pic: FRC294 Prototype base almost done

[jwfoss]

looks really nice, those plates must have taken forever to machine out like that, do you have a total weight for the drive train, and just the plates? i'm also wondering how well the transmissions hold up out of that material

[Peter Matteson]

I want to echo Greg's chain wrap comment, that center sprocket makes me nervous.

Also your front and rear standoffs (plates) dowl pinned together? I never would have thought of doing it that way. I probably would have just used counter sunk #8's. Just curious as to why you did it that way.

[spazdemon548]

Wow, I love it!!! Its good to see more teams using the clockwork spacers. There so easy to use and make for quick repairs. Do you have any drop in your center wheel?

[techtiger1]

This looks good, I like the 1 chain loop idea you'll know if running it that way works pretty quickly to. The gearboxes look great as well I am going to recommend you keep a close eye on them though with the plastic plates even though I know it's a proven design. Has there been any problems with the chasis plates trying to shift back and fourth? Also I'd like to hear the answer for the question Sean asked about the rollers. I think it is excellent man good luck with this design with some testing and tweaking it should do well.

-Drew

[EricH]

Originally Posted by techtiger1

Also I'd like to hear the answer for the question Sean asked about the rollers.

Adam already answered.

Originally Posted by AdamHeard

Well, originally it was one idler (on the tensioner) because It was easier to cantilever the tensioner and that worked better with an idler. Now that I think, We could've put a roller on the shoulder bolt just as easy. The idler below the transmission was just added because I forgot to check to see if the chain clears the shifters (doh). So, it was easier just to use an idler on hand.

[Borisdamole]

I am the son in the father son team Adam mentioned, and this robot is currently sitting in my living room. I am going to address as many questions as possible.

1. Were talking about replacing the rollers with sprockets, (budget and time permitting) because the rollers make a lot of noise when driving.

2. The plastic for the transmissions are way stronger than they look. They were designed to work with some flex, but there very stiff.

3. Yes the side plates are pinned together, the stand offs use pins and bolts(the pins take the shear load, the bolts hold everything together)

those are all the question I think i can answer off the top of my head, but if you have any others feel free to ask.

Taylor

[Madison]

How heavy is it? How about each component?

It seems such a shame to hide such nice wheels behind a big ol' plate, but the design seems sound. I think that if you're diligent about checking your chain tension, since it appears the tensioning idlers aren't spring-loaded, you won't have to worry too much about the chain wrap on the center sprocket. If the chain gets slack, though, the excess is going to gather up at the bottom and come off that sprocket.

Almost purely for aesthetic reasons, I'd try to lower the idlers along the top and bring the chain down inside the panels.

Why are you starting with 3/8" plate and pulling so much material out of it instead of say, using 1/4" -- so they're still thick enough for bearings -- and saving yourself some machining time?

[=Martin=Taylor=]

How much did it cost? Roughly how many days of work went into building it?

It looks great. Have you thought about rotation sensors?

[maclaren]

I agree with replacing the rollers with idler sprockets it would be much more efficient. The noise is the chain lobes bumping over the rollers. Noise like that means inefficient.

I'm guessing from the picture that it's #35 chain?

What size wheels are you running they look about 4"?

What shifting method are you using. Two dog shifters, a ball shifter, or what?

What speeds (FPS) are you estimating from the different gear ratios?

I have to ask do you really need four gears? I mean you don't have a huge amount of traction so having a really torquey gear ratio could mean that you don't have enough traction to actually realize that troque and your wheels would just slip out. And how fast do you really need to go the field is only 50 something feet long so 12-15 FPS means so can get across the field pretty quick. Don't get me wrong a four speed transmission is really cool and I respect the engineering and the maching that goes into the effort.

I would also be interested in the total weight of the system and the weight of the transmissions assembly.

[EricH]

Originally Posted by maclaren

What size wheels are you running they look about 4"?

I have to ask do you really need four gears? I mean you don't have a huge amount of traction so having a really torquey gear ratio could mean that you don't have enough traction to actually realize that troque and your wheels would just slip out.

I think those wheels are the same as they used last year, which would be about 6" (also, the sideplates are listed as 5" and aren't that much smaller than the wheel).And they do have a lot of traction; they've lost tread playing defense with that blue material. And a four-speed of this type would be easier to design and build than a three-speed.

[Peter Matteson]

Two more questions to bother you with.

Can we get a close up shot of your tensioner?

What do you use for axles? They don't appear to go through the plates or be driven, meaning you could simply use a grade 8 bolt through one side and threaded into the other.

Like this...

(Will post pic from my home computer tonight)

[AdamHeard]

Originally Posted by Peter Matteson

Two more questions to bother you with.

Can we get a close up shot of your tensioner?

What do you use for axles? They don't appear to go through the plates or be driven, meaning you could simply use a grade 8 bolt through one side and threaded into the other.

Like this...

(Will post pic from my home computer tonight)

Close up shots will be posted this weekend by me (or sooner if borisdamole hears the request and goes to his livingroom).

It's almost identical to last year's. Pretty much it's just a block that sits in a piece of tubing. Screws pull the black away from the chain to tension, and there is a shoulder bolt in the block that the idler sits on. It was inspired by our drive in 2005/2006 where we used pillow blocks that were tensioned that way (same way the west coast drive has been tensioned sometimes... like 968 in '06. In fact, we originally got the idea from 60).

The axles are 3/8" 7075 hex we already had laying around. Just threaded one end 3/8-16. We considered bolts, but we wanted this base to be as light as possible.

[AdamHeard]

Originally Posted by maclaren

I agree with replacing the rollers with idler sprockets it would be much more efficient. The noise is the chain lobes bumping over the rollers. Noise like that means inefficient.

I'm guessing from the picture that it's #35 chain?

What size wheels are you running they look about 4"?

What shifting method are you using. Two dog shifters, a ball shifter, or what?

What speeds (FPS) are you estimating from the different gear ratios?

I have to ask do you really need four gears? I mean you don't have a huge amount of traction so having a really torquey gear ratio could mean that you don't have enough traction to actually realize that troque and your wheels would just slip out. And how fast do you really need to go the field is only 50 something feet long so 12-15 FPS means so can get across the field pretty quick. Don't get me wrong a four speed transmission is really cool and I respect the engineering and the maching that goes into the effort.

I would also be interested in the total weight of the system and the weight of the transmissions assembly.

I'm kind of concerned about some things you are saying....

I'm not sure how we don't have a "huge" amount of traction. The coefficient of friction of that tread was measured to be 1.1-1.2. If we wanted to max it out we could go for natural rubber that 254/968 used this year and get about 1.3. I'm not sure how this isn't the maximum amount of traction teams have been able to get. Tank treads have been experimentally shown to only get a minimal increase (about 3% according to Andy Baker and testing he did with 45), if any (according to most. Paul Copioli will probably fight to the death on this one) at all.

Wheels are 6" btw, and yes #35 chain.


In terms of the transmission, it is an iteration of team 33's 4 speed; which is two crash shifters in a row. This Drivetrain is designed around the AndyMark Gen 3's (or a slightly modified 3 motor AndyMark single speed). We wanted to do something fun and different for for prototype though, and it didn't hurt that the material for the 4-speed was significantly less than the cost of two Gen 3's. Also, we figured the 4 speeds would give a better spread of gear ratios to show in person for prototyping next season (I think most people on the team who aren't into drivetrains would benefit from seeing 6fps vs 9fps vs 12 vs 16 [those aren't the actual speeds, just arbitrary numbers]).

I believe we are traction limited in the bottom two gears, and the speeds depend on the size of the output sprocket on the transmission. I think they have a 10 T on there. I have the excel at home with all the speeds (I'm going home tomorrow, and will post then). Even though the lowest gear is way past traction limited, that isn't necessarily a bad thing; it will allow for amazingly precise alignment and will be able to hold position better while drawing less current. I'm referring to a PID loop that will hold the robot's heading (even stationary, I think the triplets did that amazingly in 2006) very accurately.

EDIT: EricH; thanks for referencing that. The wheels are very similar to last year, just bit wider now. We were losing tread because we had two bolts side by side that almost cut the tread and have, so it was very easy to tear off. We fixed it before champs by changing it to single bolts like in the picture. Haven't lost a tread since. Too bad you won't be seeing it at San Diego again ... but there is allways LA! (although, I'd much rather see 294 on the field with 330 than against.... I think 294 would have a better chance of winning that match with you instead of against)

[EricH]

Originally Posted by AdamHeard

Too bad you won't be seeing it at San Diego again ... but there is allways LA! (although, I'd much rather see 294 on the field with 330 than against.... I think 294 would have a better chance of winning that match with you instead of against)

Sorry Adam--Despite Mines's spring break ending the weekend of LA, I'm not yet sure whether or not I'll be leaving SD over break. Maybe I should drop by during Week 1???

[maclaren]

As far as traction I was mostly referring to the width of the wheels. In my mind I was comparing them with wide tank treads or a 3" inch wide natural rubber wheel that we had custom wrapped with 60 durometer natural rubber a couple of years back. I realize that the normal force will not change because the weight of the robot is limited so widening the wheels only spreads out the normal force on a wider surface area. I haven't really experimented with this so I don't know what the trade off is. I know that there would be a point of dimenishing return as far as increasing the tread contact area to normal force ratio. I just know what I have observed which is I have seen tank tread and wide wheeled robots winning the pushing battle against the narrower wheeled robots. My imppresion was that the wheels on your frame were of the narrower variety. This is purely subjective. I would be interested in knowing the width of said wheels.

I would also love to do some testing with comparing different traction device and finding out what the return is on increasing the traction surface area realtive to the normal force. If my team does this experiment we will post the results of our findings.

As far as the different gear ratios being traction limited I agree that a slower ratio would definately give you more accurate control. I would love to see the spreadsheet of speeds when you get back home and have a chance to post them.

I agree with you EricH that the four speed in this type of shifting is easier to design then a three speed. I would love to see someone design and build a squential shifting three speed ball shifter I think that would be sweet. If I ever get the time to actually sit down and dore more inventor work I will make one and post the pics. One of the down sides of having a full time job and other demands on my time other than robotics.