Motion Platform Help Required

[jazzyspies]

Hello and Seasons Greetings- I'm building a simple 2 DOF motion platform, using Jim from NZ's program, with two 24v wheelchair motor/gearboxes pulling cables. The platform is mounted on a single automobile suspension spring, hence can roll and pitch, while giving a degree of "bounce". What I need help with is the electronics. I live in Surrey, SE England, and if anyone is patient enough to help, plus has some degree of experience with this motion stuff, then I'll pay a fair rate for that person to assist. Can't say fairer, can I? I've had this dream for years and the construction isn't a problem, but the electrical bits are. If you can help, then please let me have your phone number to- a.komosa@btopenworld.com Awaiting lots of enthusiastic calls..! Andrew

[Roland]

Hi Andrew,

My first advice is to go over the various websites on the subject. Jim's page is one of them, and he did list fairly complete instructions how to set things up.
I'd also advice you to check out Ian's site: http://buggies.builtforfun.co.uk/Sim/hardware.php
Ian has a ready made interface card, and uses off the shelf motor drivers. His motion software can handle both 2DoF and 3DoF platforms.
You can also check-out my site, http://www.simprojects.nl/motion_platform.htm but since I build all my electronics myself, it may not be suitable for you.

Building the electrical part of motion platforms is not really a plug and play exercise, you need to build up some experience with basic electronics. It will pay off in the end, as you also need some electrical skills to operate and maintain your setup.

[wannabeaflyer]

Hi Andrew I have been dabbling with motion cockpit dreams for some time now and can vouch for rolands suggestions i live in croydon so maybe we could hook up on PM or Facebook to swap ideas ..i have ians controller and Use Rolands info regarding Cockpit build -- currently my motion platform is built but needs refining ( lots ) but a working concept none the less i will be picking this up again after Xmas when i hope to finish building my second CNC router ( for making cockpit parts & PCBs ) be glad to Chip in with what i know so far or just be a local source to bounce ideas off -- for me the biggest drawback was Actuators ( suitable & cheap not 2 things that come easy for our choosen project ) Looking at either ians or Rolands Concepts as being the easist cost effective routes just need to decide before upgrading my exisiting system Cheers

[jazzyspies]

Thanks both of you. I've been reading Jim and Ian's pages for a couple of years! Am I correct in thinking the position data is outputed via Jim or Ian's program to a card. e.g. the Velleman, which sends signals to the bidirectional motor controller... e.g. KT5198. This sends power to the motors, the Velleman getting platform positioning info from the potentiometers? If so, then it's not two dissimilar from the RC aeroplen receiver/servo set up I used to fly. I can buy the Velleman from Maplins, but the KT5198As seem to be only available abroad, and now I'm eager to get my platform moving! I live in a little village near Dorking for those who have kindly emailed me from the UK. I think with your advice, I can get this project going.. thank you very much so far.. Andrew

[jonesthesoftware]

Hi
Don't need KT5198, you can use this H bridge with the Velleman 8055 to drive your motors, It's directly compatible.

http://www.robot-electronics.co.uk/htm/md22tech.htm

regards
geoff

[wannabeaflyer]

Hi Guys must admit its been a while since i did my 1st platform going down the road jim used so now sure about getting hold of a UK source for the KT5198 Ocean Controls card ( actually did remeber that i bought my cards from Australia but they were not the KT5198 version they were the earlier version Jim used ) anyways as Geof pointed out there is the option for the MD22 but for the extra £10 you could plump for the MD03 - 24V 20A H Bridge Motor Drive. both use the same input control signals and are good value for money --- You could go for making your own H bridge cct but for a newbie that wants to get things quite lierally moving without the debug hassle of the shelf built / tested would be my suggested route. i'll go see if i can find some photos of my frankestien and post em in a mo

100_1257.jpg

[jazzyspies]

Thanks Geoff, Roland and WF.. the latter of whom informs me my wheelchair motors might draw up the 80A peak! Does this mean the suggested motor controllers: KT5198A, MD22 and MD03 are not sufficiently robust? If so, what are my easy options? I wanted to stick with Jim's 5198 solution because he describes exactly how to wire it up and which jumper settings are used where. I need this sort of idiot guide, I'm affraid. I look forward to receiving more perals of wisdom from your kind selves. Cheers.. Andrew

[jonesthesoftware]

Hi Andrew
sorry don't have any experience with wheelchair motors, but any motor will draw heavy current when jammed or stalled because of mechanical friction/jamming. Only real electrical solution for this is to use a motor controller that has current limiting so that you can prevent high currents. If you use any of the previously mentioned boards you must add heatsinks and beef up the PCB tracks with copper wire to handle the occasional full current, but good mechanical design and limit switches are best used to prevent a stall condition arising in the first place.
regards
geoff

[Roland]

More background info

Choice of motor is crucial if you want to use the currently available low cost motor drivers that work with Jim's / Ian's software.

I had provided some information about motor choice in the past: see below thread.
http://www.mycockpit.org/forums/show...truction/page2

There is A LOT of info in the motion platform forum: (seach on motion, DC motor etc)

Wheelchair motors + gearbox may draw too much initial surge currents. You could reduce this by:
a. Using less supply voltage (12V iso 24V) but you loose torque and max RPM
b. Add some Power resistance in series with the motors. Loss of torque Resistance needs to be low, probably just using longer electrical wires to motor will be be sufficient.

KT5198 spec says it can handle considerable power. Personally I don't really like motor controllers where the MOSFET's are directly driven from the micro controller, (no real shoot-through protection) but it seems to be done more often so probably OK.

Noise issues due to glitches, ground currents ect can become nasty at higher currents. That's why I have always opted for higher voltage lower current motors.