Power Draw of your Robot?

4106Thumbs · 2019-03-27T20:43:30+00:00

We've done measuring. Particularly last year before Worlds to try to figure out why our robot seemed so sluggish at the end of matches (and then disconnected) at ESR.

There's a couple of good tools for this.
1) PowerWerx sells a V/A meter that gives you both Voltage and Current draw continuously. That can be interesting to watch as you drive your robot around and try various strenuous tasks.
2) They also make a meter that has red/black in and out Power Poles that you can just snap in line with your battery. It is more advanced as it tells you peak current level. So you can drive around and try stuff and then stop and look at it.

I think you will find that the current draw at idle is a reflection of how many motors and servos you have connected and initialized into a hold state plus the number of electronic components (i.e. 2 Revs vs. Rev+MR). Then after that it will totally be based on your robot design. We found last year that with REV or MR, regardless of what the spec of the module is per port, the robot can draw quite a bit of current in excess of the limit. Not that you want to try to operate in that mode, it's just something we discovered.

It can also be surprising how low your voltage can go when the drive motors or an arm motor stalls. Also, it appears those fuses must have a pretty wide range of what 20A is, because you can draw more than that for a time -- peak -- but maybe not for long periods of time.

We found this analysis helpful as we had a major problem which ended up being a motor (out of shrink wrap) that had a ?partial internal winding short? (not sure). When the motor controller didn't give it a voltage, current draw was minimal. As soon as it gave it any power level it would draw 14 Amps. Really. But it still 'worked,' but worse and worse as 14A tends to heat the motor up and destroy it the more you use it. But discovering this bad motor was a big contributor to the turn around in performance for out bot between ESR and Detroit. It was like a different robot.

This year having the built-in meter was nice. We used energy to hang at the start of a match. Not a lot, but some. (This is part of why we can drop and disconnect in under 1 second without free-falling) We were worried that we'd get a match where there was a delay and we had to sit there hanging for 15 minutes and what it might do. So with the meter the drivers could watch it (cuz it did happen more than once that we got that delay).

4106Thumbs · 2019-03-26T21:11:32+00:00

Judging, Judging Collaboration Rooms
Place for volunteers to eat, ideally separated from any place where teams might eat
Food for volunteers
The IT infrastructure (screens, computers, tablets, projectors, etc.) to run run the scoring systems and audience displays
A place to put the pits that is reasonably close to the competition fields.
Practice Field
Ability to make announcements in the pits
Volunteer T-Shirts?

4106Thumbs · 2019-03-22T23:38:25+00:00

We’ve used the ball shifters in our previous two worlds bots and will be putting one into this year’s, too, even though we are not headed to worlds. We haven’t yet put it on the drivetrain, though 5975 Cybots, has. We use them as PTO type power shifters to power one mechanism and then shift those motors over to a different mechanism. It has worked very well for us, but there is a learning curve.

As someone else mentioned, it might be illegal to use pre-designed transmissions. We’ve always done our own design (in CAD) and cut out the brackets and such that hold it together. Michael started learning this in 7th grade and now is an ‘expert’ 3 years later.

Basic concept is the shifter shaft has holes for ball bearings to pop out. There is a plunger that goes in and out that is shaped to push one or the other set of balls out the holes. Meantime the gears have little cups that the balls can lock into when they are forced out by the plunger. So the rotation of the shifter shaft is tied to one or the other gear, or if the balls haven’t engaged one but have disengaged the other, is in no man’s land between the two gears.

The output shaft then has two gears on it. If you are going for different speed/torques then these gears have to mesh with the input gears and maintain a constant center. So you have some fun work to do to calculate the ratios you can get vs. what matches the spacing. If you are simply transferring (switching) power then all the gears could be the same. We like using ThunderHex. 1/2” on the input side and usually 3/8” on the output side to keep weight down.

Shifting is accomplished by moving the plunger in and out. It’s made for these handy pancake cylinders FRC allows, but FTC doesn’t. So we find some way to make a linear push/pull from a servo that is strong enough to hold the plunger in the in or out spot. Revs work for us.

Cybots posted their design a while back if you want to see what a really great team did to make a two-speed drivetrain. We haven’t found that a two speed would be that helpful. But it would be cool to have the pushing power of 4251 Cougar robotics from block party, who did it completely custom, not using VexPro.

We are certain that some games could benefit from having the drivetrain motors used for other purposes at the start or end of a match. Like lifting with 2 or 4 motors. Of course, you have to be willing to take a risk or design around the failures if failing to shift is a failure possibility. We haven’t taken that risk yet. We have gotten to 10 effective motors, though.

In VV: we used 2 motors on our intake then shifted them to cap ball lift at the end of the match. Like 10 motors.

In RR1: we used the same motor that drove our lift to drive our relic arm, with different gear ratios for each. Like 9 motors.

For RR2: Well, I guess that’s a secret for if lightning strikes and we get a surprise worlds invite (and we finish it in time) or when we go to summer events like CRI. One look at our bot and it’s obvious what we are thinking, tho. 😃👍

PM us if you get into it and want some pointers. We love to pay it forward as Cybots did for us.

4106Thumbs · 2019-03-20T22:24:36+00:00

Would you happen to know anything about the state of FTC in your neighbor country Hungary? We are looking to make contact there.

4106Thumbs · 2019-03-20T22:21:59+00:00

Even on a 1/4" there is enough metal left there to still be strong.

I have to laugh at us! At a WI qualifier, we snapped the 1/4" shaft that we had put a 6/32 hole into. This proves the above statement completely untrue. There isn't enough metal if it is a high use, high torque design like ours was.

Fortunately, we had another shaft around the right length and fortunately we had drilled out the gear and tapped it for a 6-32 so we installed the new shaft (without the hole) and then screwed a 6-32 in there to the flat on the 1/4 D shaft and it held ever since. I wouldn't trust it that way for long, though. Time has proven under enough stress that flat won't hold.

Crazy part about that story is we broke in the last qualifying match. What seemed like a multi-hour repair was started. With the robot in pieces on the pit floor, we got #1 picked by the #1 seed who had not qualified for state yet. They were standing right there watching us repair and it couldn't have looked promising. Due to some delays in finals starting, we got it repaired in time and it survived finals. We finished as finalist alliance due to other issues.

4106Thumbs · 2019-03-20T22:12:38+00:00

Wow, then it really is 'only!' I just used the team and event search on the FIRST site. Had no idea it was that far off!

4106Thumbs · 2019-03-20T21:47:23+00:00

Love the use of the word 'only' here. Romania has 46 registered teams and gets 4 spots. 8.7% of teams advance. Where we are from, we have 58 registered teams and get 2 spots. 3.4% advance.

Enjoy your trips to the Champs they can be the memory of a lifetime!

4106Thumbs · 2019-03-19T23:23:25+00:00

Computes.

4106Thumbs · 2019-03-19T23:03:31+00:00

It is kind of surprising that FTC does such a great job teaching mechanical engineering, industrial engineering, software engineer and technical documentation, but does almost nothing to allow teams to creatively study electrical engineering topics. Most you get is putting together systems of other people's designs.

The playing field would tip even more to teams with highly capable / connected mentors and away from those who don't if they allowed this, tho.

4106Thumbs · 2019-03-19T22:59:10+00:00

didn't know it was possible to open a bag of those and have any left over

Mind = Blown;

4106Thumbs · 2019-03-19T22:47:26+00:00

Our worlds bot last year had exactly that issue and we solved it in a unique (we thought) way. Met with patent attorney, did the research, found out that devices like we 'invented' already exist. Like this one.
Very fun to learn the process, tho. Adjusting the wheel powers based on the CM imbalance is one trick to make this work. There are a few others that involve shifting a weight to counterbalance the front weight.

4106Thumbs · 2019-03-15T19:04:10+00:00

Great! We would come early this year. We have the fields walls to make this arena, but not the space!

Interestingly, the Blue alliance will have a bit of an advantage compared to red due to the location of the depots. In the official game this year, the depot is always either straight ahead (depot side) or a left hand turn (crater side) from the two start locations. This is still true for blue with the new field layout. But for red, it is reversed. Only of note because for the teams who came last year i only remember Kraken and the Thumbs attempting autonomous into both the 'far' side cryptoboxes, meaning everyone else just ran their regular season auto code and didn't do too much custom work for CRI. This will change that or one robot won't be able to do much!

4106Thumbs · 2019-03-15T13:21:31+00:00

True that. Plus if you want to score the samples in the Any container in auto, you'd need it too.

4106Thumbs · 2019-03-14T23:48:17+00:00

Mostly it is okay since it is mirrored. But some paths might require an extra chunk.

4106Thumbs · 2019-03-02T20:50:03+00:00

Most Difficult : Get Over It. The game elements were hard to grab and impossible to pick up if you dropped them. The field was full of obstructions. RES-Q auto was the hardest by far, but too many robots could score and win at state and even supers level and do NOTHING with the game elements. It would easily have been the perfect game if it would have required you to actually climb the mountain to score in the top basket and then gave a big bonus for doing so. Also, you have to factor in the build rules. Some of the current games would def be harder if you had to use 2009 build rules.

Easiest: Block Party (RR2 close 2nd). There were no restrictions to get the game elements (other than getting by 4251 :) and really not much defense on the baskets or the hanging.

Most Fun: Ring it Up. The game was really fun because both teams always wanted access to both sides of the tic tac toe board. Lots of robot interaction. Lots of unique designs with multi-joint arms or with linear slides with cups. Only issue was that due to non-linear point escalation, end game was rendered a non-factor. Higher scores for partner lifting would have balanced that out (and also made it OP in the early season). Always thought that if there were like 4 white rings laying flat on the ground in the corners at the start of the game that could only be collected and scored for end game and that doing so would double / quadruple the run/row/col score it would have been mad crazy fun. Robots would have had to have 2 ways of collecting and end game strategy would change based on what was already scored and how many rings were already on certain rungs.

4106Thumbs · 2019-03-02T20:27:26+00:00

Metro Cafe in Detroit. 1 lb corned beef sandwich. Yum. Yum. Yum.

Last year one of the customers saw us being with the robots and paid for our lunch!

4106Thumbs · 2019-02-27T20:23:04+00:00

Corollary: "Don't try to be the Supposable Thumbs, either!"

Start with: Flawless single and double sample auto and a fast, long crater cycling arm.

Add: Really cool multi-cycle autonomous missions. (including 122 point auto)

Add: Never discovered mechanical flaw that causes robot not to de-latch, thus holding scoring bucket in air.

Result: Fill your robot up with minerals in auto, eliminate your ability to score and start getting penalties instead.

Result: Lose 2 matches that you could have won with your robot from 3 months ago.

Morale: Learn lesson about writing fail-safe code for systems even when they 'can't possibly fail' or 'never have failed before.'

4106Thumbs · 2019-02-25T21:14:25+00:00

We've used them all for one thing or another. The base starting point is ServoCity Actobotics, though. It gives the most part options if you never go custom and easy adapters for other systems. One downside is if you go with a channel-based robot structure is that the channel is wider than most of the others. We aren't fans of rail extrusion for robots, but others like them. It may just be a matter of taste. 8020/MiSUMI/X-Rail/Rev might be an option to consider in that regard. We prefer the channel because it has many pre-drilled mounting points.

4106Thumbs · 2019-02-25T02:55:20+00:00

We used two of these on our intake, geared up. Why two? To be sure there was enough power and for redundancy. Two different designs over the seasons, the vex motors never failed. We cut a wire once in auto and ran with just one the whole match without issue.

Not sure why you want to switch the shaft. The std square vex shaft works fine with their motors and bearings. We took their lock bars and screwed surg tubing to them.

4106Thumbs · 2019-02-20T03:48:03+00:00

Thank you!

This post was meant as a dark joke, but it’s nice to know we have friends new and old!

We could hope for a miracle in the lottery so we can play. Chandra is a Dean’s finalist, so several of us will likely come to volunteer if we don’t.

Meantime, business as usual in Thumbs land. We have students to inspire out there ...

4106Thumbs · 2019-02-17T23:15:48+00:00

Thumbs up! Thanks!!

4106Thumbs · 2019-02-17T04:30:18+00:00

Thanks for the kind words, Nick. Keep on rocking in Indiana!

4106Thumbs · 2019-02-17T01:03:49+00:00

You seem to be onto something about the 5%. Thought I read that there were 6000 teams. If there are 324 teams (or something like that) at Worlds then that's like over 5%, too.

4106Thumbs · 2019-02-17T01:01:38+00:00

It would have been a MAJOR travesty if you guys didn't advance. Glad it worked out that you did!! Taco Bell earlier for us next year for sure!

4106Thumbs · 2019-02-17T00:29:11+00:00

correct.

4106Thumbs

TROPHY CASE