Over-Volting Electric motors

[SystemParanoia]

Kids have told me that they are going to be building electric race cars from a block of balsa.
they will all get a small DC motor and are allowed to use only a single 9v battery.

Teacher says they will use an elastic band to drive the car's but i feel this will be lossy and inefficient ( ive already ripped the axle out of one of my old scalextric cars to ensure drive efficiency )

my question is this..

What will yield better results from the motor ( that i do not yet have in my possession )


1. keep it simple and just Overvolt the bugger by building a voltage doubler, fit a switch, and hope the motor lasts long enough to get me the kids a trophy.

2. Use the ESC from my old RC car ( brushed ) and hope the increased torque from the PWM operation will earn the win despite much more sensible voltages ( 7.2 ) this method will allow me to use a microbit, a raspberry pi or my old radio gear to drive the motor

3. C02 rocket motor!

4. Shrug my shoulders and let the kids figure it out whilst pointing to my power tools.

[SystemParanoia]

Zad said:

If the teacher says they are using elastic bands, then I imagine that any other power source will be disqualified. Not least to stop parents dominating the thing (which they will anyway to be honest).

elastic bands are just for power transfer.

the setup of the contest seems a little strange to be fair, its a flat run along the playground with potential obstacles in the way.
no guidence is allowed and any car the goes off-course is allowed to re-run until it completes.

I can see parents with access to industrial manufacturing equipment being at a distinct advantage over the rest to be fair.

[SystemParanoia]

Goaty Bill 2 said:

The world is your Oyster; Pendle Slot Racing

I used these guys quite a few years ago. They were very good, lots of interesting power plants

I don't think a rubber band is going to work very well. You want something without much/any stretch in it.
Think in terms of the old overhead shaft driven power distribution systems you would have seen in machine shops 70+ years ago.

im loving the sidewinder axles



the axle pinion and spur gear i've liberated are a more traditional setup like this

[SystemParanoia]

thanks for the pointers guys,

Due to lack of information, I have decided to give them:

the drive axles, pinion and spur gears from a pair of scalextrix cars
tape
hammer
nails
mini glue gun
A spare 6-9v motor and random gears torn from an old toy and 9v battery for testing purposes
rubber bands
fist full of mac'd straws
note pad full of rough sketches of different ways to connect the axles and drive gears to the cars that we drew up over the course of the day.

they collect their bits and bobs from school tomorrow, so Ill have to see what we end up with, and hopefully more clarification on the rules and what kind of races there will be!

[SystemParanoia]

You mean go 4wd?

I like that thought, especially combining that with having the gear ratio set in such a way that will stall the motor whilst stationary

[SystemParanoia]

the drive doest have to be rubber band... the teachers intention is to use the rubber band like a bike chain to get power from the motor to the axle.

looking at the comments above it seems having the motor with a silly gear ratio drive the front axle

i.e

and have a twisted rubber band provide the initial oomph needed to let the motor tun said silly gear

i.e https://www.youtube.com/watch?v=qrmJqEmlsaM

the jury is out on whether it is a good idea to drive the motor with more than 9v as the provided battery may not be up-to the challenge

also, the fact that there will be obstacles on the track is i variable i have no idea how to manage in the time i have available.
with more time, i'd have built a raspberry pi robot that guided itself using the opencv library

Edited by SystemParanoia on Monday 17th July 15:18

[SystemParanoia]

update.

Kids arent allowed to bring them home so im reduced to having a glorified Consultancy role.
also the teacher has moved the goalposts and they now only have x2 Double AA battery packs giving 6 wonderful volts.

Ive given them a lesson a series vs parallel wiring telling them volts are all that matter here. more volts = more rpm etc
Ive also demonstrated to them what i mean about elastic band drive by using some old lego and the same construction tools that they have at school... i.e nothing! + pva glue





This had major traction issues that may have discouraged them about the idea entirely
The obstacles will be disposable water cups, and gentle humps.

Im absolutely gutted that i wont be able to directly help on this one

[SystemParanoia]

Daughter won!! W0000!!!

by the largest of margins too.. as nobody elses buggys were able to move under their own power

my sons was too heavy so the drivesystem just endlessly slipped.

Daughter listen to me by making it light, and keeping it simple, and also used the mc'd straws as axle housings.

she elected not to use the rubber band drive system


maybe we can use the microbit on the next upgrade

[twitter link]
https://twitter.com/tinkercademy/status/8886203652...

[SystemParanoia]

Goaty Bill 2 said:

So the combined efforts of a cross section of 30 electrical engineers / mechanical engineers and slot car fanatics managed to beat a classroom or two of school kids.

We all deserve a trophy.
I assume you will be deputising for her down the boozer later?

damn right
images here - http://imgur.com/a/dIv9R

heres my Sons team's effort:



RWD, heavy to plough through obstacles without being knocked off course

here's my daughters team's effort:



FWD, light 'to go fast quick'


they tell me they both created a bigger 'gear' using an extra wooden wheel to go onto the motor, but they ran out of time to fit it as the rest of their respective teams were useless and left them to do all the work. lol

[SystemParanoia]

As you say, im trying to instill into them a willingness to 'DO' and at least have a proper go if its a task that's far too difficult

I gave my daughter full control of the remote all weekend and unlimited veto's on netflix choices as a winners reward
I \ we all regretted it within 5 mins, but im hoping the gesture was appreciated