Robot Chassis (refresh to update)

[Nigel Goodwin]

How does he find time to do the Inchworm etc. PCB's?, he must surely spend all his time creating his great drawings!.

 

[bloody-orc]

to make a diode, resistor, or similar, it takes 1 minute.. for IC i assume 5... component placement 15 minutes... whole PCB maybe 1h

of course i don't know how long he does his stuff...

Then again Nigel, how long does it take for you to write a program for it in ASM?
1day? 2? week?

everyone has it's own "weaknesses"... some people like to write in asm, some like to make perfect CAD files, some just like to dress up like a woman and run around town square...


PS If i managed to offend someone with my examples then it was not my intention. Sorry in advance

 

[Nigel Goodwin]

to make a diode, resistor, or similar, it takes 1 minute.. for IC i assume 5... component placement 15 minutes... whole PCB maybe 1h

You're missing my point - NOT his PCB's, his great drawings of robots and board layouts.

 

[bloody-orc]

You mean the PCB in CAD program right? like on the images the nice board layout and everything?
well that's what I was talking about actually I've done some myself.

But I thing Bill can answer that question better... (don't know why i answered that in the first place)

 

[blueroomelectronics]

Glad you like the drawings, it was the only way to describe my ideas to my last employer. Beats a napkin.
One you have a library of parts built up it does not take long to draw things.

Sometimes there are macros like ruby script gears.

 

[blueroomelectronics]

Update, I've had a chance to use the SN754410 on the Mongoose prototype. Looks like a winner. Works fine, runs warm not hot with the two Tamiya motors and gearbox. So looks like the SN754410 is the new Mongoose H-Bridge.

 

[Omar.M]

That is great Bill! I ordered two ICs too, and hopefully I can try them out soon too.

I was just wondering-- what power source did you use for the Mongoose? Did you keep the motors separate from the other IC voltage?

 

[blueroomelectronics]

The motors are powered directly from the batteries, the PIC is powered the same way but with a 1N5817 diode between it and the batteries. Two 470uf 6.3V caps on each side plus 0.1uf near the ICs. The ICD2 is on the same side as the PIC. (You need batteries to run the motors)

 

[Hank Fletcher]

So looks like the SN754410 is the new Mongoose H-Bridge.

So am I going to get any cred for that?

 

[blueroomelectronics]

So am I going to get any cred for that?

Of course and another Canadian too.

 

[Omar.M]

YAY FOR MR. FLETCHER! I have to hand it to you, you can be (and probably are!) a really cool superhero. I mean, the power of persuasion is a pretty good power to have!

I can see it now, you on every cereal box!
"With his trusty sidekick, Mongoose!"

But then again, Bill would be a super hero too, because of his AMAZING drawings and robotics ideas. Heck, we'll all be super heroes .

 

[Hank Fletcher]

I know they're just words, but it still means something. Thanks, guys.

 

[blueroomelectronics]

Here's the business end of the Mongoose with SN754410 and heatsink, cutaway too.
**broken link removed**

 

[bloody-orc]

nice
this SN754410 is a nice chip indeed. just 4$ here

anyway, I saw, that it could drive 1A, but is this 1A per chip or 1A per channel or 1A per half H-bridge or what? how much do your motors draw?

 

[blueroomelectronics]

The Tamiyas run about 250ma each, full stall over an amp so a PTC fuse is in order. The SN754410 has thermal shutdown though.

It's my understanding 1A total, they can be stacked and I will have as much copper on the PCB under the chip as I can put there.

You can put a Wakefield W-651B heatsink on the SN754410, I'll add one to the drawing.
**broken link removed**

 

[Hank Fletcher]

It's my understanding 1A total, they can be stacked and I will have as much copper on the PCB under the chip as I can put there.

The info in the datasheet isn't 100% clear on this. At the top, it lists 1A per driver, which would mean 2A per chip, but it's not clear whether or not this is the peak or continuous rating. It's also not clear what kind of failure to expect when the specs are exceeded (it just says, "Look, don't expect it to run properly if you force the specs," standard component rules).

The greatest load I've ever put on one of these h-bridges was trying to stall by hand a geared car window motor. I used one h-bridge, wiring both full h-bridges in parallel for max current. I couldn't stop the motor! And it only pulled about 1.75A peak before my hand cramped. I tried this over and over again, and the same chip still works fine although it got quite warm (check out the current performance vs. chip heat remark in the datasheet, BTW). So maybe the 1A rating per driver is a continuous rating? That would certainly be consistent with the applications I've seen using the SN754410 on various websites, and with the popular notion/manufacturer's claim that the SN754410 is an improvement over the L293.

Someone ought to do some tests on one to check this out - just put a 1.75A load (something like a 12V 20W halogen bulb) on a single SN754410 chip (wired in parallel) and see what happens over time. I'd do it if I had more time on my hands, which I most certainly do not. It might be in your interest, Bill, if you're looking to limit the investment on mass produced Mongooses (Mongeese?). Is it cost effective to include a fuse given the motor ratings, and the cost of the SN754410 (or two to be completely within spec limits)? I bought some fuses when I bought my first batch of SN754410s, but then I realized that in the off-chance I designed something so poorly that it did blow it'd only be slightly more expensive to replace the SN754410 than to replace the fuse, so why bother? Maybe I got ripped off on my fuses, but like I said I never bothered to use them and have yet to wreck a SN754410.

 

[Hank Fletcher]

Just to back up my claims, check out this product:
http://www.roguerobotics.com/products/electronics/lchb

which is distributed by these places:
http://www.jameco.com/webapp/wcs/st...toreId=10001&catalogId=10001&productId=386337
http://www.robotshop.ca/home/produc...controllers/rogue-robotics-dual-h-bridge.html

The more I read the info on the TI website, the more I convince myself that it's 1A per driver, not 1A per chip. Geez, look at the mark-up for this chip with a carrier board! I gotta get me a piece of that action...

 

[blueroomelectronics]

Well if its 1.1A per side then the Tamiya gearbox will not be a problem. They DO have thermal shutdown so they will stop functioning if they get too hot. The PTC fuses are self resetting and less than $1. Also since the SN754410 should be soldered to the PCB (No socket) to get the best thermal transfer to the PCB.

Wow $26.99 US.

Thermal epoxy and the heatsink on a SN754410 should keep it cool and look cool too.

Refresh your browser to see the updated Mongoose above (with heatsink)

Here's some more about the little motors
https://www.hobbyengineering.com/H2242.html

PS the metalshop got the order for the chassis parts, just a couple of prototypes but I'll post photos when I have the parts. The PCB will be done after the bodywork.

 

[blueroomelectronics]

Here's the first Mongoose prototype photo. It's mostly a bare chassis at the moment. Better photos to follow. The solderless breadboard is just sitting on the chassis, it will have a mounting plate designed for it.

**broken link removed**

 

[bloody-orc]

WOWW! now this is some precision work man!
PS how much does it cost to send one here? Estonia, Europe. I might want to get me one of those to play with