View Full Version : Rookie Team 3729's minibot
Two motors, no gearboxes, no wheels, Lexan frame , sub 2 sec climb
http://www.youtube.com/watch?v=MwCRfFaqFo4
Andrew Lawrence
11-03-2011, 21:07
No motors! How does it get up then???
too fast trick cam can we c a close up
Grim Tuesday
11-03-2011, 21:41
Just remember, there won't be any pool noodles at competition. Unless your deployment includes them :D
MagiChau
11-03-2011, 21:44
Just remember, there won't be any pool noodles at competition. Unless your deployment includes them :D
That's a great idea, then you won't worry about having to slow down your minibot as the motors backdrive.
Dustin Shadbolt
11-03-2011, 21:56
Holy crap. No wheels but how?
The video was our first pole test. We've since slowed down the decent by back driving. Even without back driving the minibot is light enough that it's decent is slow enough that it wouldn't tear up anything even without pool noodles to land on.
Andrew Lawrence
11-03-2011, 22:14
HOW DOES IT GET UP??????????
Unless you provide a valid reason, I label this video as fixed, edited, and a lie. Give a good reason, or this will be disregarded as a photoshopped video.
Each motor armature has a two inch long 3/8 diameter extension. The extensions are covered in latex tubing and drive directly on the pole. The minbot frame is 8 inch by 3 1/2 inch 1/16 thick Lexan. There are two pieces of 6 inch long 1/2 inch aluminum tubing attached to the frame that guide the minibot off the deployment tray. The only other components are two lamp switches and the Tetrix battery.
Dustin Shadbolt
11-03-2011, 22:44
Each motor armature has a two inch long 3/8 diameter extension. The extensions are covered in latex tubing and drive directly on the pole. The minbot frame is 8 inch by 3 1/2 inch 1/16 thick Lexan. There are two pieces of 6 inch long 1/2 inch aluminum tubing attached to the frame that guide the minibot off the deployment tray. The only other components are two lamp switches and the Tetrix battery.
Ahhh! I didn't see the 720p option. I thought I saw an extension type thing on the motors! Bravo to your design. We had something like that in mind but slightly different. Again grats!
Chris is me
11-03-2011, 23:07
That's exactly what our minibot looks like and how it works.
If you are a good team, you will copy this robot.
joeweber
11-03-2011, 23:46
We tried direct driving off the motor a 3/16 shaft with sergical tubing over it and it smoked the motor. I would like to see a close up.
http://www.chiefdelphi.com/media/img/1a7/1a7c19025e1e64716a3d2e1c073822f4_s.jpg
Ask and ye shall receive
boomergeek
12-03-2011, 06:56
We tried direct driving off the motor a 3/16 shaft with sergical tubing over it and it smoked the motor. I would like to see a close up.
How much did your smoking robot weigh? In our attempts, direct drive would not bugle our 4.25 lb minibot. With a 2.25 lb minibot, direct drive works amazingly well.
The other parameter is the right amount of normal force on the pole- for a 2 lb robot, you want about 4 lbs of normal force to hold the surgical tubing of the wheels to the pole. Too much and the motors are loaded down by friction.
Vamfun did nice simulations...
http://www.chiefdelphi.com/forums/showpost.php?p=1022466&postcount=16
joeweber
12-03-2011, 07:53
How much did your smoking robot weigh? In our attempts, direct drive would not bugle our 4.25 lb minibot. With a 2.25 lb minibot, direct drive works amazingly well.
The other parameter is the right amount of normal force on the pole- for a 2 lb robot, you want about 4 lbs of normal force to hold the surgical tubing of the wheels to the pole. Too much and the motors are loaded down by friction.
Vamfun did nice simulations...
http://www.chiefdelphi.com/forums/showpost.php?p=1022466&postcount=16
I do not know the weight but we just had two motors, the battery and a very small frame of flate aluminum with most drilled out with holes to make it light. With out the battery it zipped right up.
rcmolloy
12-03-2011, 08:56
This is not new news guys. Many teams have competed in Week 1 with the same thing. It's good that a rookie caught on though. It's upsetting because by champs most teams will have the same minibot. More importantly, how much does it weigh?
Also, good luck finding a good deployment. It seems like only 4 out of 40 teams with the same mini have been able to deploy it.
Robert is right, not new news. Even though 3729 is a rookie team, it doesn't lack horsepower. It's main mentor (me) has five years FIRST experience and has mentored teams to a regional win and two trips to Atlanta. The other mentors are engineers in aerospace. The students are very sharp and were very trainable to the ways of FIRST. They learned so fast that they helped two other FIRST teams with design. One other thing, it doesn't hurt to have a full fledged CNC machine shop as a major sponsor. :D
Our team as prototyped a similar design, but can't seem to get the minibot to raise off the ground.
We used surgical tubing to cover 1/2 OD rods, but when it is turned on, all that happens are spinning shafts going nowhere...
To get traction on the pole you have to have a normal force. The normal force comes from an interference fit. For example the pole OD is 1.75 inch. The distance between the rollers has to be something less than 1.75 inch. The less it is the more normal force. You have to experiment with what works for you. Another concern is the OD of the shaft. 1/2 inch could be too big. I know 3/8 inch and 1/4 inch work for about 3 lb minibots. 1/2 inch may stall the motors. Another way of saying this is your drive ratio needs to be tuned to your robot (it's weight).
Aakash Gihwala
15-03-2011, 16:45
Hey! We're a team in atlanta, 2420, and are trying to implement this design. Our original was too heavy and clunky. With only a few days left, we're in desperate need. If you don't mind my asking, I'd like to get some specs from you.
1. Do you have a drawing of dimensions? We tried to mimic your minibot from the description in the thread and sort of have the same idea. However, our lexan keeps flexing and forces the robot to come off. Where exactly are your reinforcement pipes?
2. How far is the inner spacing in between the output shafts? Currently the inside space between the shafts is a bit under 1.75". After hours of testing, we've decided that this is too small as the motors keep stalling out. Our next plan of action for today is to, keep the spacing at a minimum of 1.75" and slightly slant them towards each other. We think if the motors are slightly biased towards the center, the minibot won't fall backwards as easily.
3. How close was the battery to the motors? Does the proximity serve as a reinforcement for the lexan? There's about an inch or more in between the motors and the battery. This allows for a lot of flexibility and we're trying to get around this.
4. What magnets did you use? We're going to test out some ceramic hard drive magnets today b/c they're really strong.
Anything information really helps. Thanks!
t.ngo143
22-03-2011, 11:41
Is their any possible why to attach the minibot with 2 motors with surgerical tubing? and make it light as possible.... My team is having troubles finding a way to attach the minibot so I was wondering if you guys can help.
t.ngo, we use the syrgical tubing as the traction media on the aluminum axles. What holds the minibot on the pole are magnets. There are a lot of variables to manipulate to make the 'whole system' work. There are tons of information here on CD that tell you 'how to do' everything you need. If you have any specific questions just ask.
PAR_WIG1350
22-03-2011, 16:25
Is their any possible why to attach the minibot with 2 motors with surgerical tubing? and make it light as possible.... My team is having troubles finding a way to attach the minibot so I was wondering if you guys can help.
If you mean 2 motors and a shaftless piece of surgical tubing between them, don't waste the motors, it can't support the battery. If your tubing has axles and you just want to connect the motors, use the holes in the front of the motor that the gearboxes were held on with. If you are trying to connect the axles to the motor, drill them out on a lathe and press fit them.
packers76
25-03-2011, 19:11
You need to change that avatar!!!!! - Team #3729
Free Willy
30-03-2011, 23:06
How did you attach the surgical tubing to the shaft? Ours keeps spinning off.
First of all we use 3/8 inch OD tubing on a 3/8 inch shaft. That means the tubing is going to have to stretch quite a bit, but once its on it is not going to slip. We put it on two ways. The first way is to run really hot tap water over the tubing and then push it on the shaft. At competition you don't have hot water. We wipe the shafts with Clorox disenfectant sheets (get tem at the grocery store) and push the tubing on. The liquid is probably alconol. Doesn't work as well as hot water but you can do it in the pits.
Alcohol works pretty good for getting the surgical tubing on the shafts. It also dries quickly without leaving any sort of residue. Get the tubing started onto the shaft. Hold the shaft and tubing vertical with the tubing pointing up. Fill the tubing with alcohol. Pinch the tubing and push down quickly. The tubing will "inflate" due to the pressure from the alcohol and slip over the shaft with almost no friction. The position of the tubing can be adjusted for a few minutes until the alcohol is all squished out or evaporates.
We forgot to bring some to the practice day so we had the meet organizers make an announcement asking if any other teams had any alcohol. It got some funny looks. :yikes:
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