Minibot climb rate
 

We have not received our FTC parts yet, obviously because the orders went in today :o . I have a couple quick questions and then a result of quick calculations based on assumptions.

What are the weights of the following items?:

NXT controller, Tetrix motor, 12v battery pack, HiTechnic motor controller.

I did some very ballpark calculations based on ideal situations. If we can build a robot weighing less than 5 Lbs, it should be able to climb the pole in less than 7 seconds.

Does that sound right?

Re: Minibot climb rate
 

What are you basing your calculations on? Overall output of the motors (ie: power)?

-Brando

Re: Minibot climb rate
 

Yep! I chose to run the calculations close the motor's max efficiency. I also chose to use the largest wheel I could find that appeared to be legal.

Re: Minibot climb rate
 

This calculation is actually very easy using the work-energy thorem.

Power = Work / Time

Work = weight * height

Therefore:

Time = (weight * height) / Power


Example:

Motor power: 8.43 W (Tetrix motor)
Efficiency: 0.85
Weight: 5 lb * 4.4545 N/lb = 22.27 N
Height to climb: 2.1 m
assume gearing for peak power.

then:

Time = (22.27 N * 2.1 m) / (8.43 W * 0.85)

Time = 6.53 sec

This is the FASTEST time. If you make the wheel big enough that the torque on the motor causes the motor to move away from the peak power point, the minibot will climb SLOWER, not faster. In other words, bigger wheels aren't always better.

Re: Minibot climb rate
 

I looks like your numbers and mine are spot on. I took a different approach, but the result is the same within .1 seconds.:yikes:

Just so others can see where I got my numbers, I ran it through the JVN Calculator.

Re: Minibot climb rate
 

Seems like everyone is forgetting the possible use of surgical tubing to shoot that bot up the pole much much faster.

Also you can use 2 TETRIX motors.

Re: Minibot climb rate
 

Who says we are forgetting?

Re: Minibot climb rate
 

That's how I would it approach it as well. 7 seconds doesn't leave much time for lining up/deployment.... *Must* *Climb* *Faster*

-Brando

Re: Minibot climb rate
 

Again, you are spot on. With only 10 seconds to deploy the Minibot and get it to climb the pole..... Every millisecond you shave off the climb rate, the better chance you have. Deployment has to be perfect. No slippage can be tolerated in the drive. It all has to be done right if you intend to grab the 30 points!

Think about dragsters. Getting off the line is just as important as how fast you go down the track. It's all about "elapsed time".

Re: Minibot climb rate
 

Yesterday we built a simple pole climber out of Vex parts with two 3-wire motors, 4 wheels, old vex microcontroller, and a battery. I'm hoping the FTC motors are more powerful (they're specs say they are) because it takes it about 10 seconds to climb 10 ft.

The minibot challenge will be more difficult than people think this year, mostly due to the timing allowed for it.

Re: Minibot climb rate
 

You might be right, but it's still a bit ambiguous. I'll refer to Gary's post
in this thread


I'm gonna need a clarification from the Q&A before I'd feel comfortable committing to getting an extra 10 seconds.

On the other hand, I want our minibot to be the first one to the top every single time, thus I'm not planning on our minibot needing an extra 10 seconds.

-Brando

Re: Minibot climb rate
 

I think this shines the light on deployment mechanisms just as much as it shines the light on the climbing minibot. Teams won't know if they're lined up properly until the 10 second mark, which means that a missed deployment is as disasterous as a slow robot.

Good catch with the <G68> rule, though I don't think it effects who wins the race. It would simply dictate whether or not last place always got the 10 points, even after the buzzer.

Re: Minibot climb rate
 

During brainstorming, my team used the minibots in the kickoff video as a reasonable estimate, which appeared to climb the pole in 4-5sec.

--Ryan

Re: Minibot climb rate
 

So the calculation above is based off one motor?

Re: Minibot climb rate
 

Question: What is the estimated ideal weight for the mini bot?

Re: Minibot climb rate
 

The first one we built was about 4 pounds. I think the final version we settle on will be more like 6-7 pounds.

Re: Minibot climb rate
 

i think my team intends to use surgical tubing to launch the mini-bot to the top in less time than 1 second. last years kicker on our robot only contacted the ball for 3 inches and was able to kick pretty far. i think we will be doing something similar for this.

Re: Minibot climb rate
 

have you tried the heavier weight yet?

Re: Minibot climb rate
 

What are the odds that a minibot launched by a slingshot will recieve a penalty?

I feel <G20> might be at risk as the slingshot might tap it after its initial release.

Re: Minibot climb rate
 

Hmm, the calculations I'm getting from both of my 'drag race' calculators, adjusted for straight vertical ascent, comes out to just over 5 seconds. I'll investigate...

Please use the other minibot threads for this question...

Re: Minibot climb rate
 

I'm curious Doug, what differences would cause your weight to increase 50-75%?

Re: Minibot climb rate
 

I would reccomend someone go and look back at their statics, dynamics, mechatronics and material science textbooks; these calculations are a little on the flimsy side.

If I were a student, I would start with a free body diagram and account for all of the forces involved. Then factor the motor in with all included drivetrain factors.

You must then base a more practical time compared to your calculated "theoretical" time. Factor things in like manufacturing tolerances, material fatigue, material temperature change, etc. and read up on how they would effect your climb rate.

Then, after your minibot is built, compare the two calculated times with the experimental time; the time it actually takes the minibot to assend to the top of the both. Run several trials and make improvements.

Re: Minibot climb rate
 

WHAT is this obsession with using surgical tubing to launch your minibot?

You can use springs to launch it just as well if not better, they just have to be part of your main robot.

Re: Minibot climb rate
 

This problem is a perfect example of one of the more selfish reasons I enjoy being a mentor on an FRC team: I have a reason to learn about other branches of Engineering outside of my original EE/ECE/CS training.

[My original back-of-the-envelope calculations gave a time of 8s with one motor, but I can now see how some of my initial assumptions were flawed.]

Re: Minibot climb rate
 

Provided the rules allow the HOSTBOT to provide upward impetus to the MINIBOT. That is not yet established (either way) in the rules.

Re: Minibot climb rate
 

Ideally, I'd say massless...but I don't think even the best teams can pull that off, plus I'm not sure a massless minibot could press the sensor at the top... You want the minibot as light as you can make it while still having the mechanism you need to climb.

Re: Minibot climb rate
 

I applied the equations in this whitepaper to JVN's Calculator (with some other mods as well) last night and came up with some interesting calculations. Over lunch today I further tested things, and have reached some conclusions:

A 5-lb minibot can reach the top in under 6 seconds
A 10-lb minibot will struggle to reach the top under 10 seconds
A 15-lb minibot probably won't make it to the top under 20 seconds ("probably" because there's a 10% fudge factor here)
There are only 5 gearing/wheel combinations that will even lift a 10-lb robot to the top in under 15 seconds, and all of those are well behind any of the 5-lb robot combinations.

Thus, the lighter the better.

Re: Minibot climb rate
 

That model is only good for a situation where the normal force is exactly opposite of the force caused by weight (mass X acceleration due to gravity) and perpendicular to the resulting force (driving forward).

In the case of a "climbing" robot, the most suitable analytical situation would assume the normal force is perpendicular to the pole the robot is latched to.

I would recommend to all students draw a diagram of all the forces on their robots before using any calculators to see if the same situation applies.

Re: Minibot climb rate
 

So now that update 1 says we have to use the motors and controller, can someone answer the original question - does anyone have the weight of the required components (battery pack, controller, motor) so we can start doing some real calcs?

Re: Minibot climb rate
 

Gary,
Which rule says that using the NXT is required?
<R92> does not say that currently.

Both D and E say "No more than one...". It does not say "One and only one".
I will admit, the rule can change. If they do, we will adjust.

Re: Minibot climb rate
 

You're right, the update only says motor and battery are required; it doesn't say controller although it says "appropriate circuitry", so what would that be other than through the controller? You can't follow the robot electrical rules and direct wire it because that would require the power panel and fuses which aren't on the allowable material list. So I still need those weights.

Re: Minibot climb rate
 

My impression is that the ROBOT electrical rules don't apply to the MINIBOT. It has its own rules. This appears to another case of confusion with when the manual should say ROBOT and when it should say HOSTBOT.

I expect great things from the Q&A. Terrible, yes, but great.

Re: Minibot climb rate
 

The first prototype was pretty flimsy. We are looking adding some more structural support and are assuming the Tetrix DC motors and battery are heavier. Once the design is optimized, we'll go through and lighten it up. We're 90% sure now that we'll build our own frame out of aluminum and not use the Tetrix materials. Hard to plan this out without the components (motor and battery). It is sad that they didn't put those in the KOP.

I'm even more convinced now, that the real challenge with the minibot is your deployment system. I have a feeling that at competition, we'll see some great minibots, but not as many great deployment systems.

Re: Minibot climb rate
 

Re: Minibot climb rate
 

Correct me if I am wrong but isn't it possible to use the Tetrix continuous rotation servos in addition to (or instead of) the allowed motors per rule <R92> A?

Re: Minibot climb rate
 

Where do you order these kits. We have never done anything with FTC. It is a stretch for us to do FRC. This is a challenge we have. Where do I order the 2010 FTC Base Kit. I looked on line but all are Back ordered. Where have you bought these from. Thanks

Re: Minibot climb rate
 

For the original question:

Last night we weighed 2 minibot motors, 2 minibot motor mounts, the FTC battery, 1 TETRIX 18" Rail, and (2) 4" wheels. Total weight was between 4 & 4.5 lbs (scale only does 0.5-lb increments, but rounds up).

I will note that we do not plan to use the NXT or the motor controllers. We cannot find specs regarding the NXT's shock rating. Without that data, and given the open-field nature of this year's game, we will not put a $200 device on the bot and call it "reliable".

Re: Minibot climb rate
 

I just received my (free, with hundreds left in stock - I will not be providing details [again] - search for it - I feel like Gary and Eric now) FIRST Choice FTC Mini Kit. Rushing (imagine me doing that) back to one of our labs, I measured the following weights for the FTC DC motor and battery pack:

Motor: 210.35 g
Battery Pack: 599.69 g

What are these strange Copiolian measurements of which I speak?

Motor: 0.464 lb.
Battery Pack: 1.322 lb.

Also, enclosed within my effectively-packaged AndyMark box was a sheet proclaiming a 30% discount on additional *in-stock* TETRIX parts for FRC teams via www.legoeducation.us/FRC. No blar comments from the peanut gallery - this is one thread that hasn't given me a headache yet.

Re: Minibot climb rate
 

ALL RIGHT! Travis is the go-to guy for FTC questions

A couple quick ones -

Weight of the wheels?

Thickness of the gears? (and weight, but I can calculate close enough)

Verify 32 diametral pitch on the gears (is the 120 tooth gear 3.75 PD?)

Thanks

Re: Minibot climb rate
 

Travis is surely not the only one with an FTC mini kit handy, as at least 800+ other teams have ordered these. ;)

Did you know that the gears were "Assembled in USA"? Probably the reason behind the cost.... Go go gadget globalization.

Mr. Ruler sez that the 120 tooth gear's PD is 3.75", and its thickness is 0.25"-ish.

Mr. Scale sez that the 120 tooth gear weighs 114.71 g / 0.25 lb. (in its thin plastic packaging - didn't want to mess up the shiny finish).

Mr. Scale also sez that the 4" wheel weighs 117.24 g / 0.26 lb.

Re: Minibot climb rate
 

The gears are .25" thick. They do have a diametral pitch of 32.

They have a bore of 8mm with four 3.5mm holes on a 16mm bolt circle. There are also eight 8mm holes on a ~59.58mm bolt circle. I think these are decorative. :)

I can corroborate Travis' weight measurements.

Re: Minibot climb rate
 

Did you get a weight on the 80 tooth gear? Or would I be close enough by extrapolating it from the 120 tooth?

By extrapolation I'm guessing the 80 tooth gear is 76.47 g.

Re: Minibot climb rate
 

I'm not in a position to do any more measurements today. Perhaps another can help out with additional measurements?

Is your math right? Gears are same thickness and have the same number/size of holes.

120T area = pi * ([120/32] / 2) ^ 2 = 11.045 sq. in.
80T area = pi * ([80/32] / 2) ^ 2 = 4.91 sq. in.

Density Ratio = 0.444

80T Weight estimate = 0.444 * 114.71 = 50.93 g

Re: Minibot climb rate
 

Interesting, but <R92>B states No more than seems to exclude a third motor.

(Team Update 1 changed A to read "A. TETRIX components that are not in violation of any other rules", and B is an other rule)

Re: Minibot climb rate
 

A computer is nothing more than an arrangement of switches. It can be mathematically proven that if you properly arrange switches, you can build memories, arithmetic logic units, registers, and many more things needed to build a modern computer. That is why you see binary, or base 2 arithmetic in computers. It is their native language.

From the robot rules - "An unlimited number of limit switches and two ordinary household light switches." is allowed on the minibot.

So it is possible to create a "computer" that has a hardwired program to perform the necessary algorithms for machine control. After all Von Neumann said that hardware and software was equivalent ! Really.. He did !

.

Re: Minibot climb rate
 

Light switch also seems vague.

http://www.google.com/imgres?imgurl=... t:429,r:7,s:0

http://t3.gstatic.com/images?q=tbn:A...ZNCpHRGzXlZwFe

The latter seems more useful, but seems less "standard." How much can we take the switch apart? If all we need is the mechanism, can we tear away at the innards?

Re: Minibot climb rate
 

You haven't even approached non-standard light switches. I'm busy pondering whether they think three way light switches are "common" or not. Cause it sure would be nice to reverse those motors.

Re: Minibot climb rate
 

Fat finger on the calculater some where. Yours looks accurate..
Thank!

Re: Minibot climb rate
 

80T Weight = 46.00 g (in packaging) - checked last night

Re: Minibot climb rate
 

If you can do that within the 12 pound weight limit using limit switches and two light switches, I'll bow to you in honor.

Re: Minibot climb rate
 

why would you want to be able to run them backwards?

Re: Minibot climb rate
 

Makes for easy/gentle retrieval if you allow your robot to climb back down to the base to patiently await you!

Re: Minibot climb rate
 

What JB said. If I can put a lightweight system on there to reverse the motors, I don't have to put on a robust retrieval system. Nor do we have to cart a reachin' stick out on the field after every match to get our minibot down. Mind you, we don't have our kit yet. The motors might backdrive quick enough that opening the circuit is adequate. I'd just like to keep my options open.

Re: Minibot climb rate
 

The top of the pole is 122 inches off the ground. your mini bot is twelve inches so the bottom of your minibot is 112 inches off the ground. the cylinder is 12 inches off the ground so if you stand on it you only need to reach 100 inches in the air or 8 feet 4 inches. so long as you have someone on your driveteam than can reach that high you will be fine.

Re: Minibot climb rate
 

I'm not so sure they'll allow us to stand on the base to get the MINIBOTS down. Interesting nonetheless.

Re: Minibot climb rate
 

You don't think the Field Staff will be using them as benches during long timeouts?

Re: Minibot climb rate
 

Yeah, standing on the base will probably get a team member a good dope slap from a ref.

Re: Minibot climb rate
 

Coming from someone who is also on an FTC team, if you build your minibot light enough to be competitive(~5lb), I doubt the motors will backdrive at all.

Re: Minibot climb rate
 

In case anyone is interested, I posted my modification of this program for the Minibot climb here.

Added the FTC motor specs, some efficiency losses and Normal force effects.

Robodox 599 Numerology 3x3x3x3x3.3 minibot @ .8 efficiency

(wheel_dia_in) x (gear_ratio) x (time_to_climb) x (speed_fps)x(weight_lbs) :)

Re: Minibot climb rate
 

Q&A defined 'light switches' at the kind you'd find at Home Depot or Lowes,. meant to switch lights in the house on or off,, and mounted in a standard wall electrical box.

My house has several 3-way switches so mounted, I bought them at Lowes, so they're OK to use.

Re: Minibot climb rate
 

A house "4 way" switch will reverse the motors...

Re: Minibot climb rate
 

*blinks*
I hadn't even heard of four way switches. That's even better!

Re: Minibot climb rate
 

4 way switches are use in rooms where lights are controlled from more than two places at once. The first two locations use 3 way's and the 3rd "or more" use 4 way's. The switch has 4 terminals on it . In one position it connects across. In the other position in cross the terminals. Great for reversing DC motors.

Re: Minibot climb rate
 

Our minibot got to the top of the pole today in 4 seconds. I'd love to share the video, but its "Top secret Confidential" stuff right now :yikes:

Re: Minibot climb rate
 

Food for thought...4 way switches will indeed help you reverse your motors but there is a cost. Even stripped down they are relatively heavy and also one must consider the rate of the descent and the endpoint velocity as your bot strikes the base platform. Not sure what the effect on the field element will be. Has anyone tested a motor aided return to the base platform?

Re: Minibot climb rate
 

wouldn't a simple resistor on the switch be enough to make it drive slower in one direction but not effect the upwards movement?

Re: Minibot climb rate
 

If resistors & diodes were allowed, perhaps when combined with a diode this would work fine.

Re: Minibot climb rate
 

gah! of course in my haste to develop a simple easy solution i forget to check the list of acceptable parts... ::rtm::

Re: Minibot climb rate
 

If you are intent on driving it down, you can switch the motors to be in series and this will at least cut the voltage in half for each motor which effectively cuts the power by 1/4 th.

But I can't imagine that the drag torque of these motors when properly geared for speed will be enough to hold the bot up the pole with no power. I don't have a number for the FTC motors but the vex 393 motors have about 1 inlb of drag torque or about 7 % of the Max torque. If the FTC are about the same % then you would only get about 21 oz in of drag per motor or a total of 42 oz in (2.6 inlb) for two motors. . The load torque for a 4 lb minibot would be 4*radius*gear_ratio which for a typical mini bot is 4*2*2 = 8 inlb. So I think the minibot should come down by its self with my assumptions.

Re: Minibot climb rate
 

I was thinking,
On->forward...contact->up... contact->off...gravity-> down.
on/off .12 lb 4 way .18 lb

Re: Minibot climb rate
 

4.5 second climb on first proto... time to lose some weight...

Re: Minibot climb rate
 

Perhaps it would also be useful to monitor wheel encoders as well. If the wheels travel 12 ft climbing a 10 ft pole, your problem isn't weight. Viewing the velocity and other derived values per wheel would be pretty interesting to evaluate different prototypes.

Greg McKaskle

Re: Minibot climb rate
 

are you allowed to use the surgical tubing on the mini bot????

Re: Minibot climb rate
 

You are absolutly correct that this information would be very usefull. The problem is, if you added the encoders and an NXT to capture that information, you would be radically changing the characteristics of the minibot. The data would not be relative to the actual performance of the bot in it's final configuration.

Re: Minibot climb rate
 

<R92> The following items are the only permitted materials for use on the MINIBOTS:
U. Rubber bands,
V. Surgical tubing,

Re: Minibot climb rate
 

Use encoders with a 15 foot cable and leave the NXT at the ground for testing purposes. Minimal impact on the robot, enough to get good data.

Re: Minibot climb rate
 

Good suggestion!
Alternatively, shorter wires and move the NXT along side by hand. Either way, any data you get is better than guessing.

Re: Minibot climb rate
 

wow congrats that quick ha ha top secret ::rtm:: what about gracious professionalism just kidding just wondering what parts you are using

Re: Minibot climb rate
 

Nothing in GP says a team has to publicly share designs, keeping a competitive edge will be especially crucial in regards to the minibot as many will be easily within range of being duplicated.

Re: Minibot climb rate
 

I have a question regarding the minibot and this seems to be the best place to ask it. Sorry if that's not correct.

R92 specifically mentions the following 2 adhesives.
G. Polycarbonate glue
R. PVC cement or cleaner

Does this really mean nothing else can be used? I'm thinking that exactly what that means, but I would like some more input.

If we indeed can only use these two adhesives and nothing else... In my limited experience, the PVC cement is not very useful on anything but PVC and/or CPVC. The "Polycarbonate glue" seems have different varieties available and some of those look like they might be useful for attaching other items on the minibot list to each other. However, it sure would be nice to just whip out the contact cement or silicone if it's kosher to do so.

Thanks for any input in advance.

Re: Minibot climb rate
 

I will give one hint: Surgical Tubing is being used. And yes, it does comply with the rules :yikes:

Re: Minibot climb rate
 

Welcome to Chiefdelphi!

As you will see mentioned in many threads here, the official answers to rules questions can only be provided through the Q&A system. Additionally, refinements to the rules come out in the Team Updates as well. All we can do here is give our opinions based on the rules.

Strictly speaking, I do not believe <R92> allows the use of any glue other than the two mentioned. One other place to check is in the Tetrix catalog linked in Team Update #3. If it is not listed in either place, then it most likely will not be allowed.

Re: Minibot climb rate
 

less than 5 pounds, so somewhere between 1-4 pounds will be good.:cool:

Re: Minibot climb rate
 

I agree. BTW, thanks for the welcome. I'm a long time lurker, 1st time poster.

You are welcome for all the fish and thank you for all the input.

Re: Minibot climb rate
 

But wouldn't surgical tubing that was wound up before deployment be considered stored energy? Otherwise you could just have a motor running and solely rely on the surgical tubing to launch you up the pole.

Re: Minibot climb rate
 

Surgical tubing that does not contribute to the vertical motion of the robot is allowed. The best exampe I can think of is a surgical tubing tied gate latch.

Re: Minibot climb rate
 

huh?

Re: Minibot climb rate
 

In that case I get it, it is going to come down to the deployment. Our current version of the mini bot can get up the pole in under 4 seconds, but it is still in the early testing stages. We have talked using surgical tubing in the delivery method...but like I said we are still working on which of our two gripper prototypes we want to proceed with.

Re: Minibot climb rate
 

we're now down to the 3-3.5 second range, and I think we could get under three with some more design tweaks and lightening. The design is still top secret, but I will tell you that it uses parts in intresting ways...:D

Re: Minibot climb rate
 

I'm calling shenanigans on a minibot under 3 seconds. Reliably deploying and shutting off while making the climb in under 3.5 seconds is even improbable @ 14V, perfect peak power, and the minimum 3.5lbs it takes for the battery, motors, switches, [custom] wheels, and just 1 ft. of attachment structure held together with magic (or rivets...).

Re: Minibot climb rate
 

3 seconds is doable. I don't think Frenchie is implying that the deployment time is included in their claim.

Re: Minibot climb rate
 

Is the mini bot allowed to have springs on it

Re: Minibot climb rate
 

We just got 2.93 seconds with our mini bot...in heavy mode. We haven't even started shaving weight off.

Re: Minibot climb rate
 

our minibot is going up in about 2.8 seconds. Not including deployment time, so it is doable, but deployment is where the race will be won.

Re: Minibot climb rate
 

theres no springs allowed on the minibot or for deployment--team update #1 said no stored energy in deployment.
and how did you ever get it in under 3 seconds if not with a spring/launcher thing??

Re: Minibot climb rate
 

The TETRIX motors are actually about 16W at peak power, not 8.43W as the spec sheet suggests. Surprisingly fast times are feasible.

Re: Minibot climb rate
 

Getting similar times on direct drive prototypes and 2-1 gear ratio prototypes... we are assuming similar times is due to gearing inefficiency and the added weight of all the extra gears, spacers, etc... The question is, how much better can we expect if we lighten up the Tetrix gears and improve gear alignment???

Re: Minibot climb rate
 

Strictly based on calculations and the specifications available, the difference in times when directly driven and when a 1:2 gearing increase is added is only 1 second.

The calculation with the gearing did not include the additional weight of the extra hardware and gears requires to add the gears.
When I calculated with the weight added, I only see a difference of .8 seconds.

Therefore, I am not surprised in the least that your times are very close. Add in a factor of human error if manually timing, and you could easily have a dead heat.

So, would lightening the hardware help? You bet!

Re: Minibot climb rate
 

I know this is a bit off topic but what size wire do you happen to use for wiring the motors?

thanks

Re: Minibot climb rate
 

So... we saw smoke when we made our bare bones minibot try to climb, with a modest overgear (0.5:1). These things can't be stalled for even a half second, apparently? I have no idea what smoked or whether or not the motors still worked, but if the motors are that delicate...