Let's Make Robots!

Not-so-mighty bot

So the Mighty Bot challenge (http://letsmakerobots.com/node/4979) got me wondering about the mechanical performance of my Qwerkbot project. It's not been optimised in any way for the task, and has no hope of winning, but maybe it's interesting for comparative purposes!

Qwerkbot weighs in at around 3lbs and is powered by a 7.2V racing pack. In the video it slowly shoves a pot of potatoes (total weight 3.5lb) the requisite metre- conveniently all the flat workspace I could find!

If you're really attentive, you might be able to spot I've added a speaker; also that the camera/sensor pan-tilt unit is shaking about worryingly, so I'm off to tighten that up...

In the red corner: QwerkBot weighs about 3 pounds.559.27 KB

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Making the wheels, or more precisely the tyres, more grippy isn't cheating. We all know about F1 drivers warming their tyres to increase adhesion - eitehr by weaving on the warm up lap (why do you think it's called that), or by using tyre heaters. And serveral times on LMR people have talked about taping tracks to make them less grippy. Chaninging tyre types may have a significant imapct on this challenge.

Similarly the surface on which you test your bot will have an imapct too. I'm not sure what would work best, but I might try something with ridges running at right angles to the directon of travel. This would give the bot wheels something to grip on and reduce the contact area between pan and floor, making it easier to start it moving.

It's harder to start than continue: try buttering the potatoes to make them more slippy (or more realistically, buttering the pot base). Can the bot's wheels be made more grippy - a bit of prit stick (a contact adhesive) in the "start" area perhaps.

 How about smaller potatoes - or maybe some peas for smaller increments in dead mass.

Put a few spuds on the robot over the drive wheels - it will help to reduce wheel spin

Ignoring the sillier comments about buttering potatoes and cheating by using adheasive (have you read the challenge requirements?) Mike does have one good piece of advise. Weight distribution!

If you look at Mighty1 you'll notice all the batteries in front of the wheels. Without a load on the back, Mighty1 sits with the batteries on the ground and the backwheels in the air.

During competition, the slight downward angle of the string causes a percentage of the 5Kg load to pull the back wheels down and giving me more traction.

That looked like it pushed the pot quite easily. After you tighten the loose screw try adding more weight untill the wheels spin or stall.
It was odd, one more potato and it couldn't seem to get going! I'd carried out a few test runs before setting up the camera. Surface matters a lot, it seems, so I'm not sure how to make this a fair test: on carpet, it can't even shift the empty pot (2lb).
Do it on the bench again but with the pot in a cardboard box. The cardboard won't grip the bench surface as well.