Motorized car MOCs: what factors most affect performance?

[Hrafn]

As a newbie, I've been somewhat disappointed by the performance of my half-finished MOC (a small 4x4 jeep-like vehicle, my first foray into studless building) and hoped to learn from more seasoned members' experiences.

For those of you who've built motorized, 4-wheel vehicles, what factors do you find most affect the performance (probably meaning mostly acceleration, hill-climbing, and handling) of your MOCs? I'm specifically asking about the MOCs themselves, not the vehicles they're based on. Obviously, what factors are most important may vary between different vehicle types - from crawlers to race cars - so please note what kind(s) of vehicles you're writing about.

In general, I would think that the power-to-weight ratio would be very important for acceleration and climbing, and center of gravity (meaning mostly the location of the battery boxes and motors) would be important for handling. To what extent do the details of suspension design matter for performance for each type of vehicle? How important is steering lock? Differentials? Ackerman steering? Suspension travel? Suspension hardness? Frame stiffness? Tire stiffness? Tire tread? And so on.

Thanks!

[nicjasno]

What you want to avoid in ANY drivetrain:

- friction

- big angles of CV and universal joints

- unnecessary torsional binding when the whole thing starts moving and force is applied (limited slip differentials are excluded from this)

All of these are irrelevant of the vehicle type that you are going to make.

[Front]

Keep number of transmissions between motor and wheel as few as possible. Gears consume power.

Build in motors in parallel for driving ? (not sure if that apply to terrain vehicles)

[MrNumbskull13]

Make sure you brace gears properly! Also keep your models as light as possible. :)

[Lakop]

Make sure you brace gears properly! Also keep your models as light as possible. :)

The above is an important one. A short wheelbase, mounting the motor and battery pack and your wheel selection. I've made my first RC car recently, it's very simple but it took a while to get it right. it was just built wrong. It was too long, the battery pack was in the wrong place and my motor was not mounted correctly. Re- built it and i'm having so much fun with it I don't want to take it apart.

H

[Ape Fight]

Weight weight weight. Power can overcome this to a degree - but as weight and power increase, load on the parts does also.

Simplicity is your friend.

[kevman]

weight is the biggest issue. I attempted to motorize the 8466 but the results were not great. too much grinding. Additinally the suspenstion is not inherently desgined for motorization. I have started building Sheepo's MPS system to build a chassis and I am pretty pleased with the motorization on that. Worth checking out if you have not already.

[Hrafn]

Thanks, everyone!

Weight and simplicity it is, then. I've already seen how much friction results from using bevel gears and having driveshafts bear weight, so I'm going to try to avoid both of those things as much as possible.

Kevman, I have seen Sheepo's MPS and admire the work he's put into it; I'm aiming for something simpler and smaller for now.

[nicjasno]

Also, avoid gearboxes if the vehicle doesn't REALLY need them, and reinforce the axle sections that are exposed with half bushes, to reduce torsion.

[Lipko]

It's also better to use bigger gears in the powertrain, as smaller gears introduce bigger axial force to transmit the same torque, and bigger axial force means bigger friction between the gears, and also between the axle and the pinholes.

[Hrafn]

It's also better to use bigger gears in the powertrain, as smaller gears introduce bigger axial force to transmit the same torque, and bigger axial force means bigger friction between the gears, and also between the axle and the pinholes.

This is an excellent point - I hadn't thought of that. The backlash from 8t gears has already caused me some problems, so I'm avoiding them whenever possible. On the other hand, for the small model I'm currently working on I doubt anything larger than 24t will fit.

[kevman]

Also, avoid gearboxes if the vehicle doesn't REALLY need them, and reinforce the axle sections that are exposed with half bushes, to reduce torsion.

Yes I agree 1000% on this statement. I loved the idea of gearboxes but have nver successfully implemented them in any of my larger models and I have come to find that I really did not need to.

[Lipko]

I agree with the gearbox thing, but in my next car, I will make a very simple, manual 2 speed gearbox, because it's no fun do drive a fast car around in a 20 m^2 room with my RC skills.

[clarkdef]

Interesting topic. Take a look at electric vehicles in reality, they don't tend to have gear boxes, because the motors make high torque from zero rpm, this is a good thing as transmissions are a waste of weight and reduce efficiency. You don't need a crawl gear on a electric motor either because they have max torque on offer anythime, meaning if you have a step power system you can crawl (power functions doesn't have this Unless you use that train remote) So a two speed system might come in handy.

Agree with everyone above, in the end it's almost boringly simple, weight, drive train friction and power.

As for handling. You need to decide what surface you will be driving on, if it's glass... or a pretty clean surface then no suspension is best, if the car becomes so powerful that it doesn't steer on acceleration pulses, then you need to add front suspension so that the front wheels stay pressed on the ground as the front lifts from the acceleration (this is pretty common with small vehicles with short wheelbases).