So this week on the Discord a lively conversation bounced around the subject of the weight of the Cattle Food that we need to transport for the Hungry Cattle challenge.
The Barn Rats team previously demonstrated a pretty successful dispenser that was able to fill a food trough to the required volume. But we had not really given any consideration or thought to the issue of what would happen if we had 3 of those dispensers hanging off the front of our robot.
Uh. That might have been a mistake…
Turns out that the short answer to the question is … we’re going to need to substantially rethink our design.
The dispenser works pretty well, as long as the robot is not trying to go anywhere. Driving it around however is a bit of a problem… Its way too front-heavy for our test chassis.
The chassis is about 180 mm square, with the dispensers sticking out about 100mm to the front of it. The robot body itself weighs 1300g. The front-mounted dispenser weighs in at about 400g empty, and 1000g when filled with 600g of dry rice, which is the amount it would take to fill 3 food troughs to 50%.
The robot has no trouble moving the mass around, even though this test chassis just uses tiny TT motors. Unfortunately backing up, or stopping from forward motion causes the whole thing to tip over…
On the flip side (poor pun intended), it DOES do a pretty good job of dispensing the rice. Most of the rice actually makes it into the food trough. The central bin with the front-dropping trapdoor does a better job than the side bins which have side-facing trapdoors. But as you can see in the photo we do manage to get the bin up to just over half full (the black stripe starts at the 50% point (thanks for the idea @keegan).
So it looks like some redesign is in order. Thinking about moving the bins “back” so their mass is mostly between the robot wheels, then having a slide to aim the rice down towards the trough. Mom always used to say that “there are no fails in life, just opportunities to learn”…
The big lesson here is “pay attention to the mass of that rice”. It is probably not insignificant compared to the mass of your robot.