thought. At CVRA we 3D print main mechanical internal parts as well as cosmetic external bodyshells. We can make stiff parts as well as bendable ones. Pretty much every idea we have is a candidate for 3D printing at some point.

So… I hear you have to use a compressed air tank for your pneumatic system, right? What if you just… 3D print it?

After all 4 bar is not such a high pressure. We are routinely using PLA filament and this material has a rather high yield tensile strength. Doing a quick “back of the envelope” calculation indicates wall thickness can be pretty low.

Prototype #1: excitement

Our first attempt was a 40x40x40mm air tank exported in STL as a solid and printed with a wall thickness of 4 layers and 20% infill. A 3mm hole was drilled on the side, and deep drilling the tank opened a clear venting channel within the infill structure. The test was a direct success. The tank was able to sustain pressures up to 6.5 bar without a hitch and be airtight enough to successfully deploy the pneumatic umbrella after a 1-hour delay.

The blue cube is the tank.

Prototype #2: adrenaline

Then came the time for a larger tank version our robot would accommodate, ramping up in volume from 40x40x40mm to 65x40x80mm, a roughly +225% increase, leaving infill aside, opting for a 6-layer wall thickness and having an internal support helping with the leveling of the innermost layer of the top wall during 3D printing.

The tank exploded into pieces just centimeters to my face when subjected to 5.5 bar pressure. I was wearing thick clothing and took the precaution to hide my face behind my arm, so nothing happened to me. But this is a clear reminder things can go wrong with only 4 bar of pressure. (Actually 2 bar are more than enough to do nasty damage. As an experiment we made a pointy steel javelin whose ejection velocity from a 6mm diameter pneumatic cylinder was really nasty enough any interference with human flesh had occurred.)

  • Rule #1: wear protective glasses when subjected to even remotely possible projections.
  • Rule #2: hide behind a protection wall when things can potentially explode.

Explosion results

This is a cross-section view of the faulty design. The internal structure is not bound to the walls.

It is supposed the pressure inside the tank inflated the walls enough to accentuate stress concentration at the inner corners and to cause one of them to yield. The rest was a chain reaction resulting in a handful of fragments flying across the shop.

Second prototype internals

Prototype #3: production model

External features remain the same as for prototype #2 since the function and bulk volume have to be maintained. Changes are found inside. End-filleted ribs fill the inside of the tank, effectively preventing the walls from inflating. Those ribs essentially serve the same purpose as the infill structure found in prototype #1.

Third prototype internals

The tank lived past repeated 6.5 bar stress tests but leaked in the corners. Acrylic spray paint was applied to the outer surfaces and the tank now performs well. As a benchmark, well over 1 hour after an initial 3.6 bar fill, the funny action runs perfectly.

Although this tank is the one used on our 2nd robot, such an air-tightening solution is still not a fully satisfactory one, mostly because of the visible paint job.

Prototype #4: beyond

An additional test was performed to assess the ability of tire sealing compounds to render bleeding 3D printed tanks air-tight. Back to the basics, a 40x40x40mm tank with 3 layers of wall thickness was printed.

As expected, it did exhibit strong—and mesmerizing—bubbling from the corners when pressurized at 6.5 bar.

The tire sealing compound used was the following one.

Tire sealing compound

After the internal surfaces of the tank were coated with liquid sealant and excess removed, we got a perfectly air-tight cube, apart from the inlet which initially leaked but soon was sealed too!

Other use cases

The air-tightening procedure described above will be applied to the internal suction channels of the hands of Debra 2016.

Résultat de la coupe de france de robotique 2016

Cette année fût compliquée pour I-Grebot avec beaucoup de contraintes personnelles impliquant des naissances et des achats de maison, nous n'avons pu consacrer que très peu de temps (2semaines) à la conception de nos robots. Mais la vraie réussite de cette année fût la création de l'équipe débutante E-Grobit qui est parvenue à concevoir une base roulante fiable et propre et à homologuer leur robot lors de la coupe de France 2016.

Résultats des matchs pour I-Grebot.

  • Premier match - I-Grebot vs Unitec: Victoire 73pts à 61pts.
  • Second match - I-Grebot vs Coffee Machine : Défaite 71pts à 85pts.
  • Troisième match - I-Grebot vs Les cools boys : Défaite 51pts à 96pts.
  • Quatrième match - I-Grebot vs Robot'Icam : Défaite 51pts à 83pts.
  • Cinquième match - I-Grebot vs A.I.G.R.I.S. Birds : Défaite 91pts à 93pts.
  • Classement final: 52ème sur 150

Tous les vidéos d'I-Grebot sur la playlist Youtube.

Résultats des matchs pour E-Grobit.

Homologation de l'équipe E-Grobit après le second tour.

  • Troisième match - E-Grobit vs ENSIL Robotik : Défaite 19pts à 55pts.
  • Quatrième match - E-Grobit vs TDS-Team : Défaite 15pts à 86pts.
  • Cinquième match - E-Grobit vs Robotech Paris UPMC : Défaite 51pts à 71pts.
  • Classement final: 145ème sur 150

Classement général de la coupe de France de robotique:

  • 1er : SPACE CRACKERS
  • 2nd : ESEO ANGERS
  • 3ème : Les cools boys

Tous les résultats sur le site live de Planètes Sciences: http://www.planete-sciences.org/robot/live/coupe2016/

 

Merci à nos partenaires

La Coupe de France 2016, c’est fini ! Bien que nous n’ayons pas brillé comme en 2015, ce fut une belle année pour Robotech Montpellier.

En attendant la vidéo récapitulative de cette année, nous tenons à remercier nos partenaires à qui nous devons nos moyens et nos succès :

Polytech Montpellier et l’Université de Montpellier pour les locaux, le matériel et l’aide financière
RS Components pour les réductions sur leur catalogue
ELA Innovation pour leur aide financière
Würth Elektronik pour leurs composants gratuits
Cirly pour leurs PCBs gratuits
Main Gauche pour leurs T-Shirt à bon compte

Cet article Merci à nos partenaires est apparu en premier sur .

5ème match : Défaite 89 à 131 contre le CRAC


à partir de 5 minutes 48

4ème match : Défait 92 à 99 contre Robot Club Toulonais


3ème match : Victoire 99 à 69 contre Wall'e'L


2ème match : défait 58 à 97 face aux Mines de Paris


1er match : victoire 84 à 64

Victoire sur le premier match contre le Club de Robotique des Arts et Métier de Paris : 84 à 64 !
La vidéo est sur YouTube, petit accrochage entre nos 2  robots, bientôt les photos de la réparation nécessaire à près ça (les deux roues motrices ne fonctionnaient plus...)

84 c'est pour : 
- 15 point pour sortir de la zone de départ
- 2 portes fermées à 10 points chacune
- 4 coquillages rapportés a la serviette à 2 point par coquillage
- un poisson récupère mais pas déposé 5 points
- un parasol déployé 20 points
- 4 blocs de sable dans la zone de construction à 2 points
- une tour (cylindre + cône) 4 + 4 points.
Avec tout ça on est 20e/120 au classement intermédiaire !
Maintenant on devrait gentiment descendre dans le classement lors des matchs suivants.
Demain 2ème match à partir de 9h


Photo des réparations :

Homologué

On s'est homologué ce matin à 9h15, on est la 36ème équipe homologué sur 149 actuellement (toutes les équipes ne sont pas encore arrivées)!


D-23: Wiring done, testing can begin

The assembly of our two robots, Debra and Goldorak, is almost over. Our electrical engineers are working hard to wire all the different motors and circuit boards (more than 30 in Debra!). Software testing on the real thing can start, and the first integration bug reports are coming…