Electric Vehicle C

[clbrown]

New user to this forum. Working to get ready to run an event at an invitational.

Can anyone provide info on how to economically buy or construct a photo-gate system (including related software that would work with a laptop or tablet) suitable for use with this event? The ones I see online are close to $200 with tax and shipping and that's not in the budget especially since I'll need 2 of them in order to run 2 simultaneous tracks.

Posted this in Hovercraft too, but thought maybe I'd get a better response over here.

Thanks for any help.

Hi; I use multiple lasers with LabView sensors, but have easy access to the equipment. A FREE version with 33 ms accuracy can be made up from a smart phone...
If you have access to an Android tablet or smart phone, check out "Lablet - Physics Sensor Lab" from Univ Auckland.(on Google play) It will let you take and time movies to the best time resolution of your device.
Setup manual lasers at the start and end lines of the timing box, so you get a red blip on the car's timing stick as it passes through each beam, then just get the time between beams. You will have to manually follow the car with the camera, so might want to use a second one as a backup. This should give 33ms resolution (30 fps) or better. This is much better than any human manual stopwatch could ever be!!!
Good luck.

[GoldDigger]

I have recently hit a road block with my fixed steering design. The inner circles of my ball bearings for my front wheels wiggle side to side about .1mm. I am using premium skate board bearings. The wiggle room translates to 10+ cm of inaccuracy. I'm stuck and might have to switch my Ackerman steering to a setup where I would pivot my entire axis instead. Do you guys have some advice? How did people get past this problem?

Also, thanks for answering my previous question Bazinga!

Ackerman steering has too many joints thus increasing uncertainty of your measurement. Id recommend switching to a pivot.

Will do.

[dragonfruit35]

I have recently hit a road block with my fixed steering design. The inner circles of my ball bearings for my front wheels wiggle side to side about .1mm. I am using premium skate board bearings. The wiggle room translates to 10+ cm of inaccuracy. I'm stuck and might have to switch my Ackerman steering to a setup where I would pivot my entire axis instead. Do you guys have some advice? How did people get past this problem?

Also, thanks for answering my previous question Bazinga!

Ackerman steering has too many joints thus increasing uncertainty of your measurement. Id recommend switching to a pivot.

Will do.

I agree, I just pivot my axle and it seems to work fine. As long as you can stay in place reasonably and have a way to adjust it it'll be good.

[GoldDigger]

Well... my vehicle didn't apply the brakes properly during today's test run....

It went flying about a good 100 feet and then rammed into a wall. Rip.

I am repairing it and hopefully my PID control will work this time :/ I don't know how to properly employ it. As for the pivoting front axle... I tested my current design out and it seems pretty accurate (Approx. 2 cm off). I guess the joints cancel out the error somehow. I will definitely switch the steering design soon, because of simplicity. Could someone please direct me on what I should do regarding PID control? I am lost. I am using pseudo-PID code with a series of if-statements.

[Dark Sabre]

GoldDigger, if you can post your Arduino (?) code, I'll be happy to offer suggestions if I have any.

[parasaurolophus]

We are trying to develop a vehicle with a reliable steering system and are struggling with the best way to do it. We don't see a way that you can have a fixed axle (aka, the car always turns in the same circle) and just simply position the vehicle different depending on the given competition distance. So, unless we are wrong, we figure that you would have to have a way to change how the axle is positioned. We were thinking of inputting our distance into our mc and then having a servo which turns the axle the distance that we need it to, but we weren't sure where to begin with the math for something like that. Also, wouldn't this method give two variables, the way that the axle turns and then the way we position the car on the start line?

[windu34]

We are trying to develop a vehicle with a reliable steering system and are struggling with the best way to do it. We don't see a way that you can have a fixed axle (aka, the car always turns in the same circle) and just simply position the vehicle different depending on the given competition distance. So, unless we are wrong, we figure that you would have to have a way to change how the axle is positioned. We were thinking of inputting our distance into our mc and then having a servo which turns the axle the distance that we need it to, but we weren't sure where to begin with the math for something like that. Also, wouldn't this method give two variables, the way that the axle turns and then the way we position the car on the start line?

You are correct that you need to both angle the car on the start line and angle the axle. Yes you will have 2 variables. You can solve for both variables using geometry or use a CAD software to plot the points and find the arc non-analytically (which I chose to do, but the math is easier if u aren't familiar with CAD). Unless you gear the servo, I doubt you'll get the accuracy required - look for a more consistent mechanical system.

[parasaurolophus]

We are trying to develop a vehicle with a reliable steering system and are struggling with the best way to do it. We don't see a way that you can have a fixed axle (aka, the car always turns in the same circle) and just simply position the vehicle different depending on the given competition distance. So, unless we are wrong, we figure that you would have to have a way to change how the axle is positioned. We were thinking of inputting our distance into our mc and then having a servo which turns the axle the distance that we need it to, but we weren't sure where to begin with the math for something like that. Also, wouldn't this method give two variables, the way that the axle turns and then the way we position the car on the start line?

You are correct that you need to both angle the car on the start line and angle the axle. Yes you will have 2 variables. You can solve for both variables using geometry or use a CAD software to plot the points and find the arc non-analytically (which I chose to do, but the math is easier if u aren't familiar with CAD). Unless you gear the servo, I doubt you'll get the accuracy required - look for a more consistent mechanical system.

Why isn't a servo accurate? What are the alternatives?

[windu34]

We are trying to develop a vehicle with a reliable steering system and are struggling with the best way to do it. We don't see a way that you can have a fixed axle (aka, the car always turns in the same circle) and just simply position the vehicle different depending on the given competition distance. So, unless we are wrong, we figure that you would have to have a way to change how the axle is positioned. We were thinking of inputting our distance into our mc and then having a servo which turns the axle the distance that we need it to, but we weren't sure where to begin with the math for something like that. Also, wouldn't this method give two variables, the way that the axle turns and then the way we position the car on the start line?

You are correct that you need to both angle the car on the start line and angle the axle. Yes you will have 2 variables. You can solve for both variables using geometry or use a CAD software to plot the points and find the arc non-analytically (which I chose to do, but the math is easier if u aren't familiar with CAD). Unless you gear the servo, I doubt you'll get the accuracy required - look for a more consistent mechanical system.

Why isn't a servo accurate? What are the alternatives?

Standard servos that use resistive potentiometers will neither yield repeatable-enough results nor will they yield small enough increments of adjustment. Look into it yourself - i cant promise an effective solution

[dcrxcode]

I'm currently working out the gearing for my electric vehicle and I'm having problems with how to apply the gears. I'm using Traxxas motor and a traxxas pinion gear, but the Traxxas spur gears are designed for the torque control slipper clutch system. I'm using 3 mm axles, and so I'm not sure how to install these.

Link: https://smile.amazon.com/Traxxas-90-too ... spur+gears

I've been thinking about getting a transmission (something like this: https://smile.amazon.com/TRAXXAS-TRANSM ... ansmission), but they seem expensive for the value they'll offer.

Any thoughts? Should I just go with a direct drive and find gears from elsewhere?