Need Robot Help!

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1

Haha, alright well, I need help looking for parts to make an electric vehicle.

Here are some parameters - basically I need some idea of what basic robotics kit (maybe?) to start. Preferably, a kit that could achieve all of these tasks alone would be golden.

Electric vehicle:

All features marked with a * are not essential, but would be GREATLY beneficial.

Runs with 8 individual cells @ 1.5 volts or less each, or 2 battery packs rated at 4.8 volts or less each.

Vehicles should be able to travel a specified distance between 5 and 10 meters. Preferably, this vehicle should be able to travel at any 1cm interval (this might not be too realistic, but I need something accurate).

The vehicle cannot be remote controlled; we must use a pencil or wooden dowel to start the car, and the car should stop by itself. So a braking system is obviously needed.

The maximum time required to travel 10 meters should be less than 45 seconds. Preferably, speed should be something we can adjust to travel a specified time for a certain distance.

The vehicle will have two wheel axles, but any number of wheels.

The widest axle length is 25cm (width of vehicle), and the distance between the center of the front axle and the center of the back axle needs to be 40cm +/- 3cm (37 cm - 43 cm). We wanted a wide car in order to be safe for the accuracy bonus, listed below.

The event is run with a center tape line that can be between 3/4’’ to 1’’. This tape is used to measure the center of the track. If this center tape line remains completely within the vehicles track between start line and finish line, an accuracy bonus is awarded.

The vehicle must go straight, in other words.

Electronics, laptops, etc. may all be used.

Any electronic aligning systems, ie environment detectors or lasers may NOT be used.

That basically sums up my event, any help would be greatly appreciated. I have a preliminary vehicle built; it is very crude - I am hoping to be able to use a microprocessor in order to make my settings more digital (versus analog).

Currently, my vehicle is run on a geared up motor @ about 100 rpm. The braking system involves a wing nut on the axle which has an obstructing platform adjacent to the axle - therefor the wing nut travels down the axle as the car moves forward. The wing nut eventually hits a switch to turn off the vehicle - stopping the vehicle.

Our current system of measuring distance is measuring the distance between the wing nut and the switch.

We are definitely hoping to upgrade our vehicle! We are hoping to use a programmable robot that is able to control these variables, while also being able to fall under the specific requirements.

Our budget is ~$500. (Hopefully we get this done with ~$300)

2

Sounds like either stepper motors or motors with attached encoders would have to be used.

3

How big are the wheels you have?

4

Typically, people solve this problem with quadrature encoders. (look them up with your favorite search engine.) Then you simply count pulses from the encoder to figure distance travelled.

For your application there was at one time a Tamiya kit that featured a single motor attached to a wood deck with tracks. Thats prolly ideal (if you can find it), and would only run $20 or so. (A single motor means both sides run identically which means no slight curve caused by an imperfect diff steer setup)

5

The wheels can be any size, but they must follow in those dimensions.

Thanks for the replies, is there any robotics kit that I could use to do this in an autonomous mode? The main settings I need to adjust are speed and distance to travel. Hopefully it can be as precise as to adjust to 1 cm - distance wise. Straightness is definitely a main problem for me right now. I can’t see to get the vehicle to go straight.

6

Since all you need to do is go in a straight line, you could build a chassis that incorporates a little bit of ability to jockey the non-driven axle back and forth slightly, and hold it in a fixed position with a turnbuckle or tie-rod, of the sort used in R/C cars. Then you can trim it a tiny bit at a time until it moves in a straight line.

Since you aren’t allowed to use lasers or sensors to detect and correct alignment, once you get it trimmed to go straight, maybe some marks on the front and rear of your chassis (place tape here) might allow you to get it lined up well enough to make the run without running over the tape.