DIY Bike Fit - Motion Tracking

thatmdee
Posts: 73
Joined: Wed Aug 17, 2016 6:54 am
Location: Newcastle

DIY Bike Fit - Motion Tracking

Postby thatmdee » Sun Dec 10, 2017 4:19 pm

Hi all,

I was wondering if anyone has done a DIY bike fit -- and if so, what was the outcome?

I've been watching some of bike fit adviser's videos (http://bikefitadviser.com/ and YouTube) who suggests some basic motion tracking using software like Kinovea. So, palpate and place some tracking dots on (I have a role of bright green sticker dots from Officeworks), film yourself in 60fps or higher, and then put the resulting video through Kinovea to track angles, etc for the purposes of adjusting your bike fit.

Has anyone tried a method like this and had any success? Seems like for high frame rate recording, you need good lighting. Any tips for a cheap DIY softbox or similar to give some nice light so high frame rate recording allows me to accurately place and track dots on the ankle, knee, hip etc?

I haven't been able to find a lot of information out there on how people have approached it, and what success (if any) they had. I started delving into the possibility of writing my own tracking app using something like OpenCV in Python or C++. But I'm a little reluctant to go deep down the rabbit hole if it's not really going to provide any benefit.

I have a trainer (Neo), phone capable of 120fps recording, a small tripod.. So I'm most of the way there (bar some additional lighting -- i.e. DIY softbox). I'm more curious to see if others have taken a similar approach, and if, with minor adjustments over time, improved their bike fit.

I suppose I could always spend a couple of hundred on a bike fit, but I'm not sure who to see locally, and there seems to be so many bike fit tools/systems out there, it's hard to know which to go with. I like learning and self-sufficiency, and if I could get a reasonable result at home, it would be good -- as I could slowly tweak the fit over time to suit.

Thanks!

g-boaf
Posts: 9561
Joined: Mon Sep 26, 2011 6:11 pm

Re: DIY Bike Fit - Motion Tracking

Postby g-boaf » Sun Dec 10, 2017 4:27 pm

You can just use any portable lights.

Other way is use any modern video capable DSLR and bump up the ISO. Use F5.6 or F4.0 too and that should give acceptable results.

thatmdee
Posts: 73
Joined: Wed Aug 17, 2016 6:54 am
Location: Newcastle

Re: DIY Bike Fit - Motion Tracking

Postby thatmdee » Sun Dec 10, 2017 4:34 pm

Thanks.. I was originally looking at LED worklights, as they don't put out any heat but seem to throw out a tonne of light, and seem to have a colour temperature of around 5000K (I know a photographer will scoff because it's probably not very accurate).. A basic tripod LED worklight is around $59 at Bunnings.

The main hurdle I've run into, is that if it's AC, it's likely to cause flickering (50Hz AC) -- unless the frame rate is a multiple of the AC's cycles per second. Unfortunately, the couple of worklights I saw seemed to be 50Hz AC input.. I couldn't see anything indicating they were transforming to DC though, which I gather would be fine.

We have a glamour mirror which uses LED bulbs, and is obviously AC.. When filmed at a high framerate, the flickering is quite bad.. So I'm working from the assumption of if I buy an LED worklight, array, or whatever -- it should probably be DC.

g-boaf
Posts: 9561
Joined: Mon Sep 26, 2011 6:11 pm

Re: DIY Bike Fit - Motion Tracking

Postby g-boaf » Sun Dec 10, 2017 5:05 pm

Yes, forgot about that. You can also just set yourself up outside? Put one of those photo backdrops behind you if you must have a featureless background.

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CaffeineAU
Posts: 61
Joined: Wed Aug 23, 2017 3:03 pm

Re: DIY Bike Fit - Motion Tracking

Postby CaffeineAU » Fri Dec 15, 2017 9:59 am

thatmdee wrote:Thanks.. I was originally looking at LED worklights, as they don't put out any heat but seem to throw out a tonne of light, and seem to have a colour temperature of around 5000K (I know a photographer will scoff because it's probably not very accurate).. A basic tripod LED worklight is around $59 at Bunnings.

The main hurdle I've run into, is that if it's AC, it's likely to cause flickering (50Hz AC) -- unless the frame rate is a multiple of the AC's cycles per second. Unfortunately, the couple of worklights I saw seemed to be 50Hz AC input.. I couldn't see anything indicating they were transforming to DC though, which I gather would be fine.

We have a glamour mirror which uses LED bulbs, and is obviously AC.. When filmed at a high framerate, the flickering is quite bad.. So I'm working from the assumption of if I buy an LED worklight, array, or whatever -- it should probably be DC.


The power supply in really cheap and nasty LED lights will not filter the rectified AC well at all, so it will flicker dramatically. A properly filtered supply will give quite clean DC and the LED's shouldn't flicker.

If there's any sort of dimming function, avoid it as it will use PWM to do the dimming and potentially cause more flicker.

Not sure what camp the Bunnings one fall in to though...

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