Finished First Mini Sumo

[frank26080115]

Videos
[youtube=425,350]zkzi5yPCPHs[/youtube]
[youtube=425,350]bQT3o7bEk_E[/youtube]

What do you guys think?

Those rubbery colourful wrist straps provide a ****load of traction (looking forward to facing you, Jon :-P ). All sensors are accurately sensitive to within 7", and IR is only emitted once every 1/4 of a second so passive sensors can't detect me. I have both active and passive sensing abilities. Runs off two 9V Duracells. Motor drivers can take 1.5A each (not in picture). Program is intelligent enough to run away if there is no time to turn around to face the opponent, and also detects frontal contact. Weighs 425g according to my kitchen scale. almost exactly 10cm x 10cm. Front wedge sits very close to the ground and covers the entire 10cm area at a 80ish degree angle.

I still need to give it some black paint.

[JonHylands]

Nice, although I suspect its going to be slow. My first mini-sumo used that same Tamiya twin-motor gearbox (http://www.huv.com/miniSumo/drone), and even with the big 2.75" tires, it was slow.

Once I built Seeker 2, there just wasn't any contest - watch the first video on my Seeker 2 page (http://www.huv.com/miniSumo/seeker2/) where Seeker 2 trashes Drone (http://www.davehylands.com/jon/Seeker2Drone-01.avi). And that was when Seeker 2 weighed it at about 290 grams. Its 495 grams now :-)

The other issue you're going to have is chewing through batteries. Seeker 2 used to use a pair of rechargable NiMh 9 volts, but I found after I while they couldn't take the abuse, and stopped charging fully. Now I use a single 6-cell AAA NiMh pack I picked up from Digikey, and it works much better (and much longer).

Nice job though. I like the smarties box battery holder...

- Jon

[Admin]

video of it beating up a box or something, please

IR is only emitted once every 1/4 of a second so passive sensors can't detect me.

But doesn't that mean your robot is blind for 3/4ths of the time?
(still, I think this is a neat idea)

I like the smarties box battery holder...

lol I didnt even notice!

[JonHylands]

With respect to passive versus active sensors, I don't know of any mini-sumos that use passive sensors. Seeker 2 uses Sharp GP2D12 analog rangefinders, and I check them 100 times per second. The whole robot runs at 100 Hz, which is necessary given how fast it is - if I try and run it at 10 Hz, it runs off the edge of the ring before the edge sensors even notice the edge...

I also have a custom close-IR sensor, which only works out to about 2" in front. If the robot detects something with that sensor while pushing, it ignores the edge sensors completely...

- Jon

[frank26080115]

Videos
[youtube=425,350]zkzi5yPCPHs[/youtube]
[youtube=425,350]bQT3o7bEk_E[/youtube]

I forgot to set a default moving direction so it stays still before seeing anything.

The first twitch is my motor driver check, I have a bunch of these toshiba chips that will burn out like mad!

I guess the range does seem a little low, might need more tweaking the threshold in software

[Admin]

I have a bunch of these toshiba chips that will burn out like mad!

Sounds like a power issue? Meaning, your motors are drawing way more current than your driver can handle . . . try heat sinking it, or stacking some in parallel . . .

This is a problem with treads, they have a lot of friction resulting in high torque applied to your motors - and hence high power draw.

[paulstreats]

also if the treads are stretched really tight between the two wheels, it will make it difficult to turn them

[frank26080115]

There isn't actually much stress on the axle, i made sure of it.

I will try and find some heat sink.

You can't solder the toshiba chips without breaking them lol, seriously, no way.

[bulkhead]

Just out of curiosity, which toshiba chips are these?

[frank26080115]

TA8050P
They are 1.5A H-bridge chips with built in diodes
Experimenter's Discount Warehouse on eBay used to sell these in packs of 27 for $15

[paulstreats]

there is an h-bridge type schematic on www.robotroom.com where there are zener diodes used to prevent over loading the power mosfet driver chip which is used to power the motor. Ive built a couple of these and they work fine, in fact i have used them with the exact same tamiya gear box without a problem in the past.

[frank26080115]

I have used that TC4424 chips before, they're pretty useful, but I always thought diodes were essential to an H bridge so I never used them much, plus they take up more board space and also you can't really attach any heat sinks without using compound.

[Admin]

Yea you need a diode. And don't use a zener diode . . . use the regular type.

MOSFETS are very sensitive to current going the wrong way (caused by voltage spikes from the motor), so the diodes serve as protection.

Many MOSFETS today come with some type of built in diode, just check the datasheet for details.

[frank26080115]

I thought those were crazy expensive (I judge by the willingness of a company to send me samples)...

are they?

[Admin]

MOSFETs cost between $2 to $6 typically. For just one, thats fairly cheap, but if you were to say buy 4 for an H-bridge that could get a little pricey.

~4 years ago I got a whole bunch of free sample MOSFETs from fairchildsemi . . . might be worth a try . . .

[paulstreats]

The zener diodes are used to protect the mosfet driver chip, if the motor tries drawing too much, the zener diodes direct the power to ground rather than into the mosfet driver, it means that if your motors are too much overloaded, they will be power down which might be a bad thing, but it saves your h-bridge from frying.
You should use normal diodes for the actual directional flow, but use reverse mounted zeners to the ground as overvoltage protection. While it does increase board space slightly, its probably worth doing to stop your board from frying.

[Admin]

the zener diodes direct the power to ground rather than into the mosfet driver

depends on if you have n-type (to ground) or p-type (to +)