Low budget 2DOF Desk racer

Hi everyone, I thought it was about time I started a post about my build. I've been reading a lot of excellent information on this site, and built a small test rig, and now it's time to build the full thing! Exciting. My inspiration is the Desk Racer from @bsft (http://www.xsimulator.net/community/threads/desk-racer-2dof.5326/). I need something compact and hopefully a bit portable. Most of all I need to spend as little as possible!

I will be using 2 wheelchair motors, from a Pride Jet Power Chair. These are 24v, but I'm not sure on their other specs. I hope they are OK.

To power them I will use the 12v batteries from the wheelchair, and then a 2x60 Sabretooth, and an Arduino.

The rest of the build will be simple as I cannot weld, looking to bolt things together, drill, saw and probably use some PVC pipe.

Here is my test rig, it's not perfect, but it really helped me understand SimTools, plugins, interface settings and get a working setup before I look at going big. I would highly recommend doing this Thanks to @eaorobbie for arduino code (http://www.xsimulator.net/community/threads/rc-model-for-motion-simulation.4600/) - this was a great help.


(yes, that is Barbie, I have 2 young girls!!)

Here are the components I have gathered for the build:


24V Motors from a Pride Jazzy Jet 3 Power Chair. Note how the drive shaft has a keyway cut.


Ebay, cheap bucket seat


Land Rover/Defender front propshaft repair Universal Joint. Handily, it's 230mm tall which is what @bsft had as his seat height on the desk racer, so once I mount it, I won't be too far away from that.


Brackets from local DIY store for the pivot arms, I cut a keyway into these. They might not be strong enough on their own, so may double them up on the motor drive shaft. I will add a thick washer with cutout, and then the nut to hold these in place.


I found these cool track rods on ebay, for an ATV Quad bike. They are adjustable from 255mm - 295mm.

The UJ pivot and seat will be mounted on 20mm plywood. I will most likely use PVC pipe and joints to make a subframe for the seat and for the track rods to connect onto. Same PVC and wood construction for the base of the whole project.

That's about it for the 'ingredients'. Obviously the 12v batteries, Arduino and Sabretooth 2x60 plus some wiring to finish the electronics, this is pretty much all done thanks to the test rig. The Arduino and Sabretooth has been tested with my motors using my own code, and also code from @RacingMat (http://www.xsimulator.net/2dof-wiper-motor-playseat/)

More to follow soon I hope!!

Good project! Have fun
Nice post layout, congrats

Your sabertooth tests will be interesting ! I'll stay tuned

Are you doing a "desk racer" style with motors below your seat or a "seat mover" style with motors at your back like in your first photo?

I'm curious because if you are doing seat mover like in your project photo, I've never saw rods connecting so low at the back of the seat. I'm not sure if that works well, I'm sensing it will be much more stressing on motors. Shoulder mount higher up would be much better solution for seat mover and it's proven that works good.

Good start benj but Those Lever's are NO where near up to task. They need to be Something along these lines.

Thanks for your replies.

@prodigy - yep the test rig is confusing and a bad implementation! I will be making a desk racer, not a shoulder mount seat mover.

@Nick Moxley - thanks for the tip and photo. How do you key the lever onto the motor shaft to stop it slipping?

In that picture you can see a set screw that was used but with some modification to the Axle bolt to give the Set screw a place to "seat" into. That unfortunately didn't turn out very well after the Main Bolt slipped loose one day (this was the axle bolt on my traction loss) and inevitably did this.


Now your going to ask why is there a hole in there also. Well I did have a small 3/32" bolt from my RC stuff that Obviously once thing's started to slip was no where near strong enough to survive so it snapped clean off. I have since gone to a 1/8 coder pin on both my Seat motor's and the traction loss motor and No problems since.
I suggest doing both side's as well, The "gear side" so the axle bolt is Locked to the Gear box gear housing and also the Nut that's capturing the axle bolt, Drill that out and throw a coder pin in there too, That way there's 100% No way the axle bolt will ever loosen off and cause issues. I DO NOT Suggest trying to drill by hand. Drill press would be required.

Nice motors there, They should really move things.
And nice to see another design spawing from desk racer.

Wow @Nick Moxley thanks for the detailed reply that's a great job you did on that.

Seeing as my driveshaft has a keyway cut out I will most probably use that. If it's good enough to haul an OAP and their shopping up a hill it should move my butt ok!

A little progress. I decided to not use the PVC pipe idea for the seat base, maybe in the future, but for now I decided that these brackets from the DIY store should be OK to get me going. They are about 4mm thick, so hopefully will be OK. I know this isn't a great solution, but this build is all about low budget and low tech!!



I kept the bucket seat on the runners it came with so that I can adjust the centre of gravity once built. This is cool for me, as I might end up putting a PVC base on the seat, including an extension for a footwell / pedals and steering wheel so my feet will be off the ground.

Nice job, really good work there

man where did you got that motor? and if it is not too much to ask... how much did you invested?

fer

They were a pair or motor's from PgSaw at a time when he did not have the standard Style gear boxes in stock. So we decided to try these. more pics can be found on my thread and they were actually 10$ cheaper than i paid for my motors. Turns out he still has 90 for sale.

http://www.ebay.com/itm/GEARMOTOR-G...824?pt=LH_DefaultDomain_0&hash=item51c2af75c0

nice job on the build

The build continues, it seems to be coming together OK, albeit very ghetto!! Please do excuse my lack of workmanship

I got the UJ mounted to a temporary wooden base, and now I can get the linkages and motors aligned. Next I can drill the holes for motor mounts and started thinking about mounting potentiometers.

Why is the pot lever also connected to the wooden seat base?
If the seat is going to move, something could break..

EDIT: Ooops, my mistake, I just realized that this is not the pot.. Need to read better, silly me

@prodigy - yep, that's not the pot, the pots are not in that build yet.

I've got the build pretty much finished and ran some preliminary testing with the Arduino, just by sending commands to the serial port.

It seems that the code from @RacingMat might need a tweak, but not had a close look yet. When I send LFF to move the left motor up, it moves the left motor perfectly, but when I send RFF to move the right motor up, it moves the right motor down...not up.

So, LFF moves the left motor clockwise, but RFF moves right motor counter-clockwise, a bit odd but probably easily fixed in the Arduino code Unless I've done something else wrong, but I don't think I have.

@benj : it's your wiring! you have to swap the positive and negative wires of your right motor and also for your pot as well, I would say.
Always try with pot not connected to motor but with your hand.

The code cannot guess how you will wire the motor ;-)
but yes, you could change the code instead of your wiring.

yours
Mat

Thanks @RacingMat - of course!! All sorted now.

My next problem is that the Arduino code is ignoring the second part of my data packet.

When I send LFF or RFF as seperate commands - all is great.

When I send LFFRFF then the R command is ignored, and if I send RFFLFF then the L command is ignored. The arduino code looks good to me, so not quite sure what I'm doing wrong now! Any advice? Thanks.

good!

>The arduino code looks good to me
yes, dozen of simracers are using the Arduino code: so it has been proven to be OK ;-)

that's strange... it's time to try with Simtools output sliders
Before that check the comport parameters on Arduino IDE, windows, Simtools

Mat

Hey Mat - thanks - your advice is really appreciated.

The com port settings all match: 115200 bps, 8, none, 1.

Output sliders on simtools do the same thing - only move 1 motor. My interface is setup as L<Axis1>R<Axis2> at 20ms - this moves the left motor but not right. If I change it around to R then L, then it moves the right motor but not the left....so odd!