Standard Motor Driver Schematic for FRC

[Alan Anderson]

Originally Posted by ProfessorAlekM

You would be surprised would students can do. It's really not hard to make motor controllers, I've made them myself before and I'm only in 9th grade.

Ah, to be a teenager and know everything again.

It's not hard to make a motor controller.

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.

...our team has spent hundreds of the dollars on motor controllers.

If you're expecting to be able to save "hundreds of the dollars" by building your own motor speed controllers, I suspect you're failing to consider a lot of details.

[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.

[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.

[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.

[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.