How would I make a "Tween" bot?


#1

I have been considering making a tween bot. (http://www.tweenbots.com) It needs to be a cute robot thats not too large to man handle yet it a bit too big to carry comfortably. I am not good at the arty side so looking for ideas.

It will also need a slow moving, none steerable drive mechanism. I have fiddled with adjustable DC-DC converters so that I get a low voltage to a DC motor. It does not work that well. I was wondering if I should consider stepper motors. I think this will give high torque and low speed. Is there a trick to driving a stepper motor at a fixed rate. Given the low tech aim I was hoping to avoid programmable parts. Another solution could be servos with the end stops removed but this would probably need a pic to drive them.

If it ever gets built I was considering letting it go in Pittville Park. Perhaps with a destination of the pump room and the cross cafe. The destination is on the flag and it auto steers to the destination using kindness.


#2

I’d go for a straightforward geared DC motor like:

In theory it should be able to get over 16 hours (at worst case 3W) directly driven from a fully charged 3s lipo like this:
http://www.hobbyking.com/hobbyking/store/_64796__Multistar_High_Capacity_3S_4000mAh_Multi_Rotor_Lipo_Pack_UK_Warehouse.html


#3

I have tried one of these below. I want it to move slowly. I used an adjustable dcdc converter to lower the voltage. However if the motor stalls because of terrain then it gets stuck. I want it to move forward at a constant slow speed without user intervention. I ether need a very low gearing, some form of feedback, or something like a stepper motor or servo that will maintain a constant speed, increasing the torque if required. With these geared dc motors I could only set the power and not set the speed.


#4

The motors from Banggood may be a lot better due to there gear ratio. Thanks for this idea. To get the low speed I could try a lower voltage or add a H bridge to a 555. I have a load of D NiMH to power it. As you said it should be low power and need to run for a few hours. I can try it on a 3s too if needed. I’ll google more motors for robots and see what is available.


#5

They have a few different RPM versions, som even lower than the 12rpm version i linked. Though you could always have a 2:1 or 3:1 gearing on a drive belt system if 5 seconds per revolution is too fast.


#6

Got a pair of these cheap on eBay. Need wheels?

http://www.ebay.co.uk/itm/322095205761?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Not sure is I want a robot or a vehicle of some sort with a cute passenger.
This guy sort my eye as a “toad of toad hall” type o f vibe but would need a car I could add the motors to.
link_http://www.ebay.co.uk/itm/301995397355?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT