Electric assisted steering for a go kart?

Hi for a project I am making an electric off road go kart, and the steering is going to consist of tie rods as that seems the most simplest. However it does require a decent amount of force to move the wheel, and I was wondering how feasible it would be to use a servo motor to assist a little bit, would this be possible?

I’ve never seen it done like this before and I was wondering what the draw backs would be, i know it would be too dangerous to do it fly by wire, so assistance is probably best. I have some experience with motors and servos having made an RC controlled car. but this is a a much bigger scale and I’m lost how I would go about it.

An idea I have is, connected to the steering column would be a pot, which would control the servo, giving the steering a little bit more force.

Frostburn:
Hi for a project I am making an electric off road go kart, and the steering is going to consist of tie rods as that seems the most simplest. However it does require a decent amount of force to move the wheel, and I was wondering how feasible it would be to use a servo motor to assist a little bit, would this be possible?

I’ve never seen it done like this before and I was wondering what the draw backs would be, i know it would be too dangerous to do it fly by wire, so assistance is probably best. I have some experience with motors and servos having made an RC controlled car. but this is a a much bigger scale and I’m lost how I would go about it.

An idea I have is, connected to the steering column would be a pot, which would control the servo, giving the steering a little bit more force.

One drawback will be the extra weight of the battery to power the servo. Another is the lack of feedback from your steering system. It needs to be self centering.

Are you old enough to drive an automobile? Then, if you have driven any modern automobile, you have driven a vehicle with servo assisted steering. The servo on my 2013 VW Jetta draws about 50 amps when necessary.

You might visit an automobile wrecking yard and see if you can find a really small power steering servo motor.

Paul

If you ask mr google there are some good examples of making high power servos from windscreen motors, using the internals from a cHeap RC servo to control it , with motor wires connection to a suitable driver circuit

If you just want assistance , then you need some form of force measurement in your mechanical System . I’m looking at this for a “tot rod” , but will be fly by wire with the steering wheel just turning a pot , with spring centralisation ( ok for 4 mph !)

Power assistance just needs a torque sensor on the steering wheel, which is used to set the power and direction of the motor assistance motor in proportion. The motor's torque gets added to your torque, but is controlled by it.

No need for any feedback as in a traditional servo system, its actually simpler.

[ One thought, there is a risk of oscillation if the gain/bandwidth product is too high, which may mean adding some low-pass filtering to the sensor signal to ensure stability, and you'd need to assess stability with a wide range of firmness of grip on the wheel - clamping it tight for instance. ]

Paul_KD7HB: One drawback will be the extra weight of the battery to power the servo. Another is the lack of feedback from your steering system. It needs to be self centering.

Are you old enough to drive an automobile? Then, if you have driven any modern automobile, you have driven a vehicle with servo assisted steering. The servo on my 2013 VW Jetta draws about 50 amps when necessary.

You might visit an automobile wrecking yard and see if you can find a really small power steering servo motor.

Paul

Thanks for the reply, batteries and current wouldn't be an issue because It'd be hooked up to one of the drive motors 12v lead acid batteries. As for self centring, I looked up how its done in normal cars, but its something to do with the caster angle? Not an inherent mechanism, I was thinking of springs/thick rubber rope which would force it to centre.

I am yes, I always assumed automobiles use hydraulics/hydro electrics when it comes to steering, but their implementations are a little too complex to fabricate, getting the appropriate servo wouldn't be an issue, it's more of how to integrate it.

hammy: If you ask mr google there are some good examples of making high power servos from windscreen motors, using the internals from a cHeap RC servo to control it , with motor wires connection to a suitable driver circuit

If you just want assistance , then you need some form of force measurement in your mechanical System . I’m looking at this for a “tot rod” , but will be fly by wire with the steering wheel just turning a pot , with spring centralisation ( ok for 4 mph !)

Ive actually taken a look around ebay and found some suitable industrial motors, that seem to be powerful enough, so finding a servo isn't too much of an issue.

Yeah my initial idea was similar to that, but my kart goes around 30+, so I don't think that'll work out. I've taken a look at some torque sensors but, but havnt really found anyone interfacing them with arduinos etc

If you can find somewhere to put the torque sensor , dealing with its output should be relatively simple.

A bigger steering wheel and some bicep work out might be an easier solution

MarkT: Power assistance just needs a torque sensor on the steering wheel, which is used to set the power and direction of the motor assistance motor in proportion. The motor's torque gets added to your torque, but is controlled by it.

No need for any feedback as in a traditional servo system, its actually simpler.

[ One thought, there is a risk of oscillation if the gain/bandwidth product is too high, which may mean adding some low-pass filtering to the sensor signal to ensure stability, and you'd need to assess stability with a wide range of firmness of grip on the wheel - clamping it tight for instance. ]

Do you have any idea on what kind of torque sensor or where I could find them? Sounds like a good idea

hammy: If you can find somewhere to put the torque sensor , dealing with its output should be relatively simple.

A bigger steering wheel and some bicep work out might be an easier solution

Would something like this work?

https://www.ebay.co.uk/itm/Vauxhall-Opel-Corsa-Combo-EPS-Electric-Power-Steering-Torque-Load-Sensor/382620004841?hash=item5915edf1e9:g:NTMAAOSwuUlb4IAN:rk:2:pf:1&frcectupt=true

That would be easier, but this if for my A level, so the more processes better mark

Frostburn: Do you have any idea on what kind of torque sensor or where I could find them? Sounds like a good idea

That's always the tricky part. Industrial parts are hugely expensive, I think its figure out how to make one. It needs to rotate with the steering column, just to make it a harder problem. Some sort of clever machanism using small loadcells (from a cheap electronic scale?) might be possible.

A quick google shows that electric assistance works using the position of the wheels and the rate of turn of the steering wheel . That might be easier using some form of position indicator on the column ( encoder), with a fixed sensor , than trying to measure force.

Actually that might be a lot simpler to implement, but its not going to work as well as proper power assist (which reduces the effect of road forces transmitted to the steering wheel by the gain factor). In hydraulic power steering the torque sensor is actually a rotary valve on a torsion bar or some such, mapping torque on the column to hydraulic fluid flow.