Which motor technology is best for acceleration?

Would a brushed or brushless (sensored or not) motor be better for acceleration? I would like to make a light weight agile vehicle to run off road at speeds less than 40 kmh. I would like to used speed differential steering so it can turn on the spot. The motors will be subjected to very rapid changes of direction.

I have been reading through various threads but they mainly seem to deal with cruising speed rather than acceleration from stall.

Stall torque is more about the controller than motor in practice.

A motor makes X amount of torque per amp. Short term torque limits are typically limited by controller phase current alone (or in extreme cases, motor iron saturation).

Continous torque is determined by the rate of heat you can remove from the motor vs the rate it's being generated. This is when efficiency and cooling start to matter.

I would think for most stuff, just a pair of direct drive hub motors would be ideal. If you're jumping it or something, perhaps inboard motors.

If you're using the motors for steering like that, I assume that whatever you're building is wheelchair- or segway-like, vs inline like bikes.

As for changing direction suddenly, as LFP says, it's about your controller's power capabilities much more than the motor type, htough you need to use motors capable of handling the power/waste heat, too.

One thing to keep in mind is that any sudden change in direction of rotation is going to mean cancelling out the velocity of at least part of the vehicle in that direction, so it's going to take a lot more sudden application of energy than it would just to accelerate it to that speed from a stop. Your system as a whole will need to be capable of dissipating the heat created by that power usage, and of operating like that repeatedly/constantly for as long as the battery lasts.


If you do lots of those sudden direction changes, especially from speed or if your vehicle has a high mass, that could be a LOT of waste heat. (even if you use regen braking to help reabsorb some of the power instead of simply shorting it out and wasting it as heat).

Thanks for the replies. I am happy to start with the controllers. Which controllers are best suited to rapid reversals? Brushed or brushless with or without sensores.

For several years I have been playing with RC differential speed steering. You might have heard of BattleBots or Robotwars. The motors and ESCs certainly get hot.

If the battle-bot "matches" are not long, then...I would be more concerned about raw performance, rather than efficiency. To provide more answers to your questions, it would be useful for you to clue everyone in on the size and type of motors/controllers that have recently been doing well in the type of competitions you are interested in.

Luke could spend a lot of time discussing the Deathbike that he built, but now that we know its for a battle-bot, all that typing would have been wasted. I'm sure the size of the components might be a minor issue to keep in mind, but up-sizing the controller will help cool it (if you have room inside the bot). I am also a fan of the idea of adding two computer-server fans to a high performance controller, one pushing air and one pulling.

We could spend a lot of time discussing the ultimate motor "type" and controller "type" combination, but if nothing that is in production and "buyable" is even close, that disciussion would also be wasted time.

This isn't for a BattleBot. It is just a similar principle. I would like to build a light weight, off road, ride on vehicle. I would like the gross vehicle mass to be under 200 kg. The main criteria is good acceleration. I want it to be agile. My question is which technology is best for acceleration. I have only used brushed motor in the past.

Power for power, brushless motors with appropriate controllers will be better than brushed. They convert more of your battery power into power at the wheel, and they don't consume themselves in the process-- as long as you run them within their limits.

Brushless hub motors are also easier to find in the highest power levels that a bicycle can tolerate.

For the fastest absolute acceleration in a bicycle format, it would be better to use a single large motor in the rear wheel than to use two smaller motors in both wheels, because at the limit, the front wheel will have little to no weight on it and will not be able to add significant power without slipping.

Restraining reaction torque at the axle may be a thornier problem to solve than getting such power out of the motor. For this you can thank the Chinese manufacturers for not stepping up their game and providing adequate torque arms integrated to the motors.

Not sure what kind of off-road vehicle you are looking for. Take a look here and tell us what you think:

http://endless-sphere.com/forums/viewtopic.php?f=6&t=51873

Thanks Chalo. I will look into brushless hubs.

Hjns, that bike of Adam's is amazing. 52 mph up hill is very fast. I would only want to go half that speed on the flat. His acceleration was more than I thought was possible from a hub motor. Thanks for the link.

https://www.kickstarter.com/projects/flykly/flykly-smart-wheel
This is cool but 800. Not a do-it-yourself thing. Its the easiest setup I've seen. Maybe u could asd something make it suitable for
What u want. Put it on a mountain bike with one speed and that might be the simplest easiest to
Maintain vehicle