This summer, a few of my team mates and I are looking at experimenting with certain drivetrains to learn the pros and cons of each combination we can test. Basically, we want to find out which drivetrains have a lot of torque, which ones have a lot of speed, and which ones have a combination of each. So far, we are going to be looking into the following:
We will also be looking at different types of wheels to see if they have any effect on the torque(for example, if they slip or not).
If anybody else has any other suggestions for motor/transmission combos for us to test, please share. We will probably post our research on here, so if anybody would like a request for a certain drive train, please let us know. Any help we can get is appreciated.
I don’t know how it works, but I’ve seen some teams implement planetary gearboxes that allow the use of Fisher Price motors in place of a CIM in a toughbox or dewalt transmission. I’ve heard of combining a Fisher price motor and a CIM in a singe gearbox.
I’m interested in seeing how that works.
Can you describe the test setup you are considering using, and the test equipment? Do you have a dynamometer so you can measure torque vs speed, or are you planning on just measuring stall torque and no-load speed?
Will you also be measuring motor current and voltage at each test point?
Banebots sells planetary gearboxes with very high stepdown gear ratios. FP motors can be adapted to fit these gearboxes by replacing the pinion gear. For more info, do a search on CD for the keywords “pinion” and “banebots”.
To be honest, we were just planning on switching transmissions and motors on past robots and pushing heavy stuff/other robots around. It would be very unscientific, watered down experimenting.
We are planning on looking into planetary gearboxes as well, like the Crazy Chicken Transmission. I’ll be sure to let my friends know about Banebots and look into their products.
Well, speed and torque depend entirely on the gear ratios and motors you use. Testing a few drivetrain configurations is an excellent idea, but make sure you don’t neglect the physics behind what you’re doing.
In my opinion, the most important characteristics of a drivebase are its maneuverability, robustness, and ease of construction. Speed and torque are easy to trade off by simply using different gears or sprockets.
For the first one, the torque vs speed motor curve for the CIM motor is available at the andymark.biz website. And the gear ratio for the toughbox is specified there too. So with just a tiny bit of physics and math, you have a good estimate (neglecting friction) of what the torque vs speed curve at the wheels would be.
For the second one, just look up the gear ratio for the Dewalt transmission and compare it the the toughbox spec. This will tell you if you will get more torque and less speed, or less torque and more speed, compared to #1.
For the third one, look up the motor specs for the Dewalt motor and compare it to the CIM. This will tell you how #3 stacks up against #2.
Dewalt motors are not legal motors since they did not come in the kit of parts. Unless you have a non FIRST application, I do not see why you would want to test them.
You could save some time and money and do some calculations before hand to give you an overall idea of what gear ratios you want with a given motor and wheel dia.
Well we are going to test some dewalt gearboxes this summer too. There other things to test besides drivetrain performance. We don’t really need to test performance since we can calculate it before hand. I doubt the theoretic calculations will be drastically different from real world results.
The real test for us is if we can convert the gearboxes to adapt a CIM or a FP in a reasonable time using tools in our wood shop. We really don’t want to find assembly and modification issues in the middle of the build season. We will work out the kinks now to save us time later.
We may also tryout fancier stuff such as automatic shifting or something like that.
Also, we want to try using the dewalt motor and gearbox (actually the whole drill) to make instant prototypes. In the past, we used a spare drill grabbing a shaft with its chuck. We want to try a more integrated system where we can bolt the drill to the prototype device, change the gear reductions easily by shifting gears and using different combinations of sprockets and finally, be able to use the drill’s trigger switch for early tests and later be able to switch to a speed controller. Hopefully, we can use this to make better prototypes.
As an additional note, if you choose to do the math remember to include basic efficiency losses. 1% per spur-style gear is usually adequate. Which means that a planetary tranny is going to be far less efficient than one with only 2 or 3 gear interactions like a toughbox.
I suggest, before you do any testing, you start reading a bit about different styles of transmissions and their strengths and weaknesses.
Yep, we have seen it already and it’s defiantly a terrific white paper.
The actual step we are concerned with is drilling out the sun gear of the planetary gear set to fit a CIM. We don’t have a mill in our woodshop and our drill presses may not be accurate enough. We are just going have to try it to see how hard (or how easy) it actually is.
Actually before the paper was released, Team 47 came to the silicon valley regional in 2004 and Dr. Joe explained to me the wonderful benefits the dewalt xrp. So, I have pretty much procrastinated for 6 years the implementation of the dewalt gearboxes on our robots. Lets keep our fingers crossed that I don’t stretch it to 7.
Testing a few drivetrain configurations is an excellent idea, but make sure you don’t neglect the physics behind what you’re doing.