Making a toy car turn....

[nmantas]

I have a unique project that I'm hoping to get some feedback on. I'm a high school teacher and I'm tasked with getting students to make wire-controlled, homemade cars.....with bottom dollar of course.

The students will have to assemble a simple drivetrain and build a vehicle from parts such as:

This vehicle will then have to be driven through a course. The motors will be wired to a simple switch(s) that will be in the driver's hand.

The main issue so far is how to make the car turn. We have discussed having the vehicle turn with fixed axles. We discussed having one rear wheel being forward while the other being reverse and only activating the reverse to turn the front (reverse would have to be geared in a way so that it would easily spin forward when the other motor is on). We talked about possibly using a trike design where the front wheels are drive but independent where straight would be both on and turning would be one on and one off (other end is caster). In a perfect world this would be something for the students to work out the system themselves but that isn't really realistic with the timeframe or the students current knowledge (think more of a forced extracurricular project that is happening in-school but not in-class with a teacher).


All of this would be much easier if we had the materials on hand to test ideas but we didn't get materials yet. I'm going to buy some test materials like the picture but am waiting for feedback from others first. I'd also like to get motor power to axle/wheels without gears so I'm thinking more along the lines of bands to make life easier and would take any feedback on that idea too.

Thanks in advance.

 

[volksnick]

The most basic remote control kids toys have a simple forward and reverse, with a rear axle that makes the vehicle turn when backed up.

If you make the rear axle to where one side pivots and the other side slides. Make the vehicle front wheel drive and when you reverse the motor, the rear axle will pivot at one wheel and allow the vehicle to turn.

 

[EdT]

If the goal is quick and simple it might be easier to drive the wheels with a simple friction drive by having the motor shaft rub on the OD of the wheel. The speed could be varied by choosing wheel size and/or putting a piece of rubber tubing over the shaft with some super glue to hold it in place. This would be a learning experience after the first few motors were glued up from too much of a good thing. Also a chance to do some simple fourth grade arithmetic to figure out how fast things will move for different wheel/shaft diameters. With a drive motor on each of two drive wheels and a simple castering arrangement for the third wheel the buggy would turn tightly if one of the drive motors is stopped. The turn could probably be broadened by pulsing the drive motor. The third wheel does not even have to be a wheel, it could be just a straight piece of music wire with a loop on the end that rubs on the "track". With this arrangement, one issue you may run into is that the motors don't run at the same speed and the thing always wants to turn a little. There are lots of solutions to that problem, but they may be beyond the scope of the project. Good luck with the project. I have worked before with a similar group doing the robot thing and you will probably find that there's one kid who "gets" it and the rest will want to play games on their phones while you build the stuff.

 

[matt_i]

Trike design, 1 wheel drive in the back, 1 to steer up front w no linkage?

 

[vavet]

Lots of great ideas. Why not let the students come up with their own ideas?
Is this an in-class project or a take-home and make it following these guidelines? Here are some parts to get you started?

 

[Bigblue&Goldie]

A little servo might work, they are pretty cheap.

https://www.robotshop.com/en/misc-servo-en.html

 

[2oolhound]

I expanded on volksnick's design by using a link rod to turn the rear axle as well and pivoting the axles at the centre. Without a front steering axle like a car both axles would need to turn to get the turning radius needed. The rear drive motor would be direct drive with a shaft on both sides. It is mounted on a pivot deck so it turns with the wheels. The front steering motor has a link arm to control the arc.

The other design is an articulating body design where the front section pivots around a centre pin.

 

[nmantas]

So many great ideas...thanks so much. The micro servos would easily provide many steering options but they are microcontroller based (at least the cheap ones). I have opted for pregeared-motor & wheel combination to experiment with (only about $3.25 each). So I'm going to play with a system of two drive wheels in the front with a rear caster trike system with steering done by applying power to only one side.

 

[wolf_from_wv]

Skid steer.

Two independent motors in the front, caster in the back, like the ThrowBot.

http://www.reconrobotics.com/products/throwbot-xt/

https://makezine.com/projects/joust-a-bot/

If you run one forward and the other backward, it turns faster.

Zero-turn lawnmower...

My basic steering blog post:
https://www.embeddedrelated.com/showarticle/906.php

 

[Ole Slewfoot]

slick wheels at front, indepenent drive mat the back
Works on the Anki Drive cars

 

[theoldwizard1]

This vehicle will then have to be driven through a course. The motors will be wired to a simple switch(s) that will be in the driver's hand.

The main issue so far is how to make the car turn. We have discussed having the vehicle turn with fixed axles. We discussed having one rear wheel being forward while the other being reverse and only activating the reverse to turn the front (reverse would have to be geared in a way so that it would easily spin forward when the other motor is on).

Let's get the terminology down. "Fixed axle" usually means both wheels fixed to one axle. Simple. One motor drives the axle which drives both wheel. Think of a go cart

What you described is a split axle. One motor for each of the rear wheels. This is probably the easiest solution, but there may be one issue. If each of the axles "free wheels"/spins when not powered, the vehicle may not be able to make tight turns. It the axles lock when unpowered, it will only make very tight turns.

Most small motors for these thing include some kind of a gear box. That will likely provide enough friction so that the axle will lock, at least partially, when not powered. If the gear box uses a "worm and gear" arrangement (the motor is 90° from the output shaft; common) the axle is fully locked when power is not applied.

 

[nmantas]

Let's get the terminology down.....

My fault for not being clear but I was referring to the fact that we talked about having a fixed axle and trying to make it work and that we also talked about having a split axle.


In any event, I finally got the chance to start playing with the parts.....got my fixed-gear motor/wheels (reverse when polarity is switched) and I also decided to pick up a cheap $5 RC car from Five Below and go cordless instead of wired to momentary DPDT switches.

The RC car has two identical dc motors.

I used the board with the RC receiver and wired it to the geared motor/wheels from Amazon.

I just mounted the thing on a dollar store food storage container to act as the 'car'. I was going to use a caster on the other end but its so squarish it doesn't need it. This thing is a blast to drive but pretty difficult to control (mostly due to the fact that the controls are not natural with one switch being up-down for one motor and the one being right-left for the other motor. Not bad for $12 total....the RC car route is way better and actually cheaper than the wired momentary switch route.

I might wire up both motors to one switch and integrate a diode on one of the motors so reverse will only work on one of them to make it easier to go straight but still bing able to turn by using reverse.

I might award extra points if you opt to create a build based on the original geared fixed axle motor and turning motor (I'd probably even give them two of the axles and one for turning).

Between the motor options and there are a few different wiring options I think we can get these kids to use their imaginations and come up with something.

 

[R.Anderson]

My fault for not being clear but I was referring to the fact that we talked about having a fixed axle and trying to make it work and that we also talked about having a split axle.


In any event, I finally got the chance to start playing with the parts.....got my fixed-gear motor/wheels (reverse when polarity is switched) and I also decided to pick up a cheap $5 RC car from Five Below and go cordless instead of wired to momentary DPDT switches.


The RC car has two identical dc motors.

I used the board with the RC receiver and wired it to the geared motor/wheels from Amazon.


I just mounted the thing on a dollar store food storage container to act as the 'car'. I was going to use a caster on the other end but its so squarish it doesn't need it. This thing is a blast to drive but pretty difficult to control (mostly due to the fact that the controls are not natural with one switch being up-down for one motor and the one being right-left for the other motor. Not bad for $12 total....the RC car route is way better and actually cheaper than the wired momentary switch route.

I might wire up both motors to one switch and integrate a diode on one of the motors so reverse will only work on one of them to make it easier to go straight but still bing able to turn by using reverse.

I might award extra points if you opt to create a build based on the original geared fixed axle motor and turning motor (I'd probably even give them two of the axles and one for turning).

Between the motor options and there are a few different wiring options I think we can get these kids to use their imaginations and come up with something.

One problem you may come across with the RC setup you have there is one remote will most likely control all the receivers in range. And multiple remotes at once will most likely be another’s issue.

 

[nmantas]

One problem you may come across with the RC setup you have there is one remote will most likely control all the receivers in range. And multiple remotes at once will most likely be another’s issue.

Five below sells the identical car in two frequencies. With the car antenna removed the range is only about 10 feet, I might remove the controller antenna as well to limit the range even further. The room is large enough that, that might suffice. If that isn't good enough what we'll do is try to slightly alter the frequencies for each car/controller (don't tell the FCC):