Submitted by chrisdube on Sat, 07/30/2011 - 06:07
Posted in
Hi,
I'm new to this forum but I've been reading a lot of the great info on this site for a few months. I finally decided to get serious about designing and building a dolly. My goal is a low cost, relatively light weight dolly that I can take backpacking. I got a lot of inspiration from the dolly v1 prototype. Here is my design so far.
The rail is 80/20, and the slider is their linear bearing system. I am thinking of getting a shorter piece of rail for backpacking and a longer (72" or so) piece for more travel.
*15 Series 1.5" x 3.0" Lite Smooth T-Slot Aluminum Extrusion, Part # 1530
*15 Series Double Flange Linear Bearing, Part #6824
Here is my shopping list from SDP/SI:
The power transmission is with a 5mm HTD pitch, 9mm wide timing belt. The motor side has a 12-tooth pulley. The free end is just two flat aluminum pieces with bearings and a shaft. I am still working on a good way to attach the timing belt to the slider and add quick release capability.
My electronics are an Arduino, DFRobot LCD Shield and an EasyDriver. I am hoping to run miniE (right here!)
I am planning on using the Anaheim Automation 17Y-302S-LW4. Stepper motors still confuse me, but assuming the ideal torque of 61 oz-in, with the 12-tooth pulley (.75in pitch diameter) that works out to just over 10 lbs of pull. I am fine with even half of that, as right now I'm using an XSi and Sigma 10-20.
Any suggestions / problems that you guys can see? My main worry is the stepper not being powerful enough. I want to avoid using a geared motor if possible, but I may have to?
Thanks,
-Chris
I love it! Great design. I
I love it! Great design. I had the same thoughts about my stepper motor when I built my dolly (http://www.elysia.nl/content/openmoco-based-timelapse-dolly-first-prototype).
I am now using a 4NM stepper motor which is cheap and easy for me to source because my shop has a next day delivery. My motor is more than strong enough, mostly because I am using a 1:20 gear ratio.
My dolly is still in its testing phase, but I find that my 1:20 gear ratio in combination with the default 8 micro steps from the EasyDriver give me a very high resolution and very smooth operation in shoot, move, shoot mode. I have a 300,000 step resolution on my 2 meter long rail. More steps is better because the linear ramping during a move gives much less stress on the drive system. My initial conclusion is that you better have 8 micro steps and 800 steps per move than no micro steps and 100 steps per move. This gives the same travelled distance, but smoother operation. I don't know if the MiniE is using some sort of linear ramping, but I guess it does?
So, my idea would be to have some sort of gearing. Not only because you get more torque, but also to enlarge the number of steps for your maximum travel distance. Maybe you can use different pulleys? A small and large pulley should work I think?
I would also check how the DP dolly and my dolly attach the belt. My initial thought were to have a fixed place on the rail where I could put a clip that holds the belt. That gave way too much stress on the belt. I changed that to its current form. You can now slide the clips on the rail which results in an adjustable belt tension. You could easily do that to by creating something similar on your drive cart.
I have a question. How do you
I have a question. How do you make these great images? I would love to do that myself. Which software did you use for this?
I still haven't ordered the
I still haven't ordered the stepper motor, so I will call Anaheim Automation and see what the lead times are for geared motors. I would have liked to keep the variation speed capabilities as high as possible and maybe allow for real time, but I guess that probably won't work out. I ordered a 12 and a 17 tooth pulley so I can have a bit of variation there (switching pulleys between motor and free side).
Cronix, the model was made in Solidworks, a very nice parametric solid modelling program. I get it free from my university department but another good alternative if you are a student is Autodesk inventor (Autodesk gives away all their products to students for free).
The SDP/SI parts came
The SDP/SI parts came today.
I just 50in of rail and slider from the 8020 ebay store.
I also ordered my motor - it is an Anaheim Automation 23L9104XCS-02. It is a used piece, but I got it for a great price on ebay. It is also weather sealed which is very nice.
I have an easydriver right now, but I may move to a better controller. With 8 microsteps/step and my current pulley, I will have a step resolution of .038mm (39,000 steps for the length of the rail). I wanted to avoid backlash and other issues associated with the gearbox, along with the possibility of higher speeds.
MiniE apparently does support sinusoidal ramping, but I have not tested it yet.
Hi, Great project you have
Hi,
Great project you have there :)
Just wondering, the linear bearings you are using are made of Ultra-high-molecular-weight polyethylene(UHMWPE or UHMW), right? Doesn't this causes more friction that using regular ball-bearings, mainly if the weight starts to increase?
Yeah the bearing surfaces are
Yeah the bearing surfaces are UHMWPE. It is a great material - coefficients of friction not much higher than Teflon, but much cheaper and more abrasion resistant. It is definitely higher friction than ball bearings, but I am happy with the system as it is lighter, smaller, cheaper, and likely more smooth than having a bunch of bearings.
I finally got all the parts except the motor, which was shipped via Fedex Smartpost - the slowest shipping service known to man - over two weeks ago... Anyways, I built some brackets for the non-motor end today and did a few other things. I tested it with about 10 lbs of load and it seems to slide smoothly with very little stiction. I was hoping to get the dolly operational as I will be in Oregon camping this weekend, but it seems that the motor will still not be here by then (Gotta love Fedex!)
Pics:
An idea to hold the timing belt. Not sure if I will stick with this:
This is also not the final design for the free end shaft. I have some bearings that I will mount somehow.
Do you know if the easydriver
Do you know if the easydriver will be able to drive the stepper motor you have ordered?
The easydriver is quite "desirable" since its quite cheap, but it can't drive motors whith more than 1.5 A, 570mA in each coil. Do you know any other "cheap" driver, easy to interface with arduino which is able to drive motors that need more amperage?
The easydriver will work with
The easydriver will work with any stepper that is rated over 750mA/coil (or actually over 150mA/coil because it can be adjusted down). So it will work for now with my motor, but it is not able to supply the motor to it's fullest potential. I'm going to see how it works out (once the motor arrives), and if I find more torque is needed, I will probably get a 2A driver from Polou: http://www.pololu.com/catalog/category/11. The one without the 5V regulator should work fine as the arduino can supply that voltage for the logic circuit.
Quote:The easydriver will
Quote:The easydriver will work with any stepper that is rated over 750mA/coil (or actually over 150mA/coil because it can be adjusted down).
To clarify - the ED is rated from 150mA - 750mA per coil. =)
!c
Looks great! Just a couple
Looks great! Just a couple of questions - did you machine the aluminum pieces yourself (for the pieces that are holding the gear in the photos)? And does the belt you selected fit in the undercarriage of the sliding platform? I was thinking of ordering a narrower belt...