Author Topic: Newbie Help  (Read 2670 times)

mav0709

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Newbie Help
« on: July 10, 2015, 09:57:30 pm »
Hello, I have built my first robot but have a few issues that I can't resolve and need some advice.  I used two Hitachi 12V drill motors hooked up to one esc thus one is running in reverse and runs slower than the other, is there a way to make them the same speed? The next issue is it is too heavy for the rc crawler tires that I have and it doesn't steer very well, any ideas on solid wheels?  It will be used in grassy areas and gravel.  The last issue is the LH screws that I used to attach my wheels keeps backing off.  I have used thread lock sealant and lock washers but to no avail.  I have pics of the bot if that helps. 

MikeNCR

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Re: Newbie Help
« Reply #1 on: July 10, 2015, 10:17:21 pm »
Hello, I have built my first robot but have a few issues that I can't resolve and need some advice.  I used two Hitachi 12V drill motors hooked up to one esc thus one is running in reverse and runs slower than the other, is there a way to make them the same speed? The next issue is it is too heavy for the rc crawler tires that I have and it doesn't steer very well, any ideas on solid wheels?  It will be used in grassy areas and gravel.  The last issue is the LH screws that I used to attach my wheels keeps backing off.  I have used thread lock sealant and lock washers but to no avail.  I have pics of the bot if that helps.

The 12v drill motors you're using are likely biased (timed) for rotation in one direction. I'm going to guess that the left side is the one that's running faster based on that. There's not a lot that can be done to deal with that when both motors are being run off a single esc. You could change the right side motor to a slightly larger diameter, however enough of a change to fix the forward direction will make the reverse direction that much worse.

When you say it's "too heavy" for the crawler wheels, what's actually happening when it's turning?

As far as the screws backing off, are you also threading the wheel onto the threaded shaft of the drill? Typically the way people make the wheel-on-drill shaft setup work is they'll tap the wheel for the right hand thread of the shaft, install the wheel on the shaft, then use loctite, a washer, and the left hand threaded screw to lock the system together. The reason this works is when the wheel tries to spin on the shaft the direction it is able to spin is the direction that tightens the screw which keeps it all together.
« Last Edit: July 10, 2015, 10:29:01 pm by MikeNCR »

mav0709

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Re: Newbie Help
« Reply #2 on: July 10, 2015, 11:15:13 pm »
Thanks Mike for the quick response, the steering issue is the bot just wants to push forward instead of turning.  I have a Hitec HS425bb servo that I am using for my steering arms.  The wheels are turned but the bot continues to push forward.

Regarding tapping the wheels, the rims are plastic and I am not sure of the thickness but I will definitely give that a try.

I might try purchasing an additional esc and try that but will that defeat the purpose of needing the servo for steering in the front?

Thanks!

MikeNCR

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Re: Newbie Help
« Reply #3 on: July 10, 2015, 11:36:58 pm »
Thanks Mike for the quick response, the steering issue is the bot just wants to push forward instead of turning.  I have a Hitec HS425bb servo that I am using for my steering arms.

The wheels are turned but the bot continues to push forward.

Regarding tapping the wheels, the rims are plastic and I am not sure of the thickness but I will definitely give that a try.

I might try purchasing an additional esc and try that but will that defeat the purpose of needing the servo for steering in the front?

Thanks!

The turning issue sounds like there may not be enough weight over the front wheels when you're trying to turn. Looking at the bot it seems like there's a substantial portion of the weight over the rear wheels which means the front wheels won't be able to help with turning as much.

On the tapping, there's a good chance it's a 3/8-24 thread but you'll want to double check the shafts to be sure (3/8" diameter, 24 threads per inch)

The second ESC could be used a few ways depending on your radio gear and what you want to do with it. If you're using ESC's that can be calibrated you can calibrate each esc with a different minimum and maximum throw to bias the throttle in each direction to counteract the timing (Left side calibrated to 100% forward, 80% reverse, right side to 80% forward, 100% reverse for example. actual values will vary)

You may also be able to use something like this inline with your esc's to adjust the minimum and maximum speed manually- https://www.servocity.com/html/servo_synchronizer.html#.VaCO6PlViko

If it's not pulling to hard to the side, once the steering's fixed it may not even be worth the hassle.

mav0709

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Re: Newbie Help
« Reply #4 on: July 11, 2015, 12:25:49 am »
Thanks again for the valuable input Mike.  I will tackle the issue of the wheels falling off then work on the  steering.  I have an additional attachment that is connected to the front which should provide much more weight to the front so maybe your theory about that will prove correct but I can't test it until I fix the wheels.  I am not sure if the esc I purchased has the option of calibrating, being my first bot, I'm working on a budget.  The link shows what esc I am using.  http://www.ebay.com/itm/320A-6-12V-Brushed-ESC-Speed-Controller-W-2A-BEC-for-RC-Car-Boat-Black-/361089095521?hash=item5412965761  I will work on the wheels next week as I am out of town for the weekend and left the shop frustrated.  Thanks again for the expert advise, I will post my findings next week so others may glean from the forum's knowledge.

mathias

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Re: Newbie Help
« Reply #5 on: July 11, 2015, 10:05:46 am »
Tangential question: how do you like that FlySky 6 channel radio? I've seen them cheap on Amazon with Prime shipping and thought about getting one. The only thing stopping me from pulling the trigger is that I'm not sure it is going to be compatible with any minimal receivers built by other companies, and I probably need to go the minimal one-circuitboard-in-shrinkwrap receiver route.

mav0709

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Re: Newbie Help
« Reply #6 on: July 11, 2015, 12:55:00 pm »
Hi Mathias, I can't give you much of an answer to the question of my opinion on the Flysky fs-ct6B due to this being my first experience with rx and tx equipment.  Its been a learning experience.  I purchased it after I watched several of the videos listed on Youtube of which I attached the link.  Hope that helps and good luck.  https://www.youtube.com/results?search_query=flysky+fs-ct6b

IanMcMahon

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Re: Newbie Help
« Reply #7 on: July 12, 2015, 01:47:07 pm »
Thought: it might be having turning issues because the drive motors are trying to drive both wheels equally rather than acting like a differential. I remember something about needing to wire the motors in series if you want differential action, but I may be completely off base.

If you disconnect one of the drive motors, does it turn better or worse? What about if you wire the motors in series?

MarkHarrison

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Re: Newbie Help
« Reply #8 on: July 12, 2015, 08:48:06 pm »
A standard servo might not have enough torque to turn the steering on a bot that heavy. It may need a high torque servo or something like one for 1/5 scale RC. Try something in the 100 oz in + range.