PDA

View Full Version : Tips on loosing weight (Not spam)


Andrew Lawrence
12-11-2011, 08:42 PM
I recently learned about these: http://www.pneuaire.com/reca44cuin.html pneumatic air tanks that are both light, and effective. My team is big on saving weight, and would like to be able to more control what our robot weighs without drilling 30,000 holes into it.

So, what are your secret tips on saving robot weight?

CNettles11
12-11-2011, 08:47 PM
Use a stick on a motor whenever possible :p

EricH
12-11-2011, 08:48 PM
Take a spreadsheet and a scale. Weigh every part, and estimate weight where you can, before the part goes on the robot. As you figure out you're close to being overweight, figure out where you can trim weight.

O'Sancheski
12-11-2011, 09:06 PM
Take a spreadsheet and a scale. Weigh every part, and estimate weight where you can, before the part goes on the robot. As you figure out you're close to being overweight, figure out where you can trim weight.

I did this in 2010 and works great. You gotta make sure to get the exact weight on each part and classify large pieces of wood/ aluminum based on weight per foot or inch to avoid confusion in the middle of build season.

P.S. It is very time consuming to weigh each part.

BrendanB
12-11-2011, 09:47 PM
Take a spreadsheet and a scale. Weigh every part, and estimate weight where you can, before the part goes on the robot. As you figure out you're close to being overweight, figure out where you can trim weight.

Can't echo this enough! Having a reasonable weight budget for subteams to stick too is key along with having an allowance for essentials like electronics and such.

Keep weight savings in mind while you are building/designing. Our team ate up weight fast on 1x1x1/8 aluminum box that could have easily been replaced by 1/16 but it was too late to change.

It is also a whole lot easier to swiss cheese while the part is not yet on the robot!

ajlapp
12-11-2011, 10:02 PM
Team RUSH hasn't used pneumatics in their robots since 2004 and this has been a tremendous weight saver in my opinion.

Initially we stopped using them because we thought the package available at the time was too heavy for the utility you achieved. We would often have one or two systems that were candidates for pneumatics....this didn't justify adding the ~8 lbs. needed for the compressor, tanks, hose etc, etc. Of course we discussed eliminating the compressor for some designs, but in the end we just eliminated the whole system.

Originally I hated that we didn't have access to pneumatics...each year I would lobby for it. Now that I recently started helping a new team, I find myself lobbying them to eliminate it to save complexity and weight. :)

Of course a lot of teams are able to integrate all motors and a complete air system while staying in weight, but it's a very liberating feeling heading to scales with 8-10 lbs. to spare.

Now that the systems have become more open and lighter I'm sure we'll take a serious look at going back.

amoose136
12-11-2011, 10:54 PM
Would any team care to post a past weight budget? I'm curious to see the average weight composition of the FRC robot.

Gary.C
12-11-2011, 11:39 PM
Save hella weight - buy aluminum gears

artdutra04
12-11-2011, 11:45 PM
Design everything ahead of time in CAD. If you set the materials appropriately, you can get an accurate estimate of your final robot weight. The more detail stuff you model, the more accurate the weight estimate will be. Changing designs in CAD to reduce weight is much easier, cheaper, and more effective than having to drill hundreds (potentially thousands) of holes in your mechanisms after they're already assembled.

Marc S.
12-12-2011, 01:21 AM
I don't know much about how you build your robots but making everything in 1/16 wall tubing instead of 1/8 will save a lot of weight and time(if you pocket 1/8). It is also stronger than pocketed 1/8 wall tubing. You can save a lot also if you use aluminum rivets instead of bolts whenever possible.Smaller wheels and custom gearboxes can save weight if done correctly(if you are unsuccessful in designing your own just copy our 2010/2011 gearboxes/drivetrain(link below)).

Ninja_Bait
12-12-2011, 06:30 AM
Design it to be underweight. That's why they give us CAD!

kramarczyk
12-12-2011, 07:46 AM
Ike put together a nice paper on robot weight reductions. http://www.chiefdelphi.com/media/papers/2220

PhantomPhyxer
12-12-2011, 07:49 AM
Start off by weighing all parts and recording that weight in an Excel Spread Sheet.
For those parts that are designed in Cad set the the material density correctly and CAD will calulate the part. Insert that number in the Excel Spread Sheet. Where possible use Aluminum. Limit the number of bolts to what you actually need to prevent rotation or shear. If you have to drill holes to mount something then use those mounting holes to mount something else if possible. That will reduce the number of bolts. If you keep track of weight only in CAD then use lump masses for those things like electrical.

The weight spread sheet can also be used for cost of your Robot because you have to account for every part on the Robot.

Fortunatily programming code does not weigh any thing! (:-)

JamesCH95
12-12-2011, 08:34 AM
I have the mindset of making everything as light as possible before adding it to the robot. "Pounds are made of ounces" is one of my favorite mantras from building race cars that I have brought to robotics. That is, we try to lighten every part before it goes on the robot. The savings seem trivial at first, but they add up to be significant.

Some tricks:
-welding the kit frame saves ~3lbs of fasteners and blocks and eliminates loosening frame fasteners from your pit checklist
-plastic bearings are super-light and can replace metallic bearings in some applications
-using 25 series chain instead of 35 series chain drops a significant amount of weight, I would not consider this on the drivetrain except as a last resort though
-designing with an eye to keep wiring runs as short as possible not only reduces weight, but improves electrical system efficiency (consider making that beautiful wiring run a little more utilitarian)
-the new air compressor is around 2.6lbs lighter than the older compressor, that's huge (FWIW I aim to use pneumatics for at least 3 small functions or 2 big functions to consider them worth the weight)
-using high-grade fasteners can drop weight if they are selected properly
-consider eliminating redundant fasteners
-consider replacing low-load fasteners with zip-ties, plastic bolts, or velcro
-speed controlling through software rather than excessive gearing where possible, one encoder weighs a lot less than another sprocket and chain set or pair of gears

There is very rarely a weight-reducing trick that saves a huge amount of weight. In my opinion good light-weighting is accomplished through a systemic discipline of cutting ounces, or fractions of ounces, wherever possible.

IKE
12-12-2011, 08:41 AM
Using thinner materials is the most frequent weight reduction I see. Often teams will use 1/8" plate where 1/16" will do (be it plastics, aluminum, or whatever...).

This is especially true wih Body panels. I frequently will see teams with large 1/8" body panels. Often 1/16" or even 0.030" thick polycarb will work just as well. In fact the 0.030" polycarb and access to a vinyl cutter make your robot looks classy, and add protection for very little weight.

When working with sheet-metal, use "shape" to add stiffness, not thickness. Adding in flanges can often increase the stiffness of a panel with very little (+10-20%) additional weight. Adding thickness will often do very little (compared to flanges), and increases the weight proportionally. Adding thickness and then removing material via a CNC, looks cool, and functionally may work well, but does require a fair amount of work or tooling.

********************************
The pneuaire.com accumulators are a great way to reduce weight and add air volume. I saw a bunch of these on 1503 last year and got the manufacturer from them. We used several on our robot, and i had a whole bunch of spares that we donated to another team that had around 10 metal accumulators on their machine.

Be careful with aluminum gears. When done right, there are some significant weight savings opportunities, but know that is is difficult to do them right. Aluminum has several properties that are quite poor for gears. Many gear experts would recommend to NEVER use aluminum. I do think they have their place, but you should be extremely careful and really need to know what you are doing.
*********************************
Beware of the attitude that "its too late to replace...". I have heard teams say this before, only to remove functional mechanisms at competition in order to make weight.

Gdeaver
12-12-2011, 08:44 AM
Composites can save weight over AL. If I remember correctly, This years arm which was made of pultrutions and polypropylene weighted 65% compared to the same structure in AL. Working with composite require methods that are different than working with metal. Do the research before using them.

Chris is me
12-12-2011, 08:55 AM
Be careful with aluminum gears. When done right, there are some significant weight savings opportunities, but know that is is difficult to do them right. Aluminum has several properties that are quite poor for gears. Many gear experts would recommend to NEVER use aluminum. I do think they have their place, but you should be extremely careful and really need to know what you are doing.

Lightening the steel gears, while not particularly FUN to do, isn't very hard and will get you a decent amount of the way there with regards to weight savings.

Composites can save weight over AL. If I remember correctly, This years arm which was made of pultrutions and polypropylene weighted 65% compared to the same structure in AL. Working with composite require methods that are different than working with metal. Do the research before using them.

I'll put in a vote for composites as well. Pultruded fiberglass is very rigid, thick stuff with a low density. Fiberglass tubing is great for something like an arm.

IKE
12-12-2011, 09:42 AM
Lightening the steel gears, while not particularly FUN to do, isn't very hard and will get you a decent amount of the way there with regards to weight savings.
.

Absolutely, I can't believe I forgot to add "lightening" steel gears. For those that are not familiar, you can either cut pockets with a mill, or undercut the gear between the teeth and the hub on a lathe (this is what we usually do). When doing this, make sure to leave a littl material underneath the root of the gear tooth as this can be a highly stressed location on a gear. Also leave material for the hub as this is either the torque transferring area, or has the bearings on an idler gear. We can often cut about 50% of the weight out of the standard AndyMark gears.

Just be careful how you "cuck up" the gears in a lathe so you do not damage the teeth.

EricH
12-12-2011, 12:26 PM
Absolutely, I can't believe I forgot to add "lightening" steel gears. For those that are not familiar, you can either cut pockets with a mill, or undercut the gear between the teeth and the hub on a lathe (this is what we usually do). When doing this, make sure to leave a littl material underneath the root of the gear tooth as this can be a highly stressed location on a gear. Also leave material for the hub as this is either the torque transferring area, or has the bearings on an idler gear. We can often cut about 50% of the weight out of the standard AndyMark gears.

Just be careful how you "cuck up" the gears in a lathe so you do not damage the teeth.
You can do the same thing with sprockets. Just be careful, for the same reasons. A couple of large sprockets have failed catastrophically in competitions after being lightweighted. I remember or remember hearing about two incidents from 2004--in one case, the sprocket turned into a pretzel; in the other, the hub broke free after the season, disabling that particular robot by removing one of its highest-traction wheels from the drivetrain.

ratdude747
12-12-2011, 12:46 PM
One trick to saving weight is to get rid of unnecessary parts.

Another thing i advise teams NOT to do is to use plastic chain where any significant torque is involved... I've seen it bomb catastrophically before... remember that with chain, one weak link ruins the whole loop.

Agreed on using 1/16" where possible...

one last tip is that if you have to resort to cheese-holing, do it to low load things higher up on the robot... having a low center of gravity is key to a stable robot. every little bit helps.

Jon Stratis
12-12-2011, 01:18 PM
The biggest way to lose weight... Ask the inspector to take his foot off the scale :p

We've never really had a problem with weight on the robot... In fact, most years it's the exact opposite! We always end up either significantly under weight, or spend some time figuring out how/where to add weight (2008 we had a 20lb steel plate bolted to the very bottom of the robot, 2009 we bolted steel plates outside of our cantilevered wheels to support the bumpers, 2010 and 2011 we were under weight - 2011 by quite a bit).

You need to consider weight with everything that goes on the robot - it's easy to "over-engineer" something by building it with bigger/stronger parts than are really needed. What's difficult is building something to be just as strong (and thus heavy) as it needs to be, and no stronger.

s_forbes
12-12-2011, 01:28 PM
Design everything ahead of time in CAD...

Quoting this for truth! Not only do you have the benefit of part masses being calculated quickly, but you also have the ability to alter and optimize the design on the fly. On all of the better robots that I've been a part of designing, weight was never even considered; we spent so much time creating an efficient design that weight didn't need any attention. A good design will by lightweight by nature.

It always amazes me how so much attention is spent on eliminating fractions of a pound in the drivetrain when usually much more can be saved with an efficiently designed manipulator. Remember to design the robot as a whole and not just each part independently.

Wayne Doenges
12-12-2011, 01:37 PM
One word...Monocoque ::safety::
No internal frame.

JamesCH95
12-12-2011, 01:41 PM
It always amazes me how so much attention is spent on eliminating fractions of a pound in the drivetrain when usually much more can be saved with an efficiently designed manipulator. Remember to design the robot as a whole and not just each part independently.

A thought that occurs when reading this: the drive-train is one of the only truly well-understood systems on an FRC robot (I think) because every year every robot needs a drive train. Repetition and redesign of drivetrains over the seasons characterizes the the required durability/strength/requirements very well. This allows the drive train to be thoroughly analyzed and designed well over years through many smaller design tweaks, as compared to a manipulator or game-specific feature that must be developed, analyzed, and optimized in weeks.

Al Skierkiewicz
12-12-2011, 02:59 PM
The biggest way to lose weight... Ask the inspector to take his foot off the scale :p

Cmon! Jeff and I only did that to you once! OK maybe twice but that was all I swear!

ratdude747
12-12-2011, 03:41 PM
One word...Monocoque ::safety::
No internal frame.

sounds like most cars anymore... unibody anybody?

Ninja_Bait
12-12-2011, 03:47 PM
I'll put in a vote for composites as well. Pultruded fiberglass is very rigid, thick stuff with a low density. Fiberglass tubing is great for something like an arm.

We used fiberglass square tubing (1x1x.125) for an arm this year. It bowed under the weight of our claw (though to be honest, the claw had Banebots gearboxes that were 3 stages too large and 35 chain for a while), and we were always afraid that our bolts would rip through the walls. It happened once, but only with 2 countersunk bolts. We immediately put fender washers on all the other ones and we survived Hartford and CMP. I would be wary about using fiberglass again for an arm. While it might be okay for an upright support or something structural, it doesn't have the strength of aluminum, and we definitely spent every match dreading the moment where our arm would shatter and shower our electronics in powder. :ahh:

If we had used aluminum, we'd have been overweight and it'd be too heavy for the motor. But honestly, it wouldn't have given us as many scares as the fiberglass did. I think we got pretty lucky, but there were always close calls. If you want to use composites, don't repeat our mistake and remember that they are not metal, no matter how much they act like it.

The biggest way to lose weight... Ask the inspector to take his foot off the scale :p

Just keep your mentor's foot under the scale; that's what we do.

Fortunatily programming code does not weigh any thing! (:-)

Our code extends past the bumper perimeter sometimes.

JamesCH95
12-12-2011, 04:14 PM
I'll put in a vote for composites as well. Pultruded fiberglass is very rigid, thick stuff with a low density. Fiberglass tubing is great for something like an arm.

As with anything, overkill can be spectacular:
http://www.carbonfibertubeshop.com/tube%20properties.html
http://www.dragonplate.com/ecart/categories.asp?cID=88

But I agree that any composite can be a great way to cut weight.

Chris is me
12-12-2011, 04:23 PM
We used fiberglass square tubing (1x1x.125) for an arm this year.

I've only used stuff in .25 inch wall thickness - much better results that way for rigidity but lightening is recommended.w

Aren_Hill
12-12-2011, 04:31 PM
The way 1625 did it last year, on accident.

Get a scale thats miscalibrated and you don't know about it, make it read around 10lbs over what the weight actually is.

This may have happened last year....showed up at wisconsin with a robot with 11 motors and 8 cylinders+compressor, at 108lbs.

Ninja_Bait
12-12-2011, 04:34 PM
I've only used stuff in .25 inch wall thickness - much better results that way for rigidity but lightening is recommended.w

I liked the two-hockey-stick arms, too (practically solid fiberglass) but our arm was just a disaster in general. It was too long, too thin, and too holey. I plan to stick with thin-walled aluminum and wise design for this year to avoid any possibility of composite catastrophe.

AdamHeard
12-12-2011, 04:44 PM
I love thin wall aluminum.

I don't want to tell teams to not use composites, but most of the time I see them used "in place" of aluminum they are used in much more volume so their lower density provides no weight advantage, and a thin-wall aluminum member would be more efficient.

I see them used right time to time, and it makes me happy every time to see something different used effectively; but that unfortunately seems to be the minority.

roystur44
12-12-2011, 07:14 PM
[QUOTE=AdamHeard;1090563]I love thin wall aluminum.

I'm surprised I haven't seen a team make a round tubular frame similiar to a bike frame or go cart frame.

If you guys have never seen a tube laser cut tube check it out on youtube

Roy

AdamHeard
12-12-2011, 07:44 PM
[QUOTE=AdamHeard;1090563]I love thin wall aluminum.

I'm surprised I haven't seen a team make a round tubular frame similiar to a bike frame or go cart frame.

If you guys have never seen a tube laser cut tube check it out on youtube

Roy

It's more difficult to work with when compared with other methods.

67 is about as close as I've seen.

BJC
12-12-2011, 07:57 PM
67 and 469 routinely make the top half of their robots out of thinwall aluminum tubing. It is VERY light, thin, and strong stuff. Instead of using 1/16 box on an arm, .0200 aluminum tubing could provide a lighter alternative. The warning that comes with this is that you need to make sure you properly design so it is not loaded in the wrong direction. Our entire 2007 double jointed arm was made out of this and it weighed maybe 5lbs max.

JamesCH95
12-12-2011, 08:21 PM
Our arm this year was around 0.065 or 0.050 1.5"OD tube, worked great.

ratdude747
12-12-2011, 08:31 PM
1024 uses thin wall tubing a lot as well... they have access to a good tube bender, so that's what gets used and, IMHO, used well.

apalrd
12-12-2011, 08:41 PM
.200 aluminum tubing

You're off by a decimal point, about.

We've used .035 thinwall aluminum for very high stress applications (arm in 2007), it's just really hard to weld...

I believe 469 uses something around the same thickness, in various diameters, for basically everything, with rivets holding everything together. Very very lightweight.

We've used material as thin as .050 and .063 in drivetrains, back in the days before mandatory bumpers (we had no bumpers, they lived).


As to tubular frames, how about this:http://www.chiefdelphi.com/media/photos/12949 and http://www.chiefdelphi.com/media/photos/12952 (same robot) - Chief Delphi 2000

JamesCH95
12-12-2011, 09:32 PM
You're off by a decimal point, about.

We've used .035 thinwall aluminum for very high stress applications (arm in 2007), it's just really hard to weld...

I believe 469 uses something around the same thickness, in various diameters, for basically everything, with rivets holding everything together. Very very lightweight.

We've used material as thin as .050 and .063 in drivetrains, back in the days before mandatory bumpers (we had no bumpers, they lived).


As to tubular frames, how about this:http://www.chiefdelphi.com/media/photos/12949 and http://www.chiefdelphi.com/media/photos/12952 (same robot) - Chief Delphi 2000

It just takes a patient welder :D
http://a7.sphotos.ak.fbcdn.net/photos-ak-snc1/v2056/113/13/28900759/n28900759_30265699_2569.jpg
This is a weld I did in college, but one of my students two years ago was welding soda cans together like this for fun in her shop class. It is certainly non-trivial, but definitely doable.

Jeff Pahl
12-12-2011, 10:58 PM
The biggest way to lose weight... Ask the inspector to take his foot off the scale :p

Cmon! Jeff and I only did that to you once! OK maybe twice but that was all I swear!

Al, it may have happened once or twice when you weren't around :D

On a serious note:

Weight management is a subject that is very near and dear to my heart after spending 15 years building spaceflight hardware. When the contracts include penalties that run on the order of $60/gram for being above the spec limit, you learn to pay a lot of attention to weight.

The first thing I tell rookie teams in any of my presentations is to buy a decent scale. It's an investment, just like any other tool. One I like is this one from Grainger. (http://www.grainger.com/Grainger/OHAUS-Digital-ShippingReceiving-Scale-1UXK3?Pid=search) It's just over $200, has a 400 lb capacity, and has a remote display so you don't have to try and get your head under the robot. The extra capacity means you can set a plywood platform on it so the robot will fit, or that you can weigh your crate before you ship to Championship after your well designed under-weight robot wins your regional:) If you really can't afford to buy a scale, try the one the wrestling team uses. Or find a local company (sponsor) that will let you use their shipping scale a few times. Buy a small scale and weigh all the parts of your robot. There really is no excuse for showing up at the competition being 10's of pounds overweight.

The rest of the secrets have been mentioned several times in this thread already:

1) Make a weight budget.

2) Enforce the weight budget.

3) See #2. If a subsystem is not going to make their part of the budget, make them negotiate with the other subsystems to see if anyone has any excess. I usually withhold 10 lbs as "Engineering Reserve". The team members would rather negotiate between themselves than try to get any of that from me. If we have any left, they get to add decorations, etc. Or I get to add weight to put the CG where it needs to be.

4) Use the CAD tools not only to pay attention to the weight of parts you design, but to decide how much work to do to to purchased parts. We use the CAD models from AndyMark, etc to evaluate different lightening schemes vs. the amount of work. Keep in mind the added benefit of reducing the rotational inertia of moving drivetrain components such as gears and wheels, just don't get carried away to the point that structural integrity is compromised.

4) Design from the beginning with weight as a design parameter. Think about how you can make each part lighter while making it strong enough at the same time. It is much easier to put holes in a part before it is assembled than after the robot is together. Avoid the "we'll just put it all together and see how much it weighs" trap at all costs. It never seems to come back apart to do the necessary work later. Making shavings before you put the electronics in is much preferred to getting metal bits inside them. The holes also look a lot nicer if they are carefully laid out, nicely finished (deburred), and if the part is painted, the holes are too. And if you design them into the part and lay them out properly, you can avoid having an over-enthusiastic freshman drill holes too close to the edge of a critical structural part.

5) Take advantage of the bumpers. You get to rigidly attach a 5" wide strip of 3/4" plywood to the side of your robot. That can provide a lot of structural support if you take it into account during your design process, and it's free weight.

6) See #2.

7) Use creative materials. Composites. Plywood (yes, really. We built most of our 2011 robot from 12mm Baltic Birch plywood). Plastics. Avoid steel unless absolutely necessary, and only for small parts where needed.

8) Pay close attention to the number of fasteners. An ounce here, an ounce there, suddenly you are talking about pounds.

9) Same goes for wiring. Plan your layout to minimize the number of inches of high current (large gauge) wiring runs. This has the added benefit of keeping the resistance down. Just make sure you don't cut everything so short you don't have any slack to work with or that things are so tight they pull out of the connectors.

10) See #2

As I have mentioned on CD before, the three things I say most often during build season are (in no particular order):
1) Is your homework done?
2) That's in the rules.
3) How much does that weigh?

If you pay attention to weight during weeks 1-5, then it is a non issue during week 6. Nothing pains me more as a Robot Inspector than to have to help a team cripple or remove their well thought out game mechanism, rendering them unable to do more on the field than drive, just because there is no way to lighten up their robot enough at the competition any other way.

My final comment on the subject: Thinking you will just drill a few holes in things when you get to the regional if you are overweight is a recipe for disaster, or at least a very non-inspirational event. If you ever think about taking this approach, please sit down and calculate how many 1/4" diameter holes you need to drill in a piece of 1/4" aluminum plate to reduce the weight by 1 lb. I promise you will be surprised.

Ian Curtis
12-12-2011, 11:42 PM
Airplanes have entire teams dedicated to track weights. (http://www.youtube.com/watch?v=TXSSUSzLwCA)

Like Burt Rutan said when building Voyager, "If you can throw it up in the air and it comes back down it's too heavy!"

As others have said, but holes in everything from the get go. It requires a little bit of for thought, but honestly it makes robots a very distinctive look. The robots (http://www.chiefdelphi.com/media/photos/25759) of (http://www.chiefdelphi.com/media/photos/14077) team (http://www.chiefdelphi.com/media/photos/21803) 40 (http://www.chiefdelphi.com/media/photos/17432) were a great inspiration to us as a 15+ lb overweight rookie team, they made everything light from the get go with predetermined wholes that look great, compared to our hodgepodge of holes all over our superstructure.

If you do end up overweight, it is very important to recognize that volume (and as such weight) goes with the square of the radius. A 1/2" diameter hole removes 4 times the weight of a 1/4" hole. Bring big bits.

We had a love/hate relationship with pneumatics. I think it is worth it if you use them for several functions (https://lh4.googleusercontent.com/-sJJA8Z8ciT0/TSoasmop6qI/AAAAAAAAC4A/-UTpJow0jX0/s800/2007-0100-105.jpg), but if you only need one or two things look long and hard at using motors and limit switches instead. In the two years 1276 didn't use pneumatics we came in well under the weight limit, but we also came in well under the year we used pneumatics for most of our actuators.

Al Skierkiewicz
12-13-2011, 07:55 AM
Al, it may have happened once or twice when you weren't around :D

It's good to know the training stuck!

Matt Goelz
12-13-2011, 08:32 PM
I'm surprised I haven't seen a team make a round tubular frame similiar to a bike frame or go cart frame.

If you search through our belt vs. chain evaluation (http://www.chiefdelphi.com/media/papers/2216) to find pictures, you will find that we made a round tube chassis for this robot test. However, the closest it got to competition was being used as a "box on wheels" robot to drive around with an attached trailer at the Muncie Scrimmage back in 2009. We used the kitbot chassis for our 2009 robot for simplicity.

ThunderTrain
01-19-2012, 07:43 PM
We weigh everything every time we change something. this way we can keep track of weight and get our workout in.