RC Car Active Suspension System - Pt3 

Nice. I like that setup. I was trying to figure out ways to get a small pump like that. Initially I was planning on hydraulic actuators. Which IMU did you use?

Thanks. That makes a lot of sense on the vibration rates. Thanks for the info on the frequencies. I haven't found literature on the specific suspension frequencies ranges that active suspensions have been built to target. I really need to build a single wheel test rig to measure the frequencies and optimize my filtering and actuator damping. I'm leaning towards having an electronic force based actuator like a linear motor which won't need as much power at this scale versus a real automobile. Also I should be able to have a much higher frequency response versus the servos. I agree with your thoughts on just controlling the roll/pitch/yaw, particularly with an off-road rc car like this. I'm think I will implement a secondary spring system so the servo doesn't have to support the weight of the car and absorb the shock loads from jumps. The servos can handle this but they need a lot of current to do so (~2 amps each).

Thanks. I think not taking into account the delay in feedback and properly filtering is what caused one of my servo's to fail. I have a simple EMA filter on the encoders which does add some smooth and a bit of delay, but I think I need to use something like the ServoEasing library that allows you to specify accelerations and velocities to the servo.

You bet!

Thanks for the tip, I hadn’t seen the BNO085 before but it seems to be better than the BNO055 and available. The servos definitely don’t respond fast enough. I’m not an expert on this, but I’m using some filtering on the IMU and the encoders which gives me something like a 5ms sample period. Then I only command the servos to a new position every 20ms. But I did burn up two of the servos because I think I’m just sending them in opposite directions every few readings. Ideally I may need to get servos with feedback so I can read the current position and not just the commanded position.

@@IndeterminateDesign What's the frequency of bumps that you're seeing in the logs? i.e. how frequently does the sign of the vertical acceleration vector change, after subtracting gravity? I could believe you're hitting over 100 bumps per second on gravel, so that may exceed your 200Hz IMU sample rate, much less the 50Hz PWM signal. It may simply be the case that modern digital logic components aren't able to respond fast enough for this type of terrain. Have you tried it on terrain with fewer, larger bumps?

So I need to do some better logging, but when the library removes the gravity vector, it seems to be consistently ~0.5G when the car is not pitching or rolling. But as soon as the chassis rolls or pitches, and the gravity vector starts to pick up values from X&Y sensors it all goes wrong. So it makes the accelerometer data fairly messy, but I'm definitely registering over 100 bumps/sec. So when I integrate the acceleration to get the velocity, I implemented a "bleed" of about 2% so that the velocity always trends a bit towards 0 to hopefully eliminate the integration error. The larger the bleed the more erratic the velocity becomes and if it's too small it just overflows either positive or negative. The encoder data at the wheels is surprisingly clean, and I'm seeing a natural frequency around 3hz front and 4hz rear. I think I burnt out the servo because the servo is just being commanded all over. I think I need to implement a safety function that takes into account the speed of the servos and sets a limit on how fast the commanded position can change.

Yes they do. In earlier videos I talk about this, but each suspension arm has an encoder. The accelerometer is primarily for the overall spring mass of the chassis.

It’s an RC10T, but it’s 30 years old so no longer made. The servos are animos DS3218 Pro. The code isn’t very stable yet as it’s just a prototype, but I’ll work to get it uploaded to my GitHub site.

That’s a great idea, I don’t have the space for that setup right now but it would be a lot more accurate to have all 4 wheels going over the bump.

Thanks, good catch!

Let me see if I can export a step file. It’s bit of a mess since I have several different designs in the same file.