Standard Motor Driver Schematic for FRC

[philso]

Originally Posted by Andrew Schreiber

How many of those issues are particular to high current designs? Does something sitting in the 15A constant 30A burst range have to worry quite as much about these issues?

It is the interaction of the circuit inductance AND the rate of change of the current that provokes issues (dV = L * dI/dt). Higher currents typically lead to higher values of dI/dT.

At work, I am working on improving a switching power supply where the peak primary current is less than 1 Amp. The person who originally did the PCB layout clearly didn't know how to do it properly. Neither did the person who designed the transformer. The circuit sprays copious amounts of electrical noise.

If one does not have a thorough understanding of how to control the parasitic inductances inherent in the physical construction of a fast-switching circuit, one WILL have trouble with issues such as noise and over/under-shoot. The parasitic elements are not indicated on a typical schematic since they are dependent on exactly how a circuit is physically implemented. It is up to the designer to determine where in the circuit the parasitic elements will be significant and how they can be mitigated. It is not black magic but it takes many years of hands-on experience to be able to do this effectively. Reading a book, attending a class and being smart are not enough.

[ProfessorAlekM]

I never said that I intended on magically designing high-powered motor controllers that could survive a nuclear blast with the power of Cadsoft Eagle auto route feature and my amazing newbie mosfet skills.

Instead I'm asking for some sort of a motor driver standard,

There where several situations during the build when we needed a plain on/off type motor controller, so I hooked up a relay board that cost ~$10 (I had it from an earlier build).

But I couldn't use it because of the amount of FRC rules in place.

And knowing Vex, if a motor controller board costs $60, it probably only costs $30-$40 in parts. Of course they still have to pay for labor, shipping, and the design process, but I'm sure the community could create just as good of a motor board as them.

It's a bit of an Apple vs Linux situation. You can buy an expensive Apple computer that 'just works', and the software is completely closed off and protected, so you never have to worry about it. Or you can use Linux, which is free and works efficiently, you would just have to assemble the software yourself, which is slightly more time consuming.

To be fair, I would prefer to use vex motor driver boards, but money isn't free flowing, and the design process is expensive.

[ProfessorAlekM]

There is also a monopoly in FRC, where everything promotes VEX and AndyMark. It would be better to start including products from a larger variety of companies, since they can't even keep their own products in stock despite the fact that they know what parts people are probably going to need for competition before the kickoff.

Vex and AndyMark produce parts and then get library support for their specific part. Since they are certified FRC suppliers, they then sell parts for more than their worth because people trust them more.

[Oblarg]

Originally Posted by Alan Anderson

It's hard to design one that interfaces with standard hobby servo signals, provides sustained performance at 40 amps and occasional transients approaching 200 amps, is proven to perform as advertised so the robot can be certified as following the rules, is rugged enough to withstand the abuse it will take on an FRC robot, doesn't pose shock or fire hazards to its users, etc. It's hard to build one to those specifications without having resources, skills, and experience,

Should anyone doubt this, I'd suggest they direct their attention to the (now thankfully defunct) Jaguar motor controllers, which were made by a professional company who (ostensibly) knew what they were doing and still suffered from all sorts of reliability issues.

[Sperkowsky]

Originally Posted by ProfessorAlekM

There is also a monopoly in FRC, where everything promotes VEX and AndyMark. It would be better to start including products from a larger variety of companies, since they can't even keep their own products in stock despite the fact that they know what parts people are probably going to need for competition before the kickoff.

Monopoly - a commodity or service in the exclusive control of a company of group.

You just named two companies that's your first issue.

Next you do know Andymark doesn't make any motor controllers they just sell them.

These companies have to make a profit off a small market. You can not expect to have more then a few suppliers for 3,000 teams.

Right now you have a lot of options for motor controllers

Jaguar Motor Controller (Part #s: MDL-BDC, MDL-BDC24, & 217-3367)Talon Motor Controller (Part #s: CTRE_Talon, CTRE_Talon_SR, & am-2195)Talon SRX Motor Controller (Part #: 217-8080 & am-2854)Victor 884 Motor Controller (Part #: VICTOR-884-12/12)Victor 888 Motor Controller (Part #: 217-2769)Victor SP Motor Controller (Part #: 217-9090)

Along with
The mindsensors sd540
And the Rev sparks

That's 8 options for motor controllers which imo is an oversaturated market already.

[ProfessorAlekM]

I was looking up the encoders on AndyMark. The encoders they sell are only $20 each when you buy them in bulk (50), and they sell them for less if buy more (it says I have to ask for a quote if more then 50), but they sell them for $40 each.

And I'm sure shipping +$5-10 in profit is not $20.

They also sold every team a base kit that can't even clear any of the obstacles, so that you would then have to buy another base kit or upgrades (Making them more money).

On top of that they knew what this years competition was, and they couldn't even keep Rhino Treads in stock during build. Some supply and demand could be going on.

I know that I'm getting off-track on my own thread, but I'm trying to conserve money for our school.

[Andrew Schreiber]

Originally Posted by ProfessorAlekM

There is also a monopoly in FRC, where everything promotes VEX and AndyMark. It would be better to start including products from a larger variety of companies, since they can't even keep their own products in stock despite the fact that they know what parts people are probably going to need for competition before the kickoff.

Vex and AndyMark produce parts and then get library support for their specific part. Since they are certified FRC suppliers, they then sell parts for more than their worth because people trust them more.

Let's ignore for a moment that BOTH the Talon and Victor are in stock currently.

Let's ignore for a moment that there are at least 2 other companies actively selling ESCs that are legal for FRC applications.

Let's ignore for a moment that there's a handful of grandfathered ESCs that are also legal for FRC applications.

I'm just going to address the fact that you are complaining about the cost of ESCs... Prior to a few years ago our ESCs were stupid expensive. I seem to recall paying $120 a pop for a Victor that was much larger, not conformally coated and not as linear. And you know what? They were still worth it then. I have never had a properly connected [1] Victor die on me. 12 years of robots, many years with practice bots, numerous test beds and demo robots... Never. I've used probably 200 Victors in the last 12 years and NEVER had a failure. I'm sure you could find something that claims to have the same specs as a Victor for about $40 on HobbyKing today, but to me the extra $20 I pay to order a product that has that kind of track record is worth it.

And if you don't care about that track record [2], there's $45 SHIPPED ESC that's legal and you're not going to find an off the shelf ESC for much less anywhere. [3]

But, for fun, let's do a thought experiment on if they were legal. I would NEVER pick a team that used custom built ESCs for their drive system. Honestly, I have qualms about picking a team that uses SD540s or Sparks in their drive system this year.[4] The average FRC team can't reliably build bumpers. An ESC is at least an order of magnitude more complicated, I have no faith in their ability to do that reliably either.




Ok, now we can bring back the 3 other points...Would building an ESC be a cool summer project? Sure. Would it be worthwhile? Absolutely. Can you do better than commercial companies? Maybe, maybe not. Is there some conspiracy by VP and AM to increase profits by gouging prices on ESCs? If you really believe this, who is your tin foil hat supplier?

Seriously though, you wanna build your own ESC? Cool, do it. But don't whine about how the only reason you're not allowed to run it in competition is so AM and VP can make more profit. [5]



-s


Edit: Addressing follow on post...

Originally Posted by ProfessorAlekM

I was looking up the encoders on AndyMark. The encoders they sell are only $20 each when you buy them in bulk (50), and they sell them for less if buy more (it says I have to ask for a quote if more then 50), but they sell them for $40 each.

And I'm sure shipping +$5-10 in profit is not $20.

They also sold every team a base kit that can't even clear any of the obstacles, so that you would then have to buy another base kit or upgrades (Making them more money).

On top of that they knew what this years competition was, and they couldn't even keep Rhino Treads in stock during build. Some supply and demand could be going on.

I know that I'm getting off-track on my own thread, but I'm trying to conserve money for our school.

1: That's par for the course for electronics. Larger orders are cheaper. You also have to take into account that stocking and inventorying parts isn't actually cheap. I'd also bet AM has much better support for if you order 3 encoders and one of them comes DOA. A lot of companies will sell you small quantities but they don't care you exist unless you order 10000 units a year.

2: You're right, the KoP frame didn't cross the obstacles. To which I have two responses - this is a freaking engineering competition, try doing some engineering and don't expect half of the game to be solved for you out of the box. And second, yes. I think it's been discussed numerous times that AM didn't know the game until the kitbot had already entered manufacturing and it was too late to change things.

3: VexPro ran out of gears... GEARS. Which do you think is easier to manufacture and stock, a complicated high cost assembly with limited use or a freaking 54T .5" hex bore gear? Go ahead, while you think that one through I'll wait. ... back? Good, so yeah, see again, inventorying is expensive and expecting AM to keep 1000 Rhino drive kits in stock on the off chance teams would want it is messed up and would actually only drive prices up more. Furthermore, they were a new product so production probably was still ramping up and had issues [6].

And furthermore, on 2 and 3, have you MET Andy Baker? Dude ain't trying to profit off of the backs of teams.


[1] I had 2 fail at one point, because I hooked the output of one into the input of another due to mis labeled wires in the depth of a robot.

[2] Though, honestly, I trust Greg not to put out a shoddy product, I'm CAN bus this year or I'd probably have used a few Sparks outside of my drive system.

[3] I've looked, extensively.

[4] Seriously, nothing against those products, but I've lost too many matches due to partners sitting dead on the field, I want that record of reliability. This may change next year or w/ more testing.

[5] And AM/VP would be a duopoly... And I guess since there's at least 3 manufacturers it'd be a.. triopoly?Idk, I don't think that's a word, I think they just call that a competitive marketplace.

[6] Like stress issues on the pulleys... which they fixed.

[Whippet]

Originally Posted by ProfessorAlekM

They also sold every team a base kit that can't even clear any of the obstacles, so that you would then have to buy another base kit or upgrades (Making them more money).

On top of that they knew what this years competition was, and they couldn't even keep Rhino Treads in stock during build. Some supply and demand could be going on.

I'm going to correct you on just this one point, since there will be plenty of people better able to address your concerns about motor controllers specifically. This year was the first time that FIRST revealed elements of the game to certain suppliers prior to kickoff. The only thing that Andymark or VEX knew prior to kickoff was that there would be obstacles for the robots to traverse and (I think) that it was a ball game. Nothing was disclosed of the size, type, or nature of the obstacles or balls. Accordingly, Andymark adjusted the Kit of Parts chassis to include 6 inch wheels rather than the 4 inch versions that have been provided for the previous two years. They did not know enough to guarantee that they would be able to move a sizable stock of Rhino modules, pneumatic wheels, etc. The same thing applies to VEX and West Coast Products.

The FRC suppliers have done an excellent job of handling supply shortages for the past few years. We recently purchased a set of hex shaft collars from Andymark and received a set of VEX collars - still in vex packaging - in the Andymark shipment. These companies do everything they can to help make sure your robot gets completed in time and I have nothing but good things to say about them.

[Ryan Dognaux]

Originally Posted by ProfessorAlekM

There is also a monopoly in FRC, where everything promotes VEX and AndyMark. It would be better to start including products from a larger variety of companies, since they can't even keep their own products in stock despite the fact that they know what parts people are probably going to need for competition before the kickoff.

Vex and AndyMark produce parts and then get library support for their specific part. Since they are certified FRC suppliers, they then sell parts for more than their worth because people trust them more.

LOL. You don't know how good we have it now in FRC. If you were around back in the early 2000's and compared what we have now with what we had then, you'd personally thank every single supplier that makes this competition more accessible to teams around the world. They've changed FIRST in a great way. The majority of teams don't have the skillset nor do they want to waste time building their own motor controllers (mine included.)

Originally Posted by ProfessorAlekM

I know that I'm getting off-track on my own thread, but I'm trying to conserve money for our school.

Instead of complaining on Chief Delphi about how much stuff costs, you could be spending time actively fundraising so that your team can afford more. Get your teammates to do it too. Little donations all add up. It's no secret that it costs money to compete. Work on fundraising so your team can purchase a few things.

[Kevin Sevcik]

Originally Posted by ProfessorAlekM

I was looking up the encoders on AndyMark. The encoders they sell are only $20 each when you buy them in bulk (50), and they sell them for less if buy more (it says I have to ask for a quote if more then 50), but they sell them for $40 each.

And I'm sure shipping +$5-10 in profit is not $20.

They also sold every team a base kit that can't even clear any of the obstacles, so that you would then have to buy another base kit or upgrades (Making them more money).

On top of that they knew what this years competition was, and they couldn't even keep Rhino Treads in stock during build. Some supply and demand could be going on.

I know that I'm getting off-track on my own thread, but I'm trying to conserve money for our school.

Andymark doesn't get specific game information ahead of time any more than any team does. I believe Andy said they were told there would be obstacles in this game or something like that, which inspired the rhino tracks. Makes it hard to design for specific obstacles. It also makes it hard to pre-buy enough stock to satisfy the demand of 3000 teams. It's obvious after kickoff that there will be a run on pneumatic tires, or banebot wheels, or whatever the hot item is. It's never obvious before kickoff.

On the cable, I suspect you didn't actually specify the encoder correctly on US-Digital. When you specify one spacer and centering tool per encoder, the price per 50 is $28. And then you add a $5 cable on top. Andymark and Vex don't have a huge markup. They can't because if they did, they couldn't compete with other suppliers like Robot Marketplace, Robotshop, Mouser, Digikey, various industrial supply houses, or any random Joe that sets up an EBay or Amazon shop. It's called capitalism.


Honestly, the best way to save money for your school is to not break things so you can save what's salvageable from year-to-year. After about 3-4 years of not exploding motor controllers or melting motors, you'll have plenty for whatever robot you're going to build. A few more years and you'll have plenty for two robots. The best way to save money in a particular season is to CAD and actually design your robot so you can minimize buying the wrong thing or express shipping something you need in 2 days before competition or bag.

[Kevin Sevcik]

Originally Posted by Ryan Dognaux

LOL. You don't know how good we have it now in FRC. If you were around back in the early 2000's and compared what we have now with what we had then, you'd personally thank every single supplier that makes this competition more accessible to teams around the world. They've changed FIRST in a great way. The majority of teams don't have the skillset nor do they want to waste time building their own motor controllers (mine included.)

Oh my gosh, but 1998 - early 2000s. I don't remember when we could finally buy stuff from somewhere other than Small Parts, but it was amazing. I mean, if you want to talk about a monopoly, THERE was a monopoly....

[BeardyMentor]

A good friend of mine, Bill French has some musings on building his own motor controller:

The expensive part is knowing how to build a controller. There are several open source projects out there, that's how i got started. For probably $60 in parts my controller can do 48V and i've measured pulling 280A through it. But .. it doesn't have brakes, regen... and i've had to take a sawzall to it twice mid race.

Just as an addendum, the reason he had to take a sawzall to it was one of the Mosfets on it had failed in the closed condition resulting in a motor stuck spinning at full throttle forward.... better be quick with the e stop. The sawzall was to cut the burnt up mosfet off the board in an expedient fashion in order to get back on the track more quickly.

[GreyingJay]

Originally Posted by ProfessorAlekM

It's a bit of an Apple vs Linux situation. You can buy an expensive Apple computer that 'just works', and the software is completely closed off and protected, so you never have to worry about it. Or you can use Linux, which is free and works efficiently, you would just have to assemble the software yourself, which is slightly more time consuming.

This is not a bad analogy.

If you were doing a mission critical presentation, say to the CEO of some big company, which would you rather use?

I would rather have something that "just works". I would like to know that when I boot up my laptop and start my presentation, it will work. That my laptop won't fail on me because, oops, apparently I didn't do that DIY upgrade correctly and I accidentally broke it. That if I do have a failure, I can say "oops, oh well, can I borrow someone else's laptop?"

And even if you say "I'm smart and I can guarantee mine wouldn't fail like that", then put yourself in different shoes. You're running a conference with hundreds of attendees. Which would you rather each of them be using? Can you trust everyone else to be as smart as you?

[kiettyyyy]

Originally Posted by Andrew Schreiber

How many of those issues are particular to high current designs? Does something sitting in the 15A constant 30A burst range have to worry quite as much about these issues?

Absolutely. See Phil's reply.